Method and device for performing roaming operation in wireless LAN

Abstract

An operation method of an AP in a wireless LAN system may include the steps in which: a first AP among a plurality of APs included in an SMD receives a first frame related to roaming initiation from a station (STA), wherein the first frame includes information related to a second AP that the STA roams to among the plurality of APs; the first AP and the second AP performs context exchange for exchanging context information necessary for roaming of the STA; and the first AP transmits to the STA a second frame related to roaming in response to the first frame.

Description

Method and device for performing roaming operations in a wireless LAN

[0001] The present disclosure relates to wireless local area network (WLAN) communication technology, and relates to a method and device for performing roaming operations in a wireless LAN.

[0002]

[0003] With the recent proliferation of mobile devices, Wireless Local Area Network (WLAN) technology, which can provide fast wireless communication services to these devices, is attracting significant attention. WLAN technology utilizes short-range wireless communication technology to enable mobile devices such as smartphones, tablets, laptops, portable multimedia players, and embedded devices to wirelessly access the Internet.

[0004] Standards for wireless LAN technology are primarily being developed by the Institute of Electrical and Electronics Engineers (IEEE) as the IEEE 802.11 standard. As the aforementioned wireless LAN technology has developed and become widespread, applications utilizing it have diversified, creating a demand for wireless LAN technology that supports higher reliability.

[0005] As applications requiring higher reliability arise, the IEEE 802.11bn standard, an ultra-high reliability (UHR) wireless LAN technology, is being developed in a single Basic Service Set (BSS) environment and / or redundant BSS environments. The goals of the IEEE 802.11bn standard may support increased data transmission speed, improved delay performance, and improved data error rate. In addition, the IEEE 802.11bn standard may support low-power operation and direct communication (peer-to-peer communication, P2P), and may support a TXOP sharing method in which a wireless LAN terminal shares a communication resource, a TXOP, between multiple access points (APs).

[0006] Additionally, a wireless LAN terminal in a wireless LAN network can support roaming, and the following describes a method for performing roaming operations.

[0007] Meanwhile, the technology that serves as the background for the invention is written to promote understanding of the background for the invention, and may include content that is not a prior art already known to a person with ordinary skill in the field to which the technology belongs.

[0008]

[0009] The present disclosure relates to a method and device for performing a roaming operation in a wireless LAN.

[0010] The present disclosure relates to a method and device for receiving data from a new wireless access point (AP) to which a wireless LAN terminal wishes to perform roaming in a wireless LAN.

[0011] The present disclosure relates to a method and device for reducing data errors that may occur during roaming operations in a wireless LAN.

[0012] The present disclosure relates to a stable roaming method and device that ensures service continuity by allowing a new AP to check the completion time of data transmission of a previous AP during roaming operation in a wireless LAN and, when data transmission is completed, transmit data to a terminal.

[0013] The present disclosure relates to a method and device for determining the most suitable AP for performing roaming based on an artificial intelligence algorithm.

[0014] The present disclosure relates to a method and device for negotiating a time at which roaming is performed based on an artificial intelligence algorithm.

[0015] The technical problems to be achieved in the present disclosure are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by a person having ordinary skill in the technical field to which the present disclosure belongs from the description below.

[0016]

[0017] According to one embodiment of the present specification, a method for operating an access point (AP) in a wireless LAN system may include a step in which a first AP among a plurality of APs constituting a single mobility domain (SMD) receives a first frame related to initiation of roaming from a station (STA), the first frame includes information related to a second AP to which the STA is roaming among the plurality of APs, a step in which the first AP performs a context exchange for exchanging context information necessary for roaming of the STA with the second AP, and a step in which the first AP transmits a second frame related to roaming to the STA in response to the first frame.

[0018] In addition, according to one embodiment of the present specification, among a plurality of access points (APs) constituting a single mobility domain (SMD), a first AP includes at least one transceiver for transmitting and receiving a signal, at least one processor for controlling the at least one transceiver, and a memory for storing instructions for causing the AP to perform a specific operation by the at least one processor, wherein the specific operation includes: receiving a first frame related to initiation of roaming from a station (STA), wherein the first frame includes information related to a second AP to which the STA is roaming among the plurality of APs, performing a context exchange for exchanging context information necessary for roaming with the second AP among the plurality of APs, and the first AP can transmit a second frame related to initiation of roaming to the STA in response to the first frame.

[0019] One SMD can be composed of multiple AP MLDs and one Controller (e.g., Wireless LAN Controller (WLC)). Alternatively, one SMD can be composed of multiple AP MLDs. One AP MLD can be composed of multiple APs. An entity within an SMD that is responsible for allowing the AP MLDs to perform specific roaming-related operations is called an SMD-Management Entity (SMD-ME). In an SMD structure with a Controller, the SMD-ME is located in the Controller, and each AP MLD has an SMD Upper MAC part for communicating with it. In an SMD structure composed of only multiple AP MLDs, the SMD-ME and the SMD Upper MAC part exist in each AP MLD. The SMD Upper MAC part located in the AP MLD can communicate with the MACs of multiple APs of the AP MLD and can communicate with the SMD-ME.

[0020] Additionally, the following may apply in common:

[0021] According to one embodiment of the present specification, a time period associated with data transmission from a first AP to a STA may be set prior to the STA roaming to a second AP.

[0022] Additionally, according to one embodiment of the present specification, a time interval is set at a time point based on at least one of a first frame transmission and a second frame reception, and a first timer is started based on the time interval, wherein the first timer is a timer that expires at a time point when roaming is performed, and when the first timer expires, the first AP can recognize that roaming of the STA to the second AP is performed and communication with the STA is impossible.

[0023] Additionally, according to one embodiment of the present specification, the first AP may transmit at least one data frame to the STA while the first timer operates based on a time interval.

[0024] Additionally, according to one embodiment of the present specification, if the first timer expires before at least one data frame transmission from the first AP to the STA is completed, the first AP may not transmit the data frame to the STA, and roaming of the STA to the second AP may be completed based on the expiration of the first timer.

[0025] Additionally, according to one embodiment of the present specification, the first AP transmits the last data frame of at least one data frame to the STA while the first timer is operating, and receives a response frame for the last data frame from the STA, wherein the last data frame may be transmitted including a last frame indicator.

[0026] Additionally, according to one embodiment of the present specification, the context information includes a sequence number (SN) of the last data frame transmitted by the first AP to the STA, and at least one of the last data frame and the response frame is transmitted to the second AP based on listening, and the SN included in at least one of the last data frame and the response frame and the SN included in the context information are compared to indicate completion of roaming of the STA to the second AP.

[0027] In addition, according to one embodiment of the present specification, in a method of operating a station (STA) in a wireless LAN system, the method may include a step of transmitting a first frame related to initiation of roaming to a first AP among a plurality of APs constituting a single mobility domain (SMD), wherein the first frame includes information related to a second AP to which the STA is roaming among the plurality of APs, and a step of the STA receiving a second frame related to roaming in response to the first frame.

[0028] In addition, according to one embodiment of the present specification, a station (STA) includes at least one transceiver for transmitting and receiving a signal, at least one processor for controlling the at least one transceiver, and a memory for storing instructions for causing the STA to perform a specific operation by the at least one processor, wherein the specific operation is: transmitting a first frame related to initiating roaming to a first AP among a plurality of APs constituting a single mobility domain (SMD), wherein the first frame includes information related to a second AP to which the STA is roaming among the plurality of APs, and the STA can receive a second frame related to initiating roaming in response to the first frame.

[0029] Additionally, the following may be commonly applied:

[0030] According to one embodiment of the present specification, a time period associated with data transmission from a first AP to a STA may be set prior to the STA roaming to a second AP.

[0031] Additionally, according to one embodiment of the present specification, a time interval is set at a point in time based on at least one of a first frame transmission and a second frame reception, and a first timer is started based on the time interval, wherein the first timer is a timer that expires at a point in time when roaming is performed, and when the first timer expires, roaming of the STA to the second AP is completed, so that the STA can communicate with the second AP.

[0032] Additionally, according to one embodiment of the present specification, the STA may perform reception of at least one data frame from the first AP while the first timer operates based on a time interval.

[0033] Additionally, according to one embodiment of the present specification, the STA transmits context information to the second AP, wherein the context information may include at least one of a pseudorandom number (PN) of the last frame received by the STA from the first AP, a packet number of the last frame received by the STA from the first AP, a pseudorandom number of the last frame transmitted by the STA to the first AP, and a pseudorandom number packet number of the last frame transmitted by the STA to the first AP.

[0034] In addition, according to one embodiment of the present specification, the STA is a wireless LAN terminal that operates according to enhanced multi-link single radio (EMLSR) that performs a listening operation performed on at least one link and transmits and receives frames on one link at a time, and the first frame that the first AP receives from the STA is an initial control frame or a data frame, and when roaming of the STA that operates based on EMLSR is performed, the TXOP (transmit opportunity) of the first AP that performs frame exchange with the STA and the TXOP of the second AP that performs frame exchange with the STA may not overlap due to a certain time interval according to a transition operation of the STA.

[0035]

[0036] According to the present disclosure, a method for performing a roaming operation in a wireless LAN can be provided.

[0037] According to the present disclosure, a method for receiving data from an AP with which a wireless LAN terminal wishes to perform roaming can be provided.

[0038] According to the present disclosure, a method for reducing data errors that may occur during roaming operations in a wireless LAN can be provided.

[0039] According to the present disclosure, a stable roaming method can be provided that ensures service continuity by allowing a new AP to check the completion time of data transmission of a previous AP during roaming operation in a wireless LAN and, when data transmission is completed, transmit data to a terminal.

[0040] According to the present disclosure, a method for determining the most suitable AP for performing roaming based on an artificial intelligence algorithm can be provided.

[0041] According to the present disclosure, a method for negotiating a time at which roaming is performed based on an artificial intelligence algorithm can be provided.

[0042] The technical problems to be achieved in the present disclosure are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art to which the present disclosure pertains from the description below. The effects that can be obtained in the present disclosure are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art to which the present disclosure pertains from the description below.

[0043]

[0044] Figure 1 is a diagram showing a communication node within a wireless LAN system to which the present disclosure is applied.

[0045] Figure 2 is a diagram showing a wireless LAN system to which the present disclosure is applied.

[0046] FIG. 3 is a diagram illustrating a machine learning unit to which the present disclosure is applied.

[0047] FIG. 4 is a flowchart illustrating a method for performing communication based on a machine learning unit to which the present disclosure is applied.

[0048] FIG. 5 is a diagram illustrating a multi-link single radio terminal roaming method to which the present disclosure is applied.

[0049] FIG. 6a and FIG. 6b are diagrams illustrating a multi-link single radio terminal roaming method to which the present disclosure is applied.

[0050] FIG. 7 is a diagram illustrating a multi-link single radio terminal roaming method to which the present disclosure is applied.

[0051] FIG. 8a and FIG. 8b are diagrams illustrating a multi-link single radio terminal roaming method to which the present disclosure is applied.

[0052] FIG. 9 is a diagram illustrating a multi-path packet forwarding roaming method to which the present disclosure is applied.

[0053] FIG. 10 is a diagram illustrating a multi-path packet forwarding roaming method to which the present disclosure is applied.

[0054] FIG. 11 is a diagram illustrating a multi-path packet forwarding roaming method to which the present disclosure is applied.

[0055] FIG. 12 is a diagram illustrating a multi-path packet forwarding roaming method to which the present disclosure is applied.

[0056] FIG. 13 is a diagram illustrating a multi-path packet forwarding roaming method to which the present disclosure is applied.

[0057] FIG. 14 is a diagram illustrating a multi-path packet forwarding roaming method to which the present disclosure is applied.

[0058] FIG. 15 is a diagram illustrating a multi-path packet forwarding roaming method to which the present disclosure is applied.

[0059] FIG. 16 is a diagram illustrating a multi-path packet forwarding roaming method to which the present disclosure is applied.

[0060] FIG. 17a and FIG. 17b are diagrams illustrating a wireless LAN same-channel roaming method to which the present disclosure is applied.

[0061] FIG. 18a and FIG. 18b are diagrams showing a wireless LAN same-channel roaming method to which the present disclosure is applied.

[0062] Figure 19 is a diagram illustrating a wireless LAN same-channel roaming method to which the present disclosure is applied.

[0063] Figure 20 is a diagram illustrating a wireless LAN same-channel roaming method to which the present disclosure is applied.

[0064] Figure 21 is a flowchart illustrating a method for performing a roaming operation in a wireless LAN to which the present disclosure is applied.

[0065] Figure 22 is a flowchart illustrating a method for performing a roaming operation in a wireless LAN to which the present disclosure is applied.

[0066]

[0067] This disclosure may be subject to various modifications and various embodiments. Specific embodiments are illustrated and described in detail in the drawings. However, this is not intended to limit the disclosure to specific embodiments, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and technical scope of the disclosure.

[0068] While terms such as first, second, etc. may be used to describe various components, these components should not be limited by these terms. These terms are used solely to distinguish one component from another. For example, without departing from the scope of the present disclosure, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component. The term "and / or" includes a combination of a plurality of related described items or any of a plurality of related described items.

[0069] When a component is referred to as being "connected" or "connected" to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components intervening. Conversely, when a component is referred to as being "directly connected" or "connected" to another component, it should be understood that there are no other components intervening.

[0070] The terminology used in this disclosure is only used to describe specific embodiments and is not intended to limit the present disclosure. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this disclosure, it should be understood that the terms "comprises" or "has" indicate the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0071] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which this disclosure pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and shall not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0072] Hereinafter, preferred embodiments of the present disclosure will be described in more detail with reference to the attached drawings. In order to facilitate an overall understanding in describing the present disclosure, identical reference numerals are used for identical components in the drawings, and redundant descriptions of identical components are omitted.

[0073] Below, a wireless communication system to which embodiments according to the present disclosure are applied will be described. The wireless communication system to which embodiments according to the present disclosure are applied is not limited to the description below, and the embodiments according to the present disclosure can be applied to various wireless communication systems. The wireless communication system may be referred to as a "wireless communication network."

[0074] FIG. 1 is a diagram illustrating a communication node within a wireless LAN system to which the present disclosure applies. Referring to FIG. 1, a communication node (100) may include at least one of a processor (110), a memory (120), a transceiver (130), an input / output interface (140), a storage device (150), and a bus (160). For example, the communication node (100) may be an access point (AP), a station (STA), an access point (AP) multi-link device (MLD), or a non-AP MLD. However, the communication node may not be limited thereto, and may be a node that performs communication with other nodes or devices based on the above-described configuration. For example, the operating channel width supported by the AP may be 20 megahertz (MHz), 80 MHz, 160 MHz, etc. The operating channel width supported by the station may be 20 MHz, 80 MHz, etc. However, the present invention may not be limited thereto.

[0075] The processor (110) within the communication node (100) can control at least one of a memory (120), a transceiver (130), an input / output interface (140), and a storage device (150) as each component within the communication node. The memory (120) within the communication node (100) can store information on commands and instructions executed by the processor (110), and the transceiver (130) can refer to a transceiver, a radio frequency (RF) unit, an RF module, or other components that perform signal transmission and reception. The input / output interface (140) within the communication node (100) is an interface for input and output, can be linked with other interfaces, and can further include a separate storage device (150). Each component within the communication node (100) can be connected by a bus (160) to communicate with each other.

[0076] However, as an example, each component included in the communication node (100) may be connected through an individual interface or individual bus centered around the processor (110), rather than a common bus (160). The processor (1110) may be connected to at least one of the memory (120), the transmission / reception device (130), the input / output interface device (140), and the storage device (150) through a dedicated interface.

[0077] The processor (110) can execute program commands stored in at least one of the memory (120) and the storage device (150). The processor (110) may refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor in which the methods according to embodiments of the present disclosure are performed. Each of the memory (120) and the storage device (150) may be configured with at least one of a volatile storage medium or a non-volatile storage medium. For example, the memory (120) may be configured with at least one of a read-only memory (ROM) or a random access memory (RAM).

[0078] FIG. 2 is a diagram illustrating a wireless LAN system to which the present disclosure applies. Referring to FIG. 2, a basic service set (BSS) of the wireless LAN system may include one AP (210) and multiple STAs (221, 222, 223, 224), and the multiple STAs (221, 222, 223, 224) may be controlled by the AP (210). However, the wireless LAN system is not limited to the BSS, and an environment consisting only of STAs without a defined service set or AP may also be considered, and is not limited to a specific form. Each wireless device within the wireless LAN system may include a medium access control (MAC) layer and a physical (PHY) layer, and communication may be performed between the wireless devices. For the convenience of explanation, the following description focuses on APs and STAs, but may not be limited thereto. For example, the following may equally apply to other communication nodes or devices and are not limited to a specific form.

[0079] Figure 3 is a diagram illustrating a machine learning unit to which the present disclosure applies. Each wireless device within a wireless LAN system may be connected to a machine learning unit (300). However, this may not be limited to this, and wireless devices not connected to the machine learning unit (300) may also operate.

[0080] For example, the processor (110) of the communication node (100) of FIG. 1 may be connected to the machine learning unit (300). The machine learning unit (900) may be connected to the processor (110) through the input / output interface device (140) of the communication node (100) to communicate. As another example, the machine learning unit (300) may be connected to the processor (110) through the bus (160) of the communication node (100) to communicate. As another example, the machine learning unit (300) may be connected to the processor (110) of the communication node (100) through a separate interface or a dedicated bus to communicate. The machine learning unit (300) may be connected to the memory (120), the transceiver (130), and the storage device (140) through the input / output interface device (140), the bus (160), or the dedicated bus to communicate, but may not be limited to a specific form.

[0081] For example, the machine learning unit (300) may include at least one ML (Machine Learning) processor (310), ML memory (320), ML input / output interface (330), and ML bus (340). The ML processor (310), ML memory (320), and ML input / output interface (330) may be connected to and communicate with each other through the ML bus (340). As another example, the ML processor (310) may be connected to and communicate with at least one of the ML memory (320) and the ML input / output interface (330) through a dedicated bus or interface. The ML processor (310) may be a central processing unit, a graphics processing unit, a dedicated processor on which methods according to embodiments of the present disclosure are performed, or a processor in which at least one of the central processing unit and the dedicated processor is combined. The ML processor (310) may include at least one of a training unit (311), a verification unit (312), a performance unit (313), and an updating unit (313). The training unit (311), the verification unit (312), the performance unit (313), and the updating unit (313) may be logical entities configured by software or hardware processing devices. For example, the ML processor (310) may perform at least one of training, verification, execution, and updating of a machine learning model. The machine learning model may be in the form of a plurality of matrices or vectors. As a specific example, the machine learning model may include weights, a transition matrix, and hyperparameters that implement and learn a single or multiple combined machine learning algorithms (e.g., a deep neural network (DNN), a convolutional neural network (CNN), a recurrent neural network (RNN), and a deep reinforcement learning (DRL) algorithm).A machine learning model may include an input layer, at least one hidden layer, and an output layer to implement a deep neural network (DNN) algorithm. Each of the input layer, hidden layer, and output layer may include at least one perceptron (e.g., an artificial neuron). The perceptron includes an activation function, input weights, and a bias. Multiple perceptrons may have inputs and outputs connected to form an input layer, a hidden layer, and an output layer. The machine learning model may include a convolution algorithm and the DNN algorithm to implement a CNN algorithm. The convolution algorithm convolves a kernel matrix with input data in matrix form and may be performed at least once on the input data. When the convolution algorithm is performed on the input data, the size of the data may be increased through concatenation or reduced through pooling. The input data on which the convolution algorithm has been performed at least once is used as input data for the DNN algorithm. For example, a machine learning model may include a DNN algorithm and a cell structure to implement an RNN algorithm. The cell structure may be a structure that remembers previous input data and inputs it on its own, and may be used in at least one perceptron of the DNN algorithm. A machine learning model may include an agent, an environment structure, and a DNN algorithm to implement a DRL algorithm. In a DRL algorithm, an agent can observe the environment and perform an optimal action based on the observed data. The environment can provide feedback as a reward to the agent based on the agent's action. Based on the above, the agent can learn a policy for taking an optimal action.Agents can use DNN algorithms to learn optimal actions.

[0082] As another example, the machine learning unit (300) may be designed to additionally implement other machine learning algorithms in addition to the aforementioned machine learning algorithms (e.g., DNN, CNN, RNN, and DRL). To this end, the machine learning unit (300) may include additional components for implementing other machine learning algorithms. The ML memory (320) within the machine learning unit (300) may store machine learning models and machine learning algorithms. The implementation of the machine learning algorithms may be performed by the ML processor (310) based on the machine learning models.

[0083] As another example, all or part of the functions of the machine learning unit (300) may be integrated into the processor (110) and memory (120) of the communication node (100). That is, the processor (110) of the communication node (100) may perform all or part of the functions of the ML processor (310), and the memory (120) may perform all or part of the functions of the ML memory (320). When the processor (110) and memory (120) of the communication node (100) perform all of the functions of the machine learning unit (300), the machine learning unit (300) may not be connected by the input / output interface (140), and the processor (110) and memory (120) may operate as the machine learning unit (300).

[0084] As another example, the machine learning unit (300) may be connected not through the input / output interface (140) of the communication node (100), but through a bus (160) or a dedicated bus or interface centered around the processor (110) of the communication node (100), but may not be limited to the above embodiment.

[0085] FIG. 4 is a flowchart illustrating a method for performing communication based on a machine learning unit to which the present disclosure is applied. Referring to FIG. 4, the machine learning unit (300) is connected to a communication node (100), collects communication data, and can perform prediction based on a machine learning model (S410). As an example, the above-described prediction may be performed by the execution unit (313) of the machine learning unit (300), but is not limited thereto. Here, the communication data collected by the machine learning unit (300) may include at least one of channel noise status, channel congestion, reception strength, collision frequency, and other information obtained from a physical layer. In addition, the communication data may include information obtained from a MAC layer, and is not limited to a specific form. The communication data collected by the machine learning unit (300) may be provided as input to the machine learning model itself. As another example, the communication data collected by the machine learning unit (300) may be provided as input to the machine learning model after being operated or processed. For example, the prediction result of the machine learning unit (300) may be at least one of a physical layer and MAC parameter (e.g., MCS (modulation and coding scheme) parameter, beamforming parameter, EDCA (enhanced distributed channel access) parameter, etc.). As another example, the prediction result of the machine learning unit (300) may be information for packet scheduling, multi-AP operation scheduling, and other scheduling, but is not limited to a specific form. As another example, the communication node (100) may receive all or part of the machine learning model from another communication node. All or part of the machine learning model may be collected by the machine learning unit (300) and is not limited to a specific form. As an example, the communication node (100) may perform communication based on the prediction of the machine learning unit (300).(S420) In addition, the machine learning unit (300) can collect communication data based on the performed communication, and based on this, machine learning model verification can be performed (S430) or machine learning model training (S440) can be performed. In addition, as an example, the machine learning model can be exchanged with other communication nodes (S450), and the exchanged machine learning model information can be used for machine learning model verification or machine learning model training. As an example, when machine learning model verification is performed, it can be verified whether the communication operation performed by the prediction of the machine learning unit (300) is appropriate. As a specific example, the machine learning model verification can be performed based on at least one of the frame collision frequency, transmission error frequency, and packet transmission delay of the communication node (100), and an operation of determining whether the communication performance of the communication node (100) has been improved can be performed.

[0086] In addition, for example, if it is determined that training of a machine learning model is necessary (e.g., if communication performance has not improved, if it is determined that the performance of a machine learning model of another communication node (e.g., all or part of the machine learning model) is superior to that of the current communication node (100), the communication node (100) may perform machine learning model training. In another example, the communication node (100) may exchange the machine learning model with other communication nodes without performing machine learning model verification or machine learning model training. In addition, for example, if it is determined that training of a machine learning model is not necessary, the communication node (100) may exchange the machine learning model with other communication nodes without performing machine learning model training.

[0087] Here, the machine learning model may be trained (or learned) based on at least one of the collected communication data and all or part of the machine learning model of another communication node. The training of the machine learning model may be performed by the training unit (311) and may be performed based on at least one of the collected communication data and the output of the machine learning model of another communication node and the machine learning model of the communication node (100).

[0088] As another example, part or all of the machine learning model of the communication node (1000) may be replaced with part or all of the machine learning model of another communication node by the updating unit (314) of the machine learning unit (300). As another example, the machine learning model (e.g., part or all of the machine learning model) of the communication node (100) may be shared with another communication node. Alternatively, the communication node (100) may operate only based on machine learning model verification and training without exchanging the machine learning model with other communication nodes, and is not limited to a specific form. As an example, in the present disclosure, at least one of changing the order, adding or removing steps, and repeating specific steps may be performed in the steps of the flowchart. In other words, the flowchart is an example describing the operation of the machine learning unit (300) of the wireless communication node (100), and the procedures and operations thereof may be modified in various ways. For example, after training a machine learning model, it may be possible to perform a machine learning model validation step again to validate the trained machine learning model, and it may not be limited to a specific form.

[0089]

[0090] A wireless LAN terminal and multiple access points (APs) can operate. The wireless LAN terminal may be referred to as a non-AP STA (station) or STA. Multiple APs may form a single mobility domain (SMD). That is, multiple APs may operate in a single mobility management domain, and additional authentication may not be required when an STA roams to another AP. A single SMD may consist of multiple AP MLDs and a controller (e.g., a Wireless LAN Controller (WLC)). Alternatively, a single SMD may consist of multiple AP MLDs. A single AP MLD may consist of multiple APs. An entity responsible for enabling the AP MLDs to perform specific roaming-related operations within the SMD may be an SMD-Management Entity (SMD-ME). In an SMD structure with a controller, the SMD-ME is located in the controller, and each AP MLD has an SMD Upper MAC part for communicating with it. In an SMD structure with only multiple AP MLDs, an SMD-ME and an SMD Upper MAC part exist in each AP MLD. The SMD Upper MAC part located in the AP MLD can communicate with the MACs of multiple APs in the AP MLD and can communicate with the SMD-ME.

[0091] In addition, the SMD is composed of multiple AP MLDs, and each AP MLD supports MLO (multi-link operation). For example, multiple APs can form an AP MLD, and multiple AP MLDs can form an SMD. For example, multiple AP MLDs may be non-collocated AP MLDs. That is, some of the APs linked under an AP MLD may also be non-collocated APs. For example, if AP 1 and AP 2 are APs that form AP MLD 1, and AP 3 and AP 4 are APs that form AP MLD 2, then AP 1 and AP 2, AP 1 and AP 4, AP 2 and AP 3, and AP 2 and AP 4 are non-collocated APs. Multiple APs within an SMD exchange control information through SMD-ME. An AP can form at least one link.

[0092] For convenience of explanation, the following description assumes that each AP among the multiple AP MLDs of an SMD constitutes a link. An STA that operates by connecting to an AP MLD of an SMD can connect to (or associate) at least one AP among the APs that constitute the AP MLD of the SMD, and can communicate through the connected AP. Connecting to an AP means connecting to the SMD to which the AP MLD to which the AP belongs belongs. In other words, connecting to an AP means performing an association (or connection) with an SMD-ME or an SMD. For convenience of explanation, the AP MLD under an SMD is referred to as an AP MLD below, but may not be limited to that name.

[0093] Additionally, the links configured by each AP below may be configured at different frequencies, and each AP may operate at different frequencies. This may be as shown in FIGS. 5 to 16.

[0094] As another example, if each AP operates at the same frequency, each AP may operate on the same channel. This may be as illustrated in FIGS. 17a to 20 . Here, operating on the same channel may mean operating on the same primary channel.

[0095] FIGS. 5 to 8 describe a case where a wireless LAN terminal, STA (station), AP 1, and AP 2, operate in a wireless LAN network. The STA may be a terminal performing an enhanced multi-link single radio (EMLSR) operation. For example, an STA performing an EMLSR operation may be referred to as an EMLSR STA, but may not be limited to that name. An EMLSR STA is a terminal that performs a listening operation on one or more links, and the listening operation is an operation that can receive only specific frames. For example, the specific frame may be an initial control frame (ICF). If an EMLSR STA receives an initial control frame on at least one link among one or more links, the EMLSR STA can perform frame transmission and reception operations on the corresponding link. On the other hand, an EMLSR STA cannot perform frame transmission and reception operations on a link on which an initial control frame has not been received. For example, the initial control frame may be a MU-RTS (multi user request to send) frame or a BSRP (buffer status report poll) frame. When the EMLSR STA completes frame transmission and reception, the EMLSR STA performs a listening operation to wait for reception of the initial control frame on one or more links again. The state in which the EMLSR STA performs the listening operation may be an EMLSR listening mode. That is, in the EMLSR listening mode, the EMLSR STA can transmit and receive frames on only one link at a time based on the listening operation. Here, the EMLSR STA performs a listening operation to wait for reception of the initial control frame, and the one or more links that perform frame transmission and reception based on reception of the initial control frame by the EMLSR STA may be an EMLSR link, but is not limited to that name.For convenience of explanation, EMLSR STA is referred to as STA below.

[0096] An STA can operate by connecting to AP 1. After connecting to AP 1 (e.g., old AP), the STA can perform data communication with AP 1. Here, the STA can search for AP 2 and determine AP 2 as an AP to perform roaming (e.g., new AP). That is, the STA may attempt to connect to AP 2 and perform communication. For example, an operation in which an STA switches connection from one AP (old AP) to another AP (new AP) and performs communication may be a roaming operation. When the STA determines the roaming operation, an AP 2 link addition procedure and an EMLSR link addition procedure may be initiated between the STA and AP 1. For example, the STA may add a link on which AP 2 operates, and may add a link on which AP 2 operates to an EMLSR link. The link addition procedure may be a multi-link reconfiguration operation or a similar operation. AP 1 can transmit a frame to the STA indicating the addition of a link on a frequency where AP 2 operates, and the STA can add the link as one of the multi-links based on the received frame. In addition, the STA can add the added link as an EMLSR link to perform EMLSR operation on the link added as a multi-link. The STA can transmit an enhanced multi-link (EML) operating mode notification (OMN) frame to AP 1 to add the EMLSR link. The EML OMN frame includes an EML control field. The STA can transmit a roaming announcement indication (RAI) frame to AP 1 to indicate the start of roaming.

[0097] For example, RAI frame transmission can replace the above-described link addition procedure and EMLSR procedure. When RAI frame transmission replaces the above-described link addition procedure and EMLSR procedure, the RAI frame can include information for the link addition procedure and the EMLSR link addition procedure (e.g., (reconfiguration) multi-link element, EML control field). When the STA transmits an RAI frame including information for the above-described link addition and EMLSR link addition procedures, the link addition and EMLSR link addition can be performed. In addition, the RAI frame can include information about AP 2, which is a roaming target AP that will perform a roaming operation (e.g., at least one of the MAC address of AP 2, the link ID (identifier) ​​on which AP 2 operates, and other information that can identify AP 2). When AP 1 receives the RAI frame, AP 1 can respond to the STA with an ACK frame. Here, AP 1 performs a context exchange with AP 2, which is a roaming target AP. Context exchange may be the exchange of information required for roaming between APs (i.e., between AP 1 and AP 2). For example, context exchange may be performed by exchanging AP to AP frames. As another example, context exchange may be performed by exchanging AP to AP frames via wired Ethernet or wirelessly. Here, the AP to AP frame may be a backbone frame, and the backbone frame is a frame that exchanges control information between APs. However, it may not be limited to that name. Roaming operation between APs may be controlled through the AP to AP frame. For example, the AP to AP frame may include, but is not limited to, a roaming initiation frame or a roaming response frame. The roaming initiation frame may be transmitted to the roaming initiating AP (e.g.,A frame transmitted to a roaming target AP (e.g., AP 2) when AP 1) receives an RAI frame from an STA, and the roaming initiation frame may include context (information about the STA). On the other hand, a roaming response frame may be a frame transmitted by a roaming target AP to the roaming initiating AP in response to a roaming initiation frame.

[0098] Information for roaming operations can be continuously exchanged between multiple APs through frame exchange. Context exchange allows AP 1 to convey STA information to AP 2, indicating that the STA is roaming to AP 2. In other words, the context contains information about the STA performing the roaming. For example, the information of the STA may include at least one of information that can identify the STA (e.g., at least one of the MAC address of the STA, the association identifier (AID) of the STA, and other information that can identify the STA), capability information of the STA (e.g., extremely high throughput (EHT) capability, ultra high reliability (UHR) capability), data information destined for the STA in the queue (e.g., sequence number (SN) information for the last frame(s) of the STA in the queue of AP 1), a pseudorandom number (PN) for security, a packet number, and information about the time when roaming is performed (e.g., timeout information), and information necessary for roaming. Here, the information about the time when roaming is performed may be information exchanged during the connection (or association) process. A context switching procedure may allow packets destined for an STA to be inputted (forwarded) to AP 2 instead of AP 1. In other words, the context switching procedure may include a data path switching procedure. The data path switching may be performed by proxy ARP, in which AP 2 transmits an address resolution protocol (ARP) frame to the network on behalf of the STA. As another example, the data path switching may also be performed by updating a switching table controlling an Ethernet port.Alternatively, data path switching may be performed using both of the methods described above.

[0099] As another example, an STA may transmit context information to AP 2 (e.g., a new AP, a target AP). The context information that the STA transmits to AP 2 may be the same as or may include part of the information included in the context exchange between AP 1 and AP 2 described above. For example, the context information that the STA transmits to AP 2 may include SN information for the last frame(s) of the STA. The SN information for the last frame of the STA may be at least one of SN information for the frame that the STA last received from AP 1 and SN information for the frame that the STA last transmitted to AP 1. Here, the DL SN of the STA and the UL SN of the STA may be distinguished. For example, information that can identify the DL SN of the STA and the UL SN of the STA may be transmitted from the STA to AP 2, and AP 2 may recognize the SN information for the last frame of the STA through the above. However, the above is merely an example and may not be limiting. For example, since the AP and STA perform a BA agreement, they can recognize the SN by transmitting only the SN without a separate identifier for the SN.

[0100] Here, the STA can transfer context information to AP 2 regardless of the context exchange procedure between AP 1 and AP 2. For example, even if context exchange between AP 1 and AP 2 is performed, the STA can also transfer context information to AP 2. As another example, the STA can transfer context information to AP 2 instead of AP 1 if context exchange between AP 1 and AP 2 is not performed.

[0101] That is, it may be possible for STA to transmit context information to AP 2, as well as the context exchange procedure between AP 1 and AP 2.

[0102] When an STA transmits an RAI frame to AP 1, the STA may not receive an initial control frame from AP 2 until it receives the last frame, which is the last part of the data input (transmitted) to AP 1. Here, the STA may operate in a normal transmission / reception state in which it transmits and receives in multiple spatial streams using all radios. As another example, even if the STA transmits an RAI frame, the STA may perform a listening operation on the links on which AP 1 and AP 2 operate (i.e., EMLSR links). Based on the listening operation, when the STA receives an initial control frame, it may transmit a CTS (clear to send) frame and then perform frame transmission / reception. When the STA-initiated TXOP (transmit opportunity) ends, the STA may perform a listening operation after an EMLSR transition delay time after transmitting the last frame of the TXOP. In the case of a TXOP initiated by AP 1, if a "PHY-RXSTART.indication primitive" is not issued from the PHY within "aSIFSTime + aSlotTime + aRxPHYStartDelay" time from the time of completion of reception of the last frame received by the STA (i.e., if a new frame is not received), the STA may perform a listening operation after the EMLSR transition delay time. As another example, if a "PHY-RXSTART.indication primitive" is not issued from the PHY within "aSIFSTime + aSlotTime + aRxPHYStartDelay" time from the time of completion of transmission of a response frame transmitted in response to the last received frame (i.e., if a new frame is not received), the STA may perform a listening operation after the EMLSR transition delay time.

[0103] When an STA (e.g., EMLSR STA) disconnects (or associates) with AP 1 due to a roaming operation and establishes a connection with AP 2, the TXOP of AP 1 and the TXOP of AP 2 may not overlap. Specifically, while AP 1 exchanges frames with the STA based on the TXOP of AP 1, AP 2 may not exchange frames with the STA. On the other hand, when an STA connects (associates) with AP 2 due to a roaming operation, while AP 2 exchanges frames with the STA based on the TXOP of AP 2, AP 1 may not exchange frames with the STA.

[0104] For example, the TXOP of AP 1 may be maintained from the time of completion of reception of the frame last received by the STA in the TXOP initiated by AP 1 to a preset time, and after an EMLSR transition is performed for a preset time, the TXOP of AP 2 may be initiated after a preset time so that the TXOP of AP 1 and the TXOP of AP 2 may not overlap. As another example, the TXOP of AP 1 may be maintained from the time of completion of transmission of a response frame transmitted in response to the frame last received by the STA in the TXOP initiated by AP 1 to a preset time, and after an EMLSR transition is performed for a preset time, the TXOP of AP 2 may be initiated after a preset time so that the TXOP of AP 1 and the TXOP of AP 2 may not overlap. Within the preset time, the STA may perform a connection with AP 2 according to a roaming operation, and may terminate the connection with AP 1. AP 1 can initiate a TXOP to transmit a frame to the STA while it is connected to the STA, but cannot initiate a TXOP to transmit a frame to the STA once the connection with the STA is terminated. On the other hand, AP 2 can initiate a TXOP to transmit a frame to the STA once the STA is connected. Therefore, after the preset time, AP 1 cannot initiate a TXOP to transmit a frame to the STA, and AP 2 can initiate a TXOP to transmit a frame to the STA.

[0105] As another example, an STA can initiate a TXOP to transmit a frame to AP 1 while it is connected to AP 1, but cannot initiate a TXOP to transmit a frame to AP 1 when it is not associated with AP 1. Meanwhile, an STA may perform a roaming operation to connect to AP 2 instead of AP 1, and the STA may initiate a TXOP to transmit a frame to AP 2 instead of AP 1. Accordingly, when an STA performs a roaming operation, the TXOP to transmit to AP 1 and the TXOP to transmit to AP 2 may not overlap.

[0106] AP 1 can transmit data frames queued for transmission to the STA to the STA. If the STA operates in a normal transmission / reception state, AP 1 can transmit data frames to the STA without transmitting an initial control frame. On the other hand, if the STA performs a listening operation, AP 1 must transmit an initial control frame to the STA before transmitting a data frame to the STA. If the STA receives the initial control frame and responds with a CTS frame, AP 1 can transmit a data frame to the STA. In the following FIGS. 5 to 8b, the above-described matters may be common to the roaming operation based on the above-described operation.

[0107] FIG. 5 is a diagram illustrating a multi-link single radio terminal roaming method to which the present disclosure applies. Referring to FIG. 5, as described above, STA (510) may transmit an EML OMN frame (601) to AP 1 to add an EMLSR link, and receive a response frame (603) after transmitting an RAI (602) frame to indicate the start of roaming. In addition, AP 1 (520) may perform a context exchange procedure, as described above.

[0108] Here, AP 1 (520) can transmit the last frame in the queue to STA (510). The MorePPDU (physical protocol data unit) bit included in the MAC header of the data frame can be used to indicate the last data frame transmitted by AP 1 (520). For example, the HT control field of the MAC header of the last data frame transmitted by AP 1 (520) can include a CAS Control subfield in the form of A-Control. The CAS Control subfield has a MorePPDU bit, and the bit can be set to 0. As another example, the last data frame can be indicated using reserved bits of the CAS Control subfield instead of using the MorePPDU bit. As another example, the last data frame can be indicated by indicating time information (e.g., one OFDM symbol time) that is longer than "PPDU length indicated by the Preamble of the data frame + SIFS + PPDU length indicated by the Preamble of the BA frame" in which the duration of the MAC header is set. The HT control field of the above MAC header may include control subfields of the A-Control type other than the CAS control subfield, and the subfield may indicate the last data frame.

[0109] As another example, the last data frame can be indicated by utilizing padding of the MAC layer. The MPDU delimiter of the A-MPDU used as MAC layer padding can be repeated after a specific delimiter parameter is set after the last MPDU of the A-MPDU. Here, if the MPDU delimiter is repeated a specific number of times or more, it can be indicated that the corresponding frame is the last data frame. As another example, if the MPDU length information of the MPDU delimiter has a specific value other than 0, it can be indicated that the corresponding frame is the last frame. For example, if the length value is set to a specific value that is not 0 but that does not allow for the configuration of a single MAC frame, it can be indicated that the corresponding frame is the last frame. Here, the information indicating the last frame described above is referred to as a 'last frame indicator', but is not limited to that name. In other words, whether it is the last frame can be indicated in various forms.

[0110] As another example, the More Data bit included in the MAC header of the data frame transmitted by AP 1 (520) to indicate the last data frame may be used to indicate the last data frame.

[0111] STA (510) may respond with a response frame (e.g. BA (BlockAck) frame, ACK frame) to the last data frame of AP 1 (520) (e.g. data frame of AP 1 including last frame indicator, 604). If STA (510) successfully receives all frames of AP 1 (520), STA (510) may indicate successful reception of all frames through BA frame (605). When AP 1 (520) completes receiving BA frame (605), AP 1 (520) may perform context exchange with AP 2 (530) again. The context exchanged with AP 2 (530) may include SN information of the last frame successfully transmitted by AP 1 (520) to STA (530). In addition, the context exchanged with AP 2 (530) may also include a 'last frame transmission completion indicator'.

[0112] For example, AP 2 (530) may consider that STA (510) is unable to receive frames until the last frame transmission from AP 1 (520) to STA (510) is completed. Therefore, AP 2 (530) may not transmit frames including an initial control frame to STA (510). When AP 2 (530) receives a last frame transmission completion indicator or corresponding information from AP 1 (520), AP 2 (530) may initiate frame transmission to STA (510). Here, the time point at which AP 2 (530) may initiate frame transmission to STA (510) may be the time point at which the last frame transmission completion indicator is received.

[0113] As another example, the time point at which AP 2 (530) can initiate frame transmission to STA (510) may be immediately after or after a time corresponding to a certain period of time (e.g., aSIFSTime + aSlotTime + aRxPHYStartDelay time or aSIFSTime + aSlotTime + aRxPHYStartDelay time + EMLSR transition delay time) after receiving the last frame transmission completion indicator and considering the frame reception waiting time and EMLSR transition delay of STA (510). That is, AP 2 (530) may initiate data frame (606) transmission to STA immediately after or after a certain period of time after receiving the last frame transmission completion indicator.

[0114] As another example, AP 1 (520) may immediately stop transmission to STA (510) even before receiving a response frame (e.g., Ack frame, BlockAck frame) for a frame designated as the last data frame from STA (510), thereby inducing transmission and reception between STA (510) and AP 2 (530). For example, if the channel quality of AP 1 (520) and STA (510) is rapidly deteriorating beyond a certain condition, if the channel quality of STA (510) measured by AP 2 (530) is higher than a threshold value compared to AP 1 (520), or if a criterion based on congestion other than channel quality is satisfied, AP 1 (520) may immediately stop transmission to STA (510) even before receiving a response frame (e.g., Ack frame, BlockAck frame) for the frame designated as the last data frame from STA (510). In the above case, AP 1 (520) may transmit an indicator indicating that the corresponding TXOP is the last TXOP for the last STA (510) regardless of whether all data up to the last data frame has been successfully transmitted. The indicator may be information included in the MAC header. Alternatively, the above-described indicator may be indicated by utilizing another length value in the method of indicating the last data frame using the MPDU delimiter. After completing the TXOP including the above-described indicator, AP 1 (520) performs an operation of exchanging contexts (e.g., updating) with AP 2 (530) and may forward untransmitted data to AP 2 (530). As another example, AP 1 may perform a context update operation including a roaming completion indicator.The STA (510) that has received an indicator indicating that it is the last TXOP can perform an EMLSR transition operation to the operating channel of AP 2 (530) immediately after the TXOP ends.

[0115] FIG. 6a and FIG. 6b are diagrams illustrating a multi-link single radio terminal roaming method to which the present disclosure is applied.

[0116] Referring to FIGS. 6A and 6B , as described above, STA (510) may transmit an EML OMN frame (601) to AP 1 (520) to add an EMLSR link, and may receive a response frame (603) after transmitting an RAI (602) frame to indicate the start of roaming. In addition, AP 1 (520) may perform a context exchange procedure, as described above.

[0117] Referring to FIG. 6A, STA (510) may want to operate with AP 2 (530) before receiving the last data frame of AP 1 (520). For example, if STA (510) determines that the communication quality with AP 1 (520) is rapidly deteriorating, STA (510) may want to operate with AP 2 (530) before receiving the last data frame of AP 1 (520). The deterioration of communication quality may be determined through the received signal strength indicator (RSSI) or the received channel power indicator (RCPI) of the received signal. For example, if the RSSI or RCPI of AP 1 (520) is below a specific threshold for initiating roaming, or if the signal quality (RSSI, RCPI) of AP 2 (530) measured by STA (510) is higher than that of AP 1 (520) by a specific threshold, STA (510) may want to operate with AP 2 (530) before receiving the last data frame of AP 1 (520). However, this may not be limited thereto.

[0118] If STA (510) is no longer operating with AP 1 (520) and wants to communicate with AP 2 (530), STA (510) may no longer be able to receive frames from AP 1 (520). The RSSI or RCPI roaming initiation specific threshold may be included in the control information (e.g., beacon, or roaming control message) transmitted (broadcasted) by AP 1 (520) or may be a preset value. Accordingly, even if AP 1 (520) transmits an initial control frame (607) to STA (510), STA (510) may not respond to AP 1 (520). AP 1 (520) may attempt to transmit the initial control frame (607) to STA (510) N times (N is a natural number). If there is no response from STA (510) even after AP 1 (520) transmits the initial control frame (607) N times, AP 1 (520) can determine that STA (510) is operating with AP 2 (530).

[0119] As another example, if STA (510) does not respond to the initial control frame (607) even once, AP 1 (520) may determine that STA (510) operates with AP 2 (530). If AP 1 (520) determines that STA (510) operates with AP 2 (530), AP 1 (520) may perform context exchange with AP 2 (530) again. The context exchanged with AP 2 (530) may include SN information of the frame that AP 1 (520) last successfully transmitted to STA (510). In addition, the context exchanged with AP 2 (530) may also include a 'STA (510) movement indicator' indicating that the STA is moving, but may not be limited to that name. Since AP 1 (520) failed to transmit a frame to be delivered to STA (510) in the queue, AP 1 (520) may delete the frame in the queue. Alternatively, AP 1 (520) may forward data to AP 2 (530) so that AP 2 (530) may transmit the frame in the queue to STA (510). Data transmission from AP 1 (520) to AP 2 (530) may be performed via a wired link (e.g., Ethernet) or via a wireless LAN link between APs. As another example, a separate channel may be configured for wireless LAN communication between APs, and is not limited to a specific form. AP 2 (530) may transmit data received from AP 1 (520) to STA (510). AP 2 (530) may receive an STA movement indicator included in a context exchange from AP 1 (520). The STA movement indicator may indicate that the STA (510) is operable with AP 2 (530).

[0120] After that, AP 2 (530) may wait to receive a frame from STA (510). As another example, AP 2 (530) may transmit an initial control frame or data frame (608) to STA (510). The time at which AP 2 (530) may initiate frame transmission to STA (510) may be the time at which it receives an STA movement indicator from AP 1 (520). As another example, the time point at which AP 2 (530) can initiate frame transmission to STA (510) is immediately after or after a time corresponding to “aSIFSTime + aSlotTime + aRxPHYStartDelay time or aSIFSTime + aSlotTime + aRxPHYStartDelay + EMLSR transition delay time” from the time point at which the STA movement indicator is received, taking into account the STA’s frame reception waiting time and EMLSR transition delay.

[0121] As another example, referring to FIG. 6B, AP 2 (530) may not perform a context exchange with AP 1 (520). Here, the operation prior to the context exchange may be the same as that of FIG. 6A described above, and AP 2 (530) may wait to receive a frame from STA (510) instead of performing a context exchange including an STA movement indicator with AP 1 (520). However, STA (510) may not be able to immediately perform communication with AP 2 (530) even if it no longer operates with AP 1 (520). For example, if STA (510) performs frame transmission and reception operation with AP 1 (520) for a predetermined period of time or longer, STA (510) may apply MediumSyncDelay timer, which is a timer for setting NAV (network allocation vector) in the link where AP 2 (530) operates, because STA (510) was not able to perform channel detection operation in the link where AP 2 (530) operates. The length of MediumSyncDelay timer may be a predetermined time. For example, the length of MediumSyncDelay timer may be aPPDUMaxTime, which is a predetermined maximum time length of PPDU. STA (510) may release the timer if it decodes a frame while MediumSyncDelay timer is operating. In addition, STA (510) may only perform CCA (channel clear assessment) operation (channel detection operation) in the section where the timer is operating. When STA (510) performs roaming, if the energy is below a certain level as a result of CCA while the MediumSyncDelay timer is running in the target AP performing roaming, STA (510) may transmit a frame of a restricted format. Here, the frame of the restricted format may be an RTS (request to send, 609) frame and a CTS (clear to send, 610) frame.STA (510) can transmit an RTS frame (609) and a CTS frame (610) to indicate to AP 2 (530) that communication is possible. Here, the MAC header of the RTS frame (609) and the CTS frame (610) has a duration field. The duration field can indicate the length of the entire time interval (TXOP) that the STA (510) wants to communicate. When the STA (510) transmits the RTS frame (609), the STA (510) can transmit the RTS frame (609) to AP 2 (530). If there is an uplink frame to be transmitted from STA (510) to AP 2 (530), STA (510) can set the value of the duration field included in the RTS frame (609) to "RTS frame transmission time + SIFS + CTS frame transmission time + SIFS uplink data frame transmission time + SIFS + BA transmission time". On the other hand, if STA (510) does not have an uplink frame to be transmitted from AP 2 (530), STA (510) can set the value of the duration field included in the RTS frame (609) to "RTS frame transmission time + SIFS + CTS frame transmission time length". AP 2 (530) can receive the RTS frame (609) from STA (510) and respond by transmitting a CTS frame (610) to STA (510). AP 2 (530) may receive (or may not receive) an uplink frame depending on the value of the duration field set by STA (510) in the RTS frame (609). If STA (510) receives a CTS frame (610) in response to the RTS frame (609), the MediumSyncDelay timer may be released. On the other hand, if STA (510) transmits an RTS frame (609) but there is no CTS frame (610) response, STA (510) may not be able to perform frame transmission during the MediumSyncDelay timer.

[0122] In addition, as an example, if STA (510) initially transmits a CTS frame while the MediumSyncDelay timer is operating, STA (510) may transmit a CTS-to-Self frame with the CTS frame. The CTS-to-Self frame is a CTS frame in which the receiver address of the MAC header is set to the MAC address of STA (510) (i.e., its own MAC address). The duration value set in the MAC header of the CTS-to-Self frame may be set to "CTS-to-Self + SIFS + Trigger Frame time." If AP 2 (530) that receives CTS-to-Self does not currently have a frame being transmitted or received, it may respond with a TF (trigger frame) after the SIFS time. If AP 2 (530) does not recognize the presence of an uplink data frame from STA (510), AP 2 (530) may only respond with TF, and the duration set in the MAC header of the TF may be set to the TF transmission time. If AP 2 (530) recognizes the presence of an uplink data frame from STA (510), the duration set in the MAC header of the TF is set to a time that includes “the transmission time of the data frame to be transmitted by the STA + SIFS + BA transmission time.” Information about the data frame to be transmitted by STA (510) may be information received from AP 1 (520). If STA (510) receives TF in response to the CTS-to-Self frame, the MediumSyncDelay timer may be released. If STA (510) transmits a CTS-to-Self frame but there is no TF response, STA (510) may not be able to perform frame transmission during the MediumSyncDelay timer.

[0123] If the STA (510) initially transmits a CTS frame while the MediumSyncDelay timer is operating, the STA (510) may transmit a CTS-to-Self frame. The CTS-to-Self frame is a CTS frame in which the receiver address of the MAC header is set to the MAC address of the STA (510) (i.e., its own MAC address). If the STA (510) has an uplink frame to transmit to AP 2 (530), the STA (510) may set the value of the duration field set in the MAC header of the CTS-to-Self frame to as much as necessary for uplink transmission. If the STA (510) does not have an uplink frame to transmit to AP 2 (530), the STA (510) may set the value of the duration field set in the MAC header of the CTS-to-Self frame to 0. This indicates that the STA (510) has no more frames to transmit after transmitting the CTS-to-Self frame.

[0124] STA (510) can release the MediumSyncDelay timer by receiving a CTS response after transmitting an RTS frame or by transmitting a CTS frame (CTS-to-Self frame).

[0125] As another example, if STA (510) transmits a CTS frame, STA (510) cannot release the MediumSyncDelay timer, and can release the MediumSyncDelay timer only after decoding the frame normally after transmitting the CTS frame. AP 2 (530) can receive the RTS frame and CTS frame of STA (510), and can know that STA (510) is in a communication state. AP 2 (530) can transmit a downlink data frame (611) starting with an initial control frame to STA (510), or can directly transmit the downlink data frame (611) to STA (510).

[0126] Referring to FIGS. 6A and 6B, AP 1 (520) may induce STA (510) to perform communication with AP 2 (530). That is, AP 1 (520) may immediately stop transmission to STA (510) and induce transmission and reception with AP 2 (530) even before receiving a response frame (e.g., Ack frame, BlockAck frame) for the frame specified as the last data frame from STA (510). For example, if the channel quality of AP 1 (520) and STA (510) is rapidly deteriorating beyond a certain condition, if the channel quality of STA (510) measured by AP 2 (530) is higher than a threshold value compared to AP 1 (520), or if a criterion based on congestion other than channel quality is satisfied, AP 1 (520) may transmit an indicator indicating that the TXOP is the last TXOP for the last STA (510) regardless of whether all data up to the last data frame has been successfully transmitted. The indicator may be information included in the MAC header. As another example, the above-described indicator may be indicated as the last data frame using an MPDU delimiter or may be indicated using a length value. After completing the TXOP including the above indicator, AP 1 (520) performs an operation of exchanging contexts (e.g., updating) with AP 2 (530) and can forward untransmitted data to AP 2 (530). In addition, a context updating operation can be performed including a roaming completion indicator. An STA that has received an indicator indicating that it is the last TXOP can perform an EMLSR transition operation to the operating channel of AP 2 (530) immediately after the TXOP ends.

[0127] FIG. 7 is a diagram illustrating a multi-link single radio terminal roaming method to which the present disclosure is applied.

[0128] Referring to FIG. 7, as described above, STA (510) may transmit an EML OMN frame (601) to AP 1 (520) to add an EMLSR link, and may receive a response frame (603) after transmitting an RAI (602) frame to indicate the start of roaming. In addition, AP 1 (520) may perform a context exchange procedure, as described above.

[0129] Here, AP 1 (520) may not be able to completely transmit the last frame in the queue to STA (510) and the time when roaming is performed may arrive. That is, AP 1 (520) may transmit only some of the frames and the time when roaming is performed may arrive. AP 1 (520) may attempt to transmit a data frame to STA (510) before the EMLSR transition delay before the time when roaming is performed. AP 1 (520) does not attempt to transmit any more data frames to STA (510) thereafter. In addition, AP 1 (520) and STA (510) may end frame exchange before the EMLSR transition delay from the time when roaming is performed. That is, AP 1 (520) and STA (510) may end TXOP before the EMLSR transition delay from the time when roaming is performed.

[0130] AP 2 (530) can initiate frame transmission to STA (510) from the time when roaming is performed. AP 2 (530) can initiate transmission of initial control frame and data frame (613) to STA (510) or initiate transmission of data frame. AP 2 (530) and STA (510) can perform communication from the time when roaming is performed. Here, since AP 1 (520) has not transmitted a frame in the queue to STA (510), the frame in the queue can be deleted. As another example, AP 1 (520) can forward data so that AP 2 (530) can transmit a frame in the queue to STA (510). AP 2 (530) can transmit data received from AP 1 (520) to STA (510).

[0131] As another example, AP 1 (520) and STA 1 (510) can communicate until roaming is performed. After roaming is performed and the EMLSR transition delay time has elapsed, AP 2 (530) and STA 2 (510) can communicate. That is, AP 2 (530) can initiate frame transmission to STA (510) after the EMLSR transition delay time has elapsed after roaming is performed.

[0132] Here, the time at which roaming is performed may be a common time for STA (510), AP 1 (520), and AP 2 (530) through a context exchange procedure and transmission of an RAI frame (602) of STA (510). Specifically, AP 1 (520) may transmit a roaming announcement response (RAR) frame in response to the RAI frame of STA (510), and STA (510) and AP 1 (520) may perform bidirectional information exchange during roaming.

[0133] FIG. 8a and FIG. 8b are diagrams illustrating a multi-link single radio terminal roaming method to which the present disclosure is applied.

[0134] Referring to FIGS. 8A and 8B, as described above, STA (510) may transmit an EML OMN frame (601) to AP 1 (520) to add an EMLSR link, and may receive a response frame (603) after transmitting an RAI (602) frame to indicate the start of roaming. In addition, AP 1 (520) may perform a context exchange procedure, as described above.

[0135] Here, AP 1 (520) can transmit the last frame in the queue to STA (510). The MorePPDU (physical protocol data unit) bit included in the MAC header of the data frame can be used to indicate the last data frame transmitted by AP 1 (520). For example, the HT control field of the MAC header of the last data frame transmitted by AP 1 (520) can include a CAS Control subfield in the form of A-Control. The CAS Control subfield has a MorePPDU bit, and the bit can be set to 0. As another example, the last data frame can be indicated using reserved bits of the CAS Control subfield instead of using the MorePPDU bit. As another example, the last data frame can be indicated by indicating time information (e.g., one OFDM symbol time) that is longer than "PPDU length indicated by the Preamble of the data frame + SIFS + PPDU length indicated by the Preamble of the BA frame" in which the duration of the MAC header is set. As another example, the More Data bit included in the MAC header of the data frame transmitted by AP 1 (520) to indicate the last data frame may be used to indicate the last data frame.

[0136] As another example, the last data frame can be indicated by utilizing padding of the MAC layer. The MPDU delimiter of the A-MPDU used as MAC layer padding can be repeated after a specific delimiter parameter is set after the last MPDU of the A-MPDU. Here, if the MPDU delimiter is repeated a specific number of times or more, it can be indicated that the corresponding frame is the last data frame. As another example, if the MPDU length information of the MPDU delimiter has a specific value other than 0, it can be indicated that the corresponding frame is the last frame. For example, if the length value is set to a specific value that is not 0 but that does not allow for the configuration of a single MAC frame, it can be indicated that the corresponding frame is the last frame. Here, the information indicating the last frame described above is referred to as a 'last frame indicator', but is not limited to that name. In other words, whether it is the last frame can be indicated in various forms. As another example, the More Data bit included in the MAC header of the data frame transmitted by AP 1 (520) to indicate the last data frame may be used to indicate the last data frame.

[0137] STA (510) may respond to the last data frame of AP 1 (520) (e.g., data frame of AP 1 including the last frame indicator, 614) with a response frame (e.g., BA (BlockAck) frame, ACK frame). If STA (510) successfully receives all frames of AP 1 (520), STA (510) may indicate that it has successfully received all frames through BA frame (615).

[0138] Referring to FIG. 8A, STA (510) may have errors in some or all of the frames received from AP 1 (520), and the BA frame (615) may indicate which frames need to be retransmitted. AP 1 (520) may retransmit the frames in which errors occurred to STA (510) even if the last frame including the last frame indicator was transmitted. STA (510) may receive the retransmitted frames, and if there are no errors in the retransmitted frames, may indicate successful reception of all frames in the BA frame (616). Upon completion of reception of the BA frame (BA frame indicating successful reception of all frames, 616) of STA (510), AP 1 (520) may perform context exchange again with AP 2 (530). The context exchanged with AP 2 (530) may include SN information of the frame that AP 1 (520) last successfully transmitted to STA (510). In addition, the context exchanged with AP 2 (530) may also include a 'last frame transmission completion indicator'. AP 2 (530) considers that STA (510) cannot receive frames until the last frame transmission from AP 1 (520) to STA (510) is completed. Therefore, AP 2 (530) may not transmit frames including an initial control frame to STA (510). When AP 2 (530) receives the last frame transmission completion indicator from AP 1 (520), AP 2 (530) may initiate frame transmission to STA (510). The time point at which AP 2 (530) may initiate frame transmission to STA (510) may be the time point at which the last frame transmission completion indicator is received.As another example, the time point at which AP 2 (530) can initiate frame transmission to STA (510) is immediately after or after the time corresponding to “aSIFSTime + aSlotTime + aRxPHYStartDelay time or aSIFSTime + aSlotTime + aRxPHYStartDelay + EMLSR transition delay time considering the frame reception waiting time of the STA and the EMLSR transition delay” from the time point at which the last frame transmission completion indicator is received.

[0139] As another example, referring to FIG. 8B, STA (510) may have an error in the frame (617) including the last frame indicator received from AP 1 (520). Specifically, there may be an error in at least one MAC protocol data unit (MPDU) or MAC service data unit (MSDU) included in the received frame (617). Here, the BA frame (618) may indicate frames that require retransmission. Here, STA (510) may want to perform roaming without receiving a retransmission frame from AP 1 (520). As an example, STA (510) may transmit the BA frame (618) including a 'last response frame' indicator. The last response frame indicator may be included in the MAC header of a QoS Null frame whose ack policy is "no ack". STA (510) can configure a BA frame and a QoS Null frame as an A-MPDU (aggregated MAC protocol data unit) and transmit them to AP 1 (520). Accordingly, AP 1 (520) can receive a response frame including a 'last response frame' indicator from STA (510). If AP 1 (520) receives a response frame including a 'last response frame' indicator, AP 1 (520) can perform context exchange with AP 2 (530) again without retransmitting the failed transmission frame to STA (510). The context exchanged with AP 2 (530) includes SN information of the frame that AP 1 (520) last successfully transmitted to STA (510) and includes a 'roaming complete' indicator. AP 1 (520) can delete frames that need to be transmitted to STA (510) (i.e., frames that have failed to be transmitted) from the queue.As another example, AP 1 (520) may forward data to AP 2 (530) so that AP 2 (530) may transmit the remaining frames of AP 1 (520) to STA (510). AP 2 (530) considers that STA (510) is unable to receive frames until the last frame transmission from AP 1 (520) to STA (510) is completed. Therefore, AP 2 (530) does not transmit frames including initial control frames to STA (510). When AP 2 (530) receives a roaming completion indicator from AP 1 (520), AP 2 (530) may initiate frame transmission to STA (510). The time point at which AP 2 (530) may initiate frame transmission to STA (510) may be the time point at which it receives the roaming completion indicator. As another example, the time point at which AP 2 (530) can initiate frame transmission to STA (510) is immediately after or after a time corresponding to “aSIFSTime + aSlotTime + aRxPHYStartDelay time or aSIFSTime + aSlotTime + aRxPHYStartDelay + EMLSR transition delay time” from the time point at which the roaming completion indicator is received, taking into account the frame reception waiting time of the STA and the EMLSR transition delay.

[0140] In addition, the embodiments related to the drawings illustrated in FIGS. 5 to 8b are utilized for wireless LAN roaming operations. Wireless LAN terminals (devices equipped with wireless LAN communication technology, such as smartphones, tablets, laptop computers, smart pads, game consoles, and head-mounted displays) may be non-AP STAs (i.e., STAs). The wireless LAN terminal may move due to the movement of a user carrying the terminal, and the signal quality of the connected AP may change depending on the movement, and other APs that are not connected may be searched for. The wireless LAN terminal decides to roam based on various factors, such as the signal quality of the searched AP and the movement tendency of the terminal. When the wireless LAN terminal decides to roam, it receives the remaining data from the connected AP and performs a roaming operation of connecting to the searched AP. At this time, the wireless LAN terminal STA (510) may support the EMLSR operation, and thus the roaming operation may be performed based on the above-described FIGS. 5 to 8b. According to the operation of the present disclosure, a wireless LAN terminal supporting EMLSR can receive data from a connected AP without loss and can resume communication with a discovered AP without delay even after performing a roaming operation. Through these embodiments, the performance and stability of the wireless LAN terminal can be increased, and the wireless LAN network can operate continuously.

[0141] The following drawings 9 to 13 describe a case where a wireless LAN terminal, STA (station), AP 1, AP 2, and a router operate in a wireless LAN network. However, this is for convenience of explanation and may not be limited thereto. STAs, APs, and routers may have MAC addresses, which are physical addresses, and STAs and routers may have IP (internet protocol) addresses. Here, the MAC address is a unicast MAC address. For example, the IP address of STA may be 111.111.111.111, and the MAC address may be AA-AA-AA-AA-AA-AA. The MAC address of AP 1 may be BB-BB-BB-BB-BB-BB, and the MAC address of AP 2 may be CC-CC-CC-CC-CC-CC. In addition, the IP address of the router may be 555.555.555.555, and the MAC address may be DD-DD-DD-DD-DD-DD-DD. Additionally, in the following, AP 1 may be referred to as the previous AP (or old AP) as the AP to which the STA is currently connected and operating. Additionally, AP 2 may be referred to as the target AP (or new AP) to which the STA is attempting to roam, but may not be limited to these names.

[0142] When an IP packet with an IP address of 111.111.111.111 arrives on the network to an STA, and the router does not recognize a MAC address to which the IP packet with 111.111.111.111 will be forwarded, the router may broadcast an Address Resolution Protocol (ARP) request packet. The STA may receive the ARP request through the AP to which it is currently connected. Additionally, the STA may transmit an ARP reply including its MAC address in response to the ARP request through the AP to which it is currently connected. Thereafter, the STA may receive wireless LAN data frames with a destination address (DA) of AA-AA-AA-AA-AA-AA through the AP to which it is currently connected. Here, the wireless LAN data frames may be wireless LAN frames reconfigured by AP 1 to forward the received IP packet over the wireless LAN.

[0143] For example, when the link quality of AP 1 falls below a certain level, the STA may search for AP 2 and determine AP 2 as an AP to perform roaming (e.g., new AP). That is, the STA may attempt to connect to AP 2 and perform communication. For example, a roaming operation may be an operation in which the STA switches connection from one AP (old AP) to another AP (new AP) and performs communication. When the STA determines the roaming operation, an AP 2 link addition (add link) procedure may be initiated between AP 1 and the STA. The link addition procedure may be the same as or similar to a multi-link reconfiguration operation. AP 1 may transmit a frame indicating the addition of a link of a frequency on which AP 2 operates to the STA, and the STA may add the received link as one of the multi-links.

[0144] When an STA indicates to start roaming, the STA may transmit a roaming announcement indication (RAI) frame to AP 1. The RAI frame may include information about AP 2, a roaming target AP to perform a roaming operation (e.g., at least one of the MAC address of AP 2, the link ID (identifier) ​​on which AP 2 operates, other information that can identify AP 2, and the roaming multicast MAC address of the STA (e.g., 01-00-5E-AA-AA-AA-AA)). The roaming multicast MAC address of the STA may be configured using the low-order last 24 bits of the MAC address of the STA plus 01-00-5E (or other specific 24 bits defined in advance). When AP 1 receives the RAI frame, AP 1 may respond to the STA with an ACK frame. AP 1, which receives the RAI frame, may transmit an AP control frame (e.g., HO Start) to AP 2, which includes at least one of the unicast MAC address of the roaming target STA, the roaming multicast MAC address of the roaming target STA, the MAC address of the old AP, the MAC address of the new AP, a sequence number (SN), and a pseudosequence number (PN), thereby indicating that the STA intends to perform roaming. The AP control frame to AP 2 may be an Ethernet frame configured with the RAI frame transmitted by the STA as a payload. The above-described matters may be commonly applied to FIGS. 9 and 13 below.

[0145] FIG. 9 is a diagram illustrating a multi-path packet forwarding roaming method to which the present disclosure is applied.

[0146] Referring to FIG. 9, STA (710) may receive an ARP request (801) from router (740), transmit an ARP response (802), and then perform a link addition operation. When STA (710) initiates roaming, it may transmit an RAI frame (803) to AP 1 (720), as described above.

[0147] Here, AP 1 (720) that received the RAI frame can transmit an ARP response (ARP replay) containing a roaming multicast MAC address (e.g. 01-00-5E-AA-AA-AA) with a MAC address matching the IP address (e.g. 111.111.111) of STA (710) to the router (740) instead of STA (710). Transmitting an ARP response (804) by AP 1 (720) instead of STA (710) can be called a Gratuitous ARP, but is not limited to that name. When AP 1 (720) receives an ARP request requesting the MAC address of STA (710) from the network after receiving the RAI frame (803), AP 1 (720) may transmit an ARP response including the roaming multicast MAC address of STA (710) used by AP 1 (720) when roaming, instead of STA (710), in response to the ARP request. For example, AP 1 (720) transmitting an ARP response to the ARP request instead of STA (710) may be Proxy ARP.

[0148] As another example, when STA (710) performs roaming, AP 2 (730), which has been instructed to roam by AP2 AP control frame, may transmit an ARP response (805) including a roaming multicast MAC address (e.g. 01-00-5E-AA-AA-AA) with a MAC address matching the IP address (e.g. 111.111.111) of STA (710) instead of STA (710). The ARP response (805) transmitted by AP 2 (730) instead of STA (710) may be a Gratuitous ARP, but is not limited to that name. When AP 2 (730) receives an ARP request requesting the MAC address of STA (710) from the network after being instructed to roam by an AP control frame to AP 2 (730), AP 2 (730) may, in response, transmit an ARP response including the roaming multicast MAC address of STA (710) used by AP 2 (730) when roaming, instead of STA (710). AP 2 (730) transmitting an ARP response to the ARP request instead of STA (710) may be referred to as Proxy ARP.

[0149] When the router (740) receives an ARP response that maps the IP address (e.g., 111.111.111.111) of the STA (710) to the roaming multicast MAC address (e.g., 01-00-5E-AA-AA-AA), the router (740) performs an ARP table update within the router (740). After the router (740) receives the ARP response and updates the ARP table, the IP packet (806) to 111.111.111.111 received by the router (740) can be broadcast to 01-00-5E-AA-AA-AA, which is the roaming multicast address to the STA (710), and the IP packet (806) can be received by AP 1 (720) and AP 2 (730).

[0150] STA (710) can support multiple links, and STA (710) can simultaneously transmit and receive frames from AP 1 (720) and AP 2 (730). AP 1 (720) and AP 2 (730) can convert frames received with the roaming multicast MAC address of STA (710) into the unicast MAC address of STA (710) (e.g. AA-AA-AA-AA-AA-AA) and transmit the wireless LAN MAC frames (807, 808) to STA (710). STA (710) can form a complete data frame from the frames received from AP 1 (720) and AP 2 (730). The complete data frame can be formed by combining parts in which no errors occur in the frames received from AP 1 (720) and AP 2 (730). STA (710) can transmit reception responses (BA, BlockAck, 809, 810) for frames received from AP 1 (720) and AP 2 (730). The reception responses can transmit different BAs indicating error states for frames received from each AP, or can form a BA (same error state) indicating error states of frames formed by combining frames received from AP 1 (720) and AP 2 (730) and transmit the result to AP 1 (720) and AP 2 (730).

[0151] When AP 2 (730) receives BA, it can determine that STA (710) has successfully performed roaming. AP 2 (730) can transmit an AP2 AP control frame (e.g. HO Complete) to inform AP 2 (730) that STA (710) has successfully performed roaming. AP 1 (720), which receives the AP2 AP control frame (e.g. HO Complete) from AP 2 (730) to inform STA (710) that roaming has been successfully performed, can transmit a RAR (Roaming Announcement Response, 811)) frame to STA (710) to instruct it to complete roaming to AP 2 (730) and switch the link. After receiving the RAR, STA (710) can transmit an ACK in response thereto and terminate communication with AP 1 (720). AP 1 (720) may terminate the connection with STA (710) after a certain period of time after transmitting RAR and delete related information of STA (710).

[0152] After completing the roaming of STA (710) by transmitting an AP2 AP control frame (e.g. HO Complete) notifying that STA (710) has successfully performed roaming, AP 2 (730) may transmit an ARP response containing the original unicast MAC address (e.g. AA-AA-AA-AA-AA-AA) to a MAC address matching the IP address (e.g. 111.111.111) of STA (710) on behalf of STA (710). The ARP response transmitted by AP 2 (730) on behalf of STA (710) may be referred to as a Gratuitous ARP.

[0153] After STA (710) completes roaming of STA (710) by transmitting an AP2 AP control frame (e.g. HO Complete) notifying that roaming has been successfully performed, when AP 2 (730) receives an ARP request requesting the MAC address of STA (710) from the network, AP 2 (730) may transmit an ARP response including the unicast MAC address of STA (710) in response to this request instead of STA (710). AP 2 (730) transmitting an ARP response to the ARP request instead of STA (710) may be proxy ARP.

[0154] When the router (740) receives an ARP response that maps the IP address (e.g., 111.111.111.111) of the STA (710) to a unicast MAC address (e.g., AA-AA-AA-AA-AA-AA), the router (740) performs an ARP table update within the router (740). After the router (740) receives the ARP response and updates the ARP table, the IP packet for 111.111.111.111 received can be transmitted to the unicast address AA-AA-AA-AA-AA-AA to the STA (710), and the IP packet can be received by AP 2 (730). The AP 2 (730) can reconstruct the IP packet into a wireless LAN data frame(s) having a destination address (DA) of AA-AA-AA-AA-AA-AA and transmit the IP packet to the STA (710). STA (710) can receive wireless LAN data frame(s) through AP 2 (730).

[0155] FIG. 10 is a diagram illustrating a multi-path packet forwarding roaming method to which the present disclosure is applied.

[0156] Referring to FIG. 10, STA (710) may receive an ARP request (801) from router (740), transmit an ARP response (802), and then perform a link addition operation. When STA (710) initiates roaming, it may transmit an RAI frame (803) to AP 1 (720), as described above.

[0157] Here, AP 1 (720) that received the RAI frame (803) can transmit an ARP response (804) including a roaming multicast MAC address (e.g., 01-00-5E-AA-AA-AA) with a MAC address that matches the IP address (e.g., 111.111.111.111) of STA (710) instead of STA (710). AP 1 (720) transmitting an ARP response instead of STA (710) may be a Gratuitous ARP. If AP 1 (720) receives an ARP request requesting the MAC address of STA (710) from the network after receiving the RAI frame (803), AP 1 (720) can transmit an ARP response including the roaming multicast MAC address of STA (710) that AP 1 (720) uses when roaming in response thereto instead of STA (710). AP 1 (720) may send an ARP response to an ARP request on behalf of STA (710), which may be proxy ARP.

[0158] AP2 can also be instructed by STA (710) to roam via AP2 AP control frame. AP 2 (730) can also transmit an ARP response (805) containing a roaming multicast MAC address (e.g. 01-00-5E-AA-AA-AA) with a MAC address matching the IP address (e.g. 111.111.111) of STA (710) on behalf of STA (710). When AP 2 (730) transmits an ARP response instead of STA (710), this can be referred to as a gratuitous ARP. After being instructed to roam by an AP2 AP control frame, if AP 2 (730) receives an ARP request requesting the MAC address of STA (710) from the network, AP 2 (730) may, in response, transmit an ARP response including the roaming multicast MAC address of STA (710) used by AP 2 (730) when roaming, instead of STA (710). AP 2 (730) transmitting an ARP response to the ARP request instead of STA (710) may be proxy ARP.

[0159] When the router (740) receives an ARP response that maps the IP address (e.g., 111.111.111.111) of the STA (710) to the roaming multicast MAC address (e.g., 01-00-5E-AA-AA-AA), the router (740) performs an ARP table update within the router (740). After the router (740) receives the ARP response and updates the ARP table, the IP packet to 111.111.111.111 received can be broadcast to the roaming multicast address 01-00-5E-AA-AA-AA to the STA (710), and the IP packet can be received by AP 1 (720) and AP 2 (730).

[0160] Here, STA (710) may be a single-link wireless LAN terminal, and STA (710) may perform frame transmission and reception only with one AP among AP 1 (720) and AP 2 (730) at a specific time. AP 1 (720) may convert a frame received with the roaming multicast MAC address of STA (710) into the unicast MAC address of STA (710) (e.g. AA-AA-AA-AA-AA-AA) and transmit the wireless LAN MAC frame (812) to STA (710). STA (710) may transmit a reception response (BA, BlockAck, 813) to the frame received from AP 1 (720).

[0161] STA (710) performs a roaming (e.g. link switch) procedure to change the AP with which it communicates when the signal quality of AP 1 (720) is not good enough to require roaming or when it is time to perform roaming. After performing roaming, STA (710) can transmit a control frame (e.g. PS-Poll) to AP 2 (730) to notify that it has been connected, and AP 2 (730) that successfully receives the control frame from STA (710) can determine that STA (710) has successfully performed roaming.

[0162] In addition, STA (710) may not transmit a control frame (e.g. PS-Poll) notifying that it is connected to AP 2 (730) after performing roaming. AP 2 (730) may transmit a QoS Null frame to STA (710) after the time when STA (710) was scheduled to roam. STA (710) may transmit a acknowledgment (BA) for the QoS Null frame received from AP 2 (730) to AP 2 (730). AP 2 (730), which receives the BA from STA (710), may determine that STA (710) has successfully performed roaming.

[0163] AP 2 (730) may transmit an AP2 AP control frame (e.g. HO Complete) to inform AP 2 (730) that STA (710) has successfully performed roaming. AP 1 (720) may transmit an AP2 AP control frame (e.g. HO ACK) including information (e.g. SN) of the last successfully received data frame by STA (710) to AP 2 (730). AP 2 (730) may use data frames received to the roaming multicast address of STA (710) to construct data frame(s) (815) following the data frame successfully transmitted by AP 1 (720) and transmit the data frame(s) to STA (710).

[0164] After completing roaming of STA (710) by transmitting an AP2 AP control frame (e.g. HO Complete) notifying that STA (710) has successfully performed roaming, AP 2 (730) may transmit an ARP response containing the original unicast MAC address (e.g. AA-AA-AA-AA-AA-AA) to a MAC address matching the IP address (e.g. 111.111.111) of STA (710) on behalf of STA (710). When AP 2 (730) transmits an ARP response on behalf of STA (710), this may be referred to as a Gratuitous ARP.

[0165] When AP 2 (730) receives an ARP request requesting the MAC address of STA (710) from the network after STA (710) completes roaming by transmitting an AP2 AP control frame (e.g. HO Complete) notifying that STA (710) has successfully performed roaming, AP 2 (730) may, in response, transmit an ARP response including the unicast MAC address of STA (710) on behalf of STA (710). AP 2 (730) transmitting an ARP response to the ARP request on behalf of STA (710) may be proxy ARP.

[0166] When the router (740) receives an ARP response that maps the IP address (e.g., 111.111.111.111) of the STA (710) to a unicast MAC address (e.g., AA-AA-AA-AA-AA-AA), the router (740) performs an ARP table update within the router (740). After the router (740) receives the ARP response and updates the ARP table, the IP packet for 111.111.111.111 received can be transmitted to the unicast address AA-AA-AA-AA-AA-AA to the STA (710), and the IP packet can be received by AP 2 (730). The AP 2 (730) can reconstruct the IP packet into a wireless LAN data frame(s) having a destination address (DA) of AA-AA-AA-AA-AA-AA and transmit the IP packet to the STA (710). STA (710) can receive wireless LAN data frame(s) through AP 2 (730).

[0167] FIG. 11 is a diagram illustrating a multi-path packet forwarding roaming method to which the present disclosure is applied.

[0168] Referring to FIG. 11, STA (710) may receive an ARP request (801) from router (740), transmit an ARP response (802), and then perform a link addition operation. When STA (710) initiates roaming, it may transmit an RAI frame (803) to AP 1 (720), as described above.

[0169] Here, the STA (710) that transmitted the RAI frame (803) can transmit an ARP response (816) including a roaming multicast MAC address (e.g., 01-00-5E-AA-AA-AA) to a MAC address matching the IP address (e.g., 111.111.111) of the STA (710) via AP 1 (720). After receiving the RAI frame (803) or after overhearing the ARP response of the STA (710), the AP 1 (720) can recognize that an IP packet to the STA (710) will be transmitted to the roaming multicast MAC address of the STA (710). After receiving an AP2 AP control frame (e.g. HO Start) from AP 1 (720), AP 2 (730) can recognize that an IP packet to STA (710) will be transmitted to the roaming multicast MAC address of STA (710).

[0170] When the router (740) receives an ARP response (816) that maps the IP address (e.g., 111.111.111.111) of the STA (710) to the roaming multicast MAC address (e.g., 01-00-5E-AA-AA-AA), the router (740) performs an ARP table update within the router (740). After the router (740) receives the ARP response and updates the ARP table, the IP packet to 111.111.111.111 received can be broadcast to the roaming multicast address 01-00-5E-AA-AA-AA to the STA (710), and the IP packet can be received by AP 1 (720) and AP 2 (730).

[0171] Here, STA (710) can support multiple links and can simultaneously transmit and receive frames from AP 1 (720) and AP 2 (730). AP 1 (720) and AP 2 (730) can convert a frame (817) received with the roaming multicast MAC address of STA (710) into a unicast MAC address of STA (710) (e.g., AA-AA-AA-AA-AA-AA) to form a wireless LAN MAC frame (818, 819) and transmit it to STA (710). STA (710) can form a complete data frame from the frames received from AP 1 (720) and AP 2 (730). The complete data frame can be formed by combining parts in which no errors occurred in the frames received from AP 1 (720) and AP 2 (730). STA (710) can transmit reception responses (BA, BlockAck, 820, 821) for frames received from AP 1 (720) and AP 2 (730). The reception responses may transmit different BAs indicating error states for frames received from each AP. In addition, STA (710) can also configure a BA (same error state) indicating error states of frames composed by combining frames received from AP 1 (720) and AP 2 (730) and transmit the BA to AP 1 (720) and AP 2 (730).

[0172] When AP 2 (730) receives BA, it can determine that STA (710) has successfully performed roaming. AP 2 (730) can transmit an AP2 AP control frame (e.g. HO Complete) to AP 2 (730) informing that STA (710) has successfully performed roaming. AP 1 (720), which has received the AP2 AP control frame (e.g. HO Complete) from AP 2 (730) indicating that STA (710) has successfully performed roaming, can transmit a RAR (Roaming Announcement Response, 822) frame to STA (710) to instruct it to complete roaming to AP 2 (730) and switch the link. After receiving the RAR frame (822), STA (710) can transmit an ACK in response thereto and terminate communication with AP 1 (720). AP 1 (720) may terminate the connection with STA (710) after a certain period of time after transmitting RAR and delete related information of STA (710).

[0173] After completing roaming, STA (710) may transmit an ARP response (823) including the original unicast MAC address (e.g. AA-AA-AA-AA-AA-AA) to a MAC address matching the IP address (e.g. 111.111.111) of STA (710) via AP 2 (730). AP 2 (730) may recognize that an IP packet to STA (710) will be transmitted to the unicast MAC address of STA (710) after transmitting RAR and receiving an ACK or after overhearing the ARP response of STA (710).

[0174] When the router (740) receives an ARP response that maps the IP address (e.g. 111.111.111.111) of the STA (710) to the unicast MAC address (e.g. AA-AA-AA-AA-AA-AA), the router (740) performs an ARP table update within the router (740). After the router (740) receives the ARP response and updates the ARP table, the IP packet for 111.111.111.111 received can be transmitted to the unicast address AA-AA-AA-AA-AA-AA to the STA (710), and the IP packet can be received by AP 2 (730). The AP 2 (730) can reconstruct the IP packet into a wireless LAN data frame(s) having a destination address (DA) of AA-AA-AA-AA-AA-AA and transmit the IP packet to the STA (710). STA (710) can receive wireless LAN data frame(s) through AP 2 (730).

[0175] FIG. 12 is a diagram illustrating a multi-path packet forwarding roaming method to which the present disclosure is applied.

[0176] Referring to FIG. 12, STA (710) may receive an ARP request (801) from router (740), transmit an ARP response (802), and then perform a link addition operation. When STA (710) initiates roaming, it may transmit an RAI frame (803) to AP 1 (720), as described above.

[0177] Here, the STA (710) that transmitted the RAI frame (803) can transmit an ARP response (824) including a roaming multicast MAC address (e.g., 01-00-5E-AA-AA-AA) to a MAC address matching the IP address (e.g., 111.111.111) of the STA (710) via AP 1 (720). After receiving the RAI frame (803) or after overhearing the ARP response (824) of the STA (710), the AP 1 (720) can recognize that an IP packet to the STA (710) will be transmitted to the roaming multicast MAC address of the STA (710). After receiving an AP2 AP control frame (e.g. HO Start) from AP 1 (720), AP 2 (730) can recognize that an IP packet to STA (710) will be transmitted to the roaming multicast MAC address of STA (710).

[0178] When the router (740) receives an ARP response that maps the IP address (e.g., 111.111.111.111) of the STA (710) to the roaming multicast MAC address (e.g., 01-00-5E-AA-AA-AA), the router (740) performs an ARP table update within the router (740). After the router (740) receives the ARP response and updates the ARP table, the IP packet to 111.111.111.111 received can be broadcast to the roaming multicast address 01-00-5E-AA-AA-AA to the STA (710), and the IP packet can be received by AP 1 (720) and AP 2 (730).

[0179] Here, STA (710) may be a single-link wireless LAN terminal, and STA (710) may perform frame transmission and reception only with one AP among AP 1 (720) and AP 2 (730) at a specific time. AP 1 (720) may convert a frame received with the roaming multicast MAC address of STA (710) into the unicast MAC address of STA (710) (e.g. AA-AA-AA-AA-AA-AA) and transmit the wireless LAN MAC frame (825) to STA (710). STA (710) may transmit a reception response (BA, BlockAck, 826) to the frame received from AP 1 (720).

[0180] STA (710) performs a roaming (e.g. link switch) procedure to change the AP with which it communicates when the signal quality of AP 1 (720) is not good enough to require roaming or when it is time to perform roaming. After performing roaming, STA (710) can transmit a control frame (e.g. PS-Poll, 827) to AP 2 (730) to notify that it has been connected, and AP 2 (730) that successfully receives the control frame from STA (710) can determine that STA (710) has successfully performed roaming.

[0181] In addition, STA (710) may not transmit a control frame (e.g. PS-Poll) notifying that it is connected to AP 2 (730) after performing roaming. AP 2 (730) may transmit a QoS Null frame to STA (710) after the time when STA (710) was scheduled to roam. STA (710) may transmit a acknowledgment (BA) for the QoS Null frame received from AP 2 (730) to AP 2 (730). AP 2 (730), which receives the BA from STA (710), may determine that STA (710) has successfully performed roaming.

[0182] AP 2 (730) may transmit an AP2 AP control frame (e.g. HO Complete) to inform AP 2 (730) that STA (710) has successfully performed roaming. AP 1 (720) may transmit an AP2 AP control frame (e.g. HO ACK) including information (e.g. SN) of the last successfully received data frame by STA (710) to AP 2 (730). AP 2 (730) may use data frames received to the roaming multicast address of STA (710) to construct data frame(s) (828) following the data frame successfully transmitted by AP 1 (720) and transmit the data frame(s) to STA (710).

[0183] After completing roaming of STA (710) by transmitting an AP2 AP control frame (e.g. HO Complete) notifying that STA (710) has successfully performed roaming, AP 2 (730) may transmit an ARP response containing the original unicast MAC address (e.g. AA-AA-AA-AA-AA-AA) to a MAC address matching the IP address (e.g. 111.111.111) of STA (710) on behalf of STA (710). When AP 2 (730) transmits an ARP response on behalf of STA (710), this may be referred to as a Gratuitous ARP.

[0184] When AP 2 (730) receives an ARP request requesting the MAC address of STA (710) from the network after STA (710) completes roaming by transmitting an AP2 AP control frame (e.g. HO Complete) notifying that STA (710) has successfully performed roaming, AP 2 (730) may, in response, transmit an ARP response including the unicast MAC address of STA (710) on behalf of STA (710). AP 2 (730) transmitting an ARP response to the ARP request on behalf of STA (710) may be proxy ARP.

[0185] When the router (740) receives an ARP response that maps the IP address (e.g., 111.111.111.111) of the STA (710) to a unicast MAC address (e.g., AA-AA-AA-AA-AA-AA), the router (740) performs an ARP table update within the router (740). After the router (740) receives the ARP response and updates the ARP table, the IP packet for 111.111.111.111 received can be transmitted to the unicast address AA-AA-AA-AA-AA-AA to the STA (710), and the IP packet can be received by AP 2 (730). The AP 2 (730) can reconstruct the IP packet into a wireless LAN data frame(s) having a destination address (DA) of AA-AA-AA-AA-AA-AA and transmit the IP packet to the STA (710). STA (710) can receive wireless LAN data frame(s) through AP 2 (730).

[0186] FIG. 13 is a diagram illustrating a multi-path packet forwarding roaming method to which the present disclosure is applied.

[0187] Referring to FIG. 13, STA (710) may receive an ARP request (801) from router (740), transmit an ARP response (802), and then perform a link addition operation. When STA (710) initiates roaming, it may transmit an RAI frame (803) to AP 1 (720), as described above.

[0188] Here, the STA (710) that transmitted the RAI frame (803) can transmit an ARP response (829) including a roaming multicast MAC address (e.g., 01-00-5E-AA-AA-AA) to a MAC address matching the IP address (e.g., 111.111.111) of the STA (710) via AP 1 (720). After receiving the RAI frame (803) or after overhearing the ARP response (803) of the STA (710), the AP 1 (720) can recognize that an IP packet to the STA (710) will be transmitted to the roaming multicast MAC address of the STA (710). After receiving an AP2 AP control frame (e.g. HO STA (710)rt) from AP 1 (720), AP 2 (730) can recognize that an IP packet to STA (710) will be transmitted to the roaming multicast MAC address of STA (710).

[0189] When the router (740) receives an ARP response that maps the IP address (e.g., 111.111.111.111) of the STA (710) to the roaming multicast MAC address (e.g., 01-00-5E-AA-AA-AA), the router (740) performs an ARP table update within the router (740). After the router (740) receives the ARP response and updates the ARP table, the IP packet to 111.111.111.111 received can be broadcast to the roaming multicast address 01-00-5E-AA-AA-AA to the STA (710), and the IP packet can be received by AP 1 (720) and AP 2 (730).

[0190] Here, STA (710) can support multiple links and can simultaneously transmit and receive frames to AP 1 (720) and AP 2 (730). AP 1 (720) and AP 2 (730) can transmit frames (830) received with the roaming multicast MAC address of STA (710) to STA (710). STA (710) can construct a complete data frame from frames (830) received from AP 1 (720) and AP 2 (730). The complete data frame can be constructed by combining error-free portions of frames received from AP 1 (720) and AP 2 (730). STA (710) can transmit reception responses (BA, BlockAck, 831, 832) for frames received from AP 1 (720) and AP 2 (730). The reception response may transmit different BAs indicating error conditions for frames received from each AP, or may construct a BA (same error condition) indicating error conditions of frames composed by combining frames received from AP 1 (720) and AP 2 (730) and transmit it to AP 1 (720) and AP 2 (730).

[0191] When AP 2 (730) receives BA, it can determine that STA (710) has successfully performed roaming. AP 2 (730) can transmit an AP2 AP control frame (e.g. HO Complete) to inform AP 2 (730) that STA (710) has successfully performed roaming. AP 1 (720), which receives the AP2 AP control frame (e.g. HO Complete) from AP 2 (730) to inform STA (710) that roaming has been successfully performed, can transmit a RAR (Roaming Announcement Response, 833) frame to STA (710) to complete roaming to AP 2 (730) and instruct it to switch the link. After receiving the RAR, STA (710) can transmit an ACK in response and terminate communication with AP 1 (720). AP 1 (720) may terminate the connection with STA (710) after a certain period of time after transmitting RAR and delete related information of STA (710).

[0192] After completing roaming, STA (710) may transmit an ARP response containing the original unicast MAC address (e.g. AA-AA-AA-AA-AA-AA) to a MAC address matching the IP address (e.g. 111.111.111) of STA (710) via AP 2 (730). AP 2 (730) may recognize that an IP packet to STA (710) will be transmitted to the unicast MAC address of STA (710) after transmitting RAR and receiving ACK or after overhearing the ARP response of STA (710).

[0193] When the router (740) receives an ARP response that maps the IP address (e.g. 111.111.111.111) of the STA (710) to the unicast MAC address (e.g. AA-AA-AA-AA-AA-AA), the router (740) performs an ARP table update within the router (740). After the router (740) receives the ARP response and updates the ARP table, the IP packet for 111.111.111.111 received can be transmitted to the unicast address AA-AA-AA-AA-AA-AA to the STA (710), and the IP packet can be received by AP 2 (730). The AP 2 (730) can reconstruct the IP packet into a wireless LAN data frame(s) having a destination address (DA) of AA-AA-AA-AA-AA-AA and transmit the IP packet to the STA (710). STA (710) can receive wireless LAN data frame(s) through AP 2 (730).

[0194] FIGS. 14 to 16 illustrate a case in which a non-AP STA (STA), AP 1, AP 2, and multiple APs including AP 1 and AP 2 operate in a wireless LAN network. In addition, a device or entity that performs an upper layer role of AP 1 and AP 2 (e.g., MLD upper MAC sublayer role) may exist. In the following, the device (or entity) is referred to as MLD, but is not limited to that name. The MLD may be an Ethernet device such as a router or a switch. The MLD may control multiple lower APs including AP 1 and AP 2. The MLD may be a device that receives packets from the network and transmits them to lower APs, and receives packets from APs and transmits them to the network. For example, the MAC address of the STA may be AA-AA-AA-AA-AA-AA. The MLD can receive data packets destined for the STA from the network and transmit the data packets to AP 1, the AP to which the STA is connected. The destination address (DA) of the data packet is the STA's MAC address, AA-AA-AA-AA-AA-AA. The STA can receive data packets (data frames) transmitted by the MLD from AP 1.

[0195] Here, the STA may want to perform a roaming operation. The roaming operation is an operation in which the STA changes its connection from the currently connected AP (old AP, AP 1) to a new AP (new AP, AP 2). When the roaming operation procedure is performed, the STA may need to receive data from both AP 1 and AP 2 simultaneously to ensure continuity of data reception. Therefore, the MLD, which receives data from the network, needs to forward the data to both AP 1 and AP 2 during the roaming operation. In addition, after the roaming operation is completed, the MLD may need to forward data only to the new AP, AP 2. Here, a link aggregation group (LAG) may be configured to perform the above-described operations.

[0196] A LAG can be composed of a group of Ethernet interfaces (e.g., physical ports of a device). The terminal that forms a LAG is called an aggregator, but is not limited to that name. The Ethernet interfaces included in the LAG use the same MAC address, which is the MAC address of the aggregator. The MAC address of the aggregator can be set to the representative MAC address of one of the device's interfaces or can be set to an arbitrary MAC address. The MLD can be a device that supports LAG. The MLD can form a LAG from all or some of the interfaces to which the APs are connected (e.g., AP 1, AP 2, AP N (e.g., 3)).

[0197] The packet transmitted to establish a LAG is a link aggregation control protocol data unit (LACPDU). LACPDU can be transmitted from aggregators that have formed a LAG. LACPDU can identify a LAG and enable transmission between interfaces on which the LAG is formed. In addition, an aggregation link can be established through transmission of an LACPDU. An aggregation link is established between aggregators that have formed a LAG and should be distinguished from a multi-link of a wireless LAN. For example, the name referred to as 'link' is a name used in a multi-link of a wireless LAN, and 'aggregation link' and 'LAG link' are names that are referred to in consideration of link aggregation and may be names that distinguish links between each other. However, it may not be limited to the name or the embodiment.

[0198] An STA may search for other APs while performing communication by connecting to AP 1. The other APs may be at least one AP including AP 2. The STA may initiate a roaming operation to AP 2 and add a link of AP 2. To add a link of AP 2, the STA may transmit a multi-link (re)configuration frame to AP 1. AP 1 may transmit the received frame to MLD. Alternatively, AP 1 may transmit the received frame to AP 2. Through this, the STA may be configured to be able to use the link of AP 2. That is, when a link of AP 2 is added to the STA, the STA may be in a state where it can communicate with AP 2. The above-described matters may be commonly applied to FIGS. 14 to 16, and FIGS. 14 to 16 below are described based on this.

[0199] FIG. 14 is a diagram illustrating a multi-path packet forwarding roaming method to which the present disclosure is applied.

[0200] Referring to FIG. 14, STA (910) may initiate a roaming operation by searching for AP 2 (930) as another AP while performing communication by connecting to AP 1 (920) and may add a link to AP 2. Thereafter, STA (910) may transmit an RAI frame (1001) to AP 1 (920) to initiate roaming, as described above.

[0201] Here, the RAI frame (1001) includes information for STA (910) to roam to AP 2 (930) (e.g., the MAC address of AP 2 (930), which is information that can identify AP 2 (930), and the link ID of AP 2 (930)). AP 1 (920) responds to the RAI frame (1001) of STA (910) with an ACK frame. STA (910) 1 can configure the Ethernet interfaces of AP 1 (920) and AP 2 (930) as a LAG. This may mean that STA (910) 1 virtually configures the LAG. After STA (910) transmits RAI frame (803), LACPDU (1002, 1003) can be transmitted to router (or MLD, hereinafter referred to as router, 940) through AP 1 (920) and AP 2 (930), respectively. The destination address (DA) of LACPDU (1002, 1003) is transmitted to multicast MAC address 01-80-C2-00-00-02. The sender address (SA) of LACPDU (1002, 1003) can be set to the aggregator MAC address of STA (910) 1. For example, the aggregator MAC address of STA (910) 1 can be set to AA-AA-AA-AA-AA-AA as the MAC address of STA (910) 1. The router (940) can also transmit an LACPDU with the same DA as the LACPDU transmitted by the STA (910). The SA of the LACPDU (1003, 1004) transmitted by the router (940) is RR-RR-RR-RR-RR-RR, which is the aggregator MAC address of the router (940). The router (940) can receive the LACPDU (1002, 1003) of the STA (910) 1 through the Ethernet interface to which AP 1 (920) and AP 2 (930) are connected. Through the LACPDU exchange process between the router (940) and the STA (910), an aggregation link can be established between the router (940) and the STA (910).

[0202] The router (940) can receive data packets destined for the STA (910) from the network. The router (940) can transmit data packets (1006, 1007) to both interfaces to which AP 1 (920) and AP 2 (930) are connected. For example, the packets (1006, 1007) received by the router (940) from the network can be divided and transmitted to AP 1 (920) and AP 2 (930). As another example, the packets (1006, 1007) received by the router (940) from the network can be transmitted equally to AP 1 (920) and AP 2 (930). The DA of the data packets (1007, 1008) transmitted by the router (940) to AP 1 (920) and AP 2 (930) is AA-AA-AA-AA-AA-AA, which is the aggregator MAC address of the STA (910). AP 1 (920) and AP 2 (930) receive packets from the router (940) and transmit them to the STA (910). That is, AP 1 (920) and AP 2 (930) transmit data frames to the STA (910). The STA (910) may transmit response frames (1009, 1010) to each AP for the frames received through the router (940) and AP 1 (920), and AP 2 (930), respectively. The response frames may be BlockAck frames. STA (910) can distinguish duplicate frames (duplicate data packets) and discard duplicate packets.

[0203] When the STA (910) completes roaming, the STA (910) may transmit an LACPDU (1011) instructing to remove AP 1 (920) from the LAG (e.g., remove the Ethernet interface of AP 1 (920) from the LAG). Alternatively, the STA (910) may transmit an LACPDU (1011) to remove the LAG. The LACPDUs (1011) may be delivered to the router (940) through at least one of AP 1 (920) and AP 2 (930). The STA (910) may terminate the connection with AP 1 (920) before or after transmitting the LACPDU (1011) and operate with AP 2 (930). The router (940) that has received the LACPDU (1011) of the STA (910) no longer transmits the data packet destined for the STA (910) to the Ethernet interface to which AP 1 (920) is connected, and can transmit the data packet destined for the STA (910) to the Ethernet interface to which AP 2 (930) is connected. The STA (910) can receive a data frame (1012) from AP 2 (930).

[0204] As another example, STA (910) may have determined AP 3 as a roaming target AP in addition to AP 2 (930). That is, AP 2 (930) and AP 3 may have been roaming candidates. If STA (910) determines AP 3 as an AP to roam to in addition to AP 2 (930), STA (910) may include information that can identify AP 2 (930) and AP 3 in the RAI frame. If STA (910) designates AP 3 as a roaming target AP, STA (910) may have transmitted LACPDUs to AP 1 (920), AP 2 (930), and AP 3, respectively, to form a LAG including AP 1 (920), AP 2 (930), and AP 3. When STA (910) completes roaming (STA (910) roams to AP 2 (930)), STA (910) can remove AP 1 (920) and AP 3 from the LAG (e.g. remove the Ethernet interface of AP 1 (920) and AP 3 from the LAG) or remove the LAG.

[0205] FIG. 15 is a diagram illustrating a multi-path packet forwarding roaming method to which the present disclosure is applied.

[0206] Referring to FIG. 15, STA (910) may initiate a roaming operation by searching for AP 2 (930) as another AP while performing communication by connecting to AP 1 (920) and may add a link to AP 2. Thereafter, STA (910) may transmit an RAI frame (1001) to AP 1 (920) to initiate roaming, as described above.

[0207] The RAI frame (1001) may include information for the STA (910) to roam to AP 2 (930) (e.g., the MAC address of AP 2 (930), which is information that can identify AP 2 (930), and the link ID of AP 2 (930)). AP 1 (920) responds to the RAI frame (1001) of the STA (910) with an ACK frame.

[0208] Here, AP 1 (920) and AP 2 (930) can exchange context information for roaming. The context information exchange may include information about the LAG configuration of AP 1 (920) and AP 2 (930).

[0209] AP 1 (920) and AP 2 (930) can configure the Ethernet interface connected to the router (940) as a LAG. This may be that AP 1 (920) and AP 2 (930) configure the LAG on behalf of the STA (910). The above-described operation may be a proxy LACP (link aggregation control) operation. After the STA (910) transmits the RAI frame (1001), AP 1 (920) and AP 2 (930) can transmit LACPDUs (1013, 1014) to the router (940), respectively. The destination address (DA) of the LACPDUs (1013, 1014) is transmitted to the multicast MAC address 01-80-C2-00-00-02. In addition, the sender address (SA) of the LACPDU (1013, 1014) may be set to the MAC address of the STA (910). For example, the SA of the LACPDU (1013, 1014) may be set to AA-AA-AA-AA-AA-AA-AA with the MAC address of the STA (910). The router (940) may also transmit the LACPDU (1015, 1016) to the same DA as the LACPDU (1013, 1014) transmitted by the APs. The SA of the LACPDU (1015, 1016) transmitted by the router (940) is RR-RR-RR-RR-RR-RR, which is the aggregator MAC address of the router (940). The router (940) can receive LACPDUs (1013, 1014) transmitted by AP 1 (920) and AP 2 (930) on behalf of STA (910) through the Ethernet interface to which AP 1 (920) and AP 2 (930) are connected. Through the LACPDU exchange process between the router (940) and STA (910), an aggregation link between the router (940) and AP 1 (920) and AP 2 (930) is established.

[0210] The router (940) receives data packets (1017, 1018) destined for the STA (910) from the network. The router (940) can transmit the data packets (1017, 1018) to both interfaces connected to AP 1 (920) and AP 2 (930). For example, the router (940) can divide the packets (1017, 1018) received from the network and transmit them to AP 1 (920) and AP 2 (930). As another example, the router (940) can equally transmit the packets (1017, 1018) received from the network to AP 1 (920) and AP 2 (930). The DA of the data packets (1017, 1018) transmitted by the router (940) to AP 1 (920) and AP 2 (930) is AA-AA-AA-AA-AA-AA-AA, which is the aggregator MAC address of the STA (910) set by AP 1 (920) and AP 2 (930). AP 1 (920) and AP 2 (930) receive the packets (1017, 1018) from the router (940) and transmit them to the STA (910). That is, AP 1 (920) and AP 2 (930) transmit data frames to the STA (910). The STA (910) can transmit response frames (1019, 1020) to each AP for the frames received through the router (940), AP 1 (920), and AP 2 (930), respectively. The response frame may be a BlockAck frame. STA (910) 1 can distinguish duplicate frames (duplicate data packets) and discard duplicate packets.

[0211] When STA (910) completes roaming, AP 1 (920) and AP 2 (930) may transmit an LACPDU (1021) instructing to remove AP 1 (920) from the LAG (e.g., remove the interface of AP 1 (920) from the LAG). Alternatively, STA (910) may transmit an LACPDU (1021) to remove the LAG. The LACPDUs (1021) may be delivered to the router (940) through at least one of AP 1 (920) and AP 2 (930). STA (910) may terminate the connection with AP 1 (920) before or after transmitting the LACPDU and operate with AP 2 (930). The router (940) that has received the LACPDU (1021) of AP 1 (920) and AP 2 (930) no longer transmits data packets destined for STA (910) to the Ethernet interface to which AP 1 (920) is connected, but transmits data packets destined for STA (910) to the Ethernet interface to which AP 2 (930) is connected. STA (910) can receive data frames from AP 2 (930).

[0212] STA (910) may have determined AP 3 as a roaming target AP in addition to AP 2 (930). That is, AP 2 (930) and AP 3 may be roaming candidates. If STA (910) has determined AP 3 as an AP to roam to in addition to AP 2 (930), STA (910) may include information that can identify AP 2 (930) and AP 3 in the RAI frame. If STA (910) has designated AP 3 as a roaming target AP, AP 1 (920), AP 2 (930), and AP 3 may have each transmitted LACPDUs to the router (940) to configure a LAG. When STA (910) completes roaming (STA (910) roams to AP 2 (930)), AP 1 (920), AP 2 (930) and AP 3 can remove AP 1 (920) and AP 3 from the LAG (e.g., remove the Ethernet interface of AP 1 (920) and AP 3 from the LAG) or remove the LAG.

[0213] FIG. 16 is a diagram illustrating a multi-path packet forwarding roaming method to which the present disclosure is applied.

[0214] Referring to FIG. 16, STA (910) may initiate a roaming operation by searching for AP 2 (930) as another AP while performing communication by connecting to AP 1 (920) and may add a link to AP 2. Thereafter, STA (910) may transmit an RAI frame (1001) to AP 1 (920) to initiate roaming, as described above.

[0215] The RAI frame (1001) includes information for STA (910) to roam to AP 2 (930) (e.g., the MAC address of AP 2 (930), which is information that can identify AP 2 (930), and the link ID of AP 2 (930)). AP 1 (920) can respond to the RAI frame (1001) of STA (910) with an ACK frame. In addition, AP 1 (920) and AP 2 (930) can exchange context information for roaming, and the context information can include information on the LAG configuration of AP 1 (920) and AP 2 (930).

[0216] AP 1 (920) and AP 2 (930) can configure the Ethernet interface connected to the router (940) as a LAG. This may be that AP 1 (920) and AP 2 (930) configure the LAG on behalf of the STA (910). The above-described operation may be a proxy LACP (link aggregation control) operation. After the STA (910) transmits the RAI frame (1001), AP 1 (920) and AP 2 (930) can transmit LACPDUs (1022, 1023) to the router (940), respectively. The destination address (DA) of the LACPDUs (1022, 1023) is transmitted to the multicast MAC address 01-80-C2-00-00-02. In addition, the sender address (SA) of LACPDU (1022, 1023) may be a MAC address randomly set by AP 1 (920) and AP 2 (930) to perform roaming operation of STA (910) 1. For example, BB-BB-BB-BB-BB-BB. The router (940) may also transmit LACPDU (1024, 1025) with the same DA as the LACPDU (1022, 1023) transmitted by the APs. The SA of LACPDU (1024, 1025) transmitted by the router (940) is RR-RR-RR-RR-RR-RR, which is the aggregator MAC address of the router (940). The router (940) can receive LACPDUs (1022, 1023) transmitted by AP 1 (920) and AP 2 (930) on behalf of STA (910) through the Ethernet interface to which AP 1 (920) and AP 2 (930) are connected. Through the LACPDU exchange process between the router (940) and STA (910), an aggregation link between the router (940) and AP 1 (920) and AP 2 (930) can be established.

[0217] The router (940) receives data packets (1026, 1027) destined for the STA (910) from the network. The router (940) can transmit the data packets (1026, 1027) to both interfaces to which AP 1 (920) and AP 2 (930) are connected. For example, the router (940) can divide the packets (1026, 1027) received from the network and transmit them to AP 1 (920) and AP 2 (930). As another example, the router (940) can equally transmit the packets (1026, 1027) received from the network to AP 1 (920) and AP 2 (930). The DA of the data packets (1026, 1027) transmitted by the router (940) to AP 1 (920) and AP 2 (930) is BB-BB-BB-BB-BB-BB, which is a random aggregator MAC address set by AP 1 (920) and AP 2 (930). AP 1 (920) and AP 2 (930) receive packets from the router (940). AP 1 (920) and AP 2 (930) know the random MAC address (aggregator MAC address) for STA (910) 1. AP 1 (920) and AP 2 (930) can know that the destination of the data packet with DA of BB-BB-BB-BB-BB-BB is STA (910), and AP 1 (920) and AP 2 (930) convert the address of the data packet (1026, 1027) to the MAC address of STA (910) (AA-AA-AA-AA-AA-AA) and then transmit it to STA (910). That is, AP 1 (920) and AP 2 (930) transmit data frames to STA (910). STA (910) can transmit response frames (1028, 1029) to each AP for the frames received through the router (940) and AP 1 (920) and AP 2 (930), respectively. The response frame may be a BlockAck frame. STA(910) 1 can distinguish duplicate frames (duplicate data packets) and discard duplicate packets.

[0218] When STA (910) completes roaming, AP 1 (920) and AP 2 (930) may transmit LACPDU (1030) indicating to remove AP 1 (920) from LAG (e.g., remove the interface of AP 1 (920) from LAG). Alternatively, STA (910) may transmit LACPDU (1030) to remove LAG. The LACPDUs (1030) may be delivered to the router (940) through at least one of AP 1 (920) and AP 2 (930). STA (910) may terminate the connection with AP 1 (920) before or after transmitting the LACPDU (1030) and operate with AP 2 (930). The router (940) that receives the LACPDU (1030) of AP 1 (920) and AP 2 (930) may no longer transmit data packets destined for STA (910) to the Ethernet interface to which AP 1 (920) is connected. The router (940) transmits data packets destined for STA (910) to the Ethernet interface to which AP 2 (930) is connected. STA (910) may receive data frames from AP 2 (930). If AP 1 (920) is removed from the LAG, the router (940) may transmit data packets destined for STA (910) to AP 2 (930) by setting the DA to BB-BB-BB-BB-BB-BB. AP 2 (930) must change its MAC address to transmit data packets to STA (910). When LAG is removed, the router (940) can transmit the DA of the data packet destined for STA (910) to AP 2 (930) as AA-AA-AA-AA-AA-AA. In this case, AP 2 (930) does not need to change the MAC address to transmit the data packet to STA (910).

[0219] STA (910) may have determined AP 3 as a roaming target AP in addition to AP 2 (930). That is, AP 2 (930) and AP 3 may have been roaming candidates. If STA (910) determined AP 3 as an AP to roam to in addition to AP 2 (930), STA (910) may have included information that can identify AP 2 (930) and AP 3 in the RAI frame. If STA (910) designated AP 3 as a roaming target AP, AP 1 (920), AP 2 (930), and AP 3 may have each transmitted LACPDUs to the router (940) to configure a LAG. When STA (910) completes roaming (STA (910) roams to AP 2 (930)), AP 1 (920), AP 2, and AP 3 can remove AP 1 (920) and AP 3 from the LAG (and remove the Ethernet interfaces of AP 1 (920), AP 3 from the LAG), or remove the LAG.

[0220] FIGS. 17A to 20 describe a case where a wireless LAN terminal, STA (station), AP 1, and AP 2, operate in a wireless LAN network. The STA can operate by connecting to (or associating with) AP 1. The STA can perform data communication with AP 1 (previous AP, old AP). The STA can search for AP 2 and determine AP 2 as an AP to perform roaming (new AP, new AP). That is, the STA may want to connect to AP 2 and perform communication (data communication). An operation in which the STA switches connection from an existing connected AP (old AP) to another AP (new AP) and performs communication may be a roaming operation. If the STA determines to perform a roaming operation, a procedure for adding a link (add link) of AP 2 between the STA and AP 1 may be initiated. Here, for the link addition procedure, even if AP 2 operates on the same channel, a link corresponding to AP 2 with a separate link ID may be created or the link addition procedure may need to be performed after creation. For example, the STA may add a link on which AP 2 operates.

[0221] The link addition procedure may be a multi-link reconfiguration operation or a similar operation. AP 1 may transmit a frame indicating the addition of a link of a frequency on which AP 2 operates to the STA, and the STA may add the link as one of the multi-links based on the received frame. That is, the STA and the AP (e.g., AP 1) may exchange frames including a (reconfiguration) multi-link element. The multi-link element may include a per-STA profile indicating information (e.g., link identifiers such as link IDs and MAC addresses) of each AP under the AP MLD and each STA under the STA MLD. In addition, the per-STA profile may include an EHT operation element. In the (reconfiguration) multi-link element, the link IDs, which are link identifiers of AP 1 and AP 2, may be different. In addition, the MAC addresses of AP 1 and AP 2 may also be different. However, the operating frequencies (operating channels) of the EHT operating elements included in the per-STA profiles for each of AP 1 and AP 2 may be the same.

[0222] An STA may transmit a roaming announcement indication (RAI) frame to AP 1 to indicate the start of roaming. For example, the link addition procedure described above may be replaced by transmitting an RAI frame. To this end, the RAI frame may include information for the link addition procedure described above (e.g., a (reconfiguration) multi-link element), and link addition may be performed by transmitting an RAI frame including the information for link addition. The RAI frame may include information about AP 2, a roaming target AP that will perform a roaming operation (e.g., at least one of a MAC address of AP 2, a link ID (identifier) ​​on which AP 2 operates, and other information that may identify AP 2). When AP 1 receives the RAI frame, AP 1 may respond to the STA with an ACK frame. Here, AP 1 performs a context exchange with AP 2, a roaming target AP. Context exchange may be the exchange of information required for roaming between APs (i.e., between AP 1 and AP 2). For example, context exchange may be performed by exchanging AP to AP frames. As another example, context exchange may be performed by exchanging AP to AP frames via wired Ethernet or wirelessly. Here, the AP to AP frame may be a backbone frame, and the backbone frame is a frame that exchanges control information between APs. However, it may not be limited to that name. Roaming operation between APs may be controlled through the AP to AP frame. For example, the AP to AP frame may be a roaming initiation frame or a roaming response frame, but is not limited thereto. The roaming initiation frame may be a frame that a roaming initiation AP (e.g., AP 1) sends to a roaming target AP (e.g.,A frame transmitted to AP 2) and a roaming initiation frame may include context (information about the STA). On the other hand, a roaming response frame may be a frame transmitted by a roaming target AP to the roaming initiating AP in response to the roaming initiation frame.

[0223] Information for roaming operations can be continuously exchanged between multiple APs through frame exchange. Context exchange allows AP 1 to convey STA information to AP 2, indicating that the STA is roaming to AP 2. The context includes information about the STA to be roamed. For example, the information of the STA may include at least one of information that can identify the STA (e.g., at least one of the MAC address of the STA, the association identifier (AID) of the STA, and other information that can identify the STA), capability information of the STA (e.g., extremely high throughput (EHT) capability, ultra high reliability (UHR) capability), data information destined for the STA in the queue (e.g., sequence number (SN) information for the last frame(s) of the STA in the queue of AP 1), a pseudorandom number (PN) for security, a packet number, and information about the time when roaming is performed (e.g., timeout information), and information necessary for roaming. In addition, the information for the roaming operation may further include information (e.g., SN, PN (pseudo number or packet number)) about the last frame received by the AP 1 from the STA.

[0224] Here, information about when roaming is performed may be information exchanged during the connection (or association) process. Through the context exchange procedure, packets destined for an STA in the network may not be input (forwarded) to AP 1, but may be input (forwarded) to AP 2. In other words, the context exchange may include a data path switching procedure. The data path switching may be performed by proxy ARP, in which AP 2 transmits an address resolution protocol (ARP) frame to the network on behalf of the STA. As another example, the data path switching may also be performed by updating the switching table controlling the Ethernet port. Alternatively, the data path switching may be performed using both of the above-described methods.

[0225] After context exchange between AP 1 and AP 2, AP 1 may transmit a roaming announcement response (RAR) frame in response to the STA's RAI frame. The RAR frame may indicate that roaming to AP 2 is to be initiated. The roaming procedure may be initiated through the exchange of the RAI frame and the RAR frame. In another example, the transmission of the RAR frame may be omitted, and the roaming procedure may be initiated by transmitting only the RAI frame.

[0226] AP 1 can transmit data frames queued for transmission to the STA to the STA. AP 1 initiates the transmission procedure of the data frame to the STA through at least one frame exchange procedure (e.g., TXOP setup). AP 1 can transmit the last frame in the queue to the STA. The MorePPDU (physical protocol data unit) bit included in the MAC header of the data frame can be used to indicate the last data frame transmitted by AP 1. For example, the HT control field of the MAC header of the last data frame transmitted by AP 1 can include a CAS Control subfield in the form of A-Control. The CAS Control subfield has a MorePPDU bit, and the bit can be set to 0. As another example, the last data frame can be indicated using reserved bits of the CAS Control subfield instead of using the MorePPDU bit. As another example, the last data frame may be indicated by having the duration of the MAC header indicate time information that is longer than "PPDU length indicated by the Preamble of the data frame + SIFS + PPDU length indicated by the Preamble of the BA frame" (e.g., one OFDM symbol time). The HT control field of the MAC header may include control subfields of a type other than the CAS control subfield, such as A-Control, and the subfield may indicate the last data frame.

[0227] As another example, the last data frame can be indicated by utilizing padding of the MAC layer. The MPDU delimiter of the A-MPDU used as MAC layer padding can be repeated after a specific delimiter parameter is set after the last MPDU of the A-MPDU. Here, if the MPDU delimiter is repeated a specific number of times or more, it can be indicated that the corresponding frame is the last data frame. As another example, if the MPDU length information of the MPDU delimiter has a specific value other than 0, it can be indicated that the corresponding frame is the last frame. For example, if the length value is set to a specific value that is not 0 but that does not allow for the configuration of a single MAC frame, it can be indicated that the corresponding frame is the last frame. Here, the information indicating the last frame described above is referred to as a 'last frame indicator', but is not limited to that name. In other words, whether it is the last frame can be indicated in various forms. As another example, the More Data bit included in the MAC header of the data frame transmitted by AP 1 (520) to indicate the last data frame may be used to indicate the last data frame.

[0228] The STA may respond to the last data frame of AP 1 (e.g., a data frame of AP 1 including a last frame indicator) with a response frame (e.g., a BA (BlockAck) frame, an ACK frame). Additionally, the received response frame that the STA transmits to AP 1 may also be transmitted with a 'last frame indicator' indicating that it is a response to the last frame transmitted by AP 1.

[0229] As another example, the reception response frame transmitted by the STA to AP 1 may include a 'last frame reception completion indicator'. This will be described later. Since AP 2 operates on the same channel as AP 1 and the STA, it may be able to receive (decode) frames transmitted by AP 1 and / or the STA. For example, AP 2 may decode frames (data frames, reception response frames) transmitted by at least one of AP 1 and the STA. AP 2 may recognize the data transmission status of AP 1 by receiving the data frame transmitted by AP 1 or checking the reception response frame transmitted by the STA. AP 2 recognizing the data transmission status of AP 1 may be recognizing at least one of, but not limited to, 'whether the data (e.g. MPDU or MSDU) transmitted by AP 1 to STA has a SN', 'whether the data transmission was successful (e.g. ACK or NACK)', and 'whether the last data destinationd to STA stored in AP 1 was transmitted'. The above-described matters may be commonly applied to FIGS. 17a to 20 below.

[0230] FIG. 17a and FIG. 17b are diagrams illustrating a wireless LAN same-channel roaming method to which the present disclosure is applied.

[0231] Referring to FIGS. 17A and 17B , STA (1110) may transmit an RAI frame (1201) to AP 1 (1120) to indicate the start of roaming. Thereafter, a context exchange may be performed between AP 1 (1120) and AP 2 (1130), and AP 1 (1120) may transmit an RAR frame (1202) in response to the RAI frame (1201) of STA (1110), as described above.

[0232] Here, STA (1110) can receive data frame (1203) including last frame indicator of AP 1 (1120). STA (1110) can successfully receive all frames of AP 1 (1120). That is, there may be no error in the frame received by STA (1110). STA (1110) can transmit BA frame (1204), which is a reception response frame, to AP 1 (1120). The reception status bitmap of BA frame (1204) can indicate that the frame has been received without error. In addition, BA frame (1204) of STA (1110) can include 'last frame reception complete' indicator. The 'last frame reception complete' indicator of STA (1110) may be configured and included in a manner identical to or similar to the 'last frame indicator' of AP 1 (1120) (e.g., configuring a BA frame and a QoS Null frame in A-MPDU manner and including an indicator in the QoS Null frame in the form of A-control). AP 1 (1120) may receive the BA frame (1204) of STA (1110) 1 and confirm that all frames have been successfully transmitted. Accordingly, AP 1 (1120) may no longer transmit data frames to STA (1110), and STA (1110) may also not transmit data frames to AP 1 (1120). STA (1110) may wait to receive a frame (e.g., data frame, 1205) from AP 2 (1130), which is a new AP. When AP 2 (1130) receives a last frame indicator included in a data frame (1203) of AP 1 (1120) or a last frame reception completion indicator included in a BA frame (1204) transmitted by STA (1110), AP 2 (1130) can transmit a data frame (1205) to STA (1110).

[0233] As another example, at least one of the data frame (1203) transmitted by AP 1 and the BA frame (1204) transmitted by STA (1110) may not include a last frame indicator and a last frame reception completion indicator. However, since AP 1 (1120) and AP 2 (1130) have performed a context exchange for roaming, AP 2 (1130) can recognize the SN of the last frame that AP 1 (1120) should transmit to STA (1110).

[0234] Here, AP 2 (113) can recognize at least one of the data frame (1203) transmitted by AP 1 (1120) and the BA frame (1204) transmitted by STA (1110) through overhearing. As described above, AP 2 (1130) can recognize the SN of the data frame from the data frame of AP 1 (1120), and when AP 1 (1120) has transmitted the last data frame (1203), AP 2 (1130) can transmit the data frame (1205) to STA (1110). As another example, AP 2 (1130) can recognize the SN of the frame received by STA (1110) from the BA frame (1204) of STA (1110). When STA (1110) receives the last data frame of AP 1 (1120), AP 2 (1130) can transmit a data frame (1205) to STA (1110).

[0235] In addition, as an example, the data transmitted by AP 1 (1120) was normally received by STA (1110), and STA (1110) transmitted a BA frame (e.g., a BA frame including a 'last frame reception completion indicator') to inform AP 1 that all frames were normally received, but the BA frame may not be normally received by AP 1 (1120). On the other hand, AP 2 (1130) may have received the above-described BA frame (1204) through listening. In the above-described case, AP 2 (1130) may recognize that the data exchange between STA (1110) and AP 1 (1120) is complete and may start transmitting a data frame (1205). When AP 2 (1130) starts transmitting a data frame (1205) to STA (1110), AP 2 (1130) and STA (1110) may perform an RTS / CTS exchange for TXOP protection. Here, if AP 1 (1120) has not received a BA frame for all frames from STA (1110) until the last frame and has not reached the roaming time, but has received a CTS frame transmitted from STA (1110) to AP 2 (1130), AP 1 (1120) may recognize that STA (1110) has completed roaming to AP 2 (1130) and may not perform retransmission.

[0236] As another example, referring to FIG. 17b, STA (1110) may receive a data frame (1203) including a last frame indicator of AP 1 (1120). Here, STA (1110) indicates that an error has occurred in the frame of AP 1 (1120). That is, an error may exist in the received frame. STA (1110) may transmit a BA frame (1206), which is a reception response frame, to AP 1 (1120). Here, the reception status bitmap of the BA frame (1206) may indicate that an error has occurred in all or part of the frame. Since STA (1110) did not properly receive the last frame, the BA frame (1206) transmitted by STA (1110) may not include the last frame reception completion indicator described above.

[0237] AP 1 (1120) can receive the BA frame (1206) of STA (1110) and attempt to retransmit the frame in which an error occurred. That is, AP 1 (1120) can transmit the frame in which an error occurred (1206) to STA (1110). If the BA frame (1206) transmitted by STA (1110) indicates a frame reception error, AP 2 (1130) can wait for frame retransmission from AP 1 (1120). That is, AP 2 (1130) does not transmit a data frame to STA (1110) until AP 1 (1120) retransmits data to STA (1110). Thereafter, STA (1110) can receive a data frame (retransmission data frame) including the last frame indicator of AP 1 (1120). For example, if an error occurs in a retransmission frame, retransmission may be performed multiple times. After that, STA (1110) can successfully receive the retransmission frame (1207) of AP 1 (1120). That is, there may be no error in the received frame. STA (1110) can transmit a BA frame (1207), which is a reception response frame, to AP 1 (1120). Here, the reception status bitmap of the BA frame (1207) may indicate that the frame has been received without an error. In addition, the BA frame (1207) of STA (1110) may include a 'last frame reception complete' indicator. AP 1 (1120) can receive the BA frame (1207) of STA (1110) 1 and confirm that all frames have been successfully transmitted. Accordingly, AP 1 (1120) may no longer transmit data frames to STA (1110), and STA (1110) may also not transmit data frames to AP 1 (1120).

[0238] After that, STA (1110) may wait to receive a frame (e.g., data frame) from new AP, AP 2 (1130). If AP 2 (1130) receives a last frame indicator included in a data frame (1207) of AP 1 (1120) or a last frame reception completion indicator included in a BA frame (1208) transmitted by STA (1110), AP 2 (1130) may transmit a data frame (1209) to STA (1110). As another example, at least one of the data frame (1207) transmitted by AP 1 and the BA frame (1208) transmitted by STA (1110) may not include a last frame indicator and a last frame reception completion indicator. Since AP 1 (1120) and AP 2 (1130) have performed context exchange for roaming, AP 2 (1130) can recognize the SN of the last frame that AP 1 (1120) should transmit to STA (1110). Here, AP 2 (113) can recognize at least one of the data frame (1207) transmitted by AP 1 (1120) and the BA frame (1208) transmitted by STA (1110) through overhearing. AP 2 (1130) can recognize the SN of the data frame in the data frame (1207) of AP 1 (1120), and when AP 1 (1120) transmits the last data frame (1207), AP 2 (1130) can transmit the data frame (1209) to STA (1110).

[0239] As another example, AP 2 (1130) can recognize the SN of the frame received by STA (1110) from the BA frame (1208) of STA (1110). When STA (1110) receives the last data frame (1207) of AP 1 (1120), AP 2 (1130) can transmit a data frame (1209) to STA (1110).

[0240] Referring to FIGS. 17a and 17b, if AP 1 (1120) has not completed transmission of the last frame destined for STA (1110) or STA (1110) has not received the last frame of AP 1 (1120), AP 2 (1130) does not transmit a data frame to STA (1110).

[0241] AP 2 (1130) can transmit a data frame to STA (1110) when it is determined through the above-described procedure that AP 1 (1120) has completed transmission of the last frame destined for STA (1110) or that STA (1110) has received the last frame of AP 1 (1120). That is, when the data frame exchange procedure between AP 1 (1120) and STA (1110) is completed, AP 2 (1130) can transmit a data frame to STA (1110).

[0242] FIG. 18a and FIG. 18b are diagrams showing a wireless LAN same-channel roaming method to which the present disclosure is applied.

[0243] Referring to FIGS. 18A and 18B , STA (1110) may transmit an RAI frame (1201) to AP 1 (1120) to indicate the start of roaming. Thereafter, context exchange may be performed between AP 1 (1120) and AP 2 (1130), and AP 1 (1120) may transmit an RAR frame (1202) in response to the RAI frame (1201) of STA (1110), as described above.

[0244] Here, AP 1 (1120) may not have transmitted the last data frame (1203) to STA (1110). AP 1 (1120) may start an 'activity timer' from at least one of the start time of transmission of a data frame for which a reception response frame has been received from the most recent STA, the completion time of transmission of a data frame for which a reception response frame has been received from the most recent STA, the start time of reception of a reception response frame received from the most recent STA, and the completion time of reception of a reception response frame received from the most recent STA. For example, in FIG. 18A, the activity timer may be started based on the completion time of transmission of a data frame for which AP 1 (1120) has received a reception response frame from the most recent STA, but is not limited to the embodiment. Here, the length (time length) of the activity timer may be a preset time. Here, the length of the activity timer may be a length that AP 1 (1120) manages solely. As another example, the length of the activity timer may be a length negotiated between AP 1 (1120) and STA (1110). The activity timer may be a timer for determining whether STA (1110) is not performing data communication with the current AP (AP 1 (1120)) and is roaming with a new AP (AP 2 (1130)). If STA (1110) does not transmit a reception response frame to AP 1 (1120) during the activity timer period and the activity timer expires (times out), AP 1 (1120) may determine that STA (1110) is performing communication with AP 2 (1130).

[0245] On the other hand, if STA (1110) transmits a reception response frame (1210) to AP 1 (1120) during the activity timer period, AP 1 (1120) may discard the existing activity timer. Here, AP 1 (1120) may newly start the activity timer from at least one of the start time of transmission of the data frame for which the reception response frame (1210) was received from the most recent STA (1110), the completion time of transmission of the data frame for which the reception response frame was received from the most recent STA, the start time of reception of the reception response frame received from the most recent STA, and the completion time of reception of the reception response frame received from the most recent STA.

[0246] When the activity timer of AP 1 (1120) expires, AP 1 (1120) may determine that STA (1110) is communicating with AP 2 (1130). Here, AP 1 (1120) may perform a context exchange with AP 2 (1130). That is, AP 1 (1120) may transmit to AP 2 (1130) information (such as SN, PN (pseudo number or packet number)) about the last frame that AP 1 (1120) transmitted to STA (1110). In addition, AP 1 (1120) may transmit to AP 2 (1130) information (such as SN, PN (pseudo number or packet number)) about the last frame that AP 1 (1120) received from STA (1110).

[0247] In addition, AP 1 (1120) may also transmit information indicating that the current STA (1110) is communicating with AP 2 (1130) to AP 2 (1130). Since AP 1 (1120) does not transmit the last frame to STA (1110), AP 1 (1120) may want to transmit frames destined for STA (1110) through AP 2 (1130), which is the AP with which STA (1110) is currently communicating. In the above case, AP 1 (1120) may transmit data frames (data packets, data traffic) destined for STA (1110) to AP 2 (1130). AP 2 (1130) may transmit the data frames transmitted by AP 1 (1120) to STA (1110). AP 2 (1130) performs a context exchange with AP 1 (1120), and AP 1 (1120) can know that STA (1110) is communicating with AP 2 (1130). AP 2 (1130) can transmit a data frame (1211) to STA (1110). The SN and PN of the data frame (1211) transmitted by AP 2 (1130) to STA (1110) may be equal to or greater than the SN and PN values ​​of the frame last transmitted by AP 1 (1120) to STA (1110) (e.g., a value greater by 1).

[0248] In at least one of the following cases: if AP 1 (1120) has not completed transmission of the last frame destined for STA (1110), if STA (1110) has not received the last frame of AP 1 (1120), or if STA (1110) has not been instructed by AP 1 (1120) that it is communicating with AP 2 (1130), AP 2 (1130) may not transmit a data frame (1211) to STA (1110).

[0249] On the other hand, AP 2 (1130) may transmit a data frame (1211) to STA (1110) in at least one of the following cases: when AP 1 (1120) completes transmission of the last frame destined for STA (1110), when STA (1110) receives the last frame of AP 1 (1120), or when STA (1110) is instructed by AP 1 (1120) that it is communicating with AP 2 (1130).

[0250] As another example, referring to FIG. 18b, AP 2 (1130) may start an 'activity timer' from at least one of the start time of transmission of the data frame most recently transmitted by AP 1 (1120) to STA (1110), the completion time of transmission of the data frame most recently transmitted by AP 1 (1120) to STA (1110), the start time of reception of the reception response frame most recently received from STA (1110), and the completion time of reception of the reception response frame most recently received from STA (1110). The length (time length) of the activity timer may be a preset time. The length of the activity timer may be a length managed solely by AP 2 (1130). As another example, the length of the activity timer may be a length determined through negotiation between AP 1 (1120) and AP 2 (1130), or a length determined through negotiation between AP 1 (1120), AP 2 (1130), and STA (1110). The activity timer is a timer for determining whether the STA (1110) is not performing data communication with the current AP (AP 1 (1120)) and is performing roaming with a new AP (AP 2 (1130)). If the STA (1110) does not transmit a reception response frame to AP 1 (1120) during the activity timer period, or if AP 1 (1120) does not transmit a data frame to STA (1110) and the activity timer expires (times out), AP 1 (1120) may determine that the STA (1110) is performing communication with AP 2 (1130).Alternatively, if STA (1110) transmits a reception response frame to AP 1 (1120) or AP 1 (1120) transmits a data frame to STA (1110) during the activity timer period, AP 2 (1130) may discard the existing activity timer and start a new 'activity timer' from at least one of the start time of transmission of the data frame most recently transmitted from AP 1 (1120) to STA (1110), the completion time of transmission of the data frame most recently transmitted from AP 1 (1120) to STA (1110), the start time of reception of the reception response frame most recently received from STA (1110), and the completion time of reception of the reception response frame most recently received from STA (1110).

[0251] When the activity timer of AP 2 (1130) expires, AP 2 (1130) may determine that STA (1110) is communicating with AP 2 (1130). AP 2 (1130) may perform a context exchange with AP 1 (1120). The context information may indicate roaming completion, which may be an indication that AP 2 (1130) is initiating communication with STA (1110). When the activity timer expires, AP 2 (1130) may transmit a data frame (1212) to STA (1110). The SN of the data frame (1212) transmitted by AP 2 (1130) to STA (1110) may be transmitted starting from the SN included in the most recently transmitted reception response frame by STA (1110) to AP 1 (1120), or may be set to a value greater than the SN included in the most recently transmitted reception response frame (e.g., a value greater than 1).

[0252] As another example, AP 2 (1130) may initiate communication with STA (1110) by initializing SN and PN (e.g., to 0). That is, AP 2 (1130) may initiate communication with STA (1110) based on the initialized values ​​rather than the SN or PN included in the most recent received response frame transmitted by STA (1110) to AP 1 (1120).

[0253] As another example, an STA may transmit context information to AP 2 (e.g., a new AP, a target AP). The context information that the STA transmits to AP 2 may be the same as or may include part of the information included in the context exchange between AP 1 and AP 2 described above. For example, the context information that the STA transmits to AP 2 may include SN information for the last frame(s) of the STA. The SN information for the last frame of the STA may be at least one of SN information for the frame that the STA last received from AP 1 and SN information for the frame that the STA last transmitted to AP 1. Here, the DL SN of the STA and the UL SN of the STA may be distinguished. For example, information that can identify the DL SN of the STA and the UL SN of the STA may be transmitted from the STA to AP 2, and AP 2 may recognize the SN information for the last frame of the STA through the above. However, the above is merely an example and may not be limiting. For example, since the AP and STA perform a BA agreement, they can recognize the SN by transmitting only the SN without a separate identifier for the SN.

[0254] Here, the STA can transmit context information to AP 2 regardless of the context exchange procedure between AP 1 and AP 2. For example, even if context exchange is performed between AP 1 and AP 2, the STA can also transmit context information to AP 2. As another example, the STA can transmit context information to AP 2 instead of AP 1 if context exchange is not performed between AP 1 and AP 2. In other words, in addition to the context exchange procedure between AP 1 and AP 2, it may also be possible for the STA to transmit context information to AP 2.

[0255] For example, the SN of a data frame transmitted by AP 2 to STA may be transmitted starting from the SN included in the most recent reception response frame transmitted by STA to AP 1, or may be set to a value greater than the SN included in the most recent transmission of the reception response frame (e.g., a value greater than 1), depending on the context information received by AP 2.

[0256] If AP 1 (1120) has not completed transmission of the last frame destined for STA (1110), if STA (1110) has not received the last frame of AP 1 (1120), or if the activity timer of AP 2 (1130) has not expired, AP 2 (1130) does not transmit a data frame to STA (1110).

[0257] On the other hand, AP 2 (1130) may transmit a data frame to STA (1110) based on at least one of the following: when AP 1 (1120) completes transmission of the last frame destined for STA (1110), when STA (1110) receives the last frame of AP 1 (1120), or when the activity timer of AP 2 (1130) expires.

[0258] Figure 19 is a diagram illustrating a wireless LAN same-channel roaming method to which the present disclosure is applied.

[0259] Referring to FIG. 19, STA (1110) may transmit an RAI frame (1201) to AP 1 (1120) to indicate the start of roaming. Thereafter, context exchange may be performed between AP 1 (1120) and AP 2 (1130), and AP 1 (1120) may transmit an RAR frame (1202) in response to the RAI frame (1201) of STA (1110), as described above.

[0260] Here, a 'roaming timer' may be started from at least one of the following: the time when STA (1110) transmits the RAI frame (1201), the time when AP 1 (1120) receives the RAI frame (1201), the time when AP 1 (1120) transmits the RAR frame (1202), the time when STA (1110) receives the RAR frame (1202), and the time when AP 1 (1120) and AP 2 (1130) complete context exchange by the RAI frame (1201) of STA (1110). The roaming timer may be a timer that expires (times out) at the time when roaming is performed. The length (time length) or expiration time of the roaming timer may be the same for all of AP 1 (1120), AP 2 (1130), and STA (1110). For example, at least one of the start time, end time, and length of the roaming timer may be a negotiated value between AP 1 (1120), AP 2 (1130), and STA (1110), or a preset value. After the roaming timer expires, STA (1110) roams to AP 2 (1130), and therefore STA (1110) cannot communicate with AP 1 (1120) thereafter. In other words, STA (1110) may not be able to transmit or receive frames between AP 1 (1120).

[0261] Here, AP 1 (1120) can transmit at least one frame to STA (1110) even after the roaming timer has been started from the specific point in time described above. For example, AP 1 (1120) can transmit at least one data frame while the roaming timer is started and running. If there are multiple buffered data frames, AP 1 (1120) can transmit multiple data frames or can transmit one data frame, and is not limited to a specific form.

[0262] For example, AP 1 (1120) may transmit the last data frame (1203) while the roaming timer is started and running. That is, AP 1 (1120) may transmit up to the last data frame (1203) among at least one data frame to be transmitted to STA (1110) while the roaming timer is running, and STA (1110) may determine whether it is the last data frame by checking the last frame indicator included in the received data frame. When STA (1110) receives the last data frame indicated by the last data frame indicator from AP 1 (1120), STA (1110) may transmit a response frame to AP 1 (1120). Additionally, STA (1110) may transmit the response frame by adding a last frame reception completion indicator. Through the above procedure, STA (1110) may complete reception of the data frame from AP 1 (1120). The above-described operation may be, but is not limited to, signaling by AP 1 (1120) to indicate that transmission of data frames (or downlink data frames) to STA (1110) is terminated before the roaming timer (or time interval) expires. For example, AP 1 (1120) may transmit information indicating the last data frame to STA (1110) while transmitting the last data frame, thereby indicating that the downlink data frame is terminated. As another example, AP 1 (1120) may indicate that transmission of data frames to STA (1110) is terminated through another indication method (e.g., transmission of any frame (e.g., management frame, control frame) including a separate last frame indicator). AP 1 (1120) may no longer transmit data frames to STA (1110), and STA (1110) may also not transmit data frames to AP 1 (1120). STA (1110) may wait to receive a frame (e.g., data frame, 1205) from a new AP, AP 2 (1130).This may mean that STA (1110) has completed roaming to AP 2 (1130).

[0263] As another example, if STA (1110) does not receive a frame from AP 1 (1120) for a certain period of time while the roaming timer is operating, AP 1 (1120) may no longer transmit data frames to STA (1110), and STA (1110) may also not transmit data frames to AP 1 (1120). STA (1110) may wait to receive a frame (e.g., data frame, 1205) from a new AP, AP 2 (1130). This may mean that STA (1110) has completed roaming to AP 2 (1130).

[0264] Meanwhile, while the roaming timer is running, the STA (1110) may want to cancel roaming to AP 2 (1130). Within the roaming timer, if the STA (1110) wants to cancel roaming and continue communicating with AP 1 (1120), the STA (1110) may transmit to AP 1 (1120) any frame or an RAI frame (more specifically, an RAI frame including link reconfiguration information for resetting a link, and the information indicating roaming cancellation). When AP 1 (1120) receives the frame from the STA (1110), the STA (1110) may cancel roaming and reopen a port (e.g., IEEE 802.1X uplink port) through which the STA (1110) can transmit an uplink frame so that the STA (1110) can transmit an uplink frame again. Additionally, AP 1 (1120) may perform a context exchange to instruct AP 2 (1120) to cancel roaming. When roaming is canceled, AP 1 (1120) may perform a DS mapping update procedure, etc., to enable frames destined for STA (1110) to be input from the network.

[0265] Here, the roaming timer may expire before AP 1 (1120) completes transmitting the last data frame (1203) to STA (1110). That is, a case may be considered where AP 1 (1120) initiates frame transmission to STA (1110) before the roaming timer expires, but the frame transmission is completed after the roaming timer expires.

[0266] For example, when AP 1 (1120) initiates a roaming operation by transmitting a RAR frame (1202) in response to receiving a RAI frame (1201) from STA (1110), a roaming timer (or a certain time interval) is set from a certain point in time, but AP 1 (1120) can transmit a data frame destined for STA (1110) within the roaming timer operation interval (or within a certain time interval from the certain point in time). Here, AP 1 (1120) can complete the transmission of the data frame to STA (1110) without interruption even after the roaming timer expires. In the above-described case, the expiration time of the roaming timer may be postponed to the time when the transmission of the frame transmitted by AP 1 (1120) to STA (1110) is completed or the time when the response frame for the frame transmitted by AP 1 (1120) to STA (1110) is received from STA (1110).

[0267] As another example, AP 1 (1120) may ensure that frame exchanges (e.g., frame transmission and reception of a response frame to a frame) transmitted to STA (1110) are always terminated before the expiration of the roaming timer. Alternatively, if the roaming timer expires while AP 1 (1120) is transmitting a frame to STA (1110), AP 1 (1120) may forcibly terminate the ongoing frame.

[0268] After that, AP 1 (1120) may no longer transmit data frames to STA (1110), and STA (1110) may not transmit frames to AP 1 (1120). When the roaming timer expires, AP 2 (1130) may transmit data frames (1213) to STA (1110), and STA (1110) may receive data frames (1213) from AP 2 (1130). When the roaming timer expires, STA (1110) may immediately perform communication operations with AP 2 (1130) depending on at least one of a case where the communication status between STA (1110) and AP 1 (1120) is poor or a case where STA (1110) wants to quickly perform a roaming operation with AP 2 (1130). On the other hand, if STA (1110) wants to receive more downlink frames remaining in AP 1 (1120), STA (1110) may wait for a certain period of time (e.g. link switching time, aSIFSTime+aSlotTime+aRXPHYStartDelay time) after expiration of the roaming timer. If STA (1110) receives a data frame from AP 1 (1120) within the certain period of time, STA (1110) may postpone expiration of the roaming timer until the time when AP 1 (1120) completes reception of the data frame or the time when AP 1 (1120) transmits a response frame to the data frame. An example of receiving a frame within the certain period of time may be as follows. If STA (1110) detects a frame within the certain period of time, STA (1110) may generate PHY-RXSTART.indication primitive. When the primitive occurs, the STA (1110) can check the MAC header of the frame being received, and if the recipient of the frame is the STA (1110), the expiration of the roaming timer can be postponed until the frame can be received and a response frame can be transmitted.However, if the receiver of the frame is not STA (1110), STA 1 can immediately perform a communication operation with AP 2 (1130) without extending the roaming timer. Thereafter, STA (1110) can immediately perform a communication operation with AP 2 (1130), or if reception of an additional data frame from AP 1 (1120) is required, STA (1110) can wait again for a certain period of time. As another example, if STA (1110) does not receive a data frame from AP 1 (1120) for the above-described certain period of time, STA (1110) can no longer perform a communication operation with AP 1 (1120) and can operate with AP 2 (1130).

[0269] When the roaming timer expires, AP 1 (1120) can perform a context exchange with AP 2 (1130). That is, AP 1 (1120) can transmit information (SN, PN (pseudo number or packet number), etc.) about the last frame that AP 1 (1120) transmitted to STA (1110) to AP 2 (1130). In addition, AP 1 (1120) can also transmit information indicating that STA (1110) is currently communicating with AP 2 (1130) to AP 2 (1130). Since AP 1 (1120) does not transmit the last frame to STA (1110), AP 1 (1120) may want to transmit frames destined for STA (1110) through AP 2 (1130), which is the AP with which STA (1110) is currently communicating. In the above case, AP 1 (1120) can transmit a data frame (data packet, data traffic) destined for STA (1110) to AP 2 (1130). Here, AP 2 (1130) can transmit the data frame transmitted by AP 1 (1120) to STA (1110). The SN and PN of the data frame transmitted by AP 2 (1130) to STA (1110) may be equal to or greater than the SN and PN values ​​of the frame last transmitted by AP 1 (1120) to STA (1110) (e.g., a value greater by 1).

[0270] As another example, AP 2 (1130) may have received a reception response frame from STA (1110) for a data frame transmitted by AP 1 (1120) to STA (1110) and may recognize SN information of the frame last received by STA (1110). If AP 2 (1130) recognizes SN information from the reception response frame of STA (1110), AP 2 (1130) may transmit a data frame to STA (1110) by giving priority to the SN information obtained from the reception response frame of STA (1110) instead of the SN information obtained through context exchange with AP 1 (1120). That is, AP 2 (1130) can set the SN of the data frame that AP 2 (1130) transmits to STA (1110) to a value that is equal to or greater than the SN indicated in the reception response frame of STA (1110) (e.g., a value greater than 1).

[0271] As another example, AP 2 (1130) may initiate communication with STA (1110) by initializing SN and PN (e.g., to 0). That is, AP 2 (1130) may initiate communication with STA (1110) based on the initialized values ​​rather than the SN or PN included in the most recent received response frame transmitted by STA (1110) to AP 1 (1120).

[0272] As another example, STA (1110) may transmit context information to AP 2 (1130). The context information that STA (1110) transmits to AP 2 (1130) may be the same as or may include part of the information included in the context exchange between AP 1 (1120) and AP 2 (1130) described above. As an example, the context information that STA (1110) transmits to AP 2 (1130) may include SN information for the last frame(s) of STA (1130). The SN information for the last frame of STA may be at least one of SN information for the frame that STA last received from AP 1 and SN information for the frame that STA last transmitted to AP 1. Here, it may be distinguished into a DL SN of STA and an UL SN of STA. For example, information that can identify the DL SN of the STA and the UL SN of the STA can be transmitted from the STA to AP 2, and AP 2 can recognize the SN information for the last frame of the STA through the above. However, the above is only an example and may not be limited thereto. For example, since the AP and the STA perform a BA agreement, they can recognize the SN even if only the SN is transmitted without a separate identifier for the SN.

[0273] Here, STA (1110) can transmit context information to AP 2 (1130) regardless of the context exchange procedure between AP 1 (1120) and AP 2 (1130). For example, even if context exchange between AP 1 (1120) and AP 2 (1130) is performed, STA (1110) can also transmit context information to AP 2 (1130). As another example, STA (1110) can transmit context information to AP 2 (1130) instead of AP 1 (1120) when context exchange between AP 1 (1120) and AP 2 (1130) is not performed. In other words, in addition to the context exchange procedure between AP 1 (1120) and AP 2 (1130), STA (1110) may also transmit context information to AP 2 (1130).

[0274] For example, the SN of the data frame transmitted by AP 2 (1130) to STA (1110) may be set to a value greater than the SN included in the most recently transmitted reception response frame by STA (1110) to AP 1 (1120) based on the context information received by AP 2 (1130), or may be transmitted with the SN included in the most recently transmitted reception response frame being set to a value greater than the SN (e.g., a value greater than 1).

[0275] If AP 1 (1120) has not completed transmission of the last frame destined for STA (1110), if STA (1110) has not received the last frame of AP 1 (1120), or if the roaming timer has not expired, AP 2 (1130) may not transmit a data frame to STA (1110).

[0276] On the other hand, if AP 1 (1120) has completed transmitting the last frame destined for STA (1110), AP 2 (1130) may transmit a data frame (1213) to STA (1110) based on at least one of the following: if STA (1110) has received the last frame of AP 1 (1120) or if the roaming timer has expired.

[0277] Figure 20 is a diagram illustrating a wireless LAN same-channel roaming method to which the present disclosure is applied.

[0278] Referring to FIG. 20, STA (1110) may transmit an RAI frame (1201) to AP 1 (1120) to indicate the start of roaming. Thereafter, context exchange may be performed between AP 1 (1120) and AP 2 (1130), and AP 1 (1120) may transmit an RAR frame (1202) in response to the RAI frame (1201) of STA (1110), as described above.

[0279] Here, AP 1 (1120) may transmit a frame (1203) to STA (1110), and STA (1110) may transmit a reception response frame (1204) to AP 1 (1120). Here, AP 2 (1130) may also receive the reception response frame (1204) of STA (1110). Due to deterioration of communication quality between AP 1 (1120) and STA (1110), AP 1 (1120) may not receive the reception response frame (BA frame, 1204) of STA (1110). If AP 1 (1120) does not receive the reception response frame of STA (1110), AP 1 (1120) may unnecessarily retransmit the frame to STA (1110). Considering the above-described situation, AP 2 (1130) may indicate the frame reception status of STA (1110) to AP 1 (1120). When AP 2 (1130) receives the reception response frame (1204) of STA (1110), AP 2 (1130) may indicate the frame reception status of STA (1110) to AP 1 (1120). For example, AP 2 (1130) may transmit the reception status bitmap of the BA frame (1204) of STA (1110) and information for interpreting the reception status bitmap to AP 1 (1120) through an AP-to-AP frame. As another example, AP 2 (1130) may transmit the BA frame (1204) of STA (1110) to AP 1 (1120).

[0280] Accordingly, although AP 1 (1120) did not receive the reception response frame of STA (1110), it can recognize the frame reception status of STA (1110) from AP 2 (1130). AP 1 (1120) can update the BlockAck scoreboard through the frame reception status of STA (1110) received from AP 2 (1130). That is, AP 1 (1120) can update the scoreboard that records the reception status even without receiving the reception response frame of STA (1110). If STA (1110) has received all frames (i.e., STA (1110) has received the data frame of AP 1 (1120) without error), AP 1 (1120) may not perform a retransmission operation. On the other hand, if there is an error in the frame received by STA (1110) (e.g., if there is an error in all or part of the frame), AP 1 (1120) may retransmit the entire frame or retransmit (1214) a part of the frame in which an error occurred. Here, since AP 2 (1130) has indicated the reception status of STA (1110) to AP 1 (1120) and AP 1 (1120) has not received the reception response frame of STA (1110), AP 1 (1120) may recognize that the communication quality with STA (1110) has deteriorated. Therefore, AP 1 (1120) may increase the transmission power of the frame transmitted to STA (1110) and lower the modulation and coding scheme (MCS). For example, lowering the MCS may mean transmitting the frame more robustly.

[0281] As another example, AP 1 (1120) may recognize that the communication quality with STA (1110) has deteriorated, and accordingly, AP 1 (1120) may perform a context exchange with AP 2 (1130). Here, the context exchange may include at least one of information on the last frame transmitted to STA (1110) and information on frames that could not be transmitted to STA (1110), but is not limited thereto. That is, AP 1 (1120) may instruct AP 2 (1130) and / or STA (1110) to allow AP 2 (1130) to perform communication with STA (1110).

[0282] It may be considered that data transmitted by AP 1 (1120) was normally received by STA (1110), and STA (1110) transmitted a BA frame (e.g., a BA frame including a 'last frame reception completion indicator') to inform AP that all frames were normally received, but the BA frame was not normally received by AP 1 (1120), and AP 2 (1130) receives the BA frame. In the above case, AP 2 (1130) may recognize that data exchange between STA (1110) and AP 1 (1120) is completed and may start transmitting data frames. When AP 2 (1130) starts transmitting data frames with STA (1110), it may exchange RTS / CTS to protect TXOP. For example, if AP 1 (1120) has not received a BA frame for all frames up to the last frame from STA (1110) and has not reached the roaming time, but has received a CTS transmitted from STA (1110) to AP 2 (1130), AP 1 (1120) may recognize that STA (1110) has completed roaming to AP 2 (1130) and may not perform retransmission.

[0283] In order for the STA to search for AP 2, which is a roaming target AP for performing a roaming operation in FIGS. 5 to 20, the machine learning algorithm and machine learning unit illustrated in FIGS. 1 to 4 may be used. For example, the STA may search for various APs including AP 2, and continuously input the communication quality and changes in the communication quality of the searched APs into the machine learning unit. The machine learning unit of the STA may determine AP 2 as the most suitable AP for performing roaming, and may want to perform roaming with AP 2. The machine learning algorithm and machine learning unit may be used to determine when AP 1 and AP 2 perform roaming. For example, AP 1 may measure the communication quality of the STA, and the machine learning algorithm may predict the final roaming time of the STA by inputting the communication quality of the STA, and may negotiate the time of performing roaming with AP 2 based on the final roaming time of the STA.

[0284] FIG. 21 is a flowchart illustrating a method for performing a roaming operation in a wireless LAN applied to the present disclosure. Referring to FIG. 21, among a plurality of APs constituting an SMD, a first AP may receive a first frame related to initiating roaming from an STA. (S2110) As an example, the APs of the AP MLD constituting the SMD may include, but are not limited to, at least one transceiver for transmitting and receiving signals, at least one processor for controlling the at least one transceiver, and a memory for storing commands for causing the AP to perform a specific operation by the at least one processor. Here, the first frame may include information related to a second AP to which the STA is roaming among the plurality of APs. Thereafter, the first AP may perform a context exchange to exchange context information necessary for roaming of the STA with the second AP (S2120), and the first AP may transmit the second frame to the STA. (S2130) As an example, it may be the same as FIGS. 5 to 20 described above. Here, as an example, a time interval related to data transmission from the first AP to the STA may be set before the STA roams to the second AP. The time interval may be set at a time point based on at least one of the first frame transmission and the second frame reception. In addition, a first timer may be started based on the time interval, and the first timer may be a timer that expires at the time when roaming is performed. When the first timer expires, the first AP may recognize that the STA has roamed to the second AP and that communication with the STA is impossible.

[0285] Additionally, as an example, the first AP may transmit at least one data frame to the STA while the first timer operates based on a time interval. Additionally, if the first timer expires before the transmission of at least one data frame transmitted by the first AP to the STA is completed, the first AP may not transmit the data frame to the STA, and roaming of the STA to the second AP may be completed based on the expiration of the first timer. Additionally, the first AP may transmit the last data frame among the at least one data frame to the STA while the first timer operates. Thereafter, the first AP may receive a response frame for the last data frame from the STA, and the last data frame may be transmitted including a last frame indicator. Additionally, the context information includes a sequence number (SN) of the last data frame transmitted by the first AP to the STA, and at least one of the last data frame and the response frame is transmitted to the second AP based on listening, and the SN included in at least one of the last data frame and the response frame is compared with the SN included in the context information to indicate completion of roaming of the STA to the second AP.

[0286] Additionally, other matters may be as described above in FIGS. 5 to 20.

[0287] FIG. 22 is a flowchart illustrating a method for performing a roaming operation in a wireless LAN applied to the present disclosure. Referring to FIG. 22, an STA may transmit a first frame related to initiating roaming to a first AP among the APs of a plurality of AP MLDs constituting an SMD. (S2210) As an example, the STA may include, but is not limited to, at least one transceiver for transmitting and receiving signals, at least one processor for controlling the at least one transceiver, and a memory for storing commands for causing the AP to perform a specific operation by the at least one processor. Here, the first frame may include information related to a second AP to which the STA is roaming among the plurality of APs. Here, context information necessary for roaming of the STA may be exchanged between the first AP and the second AP. Thereafter, the STA may receive the second frame from the first AP. (S2220) As an example, the operations of the first AP, the second AP, and the STA may be the same as those of FIGS. 5 to 20 described above.

[0288] Here, a time interval related to data transmission from the first AP to the STA may be set before the STA roams to the second AP. Furthermore, the time interval may be set at a point in time based on at least one of the first frame transmission and the second frame reception, and a first timer may be started based on the time interval. The first timer is a timer that expires at the time when roaming is performed, and when the first timer expires, the STA's roaming to the second AP is completed, allowing the STA to communicate with the second AP.

[0289] Additionally, the STA may perform reception of at least one data frame from the first AP while the first timer operates based on a time interval. Here, the STA transmits context information to the second AP, and the context information may include at least one of a pseudorandom number (PN) of the last frame received by the STA from the first AP, a packet number of the last frame received by the STA from the first AP, a pseudorandom number of the last frame transmitted by the STA to the first AP, and a pseudorandom number packet number of the last frame transmitted by the STA to the first AP.

[0290] In addition, the STA is a wireless LAN terminal that operates according to enhanced multi-link single radio (EMLSR) that performs a listening operation performed on at least one link and transmits and receives frames on one link at a time, and the first frame that the first AP receives from the STA is an initial control frame or a data frame, and when roaming of the STA that operates based on EMLSR is performed, the TXOP (transmit opportunity) of the first AP that performs frame exchange with the STA and the TXOP of the second AP that performs frame exchange with the STA may not overlap due to a certain time interval according to a transition operation of the STA.

[0291] Other matters may be as described above in FIGS. 5 to 20.

[0292] The methods according to the present disclosure may be implemented in the form of program instructions that can be executed by various computer means and recorded on a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, etc., alone or in combination. The program instructions recorded on the computer-readable medium may be those specifically designed and configured for the present disclosure or may be known and available to those skilled in the art of computer software. Examples of the computer-readable medium include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, and flash memory. Examples of program instructions include not only machine language codes generated by a compiler, but also high-level language codes that can be executed by a computer using an interpreter, etc. The above-described hardware devices may be configured to operate as at least one software module to perform the operations of the present disclosure, and vice versa. Although the present disclosure has been described with reference to the above embodiments, it will be understood by those skilled in the art that various modifications and changes can be made to the present disclosure without departing from the spirit and scope of the present disclosure as set forth in the claims below.

[0293]

[0294] The above may also apply to other systems.

Claims

1. In the operating method of an access point (AP) in a wireless LAN system, A step in which a first AP among a plurality of APs forming a single mobility domain (SMD) receives a first frame related to roaming initiation from a station (STA), wherein the first frame includes information related to a second AP among the plurality of APs to which the STA is roaming; A step in which the first AP performs a context exchange to exchange context information necessary for roaming of the second AP and the STA; and An operating method comprising the step of the first AP transmitting a second frame related to roaming to the STA in response to the first frame.

2. In paragraph 1, An operating method, wherein a time period related to data transmission from the first AP to the STA is set before the STA roams to the second AP.

3. In paragraph 2, The above time interval is set at a point in time based on at least one of the first frame transmission and the second frame reception, A first timer is started based on the above time interval, wherein the first timer is a timer that expires at the time when roaming is performed, An operating method in which, when the first timer expires, the first AP recognizes that roaming of the STA is performed to the second AP and communication with the STA is impossible.

4. In paragraph 3, An operating method, wherein the first AP transmits at least one data frame to the STA while the first timer operates based on the time interval.

5. In paragraph 4, An operating method in which, if the first timer expires before the transmission of at least one data frame transmitted by the first AP to the STA is completed, the first AP does not transmit the data frame to the STA, and roaming of the STA to the second AP is completed based on the expiration of the first timer.

6. In paragraph 4, The first AP transmits the last data frame of the at least one data frame to the STA while the first timer is operating, and receives a response frame for the last data frame from the STA. A method of operation in which the last data frame is transmitted including a last frame indicator.

7. In paragraph 1, The above context information includes the sequence number (SN) of the last data frame transmitted by the first AP to the STA, At least one of the last data frame and the response frame is transmitted to the second AP based on listening, An operating method in which the completion of roaming of the STA to the second AP is indicated by comparing the SN included in at least one of the last data frame and the response frame with the SN included in the context information.

8. Among the multiple access points (APs) that constitute a single mobility domain (SMD), in the first AP, At least one transceiver for transmitting and receiving signals; At least one processor controlling at least one transceiver; and A memory storing instructions that cause the AP to perform a specific operation by at least one processor, The above specific actions are: Receive a first frame related to roaming initiation from a station (STA), wherein the first frame includes information related to a second AP to which the STA is roaming among the plurality of APs, Performs a context exchange to exchange context information required for roaming with a second AP among the above multiple APs, and A first AP, wherein the first AP transmits a second frame related to roaming initiation to the STA in response to the first frame.

9. In the operation method of a station (STA) in a wireless LAN system, A step of transmitting a first frame related to initiation of roaming to a first AP among a plurality of APs forming a single mobility domain (SMD), wherein the first frame includes information related to a second AP to which the STA is roaming among the plurality of APs; and A method of operation, comprising the step of the STA receiving a second frame related to roaming in response to the first frame.

10. In paragraph 9, An operating method, wherein a time period related to data transmission from the first AP to the STA is set before the STA roams to the second AP.

11. In paragraph 10, The above time interval is set at a point in time based on at least one of the first frame transmission and the second frame reception, A first timer is started based on the above time interval, wherein the first timer is a timer that expires at the time when roaming is performed, An operating method in which, when the first timer expires, roaming of the STA to the second AP is completed and the STA communicates with the second AP.

12. In paragraph 11, An operating method in which the STA receives at least one data frame from the first AP while the first timer operates based on the time interval.

13. In paragraph 12, An operating method in which the STA transmits context information to the second AP, wherein the context information includes at least one of a pseudorandom number (PN) of the last frame received by the STA from the first AP, a packet number of the last frame received by the STA from the first AP, a pseudorandom number of the last frame transmitted by the STA to the first AP, and a pseudorandom number packet number of the last frame transmitted by the STA to the first AP.

14. In paragraph 8, The above STA is a wireless LAN terminal that operates according to enhanced multi-link single radio (EMLSR) that performs listening operations performed on at least one link and transmits and receives frames on one link at a time. The first frame received by the first AP from the STA is an initial control frame or a data frame, An operating method in which, when roaming of the STA operating based on the EMLSR is performed, the TXOP (transmit opportunity) of the first AP in which the first AP performs frame exchange with the STA and the TXOP of the second AP in which the second AP performs frame exchange with the STA do not overlap due to a certain time interval according to the transition operation of the STA.

15. At the station (STA), At least one transceiver for transmitting and receiving signals; At least one processor controlling at least one transceiver; and A memory storing instructions that cause the STA to perform a specific operation by at least one processor, The above specific actions are: Transmitting a first frame related to initiation of roaming to a first AP among a plurality of APs forming a single mobility domain (SMD), wherein the first frame includes information related to a second AP to which the STA is roaming among the plurality of APs, and An STA, wherein the STA receives a second frame related to roaming initiation in response to the first frame.

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