Seamless wi-fi multi-link handover

Abstract

A communication control device is configured to control a wireless communication circuitry of a first access point (AP) configured to communicate with a multi-link device (MLD) via a different link than a second AP, the communication control device comprising control circuitry configured to control the wireless communication circuitry of the first AP to: transfer, upon the addition of a second link between the MLD and the second AP while a first link between the MLD and the first AP is enabled, context information to the second AP, wherein the transferred context information configures the second AP to communicate with the MLD and is transferred per traffic category; receive a data unit to be delivered to the MLD, the data unit having a traffic category identifier identifying the traffic category of said data unit; transmit the received data unit to the MLD if the context information for the traffic category of said data unit has not yet been transferred to the second AP; and forward the received data unit to the second AP for transmission to the MLD by the second AP if the context information for the traffic category of said data unit has already been transferred to the second AP.

Description

WITTEWELLERP A T E N T A N W A L T EApplicants:Sony Group Corporation 30.10.2025 1-7-1 Konan 4727P382WO - SKMinato-KuTokyo 108-0075JAPANSONY Europe Limited The Heights, Brooklands, Weybridge, SurreyKT13 0XWUNITED KINGDOMCOMMUNICATION CONTROL DEVICE AND MLD CONTROL DEVICEBACKGROUNDFIELD OF THE DISCLOSURE

[0001] The present disclosure relates to a communication control device and an MLD control device as well as to corresponding methods.DESCRIPTION OF RELATED ART

[0002] In mobile scenarios, when a communication device (e.g. a station (STA)) moves, the connectivity to another communication device (e.g. an access point (AP)) may get lost, for instance due to too strong path loss. Therefore, a STA typically associates with or roams to a different AP belonging to the same extended service set (ESS) in due time to avoidconnectivity loss. However, nowadays, the association takes time as it requires, e.g., regeneration of keys and renegotiation of agreements. During this time no data transfer is possible.

[0003] The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventor(s), to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.SUMMARY

[0004] It is an object to enable seamless roaming without or with only short interruption of data transfer.

[0005] According to an aspect there is provided a communication control device configured to control a wireless communication circuitry of a first access point (AP) configured to communicate with a multi-link device (MLD) via a different link than a second AP, the communication control device comprising control circuitry configured to control the wireless communication circuitry of the first AP to: transfer, upon the addition of a second link between the MLD and the second AP while a first link between the MLD and the first AP is enabled, context information to the second AP, wherein the transferred context information configures the second AP to communicate with the MLD and is transferred per traffic category; receive a data unit to be delivered to the MLD, the data unit having a traffic category identifier identifying the traffic category of said data unit; transmit the received data unit to the MLD if the context information for the traffic category of said data unit has not yet been transferred to the second AP; and forward the received data unit to the second AP for transmission to the MLD by the second AP if the context information for the traffic category of said data unit has already been transferred to the second AP.

[0006] According to a further aspect there is provided an MLD control device configured to control a wireless communication circuitry of a multi-link device (MLD) configured to communicate with a first access point (AP) and a second AP via separate links, the MLD control device comprising control circuitry configured to control the wireless communication circuitry of the MLD to: receive a data unit to be delivered to a distribution system (DS), the data unit having a traffic category identifier identifying the traffic category of said data unit; transmit the received data unit to the first AP via a first link if the first AP holds context information for the traffic category of said data unit, said context information configuring the first AP to communicate with the MLD; and transmit the received data unit to the second AP via a second link for forwarding it to the DS via the first AP if the second AP holds context information for the traffic category of said data unit, said context information configuring the second AP to communicate with the MLD.

[0007] According to still further aspects corresponding methods, a computer program comprising program means for causing a computer to carry out the steps of the method disclosed herein, when said computer program is carried out on a computer, as well as a non-transi- tory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method disclosed herein to be performed are provided.

[0008] Embodiments are defined in the dependent claims. It shall be understood that the disclosed methods, the disclosed computer program and the disclosed computer-readable recording medium have similar and / or identical further embodiments as the claimed devices and as defined in the dependent claims and / or disclosed herein.

[0009] The present disclosure presents an improved concept of seamless roaming for a station (STA) of an MLD (that may hold two or more STAs) from a source AP (also called first AP) to a target AP (also called second AP) which allows partial data service to the STA during the roaming. While conventionally the data service to a STA is paused during roaming due to transfer of communication parameters among the APs, one of the aspects of the disclosure is to do said transfer partially, i.e., per traffic category, which allows uninterrupteddata service to the STA by other traffic categories. During the proposed roaming procedure, a few traffic categories may be served to the STA by the source AP, a few other traffic categories may be served to the STA by the target AP, and zero or one traffic category may not be used, because it is in the process of roaming. To further improve user experience, in an embodiment, mapping some traffic categories to other traffic categories may be used, which may provide zero service interruption during roaming, data delivery with high diversity as well as high reliability.

[0010] In the context of the present disclosure, the expressions “separate link” and “different links” shall be understood such that the links are separate / different in the sense that they are managed or created by different APs, but both links may or may not be on the same carrier frequency.

[0011] The foregoing paragraphs have been provided by way of general introduction and are not intended to limit the scope of the following claims. The described embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWING

[0012] A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:Fig. 1 shows a schematic diagram of a communication system.Fig. 2 shows a schematic diagram of a second embodiment of a communication system.Fig. 3 shows a schematic diagram of a third embodiment of a communication system.Fig. 4 shows a diagram illustrating context transfer.Fig. 5 shows a schematic diagram of a first embodiment of a communication system according to the present disclosure.Fig. 6 shows a diagram illustrating the downlink behavior of an UP filter of an AP.Fig. 7 shows a diagram illustrating the uplink behavior of an UP filter of an AP.Fig. 8 shows a diagram illustrating the downlink behavior of an UP filter of the MLD.Fig. 9 shows a diagram illustrating the uplink behavior of an UP filter of an MLD.Fig. 10 shows a diagram illustrating an embodiment of per-TID context transfer according to the present disclosure.Fig. 11 shows a flowchart illustrating the entire operation of context transfer according to an embodiment of the present disclosure.Fig. 12 shows a table of the mapping between UP, access category (AC) and corresponding TIDs.Fig. 13 a schematic diagram of another embodiment of per-TID context transfer according to the present disclosure using TID-remapping.Fig. 14 shows a diagram of default mapping and two options for remapping.Fig. 15 shows an embodiment of a data unit including in its MAC header an UP identifier.Fig. 16 shows a diagram of the effect of TID remapping on order keeping.Fig. 17 shows a diagram illustrating a first embodiment for solving the order keeping issue according to the present disclosure.Fig. 18 shows a diagram illustrating a second embodiment for solving the order keeping issue according to the present disclosure.Fig. 19 shows diagrams illustrating the pre- and post-processing of the UP filter for TID remapping according to embodiments of the present disclosure.Fig. 20 shows a flowchart illustrating the envisioned operation of seamless roaming with TID remapping.Fig. 21 shows a diagram illustrating the envisioned operation for joint connectivity with remapping.Fig. 22 shows the pre- and post-processing of the remapping operation for joint connectivity according to embodiments of the present disclosure.Fig. 23 shows a diagram illustrating the envisioned operation for high reliability with remapping.Fig. 24 shows a diagram depicting the envisioned operation for high reliability with synchronized sequence number according to an embodiment.Fig. 25 shows a diagram depicting the envisioned operation for high reliability with synchronized sequence number according to another embodiment.Fig. 26 shows the pre- and post-processing of the remapping operation for high reliability according to embodiments of the present disclosure.Fig. 27 shows a schematic diagram of a second embodiment of a communication system according to the present disclosure.Fig. 28 shows a diagram illustrating an embodiment of the layout of the main communication devices in an embodiment of the present invention.Fig. 29 shows a flowchart of a first embodiment of a communication control method according to the present disclosure.Fig. 30 shows a flowchart of an embodiment of an MLD control method according to the present disclosure.Fig. 31 shows a flowchart of a second embodiment of a communication control method according to the present disclosure.Fig. 32 shows a flowchart of a third embodiment of a communication control method according to the present disclosure.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0013] The present disclosure may be applied in mobile scenarios, in which the connectivity of a moving station (STA) to an access point (AP) may get lost due to too strong path loss. To avoid connectivity loss a STA typically associates with or roams to a different AP belonging to the same extended service set (ESS) in due time, which may take time for regeneration of (encryption / decryption) keys and renegotiation of agreements (such as Block Acknowledgement (Back) agreement) and prevents data transfer during this time. Embodiments of the present disclosure may make use of a distribution system (DS) for routing the data flows and a control entity (CE; also referred to as control device herein). The CE controls multiple APs and the DS.

[0014] Figs. 1 and 2 show schematic diagrams of a first and second embodiment of a communication system. The control entity (CE) 10 is a device that resides in the same network asat least two APs 20 (AP1) and 30 (AP2). Physically, the CE 10 may be attached to an AP 20, 30 or may be a separate device within the network. It is connected to either at least two APs 20, 30, as shown in Fig. 1, or to a CE of at least one more APs, e.g., to AP1 20 as shown in Fig. 2. When the CE 10 is attached to an AP, it may have an internal link to the attached AP and a network link (backhaul) to other APs or a CE of other APs. The CE 10 and the APs 20, 30 exchange configuration information (i.e. non-user data information) as shown in Fig. 1. Both APs 20, 30 establish links 101 , 102 (link 1 and link 2) to STAs 40 (STA1) and 50 (STA2). Both STAs 40, 50 are organized in a non-AP multi-link device (MLD) 60. The non-AP MLD 60 converges the traffic flows of the two STAs 40, 50 within a device.

[0015] The CE 10 may control both APs 20, 30 via their station management entity (SME) 21 , 31 as shown in Fig. 3 depicting a schematic diagram of a third embodiment of a communication system. CE 10 and APs 20, 30 are connected via a wired or wireless or hybrid communication link 107, 108. The connection may also use the same or a different distribution system (DS) 70 as for the user data transfer. For data transfer the APs 20, 30 are connected to the DS, e.g., via communication links 103, 104. The CE 10 is connected to the DS 70, e.g., via communication link 106. The DS 70 may provide multiple links between each connected device (e.g. 10, 20, 30). Those links may be wired, wireless or hybrid.

[0016] The CE 10 generally has a Medium Access Control (MAC) address. Any frame addressed to the CE 10 identified via its MAC address will be forwarded to the CE 10 by an AP 20 or 30. The MAC address is important for association and encryption key generation, including a temporal key (TK). No (user) data frame is addressed to the CE’s MAC address. There is generally a single CE 10 with a unique MAC address for at least two APs. However, it is also possible that each AP 20, 30 may come with its own CE, i.e., a CE of AP 20 may have the same MAC address as another CE of AP 30, particularly if it is ensured that the non-AP MLD 60 connects to a unique CE. For example, the non-AP MLD 60 can only connect to a CE which belongs to the AP through which the non-AP MLD 60 is connected to the DS 70.

[0017] The AP 20 currently serving the non-AP MLD 60 holds context information 200 (also referred to as context), as shown in Fig. 3. The context information 200 is informationimportant for transmission or reception of data frames. Without context information, a frame exchange may not happen or may not be successful. The context information contains at least information about sequence numbers (SN) and packet number (PN). The (complete) context information 200 may include one or more of the following information: a reset indication of PN and / or SN; for instance, for SN this means restarting at 0 and for PN this means using a higher PN than before (e.g. increment the old PN by a value such that new PN can be easily signaled, e.g., by rounding up to next 2Nwith N being an integer because a PN may not repeat for the same TK; the current PN and / or SN; encryption keys, e.g., a pairwise transient key (PTK) and / or a group temporal key (GTK); association / capability data including Physical Layer (PHY) and / or MAC capabilities of AP and / or non-AP STA to determine common communication features that can be used; negotiated agreements including mechanisms configured for an AP - non-AP pair to improve data transfer such as a BlockAck agreement, target wake time (TWT) agreement, etc.;BAck scoreboard: content of a scoreboard maintained at a receiver side and holding information about successfully and erroneously received data units indexed by SN; receive buffer including successfully received data units which have not yet been forwarded to higher layer, e.g., due to an erroneous data unit with lower SN; and transmit buffer including data units which have not yet been transmitted, e.g., due to a channel busy condition.

[0018] The context information can be transferred between two APs 20, 30 via a direct link 100 as shown in Fig. 3. Thereby, it may be exchanged directly between the APs (Fig. 3) or between the CEs of the APs (not shown) or it may be exchanged between APs 20, 30 via the DS 70, where the connection between the APs 20, 30 and the CE 10 may be established via the same DS 70 that is used for user data transfer.

[0019] A CE generally knows all APs that a non-AP MLD may potentially use during roaming. The CE authenticated all those APs. The CE can securely communicate with those APs. The CE is aware of capabilities (i.e. , supported features) of each AP. These steps mayhappen before the following process for all APs or on a step-by-step basis, i.e., successively onboarding of new APs during setup or on demand basis. The connection between the AP and the CE may be via the DS or via an internal interface if the AP and CE reside in the same device as e.g. shown in Fig. 2.

[0020] It shall be noted in this context that in the figures showing frame exchanges, a potential acknowledgement or confirmation message has not been explicitly drawn for simplicity reasons. However, it may make sense to acknowledge the receipt of any frame by the destination even not shown in the figures.

[0021] The embodiments described above can enable seamless roaming which means that the MLD which holds at least two STAs or non-AP devices can roam or move from one AP (source AP) to another AP (the target AP) with very low latency and / or data service interruption. Since source and target AP are located at different locations, a mobility domain can be built up, in which the non-AP MLD experiences high quality of (data) service (QoS) although the range of a single AP is limited. The architecture behind seamless roaming consists of serval APs which are connected to the DS. The DS can be considered as the (e.g. wired) network to which the APs are connected to. It has the task of distributing data units among several devices, including APs and STAs, according to their destination and / or source address. At one point in time, a non-AP MLD may not be connected or may be connected via a single AP to the DS, because otherwise multiple routes from a source to a destination device would exist which is not supported by the DS. Therefore, connection 103 or connection 104 or no connection is active but never both connections 103 and 104. During a seamless roaming phase, the connection to the DS, also called DS mapping change, changes from the source AP (e.g. AP1 20) to the target AP (e.g. AP2 30).

[0022] The control entity 10 controls the seamless roaming operation, the DS mapping changes, and acts as a single point of contact for the non-AP MLD 60 that stays unchanged during the roaming phase. Before a DS mapping change can happen, a context transfer from source AP to target AP happens. The context information includes data that is required to for communication between an AP and a STA. The context information resides initially at the source AP and needs to be transferred to the target AP. Fig. 4 shows a diagram illustrating context transfer 201. During the context transfer 201, no uplink (UL) (non-AP MLDto AP) communication can happen. During the context transfer, downlink (DL) (AP to non- AP MLD; 202) communication can only happen for preprocessed data units. In other words, the data units are preprocessed such that remaining operations until transmission do not require any modification to the context. Before the context transfer 201 , UL and / or DL may take place between AP1 20 and MLD 60 (arrow 203), and after the context transfer 201 , UL and / or DL may take place between AP2 30 and MLD 60 (arrow 204). Depending on the content of the context information, the context transfer may take significant time for actual transmission and time to obtain channel access.

[0023] The present disclosure seeks to minimize the uplink and / or downlink (data) service interruption during roaming and to allow seamless connectivity (at least) during roaming, meaning that some data can be communicated between AP(s) and non-AP MLD during a context transfer.

[0024] According to the present disclosure the context is transferred per traffic category, for instance per traffic identifier (TID) or per user priority (UP). In this context, the UP is a priority value associated with a data unit. At a MAC service access point (SAP), which is the connection to a higher layer of a WLAN chipset or the DS, the UP is provided together with the data unit. A WLAN chipset typically assigns a TID to each data unit based on the UP for internal processing. In an embodiment, there is a total of 8 TIDs with values 0...7 for which a default mapping exists and another 8 TIDs with values 8... 15 for which a mapping can be defined by a so called “traffic specification” (TSPEC) via a negotiation between two devices. As illustrated in Fig. 12 showing a table of the mapping between UP, access category (AC) and corresponding TIDs, the mapping of TIDs 0...7 equals the UP and it determines the priority of the queue in which the related data unit is put. There are four priorities: background (BK), best effort (BE), video (VI), and voice (VO) with BK having the lowest and VO the highest priority. The higher the priority, the earlier a packet is transmitted on average.

[0025] In an embodiment, the AP, which is connected to the DS, forwards data units to be transmitted to the other AP for the TID whose context has been already transferred to the other AP. If the other AP receives data, it forwards the received data units to the AP which is connected to the DS and which forwards the data units from the other AP to the DS. In afurther embodiment, traffic with a certain UP is mapped to a TID such that the TID that currently cannot be used, because the context of said TID is transferred for example, is avoided.

[0026] Fig. 5 shows a schematic diagram of a first embodiment of a communication system according to the present disclosure. The architecture for seamless roaming shown in Figs. 1 to 3 is changed to support traffic category specific context transfer, in this embodiment TID specific context transfer. It is assumed that the DS is mapped to AP1 via connection 103 and connection 104 is inactive. Different from the embodiments shown in Figs. 1 to 3, before each core AP 21 , 31 of each AP 20, 30 and before each core non-AP MLD 61 of each non-AP MPD 60, a UP filter 22, 32, 62 is provided.

[0027] At AP side, the UP filters 22, 32 are logically connected to each other via link 109. In DL, incoming data units from the DS 70 are filtered according to their UP. Data units with the same UP go either to core AP1 21 or to core AP2 31. Fig. 6 shows a diagram illustrating the DL behavior of the UP filter 22 (Fig. 6A) and UP filter 32 (Fig. 6B). As shown in Fig. 6, when an UP filter receives data units from another UP filter in DL, it forwards them to its co-located AP. In UL, outgoing data units are forwarded to the DS 70 if received from core AP1 or are forwarded to the UP filter of AP1 if received from core AP2. Fig. 7 shows a diagram illustrating the UL behavior of the UP filter 22 (Fig. 7A) and UP filter 32 (Fig. 7B). As shown in Fig. 7, when an UP filter receives data units from another UP filter in UL, it forwards them to the DS 70.

[0028] The data forwarding among UP filters works conceptually as follows in an embodiment: Once the UP filter receives a data unit from the DS with a UP, whose TID is mapped to the other AP, it encapsulates the data unit including the original source and destination address in another data units with source address equal to the co-located AP and the destination address equal to the other AP and instructs the DS to deliver this newly created data unit. The receiving UP filter removes the encapsulation and forwards it to its co-lo- cated AP. The operation in UL is conceptually the same but inverted.

[0029] At non-AP MLD side, there is just one UP filter 62. In DL, i.e., when the non-AP MLD 60 receives, the UP filter 62 combines the data streams received from both STAs 40, 50 and forwards them to the MAC SAP of the STA. Fig. 8 shows a diagram illustrating the DL behavior of the UP filter 62. In UL, i.e., when the non-AP MLD 60 transmits, the UP filter 62 checks the UP of each incoming data unit and transmits data units via the STA which is connected to the AP holding the corresponding context. For example, if STA1 40 is connected to AP1 20 holding the contexts for TID 0...3, the UP filter 62 forwards data units with TID 0...3 to STA1 40 and all other data units with other TIDs to STA2 50 connected to AP2 30 holding contexts for TID 4...7. Fig. 9 shows a diagram illustrating the UL behavior of the UP filter 62.

[0030] Fig. 10 shows a diagram illustrating an embodiment of per-TID context transfer 210 according to the present disclosure. It is assumed that the contexts of all TIDs reside at the source AP (AP1 20) initially, and AP1 20 serves DL and UL traffic to a STA 40, 50 of the non-AP MLD 60 (arrow 211). At the point in time, when the context transfer 210 of TID 0 is initiated, only buffered DL data for TID 0 can be delivered to the non-AP MLD 60 (arrow212) and the UL is paused. All other TIDs are not affected, and DL and UL data can be delivered to / from the non-AP MLD 60 via AP1 20. After the context transfer is done (arrow213), AP1 20 holds the contexts for TID 1...7 and the target AP (AP2 30) holds the context of TID 0; hence, DL / UL data service for the non-AP MLD 60 is provided by AP1 20 for TIDs 1 ...7 (arrow 213) and by AP2 30 for TID 0 (arrow 214). AP1 20 can still transmit buffered DL data to the non-AP MLD 60 (arrow 215) if any DL data is available. A data unit associated with TID 0 received from the DS 70 which is connected to AP1 20 is now forwarded to AP2 30 for transmission. Similarly, a data unit received by AP2 30 for TID 0 is forwarded to AP1 20 for forwarding to the DS 70.

[0031] By comparing Figs. 4 and 10, it becomes apparent that the context transfer 201 takes longer in Fig. 4 because all TIDs are transferred at the same time. There is no service to the non-AP MLD 60 for UL for the time of context transfer for any TID in Fig. 4, whereas in Fig. 10 only the currently transferred TID is affected. Only buffered DL traffic can be served for all TIDs during context transfer in Fig. 4, whereas in Fig. 10 this only applies for the currently transferred TID, while all other TIDs can obtain fresh DL data units. There is no data forwarding in Fig. 4, but a DS mapping change, whereas in Fig. 10 dataforwarding happens for the transferred TIDs. A DS mapping change happens latest after all TIDs have been transferred.

[0032] In the context of the present disclosure the context information is defined as follows and can be separated into static and dynamic context information. The static context information is context that changes rarely, at least not during the seamless roaming operation. Therefore, it may be exchanged at the very beginning of the context transfer, i.e., just before the context of the first TID is transferred. Depending on implementation, the static information typically includes one or more of (preferably all of):• Encryption keys such as PTK (pairwise transient key) and GTK (group temporal key) configure the encryption mechanism.• AP and non-AP MLD capabilities indicating their PHY and / or MAC capabilities.• Agreements between AP and a STA of a non-AP MLD including for example Block- Ack agreement, TWT (target wake time) agreement and others.• Packet number (PN). The PN is a number that is assigned to every transmitted packet to secure encryption. It is therefore dynamic context. However, the only requirement from evaluation point of view is that the PN is monotonically increasing. Thus, it is possible to split the available PN space into two parts: A PN space with low numbers for the source AP and another PN space with high numbers for the target AP. When a STA performs roaming, it may see substantially higher PN when the first packet from the target AP is received.

[0033] The dynamic context information is context that changes frequently, also during the seamless roaming operation. Therefore, it needs to be transferred instantly. Depending on implementation, the context information includes one or more of (preferably all of):• The sequence number (SN) is used to track the order of data units arriving at receiver to avoid duplicates and out-of-order delivery. Also, it is the index for the Ack information in the BlockAck.• Transmit buffer content consist of packets that have not yet had the chance to be transmitted or that have not yet been successfully transmitted. Depending on implementation, the transmit buffer may be emptied also during the “buffered downlink” phase.• Receive buffer content consists of packets that could not have been forwarded to the DS, because other packets with lower sequence number are yet missing, e.g., due to a failed transmission. Depending on implementation, those missing packets can be dropped resulting in a data loss, however.

[0034] Generally, all context information can be treated as TID specific. The PN is taken from a common increasing counter for all TIDs, but the evaluation for increasing PN is per TID.

[0035] Fig. 10 shows the envisioned operation for one TID, whereas the entire operation 300 according to an embodiment of the present disclosure is depicted as flowchart in Fig. 11. Initially (step 301), the non-AP MLD 60 is with AP1 20 only. In step 302, seamless roaming is prepared by exchanging static context. In step 303, dynamic context is transferred TID- wise. In step 304, UP filters are reconfigured once the context of a TID is transferred. In step 305, non-context-transferred TIDs are served by AP1 20, context-transferred TIDs are served by AP2 30, UP filters 22, 32 at both APs 20, 30 as well as UP filter 62 at the non-AP MLD 60 are appropriately configured. In step 306, DS mapping changes from AP1 20 to AP2 30 and UP filters 22, 32 as well as UP filter 62 at the non-AP MLD 60 are appropriately configured. Finally (step 307), the non-AP MLD 60 is with AP2 30.

[0036] Thus, essentially, the context is transferred TID-wise until all TIDs are transferred. The UP filters 22, 32 may be appropriately configured by the control entity 10. The UP filter 62 may be appropriately configured by the non-AP MLD 60. When all TIDs are transferred, the DS mapping is changed from AP1 20 to AP2 30; hence, after a successful transfer, all traffic goes via the DS 70 to the target AP (AP2) and no data forwarding among UP filters of the two APs happens anymore. It may be also envisioned that the DS mapping change happens earlier, e.g., when more than half of the TIDs have been transferred to the target AP. Thus, the data forwarding happens from target AP to source AP for those TIDs that are still with the source AP. This may reduce traffic load of the DS, because it minimizes data forwarding.

[0037] Generally, each TID has a corresponding TID as depicted in Fig. 12. Corresponding means that a different TID maps to same access category (AC) and / or has samedesignation. By adding some pre- and post-processing to the UP filter, a true seamless handover without service interruption can be implemented in another embodiment of the present disclosure as follows. The pre- and post-processing add functionality to the UP filter such that a UP to TID mapping different to the standard mapping can be done. In this case the control entity controls the actual UP to TID mapping on both APs such that the TID of which the context is currently transferred is not used.

[0038] Fig. 13 shows a schematic diagram of another embodiment of per-TID context transfer 210 according to the present disclosure using TID-remapping. It is based on the assumptions made for Fig. 10. Before the roaming operation is initiated, data units with a certain UP (UP=0) are associated with TID A (TID 0) (block 220). As TID A (TID 0) would experience a service interruption during its context transfer 210, the certain UP (UP=0) is remapped to the corresponding TID B (TID 3), before the context transfer of TID A (TID 0) (block 221). This is illustrated in more detail in Fig. 14 showing a diagram of default mapping and two options for remapping. The upper row shows default mapping of each UP to a single TID. The middle row shows a first option of remapping during roaming wherein UP=0 is remapped to TID 3 during the roaming of TID 0. The lower row shows a second option of remapping during roaming wherein UP=0 remains mapped to TID 0 but is additionally remapped to TID 3 during the roaming of TID 0 for higher reliability as described below. Once TID A’s (TID 0) context has been transferred, the remapping is inverted such that data units with the certain UP (UP=0) are mapped to TID A (TID 0) again (block 222). Since TID A (TID 0) is now with the target AP (AP2), data forwarding from AP1 , which is connected to the DS, to AP2 is needed for TID A.

[0039] TID remapping has prerequisites and related solutions. If the TID, to which the UP is remapped is used by another traffic, there may be an ambiguity at receiver side, because the non-AP MLD’s MAC SAP outputs a UP based on the TID. For example, if, during a roaming phase, UP A is remapped to TID B and UP B is still mapped to TID B, the receiver cannot know if the data units received via TID B correspond to UP A or UP B. If this is an issue, because UP A and UP B have anyway the same designation, a solution is to have a separate signaling within WLAN that indicates to the receiver which UP a data unit originally had. This information is then evaluated by the receiver to set the UP accordingly.Fig. 15 shows an embodiment of a corresponding data unit including in its MAC header an UP identifier indicating the UP that the data unit originally had.

[0040] As an alternative of choosing a corresponding TID as depicted in Fig. 12, it is also possible to use higher TIDs from 8... 15 with TSPEC agreement as a corresponding TID.

[0041] There is no order keeping in between TIDs. Thus, when TID remapping is applied, it may happen that data units with the same UP arrive not in order, because of TID remapping. This issue is illustrated in Fig. 16 showing a diagram of the effect of TID remapping on order keeping. It is assumed that the first three data units (#1 to #3) are mapped to TID B (as #1 b, #2b, #3b) and the second three data units (#4 to #6) are mapped to TID A (as #1a, #2a, #3a). The order keeping is ensured by BAck mechanism for each TID separately. It is further assumed that the data units of TID B are initially transmitted after data unit #3 arrived and data units of TID A are initially transmitted after data unit #6 arrived. Furthermore, the channel access is such that the queue of TID B obtains initial channel access before TID A. Depending on the point in time, when data units are released to a higher layer, the order of the data units of different TIDs can be mixed. In case (a), it is assumed that all DUs are received in order, i.e. , order keeping across TIDs is fine. In case (b), it is assumed that data units #2b and #3b are received in error and retransmitted after the initial transmission of TID A which is assumed to be error free. As can be seen, the order of data units is messed up. In case (c), it is assumed that data units #1 b, #2b, and #3b need retransmission as well as #3a, which obviously leads to a different order compared to the order at the transmitter.

[0042] The order keeping issue may be solved easily when TIDs reside at one AP. This is for example the case at the beginning of the remapping, when context of TID A and TID B are yet with one AP. Then, the AP can control the order keeping internally by finishing data units of TID A first, before data units of TID B are transmitted, even in case of retransmissions of TID A for example. However, the order keeping issue is more difficult to solve when TIDs reside at two APs. This is for example the case when the TID remapping ends and TID B is served by AP1 and TID A is served by AP2 (transition from block 221 to 222). In this case the following solutions may apply according to embodiments of the present disclosure.

[0043] Fig. 17 shows a diagram illustrating a first embodiment for solving the order keeping issue according to the present disclosure for the cases (a), (b) and (c) shown in Fig. 16. According to this embodiment, a higher-layer sequence number is contained in the data units and evaluated outside of the PHY and MAC layer of Wireless LAN in a higher-layer. The higher layer sequence number is illustrated with increasing letters in brackets (e.g. (A), (B), ...). Regardless of the exemplary reception scenario, the higher layer sequence number evaluation causes the data units to be in order. In some embodiments the sequence number is dropped after its evaluation; hence, it is not contained in the output data stream anymore.

[0044] Fig. 18 shows a diagram illustrating a second embodiment for solving the order keeping issue according to the present disclosure for the cases (a), (b) and (c) shown in Fig. 16. According to this embodiment, an indication is conveyed from AP1 to AP2 indicating to AP2 that AP1 finished data transfer on TID A, and AP2 may start transmitting on TID B. Essentially, AP2 may use TID B not earlier than it received this indication from AP1 either wirelessly or via the DS or via the CE. The data units of TID B are transmitted first. If data units are erroneously received, they are successfully retransmitted before AP1 indicates to AP2 that it has completed data transfer of TID B. Obviously, in all three cases, the data units are conveyed in order.

[0045] Fig. 19 shows diagrams illustrating the pre- and post-processing of the UP filter for TID remapping according to embodiments of the present disclosure in more detail. Fig. 19A shows the transmit processing at AP in which it is checked if the UP equals to the currently transferred TID. If yes, the UP is set to the corresponding TID; if not, the UP is kept unchanged. Fig. 19B shows the receive processing at the non-AP MLD in which the remapping process at AP is essentially reverted. This step may be required at non-AP MLD side, because the UP parameter is output via MAC SAP together with the data unit for use in higher layers; hence, the TID remapping should be transparent for higher layers. A similar processing is made for reception and transmission at the AP (Fig. 19C) and the non- AP MLD (Fig. 19D), respectively.

[0046] Fig. 20 shows a flowchart illustrating the envisioned operation 400 of seamless roaming with TID remapping. In this operation 400, steps 401 to 403 and 406 to 408 correspond tosteps 301 to 303 and 305 to 307 of the operation 300 shown in Fig. 11. In step 404, the UP of the currently transferred TID is mapped to the corresponding TID and UP filters are configured to perform the mapping correspondingly. In step 405, UP filters are reconfigured and the mapping to corresponding TID is reverted once the context of a TID is transferred.

[0047] Basically, the TID remapping for seamless roaming can also be done continuously to enhance diversity of the data units received at the non-AP MLD. Fig. 21 shows a diagram illustrating the envisioned operation for joint connectivity with remapping. Data units #1, #2 and #5 are mapped to TID B, data units #3, #4 and #6 are mapped to TID A. As can be seen in Fig. 21 , the same issues of order keeping may exist as illustrated above with reference to Fig. 16 and the same solutions as illustrated above with reference to Figs. 17 and 18 may be envisioned.

[0048] Fig. 22 shows the pre- and post-processing of the remapping operation for joint connectivity according to embodiments of the present disclosure in more detail. Fig. 22A shows the preprocessing at AP side for transmission (downlink) of a data unit. Fig. 22B shows the postprocessing at AP side for reception (uplink) of a data unit. Fig. 22C shows the postprocessing at non-AP MLD side for reception (downlink) of a data unit. Fig. 22D shows the preprocessing at non-AP MLD side for transmission (uplink) of a data unit.

[0049] In another embodiment, to achieve high reliability, data units may be mapped to both TIDs; hence, each TID transfers the same data units as shown in Fig. 23 showing a diagram illustrating the envisioned operation for high reliability with remapping. As can be seen, order keeping is not really an issue. Because data units are duplicated over TIDs and there is a per TID order keeping, the merged data flow keeps the order, but duplicates should be eliminated. As can be seen in Fig. 23, already received data units may be received again at a later point in time. Thus, there is a need for duplicate detection. On top of that, a transmitter synchronization may be provided, because it may happen that a first AP obtains more often channel access than a second AP; hence, the first AP is advancing the data unit transmission, whereas the second AP transmits at a significant later point in time a duplicated version of the data unit, which may however be already received.

[0050] A simple solution to the duplication issue is the use of a higher layer sequence number as shown in Fig. 17. However, the issue of a misalignment among the APs still exists which may however not be a severe problem if the date rate is small compared to the link capacity for both links.

[0051] Another solution is that the APs synchronize their sequence numbers for the respective TIDs which contain duplicated data units. This means that the same duplicated data unit gets assigned the same sequence number. By doing so, the non-AP MLD can filter and discard duplicated data units. Fig. 24 shows a diagram depicting the envisioned operation for high reliability with synchronized sequence number according to an embodiment. Both APs transmit the data units to the non-AP MLD via their own TID, which filters according to the sequence number and drops duplicated data units such that only unique data units are output at the MAC SAP. In case (a) no transmission error is assumed, whereas in case (b) data units #2 and #3 via TID B are assumed to be erroneous.

[0052] Furthermore, the non-AP MLD reports to its AP the sequence number of all successfully received data units, not only those that were transmitted by its AP. Thus, the BAck transmitted by the non-AP MLD via a particular STA may include not only the reception status of the data units received from the STA’s AP, but also from APs of other STAs. In other words, each BAck contains the reception status of each TID. With this information, the AP can identify which data units have been already received and do not require duplicated transmission. Therefore, if an AP identifies that a data unit with a particular sequence number has already been successfully received by the non-AP MLD, it will discard that data unit from the transmit queue.

[0053] Since the BAck is typically transmitted at the end of a PPDU, the respective AP learns at the end of the said PPDU that it may have transmitted duplicated data before, which would be a waste of channel capacity. Therefore, it may be better for the AP to request a BAck before transmitting actual data by using, e.g., a BAck request frame and then adapt the content of the following PPDU accordingly. This is depicted in Fig. 25 showing a diagram depicting the envisioned operation for high reliability with synchronized sequence number according to another embodiment. Before each PPDU transmission it is assumed that a BAck is sent from the non-AP MLD (e.g. after BAck request) which indicates beforedata unit #1 is transmitted, that no data unit has been successfully received. In the lower part of Fig. 25 and before transmission of data unit #2 via TID A, the BAck indicates that data unit #1 has been successfully received, but data unit #2 and #3 were erroneous. Thus, TID A will transmit #2 to #4. Before data units #5 is transmitted the BAck indicates that all data units up to #4 were successfully received for which reason data unit #5 and #6 are transmitted.

[0054] Fig. 26 shows the pre- and post-processing of the remapping operation for high reliability according to embodiments of the present disclosure in more detail. Fig. 26A shows the preprocessing at AP side for transmission (downlink) of a data unit. Fig. 26B shows the postprocessing at AP side for reception (uplink) of a data unit. Fig. 26C shows the postprocessing at non-AP MLD side for reception (downlink) of a data unit. Fig. 26D shows the preprocessing at non-AP MLD side for transmission (uplink) of a data unit.

[0055] Fig. 27 shows a schematic diagram of a second embodiment of a communication system according to the present disclosure. Compared to the first embodiment of the communication system shown in Fig. 5, each of the UP filters 22, 32, 62 comprises a core UP filter 23, 33, 63 and a remapping unit 24, 34, 64. The remapping unit 24, 34, 64 performs either the remapping or the duplication as described above (e.g. with reference to Figs. 19, 22, 26), but not both at the same time. The core UP filter 23, 33, 63 performs the operation of the UP filter as described above (e.g. with reference to Figs. 6, 7, 8, 9).

[0056] Fig. 28 shows a diagram illustrating an embodiment of the layout of the main communication devices in an embodiment of the present invention. According to this embodiment the first AP 20 and the second AP 30 each comprise a communication control device 25, 35 that controls a wireless communication circuitry 26, 36 of the respective AP to communicate with the MLD 60. The communication control device 25, 35 may further comprise control circuitry 27, 37 to control the wireless communication circuitry of the respective AP. The wireless communication circuitry 26, 36 and / or the control circuitry 27, 36 may implement the components of the respective AP as illustrated above, in particular the core AP and UP filter, and may carry out the respective functions of these components.

[0057] Further, according to this embodiment the MLD 60 comprises an MLD control device 65 that controls a wireless communication circuitry 66 of the MLD, e.g. by use of control circuitry 67. The wireless communication circuitry 66 and / or the MLD control circuitry 67 may implement the components of the MLD as illustrated above, in particular the core non-AP MLD and UP filter, and may carry out the respective functions of these components.

[0058] Fig. 29 shows a flowchart of a first embodiment of a communication control method 500 according to the present disclosure for controlling a wireless communication circuitry of a first AP configured to communicate with an MLD via a different link than a second AP. In a first step 501, upon the addition of a second link between the MLD and the second AP while a first link between the MLD and the first AP is enabled, context information is transferred to the second AP, wherein the transferred context information configures the second AP to communicate with the MLD and is transferred per traffic category. In a second step 502, a data unit to be delivered to the MLD is received, the data unit having a traffic category identifier identifying the traffic category of said data unit. In a third step 503, the received data unit is transmitted to the MLD if the context information for the traffic category of said data unit has not (or not yet) been transferred to the second AP. Otherwise, in step 504, the received data unit is forwarded to the second AP for transmission to the MLD by the second AP if the context information for the traffic category of said data unit has (already) been transferred to the second AP. Step 505 of checking if the context for the traffic category of the received data unit has been transferred already may be provided after step 502.

[0059] Fig. 30 shows a flowchart of an embodiment of an MLD control method 600 according to the present disclosure to control a wireless communication circuitry of an MLD configured to communicate with a first AP and a second AP via separate links. In a first step 601, a data unit to be delivered to a distribution system (DS) is received, the data unit having a traffic category identifier identifying the traffic category of said data unit. In a second step 602, the received data unit is transmitted to the first AP via a first link if the first AP holds context information for the traffic category of said data unit, said context information configuring the first AP to communicate with the MLD. Otherwise, in step 603, the received data unit is transmitted to the second AP via a second link for forwarding it to the DS via the first AP if the second AP holds context information for the traffic category of said dataunit, said context information configuring the second AP to communicate with the MLD. Step 604 of checking if the context for the traffic category of the received data is with the first AP or the second AP may be provided after step 601.

[0060] Fig. 31 shows a flowchart of a second embodiment of a communication control method 700 according to the present disclosure for controlling a wireless communication circuitry of a first AP configured to communicate with an MLD via a different link than a second AP. In a first step 701 , a data unit to be delivered to the MLD is received, the data unit having a traffic category identifier identifying the traffic category of said data unit. In a second step 702, the received data unit is transmitted to the MLD if the context information for the traffic category of said data unit has not yet been transferred to the second AP. In a third step 703, the received data unit is forwarded to the second AP for transmission to the MLD by the second AP if the context information for the traffic category of said data unit has already been transferred to the second AP. Step 704 of checking if the context for the traffic category of the received data unit has been transferred already may be provided after step 701.

[0061] Fig. 32 shows a flowchart of a third embodiment of a communication control method 800 according to the present disclosure for controlling a wireless communication circuitry of a first AP configured to communicate with an MLD via a different link than a second AP. In a first step 801 , a request is received to add a second link between the MLD and a second AP while a first link between the MLD and a first AP is enabled. In a second step 802, upon the addition of a second link between the MLD and the second AP while a first link between the MLD and the first AP is enabled, context information is transferred to the second AP, wherein the transferred context information configures the second AP to communicate with the MLD and is transferred per traffic category.

[0062] It shall be noted that the first and / or second and / or third embodiments of the communication control method may also be used in partial or complete combination. For instance, the steps of the second and third embodiments may be used in combination in this order.

[0063] The device may be implemented by respective units or circuitry, e.g. a processor, processing circuitry, a computer, dedicated hardware, etc., that carries out the functions of the device. Alternatively, a common unit or circuitry, e.g. a common processor or computer, may implement the various functions of the device, or separate units or elements may be used that together represent the circuitry.

[0064] Thus, the foregoing discussion discloses and describes merely exemplary embodiments of the present disclosure. As will be understood by those skilled in the art, the present disclosure may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present disclosure is intended to be illustrative, but not limiting the scope of the disclosure, as well as other claims. The disclosure, including any readily discernible variants of the teachings herein, defines, in part, the scope of the foregoing claim terminology such that no inventive subject matter is dedicated to the public.

[0065] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0066] In so far as embodiments of the disclosure have been described as being implemented, at least in part, by software-controlled data processing apparatus, it will be appreciated that a non-transitory machine-readable medium carrying such software, such as an optical disk, a magnetic disk, semiconductor memory or the like, is also considered to represent an embodiment of the present disclosure. Further, such software may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0067] The elements of the disclosed devices, apparatus and systems may be implemented by corresponding hardware and / or software elements, for instance appropriate circuits or circuitry. A circuit is a structural assemblage of electronic components including conventionalcircuit elements, integrated circuits including application specific integrated circuits, standard integrated circuits, application specific standard products, and field programmable gate arrays. Further, a circuit includes central processing units, graphics processing units, and microprocessors which are programmed or configured according to software code. A circuit does not include pure software, although a circuit includes the above-described hardware executing software. A circuit or circuitry may be implemented by a single device or unit or multiple devices or units, or chipset(s), or processor(s).

[0068] It follows a list of further embodiments of the disclosed subject matter:1. A communication control device configured to control a wireless communication circuitry of a first access point (AP) configured to communicate with a multi-link device (MLD) via a different link than a second AP, the communication control device comprising a control circuitry configured to control the wireless communication circuitry of the first AP to: transfer, upon the addition of a second link between the MLD and the second AP while a first link between the MLD and the first AP is enabled, context information to the second AP, wherein the transferred context information configures the second AP to communicate with the MLD and is transferred per traffic category; receive a data unit to be delivered to the MLD, the data unit having a traffic category identifier identifying the traffic category of said data unit; transmit the received data unit to the MLD if the context information for the traffic category of said data unit has not yet been transferred to the second AP; and forward the received data unit to the second AP for transmission to the MLD by the second AP if the context information for the traffic category of said data unit has already been transferred to the second AP.2. The communication control device according to embodiment 1 , wherein the traffic category identifier of said data unit is a user priority (UP) identifier indicating a priority value of said data unit or a traffic identifier (TID) classifying said data unit.3. The communication control device according to embodiment 2,wherein the traffic category identifier of said data unit is a UP identifier that is mapped to a TID; wherein the context information comprises multiple TID-specific context information parts including one context information part per TID; and wherein the control circuitry is configured to control the wireless communication circuitry of the first AP to check if the TID-specific context information part of the TID, to which the UP identifier of the received data unit is mapped to, has already been transferred to the second AP or not; and decide whether to transmit the received data unit to the MLD or forward it to the second AP based on the result of this check.4. The communication control device according to any one of the preceding embodiments, wherein the control circuitry is configured to control the wireless communication circuitry of the first AP to receive data units from a distribution system (DS) to transmit to the MLD directly or to transmit via the second AP to the MLD and to receive data units from the MLD directly for forwarding to the DS or to receive via the second AP for forwarding to the DS.5. The communication control device according to any one of the preceding embodiments, wherein the control circuitry is configured to control the wireless communication circuitry of the first AP, if the context information for the traffic category of the received data unit has already been transferred to the second AP, to encapsulate the received data unit into an encapsulated data unit including the first AP as source and the second AP as destination; and forward the encapsulated data unit to the second AP or to a distribution system (DS) for transfer to the second AP.6. The communication control device according to any one of the preceding embodiments, wherein the control circuitry is configured to control the wireless communication circuitry of the first AP, during the transfer of context information for a particular traffic category, tonot transmit a data unit to the MLD or only transmit a data unit to the MLD if it has been buffered by the first AP, if said data unit has said particular traffic category; and transmit a data unit to the MLD, if it does not have said particular traffic category.7. The communication control device according to any one of the preceding embodiments, wherein the control circuitry is configured to instruct the distribution system (DS) to change the mapping from the first AP to the second AP after the context information for one or more or all of the traffic categories have been transferred from the first AP to the second AP.8. The communication control device according to embodiment 3, wherein the control circuitry is configured to control the wireless communication circuitry of the first AP to remap a UP identifier that is mapped to a first TID to a second TID before the TID- specific context information part of the first TID is transferred to the second AP; and map said UP identifier back to the first TID after the TID-specific context information part of the first TID has been transferred to the second AP.9. The communication control device according to embodiment 2, wherein a received data unit includes a traffic category identifier, or the control circuitry is configured to control the wireless communication circuitry of the first AP to include a traffic category identifier into a received data unit, the traffic category identifier allowing the MLD to identify and set the original UP of said data unit.10. The communication control device according to embodiment 3, wherein the control circuitry is configured to control the wireless communication circuitry of the first AP, to add a second link between the MLD and the second AP without a request, and to change the mapping between UP identifier and first and second TID instantly by remapping a UP identifier that is mapped to a first TID to a second TID before the TID-specific context information part of the first TID is transferred to the second AP; and mapping said UP identifier back to the first TID after the TID-specific context information part of the first TID has been transferred to the second AP.11. The communication control device according to embodiment 10, wherein the control circuitry is configured to control the wireless communication circuitry to remap a UP identifier from a first TID to a second TID, wherein the context of first TID resides at the first AP and the context of the second TID resides at the second AP, and / or to mutually change the remapping.12. The communication control device according to any one of the preceding embodiments, wherein a received data unit includes a sequence number, or the control circuitry is configured to control the wireless communication circuitry of the first and / or second AP to attach a sequence number to a received data unit.13. The communication control device according to any one of the preceding embodiments, wherein the control circuitry is configured to control the wireless communication circuitry of the first AP to notify the second AP with a completion indication, the completion indication indicating to the second AP that the first AP has finished data transmission of first data units to the MLD, the first data units having a first traffic category having a lower time order indication than second data units having a second traffic category, for which the context information has been transferred to the second AP already, wherein the time order indication indicates the order of the respective data units in time, and / or the second AP is allowed to transmit the second data units to the MLD.14. The communication control device according to any one of the preceding embodiments, wherein the control circuitry is configured to control the wireless communication circuitry of the first AP, with or without a request to add a second link between the MLD and the second AP, to transmit received data units to the MLD and forward the received data units to the second AP for transmission to the MLD by the second AP.15. The communication control device according to embodiment 14,wherein the control circuitry is configured to control the wireless communication circuitry of the first and second AP to attach same sequence numbers to the same received data units.16. The communication control device according to embodiment 14 or 15, wherein the control circuitry is configured to control the wireless communication circuitry of the first AP to request the MLD to report successfully received data units to the first AP; and adapt the transmission of subsequent data units based on the report of the MLD.17. An MLD control device configured to control a wireless communication circuitry of a multi-link device (MLD) configured to communicate with a first access point (AP) and a second AP via separate links, the MLD control device comprising control circuitry configured to control the wireless communication circuitry of the MLD to: receive a data unit to be delivered to a distribution system (DS), the data unit having a traffic category identifier identifying the traffic category of said data unit; transmit the received data unit to the first AP via a first link if the first AP holds context information for the traffic category of said data unit, said context information configuring the first AP to communicate with the MLD; and transmit the received data unit to the second AP via a second link for forwarding it to the DS via the first AP if the second AP holds context information for the traffic category of said data unit, said context information configuring the second AP to communicate with the MLD.18. The MLD control device according to embodiment 17, wherein the control circuitry is configured to control the wireless communication circuitry of the MLD to transmit the received data unit to the first AP via a first station (STA) connected to the first AP if the first AP holds the context information for the traffic category of said data unit; and transmit the received data unit to the second AP via a second STA for forwarding it to the first AP by the second AP if the second AP holds the context information for the traffic category of said data unit.19. The MLD control device according to embodiment 17 or 18, wherein the control circuitry is configured to control the wireless communication circuitry of the MLD, during the transfer of context information for a particular traffic category, to not transmit a data unit to the first AP or the second AP, if said data unit has said particular traffic category; and transmit a data unit to the first AP or the second AP, if it does not have said particular traffic category.20. The MLD control device according to embodiment 17, 18 or 19, wherein the control circuitry is configured to control the wireless communication circuitry of the MLD to receive same data units from the first AP and the second AP or to receive data units alternately from the first AP and the second AP; and sort the data units in the correct order and / or delete duplicate data units based on a sequence number included in the data units or a sequence number attached to the data units.21 . The MLD control device according to embodiment 20, wherein the control circuitry is configured to control the wireless communication circuitry of the MLD to report successfully received data units to the first AP and / or the second AP.22. A communication control method for controlling a wireless communication circuitry of a first access point (AP) configured to communicate with a multi-link device (MLD) via a different link than a second AP, the communication control method being configured to control the wireless communication circuitry of the first AP to: transfer, upon the addition of a second link between the MLD and the second AP while a first link between the MLD and the first AP is enabled, context information to the second AP, wherein the transferred context information configures the second AP to communicate with the MLD and is transferred per traffic category; receive a data unit (DU) to be delivered to the MLD, the data unit having a traffic category identifier identifying the traffic category of said data unit;transmit the received data unit to the MLD if the context information for the traffic category of said data unit has not yet been transferred to the second AP; and forward the received data unit to the second AP for transmission to the MLD by the second AP if the context information for the traffic category of said data unit has already been transferred to the second AP.23. MLD control method configured to control a wireless communication circuitry of a multi-link device (MLD) configured to communicate with a first access point (AP) and a second AP via separate links, the MLD control method being configured to control the wireless communication circuitry of the MLD to: receive a data unit to be delivered to a distribution system (DS), the data unit having a traffic category identifier identifying the traffic category of said data unit; transmit the received data unit to the first AP via a first link if the first AP holds context information for the traffic category of said data unit, said context information configuring the first AP to communicate with the MLD; and transmit the received data unit to the second AP via a second link for forwarding it to the DS via the first AP if the second AP holds context information for the traffic category of said data unit, said context information configuring the second AP to communicate with the MLD.24. A communication control device configured to control a wireless communication circuitry of a first access point (AP) configured to communicate with a multi-link device (MLD) via a different link than a second AP, the communication control device comprising control circuitry configured to control the wireless communication circuitry of the first AP to: receive a data unit to be delivered to the MLD, the data unit having a traffic category identifier identifying the traffic category of said data unit; transmit the received data unit to the MLD if the context information for the traffic category of said data unit has not yet been transferred to the second AP; and forward the received data unit to the second AP for transmission to the MLD by the second AP if the context information for the traffic category of said data unit has already been transferred to the second AP.25. A communication control device configured to control a wireless communication circuitry of a first access point (AP) configured to communicate with a second AP, each AP being configured to communicate with a multi-link device (MLD) via a separate link, the first communication control device comprising AP control circuitry configured to control the wireless communication circuitry of the first AP to: receive a request to add a second link between the MLD and a second AP while a first link between the MLD and a first AP is enabled; and transfer, upon the addition of a second link between the MLD and the second AP while a first link between the MLD and the first AP is enabled, context information to the second AP, wherein the transferred context information configures the second AP to communicate with the MLD and is transferred per traffic category.26. A communication control method for controlling a wireless communication circuitry of a first access point (AP) configured to communicate with a multi-link device (MLD) via a different link than a second AP, the communication control method being configured to control the wireless communication circuitry of the first AP to: receive a data unit to be delivered to the MLD, the data unit having a traffic category identifier identifying the traffic category of said data unit; transmit the received data unit to the MLD if the context information for the traffic category of said data unit has not yet been transferred to the second AP; and forward the received data unit to the second AP for transmission to the MLD by the second AP if the context information for the traffic category of said data unit has already been transferred to the second AP.27. A communication control method for controlling a wireless communication circuitry of a first access point (AP) configured to communicate with a multi-link device (MLD) via a different link than a second AP, the communication control method being configured to control the wireless communication circuitry of the first AP to: receive a request to add a second link between the MLD and a second AP while a first link between the MLD and a first AP is enabled; and transfer, upon the addition of a second link between the MLD and the second AP while a first link between the MLD and the first AP is enabled, context information to thesecond AP, wherein the transferred context information configures the second AP to communicate with the MLD and is transferred per traffic category.28. A non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method according to any one of embodiments 24 to 27 to be performed.29. A computer program comprising program code means for causing a computer to perform the steps of said method according to any one of embodiments 24 to 27 when said computer program is carried out on a computer.

Claims

CLAIMS1. A communication control device configured to control a wireless communication circuitry of a first access point (AP) configured to communicate with a multi-link device (MLD) via a different link than a second AP, the communication control device comprising a control circuitry configured to control the wireless communication circuitry of the first AP to: transfer, upon the addition of a second link between the MLD and the second AP while a first link between the MLD and the first AP is enabled, context information to the second AP, wherein the transferred context information configures the second AP to communicate with the MLD and is transferred per traffic category; receive a data unit to be delivered to the MLD, the data unit having a traffic category identifier identifying the traffic category of said data unit; transmit the received data unit to the MLD if the context information for the traffic category of said data unit has not yet been transferred to the second AP; and forward the received data unit to the second AP for transmission to the MLD by the second AP if the context information for the traffic category of said data unit has already been transferred to the second AP.

2. The communication control device according to claim 1 , wherein the traffic category identifier of said data unit is a user priority (UP) identifier indicating a priority value of said data unit or a traffic identifier (TID) classifying said data unit.

3. The communication control device according to claim 2, wherein the traffic category identifier of said data unit is a UP identifier that is mapped to a TID; wherein the context information comprises multiple TID-specific context information parts including one context information part per TID; and wherein the control circuitry is configured to control the wireless communication circuitry of the first AP to check if the TID-specific context information part of the TID, to which the UP identifier of the received data unit is mapped to, has already been transferred to the second AP or not; anddecide whether to transmit the received data unit to the MLD or forward it to the second AP based on the result of this check.

4. The communication control device according to claim 1 , wherein the control circuitry is configured to control the wireless communication circuitry of the first AP to receive data units from a distribution system (DS) to transmit to the MLD directly or to transmit via the second AP to the MLD and to receive data units from the MLD directly for forwarding to the DS or to receive via the second AP for forwarding to the DS.

5. The communication control device according to claim 1 , wherein the control circuitry is configured to control the wireless communication circuitry of the first AP, if the context information for the traffic category of the received data unit has already been transferred to the second AP, to encapsulate the received data unit into an encapsulated data unit including the first AP as source and the second AP as destination; and forward the encapsulated data unit to the second AP or to a distribution system (DS) for transfer to the second AP.

6. The communication control device according to claim 1 , wherein the control circuitry is configured to control the wireless communication circuitry of the first AP, during the transfer of context information for a particular traffic category, to not transmit a data unit to the MLD or only transmit a data unit to the MLD if it has been buffered by the first AP, if said data unit has said particular traffic category; and transmit a data unit to the MLD, if it does not have said particular traffic category.

7. The communication control device according to claim 1 , wherein the control circuitry is configured to instruct the distribution system (DS) to change the mapping from the first AP to the second AP after the context information for one or more or all of the traffic categories have been transferred from the first AP to the second AP.

8. The communication control device according to claim 3,wherein the control circuitry is configured to control the wireless communication circuitry of the first AP to remap a UP identifier that is mapped to a first TID to a second TID before the TID- specific context information part of the first TID is transferred to the second AP; and map said UP identifier back to the first TID after the TID-specific context information part of the first TID has been transferred to the second AP.

9. The communication control device according to claim 2, wherein a received data unit includes a traffic category identifier, or the control circuitry is configured to control the wireless communication circuitry of the first AP to include a traffic category identifier into a received data unit, the traffic category identifier allowing the MLD to identify and set the original UP of said data unit.

10. The communication control device according to claim 3, wherein the control circuitry is configured to control the wireless communication circuitry of the first AP, to add a second link between the MLD and the second AP without a request, and to change the mapping between UP identifier and first and second TID instantly by remapping a UP identifier that is mapped to a first TID to a second TID before the TID-specific context information part of the first TID is transferred to the second AP; and mapping said UP identifier back to the first TID after the TID-specific context information part of the first TID has been transferred to the second AP.

11. The communication control device according to claim 1 , wherein a received data unit includes a sequence number, or the control circuitry is configured to control the wireless communication circuitry of the first and / or second AP to attach a sequence number to a received data unit.

12. The communication control device according to claim 1 , wherein the control circuitry is configured to control the wireless communication circuitry of the first AP to notify the second AP with a completion indication, the completion indication indicating to the second AP that the first AP has finished data transmission of first data units to the MLD, the first data units having a first traffic category having a lower time order indication than seconddata units having a second traffic category, for which the context information has been transferred to the second AP already, wherein the time order indication indicates the order of the respective data units in time, and / or the second AP is allowed to transmit the second data units to the MLD.

13. An MLD control device configured to control a wireless communication circuitry of a multi-link device (MLD) configured to communicate with a first access point (AP) and a second AP via separate links, the MLD control device comprising control circuitry configured to control the wireless communication circuitry of the MLD to: receive a data unit to be delivered to a distribution system (DS), the data unit having a traffic category identifier identifying the traffic category of said data unit; transmit the received data unit to the first AP via a first link if the first AP holds context information for the traffic category of said data unit, said context information configuring the first AP to communicate with the MLD; and transmit the received data unit to the second AP via a second link for forwarding it to the DS via the first AP if the second AP holds context information for the traffic category of said data unit, said context information configuring the second AP to communicate with the MLD.

14. The MLD control device according to claim 13, wherein the control circuitry is configured to control the wireless communication circuitry of the MLD to transmit the received data unit to the first AP via a first station (STA) connected to the first AP if the first AP holds the context information for the traffic category of said data unit; and transmit the received data unit to the second AP via a second STA for forwarding it to the first AP by the second AP if the second AP holds the context information for the traffic category of said data unit.

15. The MLD control device according to claim 13, wherein the control circuitry is configured to control the wireless communication circuitry of the MLD, during the transfer of context information for a particular traffic category, tonot transmit a data unit to the first AP or the second AP, if said data unit has said particular traffic category; and transmit a data unit to the first AP or the second AP, if it does not have said particular traffic category.

16. The MLD control device according to claim 13, wherein the control circuitry is configured to control the wireless communication circuitry of the MLD to receive same data units from the first AP and the second AP or to receive data units alternately from the first AP and the second AP; and sort the data units in the correct order and / or delete duplicate data units based on a sequence number included in the data units or a sequence number attached to the data units.

17. The MLD control device according to claim 16, wherein the control circuitry is configured to control the wireless communication circuitry of the MLD to report successfully received data units to the first AP and / or the second AP.

18. A communication control method for controlling a wireless communication circuitry of a first access point (AP) configured to communicate with a multi-link device (MLD) via a different link than a second AP, the communication control method being configured to control the wireless communication circuitry of the first AP to: transfer, upon the addition of a second link between the MLD and the second AP while a first link between the MLD and the first AP is enabled, context information to the second AP, wherein the transferred context information configures the second AP to communicate with the MLD and is transferred per traffic category; receive a data unit to be delivered to the MLD, the data unit having a traffic category identifier identifying the traffic category of said data unit; transmit the received data unit to the MLD if the context information for the traffic category of said data unit has not yet been transferred to the second AP; and forward the received data unit to the second AP for transmission to the MLD by the second AP if the context information for the traffic category of said data unit has already been transferred to the second AP.

19. MLD control method configured to control a wireless communication circuitry of a multi-link device (MLD) configured to communicate with a first access point (AP) and a second AP via separate links, the MLD control method being configured to control the wireless communication circuitry of the MLD to: receive a data unit to be delivered to a distribution system (DS), the data unit having a traffic category identifier identifying the traffic category of said data unit; transmit the received data unit to the first AP via a first link if the first AP holds context information for the traffic category of said data unit, said context information configuring the first AP to communicate with the MLD; and transmit the received data unit to the second AP via a second link for forwarding it to the DS via the first AP if the second AP holds context information for the traffic category of said data unit, said context information configuring the second AP to communicate with the MLD.

20. A non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method according to claim 18 or 19 to be performed.

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