How to change the value of the extended unique identifier for a non-AP station associated with an AP station.

Abstract

The present invention relates to a method of communication between a first station and a second station, wherein the first station can change an identifier from a current identifier to a new identifier, and the method comprises, during a margin period, setting a set of identifiers including the current identifier and the new identifier as the first station's valid identifier for received frames, and setting one of the current identifier or the new identifier as the first station's valid identifier for outgoing frames.

Description

Technical Field

[0001] The present invention relates to wireless communication, and more particularly to user privacy during wireless communication.

Background Art

[0002] The approaches described in this section may be pursued, but are not necessarily approaches that have been previously conceived or pursued. Thus, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims of this application and are not recognized as prior art by inclusion in this section. Further, all embodiments are not necessarily intended to solve all or any of the problems presented in this section.

[0003] Today, the development of wireless systems has brought privacy concerns driven by the user needs and requirements of the General Data Protection Regulation (GDPR) to the forefront. While the global wireless industry continues to improve wireless services and the user experience, it is facing an increasing need to protect users' personally identifiable information from increasingly sophisticated user tracking and user profiling activities.

[0004] In particular, the Media Access Control (MAC) address of a user's device constitutes part of the data that can be used to track this user. In fact, wireless network access points (APs) can monitor the location of a user's mobile device (tablet, laptop, cell phone, etc.) without the user's consent by means of the user's MAC address. This is because cell phones are configured to discover nearby access points to the wireless network. As a user moves, their cell phone sends requests to determine if there are access points nearby, and these requests identify the cell phone sending these requests, including, in particular, the cell phone's MAC address. Access points that hear these requests can respond. In the context of Wi-Fi networks as defined by the IEEE 802.11 standard (Wi-Fi is a trademark), this procedure is called sending and receiving probe requests / responses.

[0005] Therefore, even if a mobile phone is not connected to a Wi-Fi network, nearby access points can still receive its MAC address. It is then possible to track the user by reconstructing the user's trajectory from the access point that transmitted the MAC address of the user's mobile phone. In addition, if a mobile phone is associated with one of the access points (i.e., the user is connected to the associated Wi-Fi network via that access point), and the user has previously provided personally identifiable information (such as name and address), the access point may record the phone's MAC address in a database in association with that identification information. Therefore, even if the user is not connected to a Wi-Fi network, this identification information can be recovered by comparing the MAC address included in the probe request with the MAC address previously used for association.

[0006] In the context of Wi-Fi networks, the IEEE 802.11 Working Group has proposed a solution to limit the risk of tracked users, which involves dynamically changing the MAC address of user devices. This mechanism is called the Randomized Change MAC (RCM) procedure. It was first introduced as a privacy enhancement feature by the 802.11aq Pre-Association Service Discovery Task Group and was eventually included in the standard IEEE Std 802.11-2020. It involves periodically changing the MAC address of non-AP stations or STAs (i.e., stations that are not access points) to a random value, while non-AP stations are not associated with a network (or equivalently, with an access point). Non-AP stations can construct randomized MAC addresses from a locally managed address space, as defined in IEEE Std 802(registered trademark)-2014 and IEEE Std 802c(registered trademark)-2017.

[0007] More specifically, a new Management Information Base (MIB) variable is specified that can be controlled by an external management entity. This variable is called "dot11MACPrivacyActivated". When dot11MACPrivacyActivated is set to "true", non-AP stations can apply certain mechanisms to enhance privacy at the MAC level, including RCM.

[0008] A device's MAC address (EUI-48 address) is an Extended Unique Identifier (EUI) consisting of 48 bits. It can be managed universally or locally. Universally managed addresses are uniquely assigned to devices by the manufacturer. Conversely, locally managed addresses are assigned to devices by software or network administrators and replace the physically imprinted address. The second least significant bit of the first octet of the MAC address, i.e., the seventh bit of the first octet of the address, is also called the "U / L bit" (in the case of the "Universal / Local bit") and indicates whether it is managed universally (when set to 0) or locally (when set to 1). The least significant bit of the first octet of the MAC address, i.e., the eighth bit of the first octet of the address, also called the "I / G bit" (in the case of the "Individual / Group bit"), indicates whether the frame is sent to only one receiving device (indicating unicast transmission when set to 0) or to multiple devices (indicating multicast transmission when set to 1). When the RCM mechanism is operating at a non-AP station, the MAC address of the non-AP station is changed randomly (e.g., periodically). More specifically, the U / L bit is set to 1, the I / G bit is set to 0, and the remaining 46 bits are randomly generated using a pseudo-random function (PRF) or can be obtained by any other means (e.g., received from an AP or obtained from an address in a predefined list).

[0009] Within the scope of IEEE 802.11bi, a solution has been proposed for changing a station's MAC address in an associated manner, which relies entirely on the fact that both AP and non-AP stations operate the MAC address change at the same moment on their respective sides. Obviously, changing the MAC address of an unassociated station is not a problem. This moment can be determined dynamically (the duration between the two changes may be variable over time) or based on a fixed frequency. The problem with all these proposed solutions is that the moment of the station's MAC address change must be precisely synchronized on both sides (AP and non-AP). Without precise synchronization, a receiving station may discard frames addressed with a MAC address that is considered valid only by the emitter (sending) side.

[0010] To overcome this problem, it has recently been proposed to rely on an instant defined by absolute time (timing synchronization function or TSF time), or an instant associated with the reception of a frame (typically a beacon frame). Unfortunately, the proposed solution relies on beacon frame reception and cannot guarantee perfect synchronization, so the proposed solution is still plagued by the risk of dropping frames upon reception. Conventional solutions cannot guarantee perfect synchronization between the clock of a non-AP station and the clock of an AP. One reason for this is that the internal crystal supporting the 1MHz clock of an 802.11 station (AP or non-AP station) can have a drift of up to 100ppm, as defined in the 802.11 standard. This 100ppm clock drift ends up being a relative clock drift difference of up to 20us per 100ms in a typical interval between two beacon receptions between an AP and a non-AP station. This difference, while seemingly insignificant in itself, allows for the generation of frame drop and retransmission, and the development (expansion) of an associated congestion window that slows down future transmissions of frames.

[0011] In addition to this relatively small drift, a bigger problem arises when a non-AP station goes into sleep mode for an extended period, i.e., enters a dozed state. This is because, in that case, the clock drift can be much larger when the station wakes up. For example, if a station sleeps for 10 minutes, the clock drift can reach 120ms because the station cannot receive a beacon that can resynchronize its internal clock during sleep. In this last situation, the awake station may use the wrong MAC address until it receives a new beacon frame, typically up to 100ms later, assuming the first received beacon was received successfully. This generates a large number of dropped frames and associated retransmissions.

[0012] As mentioned earlier, achieving perfect synchronization (equivalent to an internal clock tick of less than 1us) is extremely difficult, and the industry generally acknowledges that an acceptable clock drift is around 25us. Therefore, there is a need for methods for stations (AP or non-AP stations) to avoid dropping frames when MAC addresses change, even if each clock is not perfectly synchronized. [Overview of the project]

[0013] This invention was devised to address one or more of the aforementioned problems.

[0014] According to a first aspect of the present invention, a method of communication between a first station and a second station is provided, wherein the first station can change the identifier from the current identifier to a new identifier, and this method is performed during the margin period at the first station, -Setting a set of identifiers, including the current identifier and the new identifier, as a valid identifier for the first station to receive the frame, - This includes setting either the current identifier or a new identifier as a valid identifier for the first station transmitting the frame.

[0015] In one embodiment, a set of valid identifiers is applied to the receiver address (RA) field in the received frame.

[0016] In one embodiment, a single identifier is applied to the transmitter address (TA) field within the transmission frame.

[0017] According to another aspect of the present invention, a method of communication between a first station and a second station is provided, wherein the first station can change the identifier from the current identifier to a new identifier, and this method allows the second station to do so during a margin period. -Setting a set of identifiers, including the current identifier and the new identifier, as a valid identifier for the first station to receive the frame, - Set either the current identifier or a new identifier as a valid identifier for the first station transmitting the frame, Includes.

[0018] In one embodiment, a set of valid identifiers is applied to the transmitter address (TA) field in the received frame.

[0019] In one embodiment, a single identifier is applied to the receiver address (RA) field in the transmission frame.

[0020] In one embodiment, the method further includes determining the start time of the usage period at which the identifier of the first station changes from the current identifier to a new identifier.

[0021] In one embodiment, the margin period is a forward margin period that begins before the start of the usage period.

[0022] In one embodiment, when the method receives a frame addressed to the first station using a new identifier during the forward margin period, it further includes shifting the start time of the usage period, or a subsequent usage period, forward based on the time difference between the reception of the frame and the determined start time of the usage period.

[0023] In one embodiment, the margin period is a backward margin period that ends after the start of the usage period.

[0024] In one embodiment, when the method receives a frame addressed to the first station having the current identifier during the backward margin period, it further includes shifting the start time of a subsequent usage period backward based on the reception time of the frame.

[0025] In one embodiment, the first station is a non-access point (AP) station and the second station is an AP station.

[0026] In one embodiment, the identifier of the station is a MAC address.

[0027] According to another aspect of the present invention, - means for changing the identifier of the first station from the current identifier to a new identifier; - means for setting, during the margin period for receiving a frame, a set of identifiers including the current identifier and the new identifier as the valid identifier of the first station; - means for setting, during the margin period for transmitting a frame, one of the current identifier or the new identifier as the valid identifier of the first station; A station is provided that includes the above.

[0028] According to another aspect of the present invention, a non-transitory computer-readable medium storing a program that causes a wireless device to execute the method of the present invention when executed by a microprocessor or computer system within the wireless device is provided.

[0029] At least a portion of the methods according to the present invention can be implemented on a computer. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment (including firmware, resident software, microcode, etc.), or an embodiment combining software and hardware embodiments, all of which may be commonly referred to herein as “circuits,” “modules,” or “systems.” Furthermore, the present invention can take the form of a computer program product embodied on any tangible medium of expression having computer-usable program code embodied on that medium.

[0030] Since the present invention can be implemented in software, it can be implemented as computer-readable code for provision to a programmable device on any suitable carrier medium. Tangible non-transient carrier media may include storage media such as floppy disks®, CD-ROMs, hard disk drives, magnetic tape devices, or solid-state memory devices. Transient carrier media may include signals such as electrical signals, electronic signals, optical signals, acoustic signals, magnetic signals, or electromagnetic signals, such as microwave or RF signals. [Brief explanation of the drawing]

[0031] Next, embodiments of the present invention will be described with reference to the following drawings, merely as examples. [Figure 1] Figure 1 illustrates an example of a network system in which several embodiments of the present invention may be implemented. [Figure 2a] Figure 2a shows examples of steps performed at a non-AP station or AP station before changing the non-AP MAC address, according to some embodiments of the present invention. [Figure 2b] Figure 2b shows examples of steps performed at a non-AP station or AP station after changing the non-AP MAC address, according to some embodiments of the present invention. [Figure 3] Figure 3 shows an example of the steps performed by a non-AP station or an AP station to initiate a MAC address change period. [Figure 4] Figure 4 shows examples of steps performed by a non-AP station or by an AP station to close the period of MAC address change for a non-AP station, according to some embodiments of the present invention. [Figure 5] Figure 5 shows a first example of a sequence of steps to perform the procedure for changing the MAC address of a non-AP station associated with an AP station. [Figure 6] Figure 6 illustrates an example sequence of steps for operating a procedure to change the MAC address of a non-AP station associated with an AP station, according to some embodiments of the present invention, which is applicable in the case of a non-AP station clock that is lagging behind the AP. [Figure 7] Figure 7 illustrates an example sequence of steps for operating a procedure to change the MAC address of a non-AP station associated with an AP station, according to some embodiments of the present invention, which is applicable when the non-AP station clock is ahead of the AP clock. [Figure 8] Figure 8 shows the processing of TA and RA addresses on both the non-AP station side and the AP side for different examples of forward and backward margin periods. [Figure 9] Figure 9 shows the processing of TA and RA addresses on both the non-AP station side and the AP side for different examples of forward and backward margin periods. [Figure 10] Figure 10 schematically shows an example of a communication device configured to carry out at least some embodiments of the present invention. [Modes for carrying out the invention]

[0032] The RCM procedure is a method for obfuscating multiple parameters (including MAC address) of a CPE (Client Privacy Enhancement) client simultaneously while that client is associated with a CPE AP. This is based on a standardized PRF (Section 12.7.1.2 - IEEE Std 802.11-2020) that is executed in parallel by CPE clients and CPE APs with the same input parameters.

[0033] This procedure consists of three main steps.

[0034] 1) During or after the association, encryption information (SERCM key) is shared between the AP and the non-AP STA. 2) Depending on the requirements of AP or non-AP STA, a single run of a standardized PRF is used to compute and generate new uncorrelated values ​​or new masks, with both AP and non-AP STA running in parallel. 3) At the start of the transition period, both AP and non-AP STA begin obfuscating the CPE parameters.

[0035] The purpose of this document is to focus on the period surrounding changes to CPE parameters, also known as Frame Anonymization (FA) parameters.

[0036] The moment of change in a CPE parameter defines a series of usage periods (1, ..., n, n+1, ...) also called an "Epoch" or Enhanced Data Privacy (EDP) Epoch, during which a given value of the CPE parameter (e.g., MAC address) is used. In some embodiments, the usage period begins with a transition period during which both the old value of the CPE parameter (for the previous usage period "n") and the new value (for the current usage period "n+1") may be considered. In some implementations, constraints may apply to the use of the old value during the transition period. For example, the old MAC address @MAC(n) may be permitted to be used as the transmitter address for sending an already generated and buffered frame, but the old MAC address @MAC(n) can no longer be used for generating a new frame after the current usage period (n+1) has begun. In other implementations, the change in the CPE parameter between two usage periods is strictly enforced, i.e., no transition period is implemented, and only the CPE parameter (n) for a given usage period "n" may be used.

[0037] According to embodiments of the present invention, two new phases (periods) are introduced into the "Seamless Enhanced RCM (SERCM)" procedure to overcome the lack of complete clock synchronization between AP and non-AP stations. These periods are intended to absorb potential clock drift between the station and the AP.

[0038] A first period, called the forward margin, is defined between the RCM ready time and the start of the next usage period (and therefore, the start of the transition period, if any), before the next usage period begins. The forward margin is useful when the station is behind the AP. The forward margin allows the station to decode received frames addressed with the new MAC address @MAC(n+1) even though the usage period has not yet started (on the station / receiver). In other words, during this first period, the station is ready to receive frames addressed with that new MAC address "n+1", but the station is not allowed to use this new MAC address in transmitted frames until the new usage period "n+1" has effectively started.

[0039] A second period, called the back margin, is defined after the start of the usage period and between the start of the usage period and the RCM completion time. The back margin is useful when the station is ahead of the AP. The back margin allows the station to decode received frames addressed with the old MAC address @MAC(n) even though the usage period has already started (on the receiving end). In other words, during this second period, the station is still configured to receive frames addressed with its old MAC address "n", but the station is no longer permitted to use this old MAC address in transmitted frames.

[0040] If a transition period exists, a back margin may be defined between the end of the transition period and the RCM end time. In this way, the old MAC address "n" can still be used during the transition period in a transmitted frame to flush the buffered frame generated by @MAC(n). In a variation, if a transition period exists, there is no (not implemented) back margin. In this case, the transition period acts as a back margin with relaxed constraints on the use of the old MAC address in a transmitted frame. When a transition period is used in place of a back margin, the duration of the transition period may be adjusted accordingly, for example, to last until the RCM ends.

[0041] The RCM(n) preparation time can be fixed and determined by the AP as a parameter of the BSS (for example, sent as an information element during the association procedure) and can be determined relative to the use period(n) start time by removing the margin time Mt.

[0042] Alternatively, the margin time Mt may be determined as a percentage of the Epoch duration. This is particularly useful for variable duration Epochs, e.g., random duration Epochs. In this case, the margin can reflect the maximum clock shift between the AP and the station, and between two MAC address changes. If Tc is the time until the next MAC address change, the margin time Mt can be determined, for example, by the formula Mt = 100ppm × 2 × Tc, where 100ppm is the minimum precision of the internal crystal in the 802.11 standard. For example, if Tc = 10 minutes, then Mt = 100ppm × 2 × 600s = 120ms.

[0043] In determining the RCM(n) completion time, in one embodiment, the same margin value as the RCM preparation time is applied, but after the start time of the usage period (n). In a modified example, if a transition period exists, the duration of the transition period is subtracted from the calculated margin so that the RCM(n) completion time effectively becomes margin time after the start of the period, regardless of whether a transition period exists or not.

[0044] If the time between two CPE parameters, for example, MAC addresses, is determined as a multiple of the Target Beacon Transmission Time (TBTT), then Tc can be determined by multiplying the number of beacons between the two CPE parameter changes by the TBTT value. This value can then be used to determine the margin time Mt.

[0045] In one embodiment, the RCM(n+1) preparation time for usage period n+1 is equal to the RCM(n) completion time for the previous usage period n. In this embodiment, as soon as the previous MAC address change is complete, the station can prepare the following:

[0046] The MAC address change time between APs and non-APs is ensured by introducing a margin for MAC address change time.

[0047] Global user privacy is enhanced by allowing stations to modify their set of CPE parameters, even in the event of clock drift or loss of beacon counter synchronization.

[0048] According to some embodiments of the present invention, a method is provided for changing the value of an identifier of a non-access point (non-AP) station associated with an access point (AP) station, such as the MAC address or extended unique identifier (EUI) of the non-AP station. Both the non-AP station and the AP station start the identifier change process simultaneously and have the same duration to perform the actual identifier change. During the transition period (the period between the start and end of the identifier change procedure), both the new identifier and the current identifier are valid and can be used by the AP station and / or non-AP station. For this purpose, a new identifier, called a transient identifier, is associated with the non-AP station. At the end of the transition period, the current identifier is replaced by the transient identifier, and the current identifier is no longer used.

[0049] During the transition period, AP stations and non-AP stations monitor the identifier used for frame transmission to determine whether the identifier change is valid. To reduce the transition duration, stations may use a different identifier than the sender identifier to acknowledge receipt of a frame in response to the transmission of a buffered frame with the current identifier or the new identifier.

[0050] Please note that an AP or non-AP station can request a MAC address change for a non-AP STA.

[0051] The usage period duration may be exchanged during the association procedure, for example, in a dedicated information element broadcast in the AP's beacon frame, or in a probe request that may be exchanged during the association procedure, or in a probe response frame. In this case, the AP can initiate regular changes for all non-AP STAs (at once). Alternatively, the duration may be indicated in the EUI change request frame. In such embodiments, a non-AP station can initiate its MAC address change by sending a change request to the AP.

[0052] To ensure the duration of the transition period, both AP stations and non-AP stations can start timers using the transition period value.

[0053] For illustrative purposes, the examples provided below concern changing the MAC address value of a non-AP station. The same applies to changing another identifier for a non-AP station, such as its Station AID or EUI value.

[0054] Figure 1 shows an example of a network system in which several embodiments of the present invention may be implemented.

[0055] For illustrative purposes, Figure 1 represents an 802.11 network (i.e., a Wi-Fi network) system 100, comprising four wireless devices, namely an access point station (AP) 105 and three non-AP stations (non-AP STAs) 110a, 110b, and 110c. Of course, the number of non-AP stations 110a, 110b, and 110c may differ from three. The AP station 105 provides wireless connectivity between the non-AP stations 110a, 110b, and 110c and a wider network, such as the Internet (not shown). The connection of one of the non-AP stations 110a, 110b, and 110c to the AP 105 may be performed by a standardized process called association. Once a non-AP station is associated with an AP station, the non-AP station can send data to the network and receive data from the network via the AP station.

[0056] AP Station 105 may comprise, be implemented as, or be known as, a Node B, a Radio Network Controller (RNC), an Advanced Node B (eNB), a 5G Next Generation Base Station (gNB), a Base Station Controller (BSC), a Base Transceiver Station (BTS), a Base Station (BS), a Transceiver Function (TF), a Radio Router, a Radio Transceiver, a Basic Service Set (BSS), an Extended Service Set (ESS), a Radio Base Station (RBS), or any other term. It may be a standalone product or integrated into a device, for example, in a Broadband Remote Access Server (BRAS).

[0057] Non-AP stations 110a, 110b, and / or 110c comprise, are implemented as, or may be known as, subscriber stations, subscriber units, mobile stations (MS), remote stations, remote terminals, user terminals (UT), user agents, user devices, user equipment (UE), user stations (STA), or any other terms. In some embodiments, a non-AP station may be or comprise a cellular telephone, cordless telephone, Session Initiation Protocol (SIP) telephone, Wireless Local Loop (WLL) station, Personal Digital Assistant (PDA), handheld device with wireless connectivity, or any other suitable processing device connected to a wireless modem. Thus, one or more embodiments taught herein may be incorporated into a telephone (e.g., a mobile phone or smartphone), a computer (e.g., a laptop), a tablet, a portable communication device, a portable computing device (e.g., a personal data assistant), an entertainment device (e.g., a music or video device, or a satellite radio), a Global Positioning System (GPS) device, or any other suitable device configured to communicate via wireless or wired media. In some embodiments, some of the non-AP stations 110a, 110b, and 110c may be wireless nodes. Such wireless nodes may, for example, provide connectivity to a network (e.g., a wide area network such as the Internet or a cellular network) via wired or wireless communication links.

[0058] AP Station 105 manages a set of stations that aggregate access to wireless media for communication purposes. All stations (AP Station 105 and non-AP Stations 110a, 110b, and 110c) form a service set sometimes called a Basic Service Set (BSS) (although other terminology may be used). AP Station 105 can manage two or more BSSs, and it should be noted that each BSS is uniquely identified by a specific Basic Service Set Identifier (BSSID) and managed by a separate virtual AP Station implemented at the physical AP Station 105.

[0059] Figure 2a shows examples of steps performed at a non-AP station or AP station before changing the non-AP MAC address, according to some embodiments of the present invention.

[0060] The algorithm shown in Figure 2a is executed by a non-AP station or an AP station during the RCM preparation time, for example, the time referenced by 600 or 605 in Figure 6 or Figure 7. As a reminder, the RCM preparation time is the start of the forward margin period introduced in this disclosure.

[0061] In step 200, a new MAC address is determined, denoted as @MAC(n+1), which will be used to replace the current MAC address denoted as @MAC(n). Associated obfuscated parameters are determined along with the new MAC address. These obfuscated parameters are those that need to be obfuscated in connection with the change of MAC address. The methods for determining the MAC address and parameters are outside the scope of this invention. Step 200 is preferably performed at the beginning of the forward margin, but it is clear that step 200 may be performed at any point prior to this. The important point is that @MAC(n+1) and associated parameters are determined at RCM ready, resulting in the same outcome on both the AP and non-AP sides.

[0062] Unfortunately, as already mentioned, RCM preparation times can differ significantly between the AP side and the non-AP side. Therefore, in the event of a significant difference, step 210 is performed to avoid unnecessary frame discarding.

[0063] Step 210 adds @MAC(n+1) to the list of MAC addresses that are considered valid in the received frame, so that they may be used in the future.

[0064] For non-APs, this is a list of MAC addresses that appear in the Receiver Address (RA) field of received frames that are not ignored by the non-AP station and are decoded. For non-AP stations, this list typically corresponds to the non-AP station's unicast MAC address and the group MAC address to which the non-AP station belongs. Typically, a non-AP station has only one fully valid unicast MAC address, meaning it is valid as either a sending MAC address or a receiving MAC address at any given time, although in some embodiments, a non-AP station may have a set of fully valid MAC addresses. Step 210 may then accommodate a change in at least one of the fully valid MAC addresses.

[0065] For AP stations, this list corresponds to a list of MAC addresses of non-AP stations associated with the AP that are received within the Transmitter Address (TA) filed on the received frame. This list is used to discard frames received by APs that are not transmitted by registered stations. Of course, this list is not used during association procedures.

[0066] By adding the new address @MAC(n+1) to the list of valid addresses in the received frame, a non-AP station accepts receiving and decoding frames with the RA field corresponding to the new address, even if the receiving station has not yet commenced its usage period; that is, the station still uses the current address @MAC(n) in the TA field of the frames it transmits.

[0067] It is important to note that at that point, the new MAC address @MAC(n+1) is not yet fully valid; it is only valid for received frames and cannot be used for transmitted frames.

[0068] Figure 2b shows examples of steps performed at a non-AP station or AP station after changing the non-AP MAC address, according to some embodiments of the present invention.

[0069] The algorithm shown in Figure 2b is executed by a non-AP station or an AP station at the end of the backward margin period, which means RCM completion, for example, the time referenced by 610 or 615 in Figure 6 or 7.

[0070] After the transition period is deemed to have ended by the station, the station stops using the current address @MAC(n) in transmitted frames. This means that during the back margin time, the station can still receive frames with either the current or new address, while transmitted frames can only use the new address.

[0071] Subsequently, at the end of the back margin period, the station performs step 220.

[0072] Step 220 removes the current MAC address @MAC(n) from the list of MAC addresses that are considered valid in the received frame. By doing so, the station or non-AP station then discards any received frame addressed using this MAC address.

[0073] In step 230, since @MAC(n) is no longer valid in either the received frame or the transmitted frame, @MAC(n) can be discarded (no longer used by the station), and all associated obfuscation parameters can be removed from the station's internal memory. Step 230 then allows the memory dedicated to storing the MAC address and associated parameters to be freed.

[0074] Figure 3 shows examples of steps performed by a non-AP station or an AP station to initiate a MAC address change period (transition period) according to some embodiments of the present invention. Figure 3 shows the steps of the algorithm performed by the non-AP station and the AP, respectively, at times 621 and 611 in Figure 6.

[0075] In step 300, the station replaces its current MAC address @MAC(n) with a new MAC address @MAC(n+1) as the effective address of the non-AP station whose MAC address is being changed. In doing so, each new frame generated by the non-AP station for transmission is addressed with @MAC(n+1) by setting the TA field value to the @MAC(n+1) value. Note that in this disclosure, the new address is already set for reception during the forward margin period. This means that, in contrast to the prior art, step 300 sets a new address for generating frames to be transmitted. On the AP side, step 300 sets the effective MAC address value of the non-AP station to @MAC(n+1) in the internal list of registered non-AP stations. As a result, each new frame generated by the AP and sent to the non-AP station is addressed with @MAC(n+1) by setting the RA field of the frame that has @MAC(n+1) on the non-AP station.

[0076] After step 300 is performed, step 310 is performed, and frames that were buffered for transmission before step 300 are sent preferentially. This step avoids discarding frames that have already been buffered and addressed by @MAC(n), and subsequently avoids interrupting ongoing transmissions. During the transition period, both @MAC(n) and @MAC(n+1) are considered fully valid (the addresses are valid in both received and transmitted frames).

[0077] In some embodiments, the transition period is null (RCM start time = RCM end time). This means that buffered traffic in @MAC(n) is not preferentially sent and is discarded in step 410 in Figure 4. This allows for a simpler implementation.

[0078] Figure 4 shows examples of steps performed by a non-AP station or by an AP station to close the MAC address change period of a non-AP station according to some embodiments of the present invention, which means the end of the transition period.

[0079] The steps of the algorithm in Figure 4 are executed at the end of the transition period, for example, at the maximum SERCM change end time corresponding to the transition end time 625 or 616 in Figure 6.

[0080] In step 400, the station removes the current MAC address @MAC(n) from the list of MAC addresses valid for the transmitted frame. This means that after step 400, the station is no longer permitted to transmit frames addressed using the current address @MAC(n). For example, an AP cannot send a frame to a non-AP station by setting the RA field of the transmitted frame to the @MAC(n) value, and a non-AP station cannot send a frame to the AP with a TA field set to the current MAC address @MAC(n). Note that the current MAC address @MAC(n) remains valid for received frames for a backward margin period that did not exist in the prior art.

[0081] In step 410, since the emission of frames addressed to the current MAC address is no longer permitted, any potential frames buffered for transmission or retransmission addressed to the current MAC address are discarded.

[0082] After step 410 is performed, according to the embodiment, a back margin period begins. During this period, all transmitted frames are sent with the new MAC address @MAC(n+1), but received frames can use the current or new MAC address.

[0083] In summary, the algorithms in Figures 2a, 2b, 3, and 4 aim to achieve the following behaviors in a station, non-AP, or AP according to embodiments of the present invention.

[0084] Before the RCM preparation time, which is before the forward margin period, only the current MAC address is valid for both transmitted and received frames. During RCM ready time, the station begins accepting received frames with the new MAC address, while the current one remains valid for transmitted frames.

[0085] At the start of the transition period (if any), the new MAC address is used to generate the transmit frame, while both addresses are valid for both the receive and transmit frames.

[0086] At the end of the transition period corresponding to the start of the back margin period, only the new MAC address can be used to send a frame, while both addresses are valid for receiving frames.

[0087] At the end of the back margin period, only the new MAC address becomes valid for both transmitted and received frames.

[0088] Figure 5 shows a first example of a sequence of steps for operating a procedure to change the MAC address of a non-AP station associated with an AP station, according to several embodiments.

[0089] The MAC address change procedure essentially consists of two phases. During the first phase, new MAC addresses (and potentially all associated parameters that need to be obfuscated, such as sequence numbers) are calculated for one or more non-AP stations, and the AP stations and one or more non-AP stations identify the effective change start time corresponding to the start of their usage period. The second phase corresponds to the effective change of MAC addresses for these non-AP stations (when their usage period begins). The effective change of MAC addresses begins at a time called the SERCM change start time and ends at the latest at a time called the maximum SERCM change end time, from which the newly calculated MAC addresses are used for sending and receiving data between the non-AP stations under consideration and the AP stations they are associated with. Thus, during the change procedure, each non-AP station under consideration changes its MAC address from its current value @MAC(n) to a new value @MAC(n+1). During the transition period, both the current and new values ​​of the MAC addresses are valid.

[0090] The SERCM change start time 510, which represents the start of the transition period, can be determined by determining the absolute moment of change (typically by determining a specific value of the TSF) or by determining a specific beacon transmission (typically by determining the beacon index value corresponding to the moment of change).

[0091] The new MAC address must be calculated by the non-AP station and the AP station before its effective use during the transition period.

[0092] At SERCM change start time 510, non-AP stations and AP stations initiate the effective address change procedure, and at the maximum SERCM change end time 515 (or earlier), they modify their respective registries by updating the MAC address of each non-AP station considered from @MAC(n) to @MAC(n+1).

[0093] In other words, at the start of the transition period, both the AP and the non-AP STA begin changing the MAC address for the non-AP STA that is being modified.

[0094] The method by which AP stations and non-AP stations determine the new MAC address to be used is outside the scope of this disclosure. AP stations and non-AP stations may, for example, store a list of MAC addresses, and each time a MAC address change must be performed, the next value in the list is selected as the new MAC address. However, such an embodiment may present security issues if a third party accesses the list. Alternatively, the same function may be used by a non-AP station and the AP station it is associated with to determine, for example, the index of the next MAC address to use in a given list of MAC addresses. This index may be determined advantageously randomly.

[0095] Another MAC address selection method can be used. For example, it could be based on the use of a pseudo-random function (PRF) with the same input parameters. Thus, both the non-AP station and the AP station it is associated with will obtain the same address value @MAC(n+1).

[0096] To ensure the effectiveness of MAC address changes in enhancing station privacy, stations that change their MAC address also obfuscate a set of parameters (e.g., sequence number, scrambled code, AID) that could help potential eavesdroppers track the station.

[0097] Returning to Figure 5 and referring to Figure 1, the change procedure is shown for non-AP stations 110a and 110b of the BSS, which have been initiated by AP station 105 and whose initiation procedure has been performed. In other words, according to these embodiments, AP station 105 must change the MAC addresses of the non-AP stations 110a and 110b whose initiation procedure has been performed, and the non-AP stations 110a and 110b simultaneously begin changing their respective MAC addresses (SERCM change initiation time 510).

[0098] For illustrative purposes, the SERCM change start time 510 can be expressed in terms of multiple target beacon transmission time (TBTT) (as shown in Figure 5). Of course, the SERCM change start time 510 may be expressed differently, for example, as the actual time based on the TSF transmitted by the beacon.

[0099] According to the IEEE 802.11 standard, an AP station periodically (every TBTT) sends beacon frames to non-AP stations of the BSS, which are management frames containing network information. Therefore, a beacon frame can include a field that stores an information item to indicate the SERCM change date. For example, such an information item could indicate that a MAC address change is in progress and represent the value of a counter that is decremented within each consecutive beacon frame sent by the AP station to indicate the SERCM change date. For example, in addition to the TSF timer, which is shown in all beacons for time synchronization of the associated non-AP STA, each beacon frame sent by AP station 105 to non-AP stations 110a and 110b of the BSS may include a beacon counter that is updated with each beacon transition (increase or decrease), as shown by beacons 500, 505, and 510.

[0100] The new addresses for non-AP stations 110a and 110b are determined at any time between steps 500 and 510, i.e., after the MAC address change is requested but before the effective MAC address change is initiated.

[0101] All transmissions between AP station 105 and non-AP stations 110a and 110b that occur after the maximum SERCM change completion time of 515 will be performed using the new MAC addresses of non-AP stations 110a and 110b.

[0102] The transition duration between the SERCM change start time 510 and the maximum SERCM change end time 515 (indicated by reference number 520) favorably allows AP stations and non-AP stations to transmit frames addressed with the current MAC address @MAC(n) buffered in the transmit buffer. This allows MAC address changes without interrupting ongoing transmissions, ensuring that frequent MAC address changes do not negatively impact performance.

[0103] Even when the embodiment described with reference to Figure 5 uses beacon frames, it should be understood that other types of frames can be used similarly, for example, using the absolute time of the SERCM change start time.

[0104] Figure 6 shows an example sequence of steps to operate a procedure for changing the MAC address of a non-AP station associated with an AP station, according to some embodiments of the present invention, which is applied when the clock of the non-AP station is lagging behind that of the AP.

[0105] Next, Figure 6 shows, from the perspective of a non-AP station, valid addresses for transmission (TA file value of transmitted frames) or reception (RA field value of received frames) along different steps of the randomization and modification MAC address procedure according to several embodiments of the present invention.

[0106] For simplicity, only the perspective from a non-AP station is shown in this diagram; however, the steps performed on the AP side at different points in the SRCM procedure are described in more detail in Figures 2a, 2b, 3, and 4.

[0107] In Figure 6, the time difference between the non-AP station and the AP station is shown by the non-AP clock drift 630.

[0108] In this example, the non-AP station is slower, so its RCM preparation time of 605 occurs after the AP RCM preparation time of 600.

[0109] At moment 605, the non-AP station performed steps 200 and 210 in Figure 2a, enabling it to be ready to receive frames already addressed with the new MAC address @MAC(n+1), even though the non-AP station had not yet initiated its usage period. This mechanism allows, for example, frames sent by the AP at the start of its transition period and addressed by the new MAC address @MAC(n+1) to be correctly decoded by the non-AP station despite its slow internal clock.

[0110] Here, it is interesting to note that in an alternative embodiment, a non-AP station that receives a frame addressed with the new @MAC(n+1) after the RCM preparation time and before its future transition start time may determine that it is lagging behind the AP, and that its transition period and RCM completion time may be shifted by the difference between its theoretical future transition start time 611 and the moment of receipt of the first frame sent by the AP and addressed with the new MAC address @MAC(n+1). The clock of the non-AP station may be adjusted accordingly. Then, clock drift between the AP station and the non-AP station can be reduced.

[0111] This alternative embodiment, applicable only to non-AP stations, allows non-AP stations to shorten their SERCM procedure and subsequently release their internal memory earlier. In addition, if all non-AP stations implement such an alternative embodiment, the AP can significantly reduce the time between the end of its transition period 615 and its RCM completion time 610, because the probability of the AP receiving frames addressed at the current MAC address @MAC(n) after the end of its transition period is very low (if they are slow, all non-AP stations will shift their transition periods). This reduces the time the AP must maintain in memory the current and new MAC addresses (and associated parameters) of all relevant non-AP stations.

[0112] In another embodiment, the transition period may be null. In this embodiment, if there are some frames already addressed with old MAC addresses that have been buffered for transmission on the non-AP side or AP side, those frames are discarded at the start of the usage period (and thus it is assumed that the end of the transition period occurs immediately after the start time).

[0113] At moment 611, the non-AP station initiates a valid change of MAC address entering its usage period (and transition period) by performing steps 300 and 310 in Figure 3. After steps 300 and 310 are performed, both the current and new MAC addresses (@MAC(n) and @MAC(n+1)) are fully valid simultaneously. This means that during the transition period, the non-AP station can send or receive frames addressed with either of the fully valid MAC addresses. Typically, the non-AP station can receive frames with the RA field set to @MAC(n) or @MAC(n+1) and send frames with the TA field set to @MAC(n) or @MAC(n+1).

[0114] At moment 616, the non-AP station terminates the transition period by performing steps 400 and 410 in Figure 5. After the end of the transition period (moment 616), the non-AP station may receive frames from APs that have an RA field addressed with the current MAC address @MAC(n), but should not send frames to APs that no longer have a TA field set to the current MAC address @MAC(n), and should instead use only the new MAC address @MAC(n+1).

[0115] At moment 615, the non-AP station performs steps 220 and 230 in Figure 2b to terminate the SRCM procedure and free its internal memory.

[0116] Figure 7 shows an example sequence of steps for operating a procedure to change the MAC address of a non-AP station associated with an AP station, according to some embodiments of the present invention, which is applicable when the non-AP station clock is ahead of the AP clock.

[0117] This figure is very similar to Figure 6 and highlights the prior existence of non-AP stations compared to AP stations.

[0118] The steps performed at different moments in the SERCM procedure are the same as those described in relation to Figure 6, except that alternative embodiments for compensating for clock drift may be implemented differently based on an analysis of the MAC addresses used by the AP. For example, receiving one or more frames from an AP addressed with an old MAC address after the transition period has ended means that a non-AP station was present prior to the AP. The non-AP may then consider the time it received those frames (or preferably the last received frames) as a criterion for estimating the clock drift and making appropriate adjustments to reduce it.

[0119] Please note that, if the RCM completion time is determined appropriately, frames addressed with the old MAC address should not be received by non-AP stations after the RCM completion time.

[0120] Figure 8 shows the processing of both TA and RA addresses on the non-AP station and AP sides. The AP clock is considered the reference. Clock drift can be positive or negative. The margins considered are set to handle both situations. Transition periods are not shown (they may or may not exist). The focus is on the validity period and / or usage period of the MAC address. The usage period (n) is, for example, the epoch period.

[0121] On the non-AP station side, • TA address of the frame transmitted by STA, • The valid RA address of the frame received by the STA from the AP.

[0122] On the AP side, • The valid TA address of the frame received from the AP by the STA. • The RA address of the frame that the AP sends to the STA.

[0123] In some embodiments, it can have a regular variable epoch period (~10 minutes), The average values ​​over approximately 10 minutes are randomized.

[0124] The STA MAC address change start time is calculated without any information being sent or received between the STA and AP.

[0125] The purpose of such embodiments is to make it difficult for eavesdroppers to determine the moment of change without overhead.

[0126] Next, RCM procedure synchronization ("margin" management) can be summarized as follows:

[0127] • Before epoch transition: RCM preparation: pxTBTT before epoch transition. The station will only send MPDUs addressed with the old MAC address.

[0128] The station must be ready to receive MPDUs addressed with the old MAC address or the (future) new MAC address.

[0129] • Goal: Avoid synchronization issues (non-AP STA delay) • Epoch transition: Duration ~ nxTBTT • Resending an old MPDU uses the parameters from the old epoch.

[0130] A-MPDU aggregation, TXOP, includes either only old MPDUs or only new MPDUs.

[0131] • The station may send buffered MPDUs that are already addressed with an old MAC address.

[0132] The station sends a new MPDU addressed with the new MAC address.

[0133] The station can receive MPDU addresses that have either the old MAC address or the new MAC address. • Objective: Allow soft transitions (without communication interruption) • After epoch transition: RCM Done: pxTBTT after transition The station will only send MPDUs addressed with the new MAC address.

[0134] The station must be ready to receive MPDUs addressed with either the new or old MAC address.

[0135] • Goal: Avoid synchronization issues (non-AP STA beforehand) In particular, in implementations where the transition duration is long enough to ignore the backward margin, a non-AP STA or AP STA can handle the state machine for performing embodiments of the present invention. In this embodiment, for clarity, we assume that a station can register with an EDP Epoch sequence to indicate to its AP that the station is following a continuous change of address, for example, according to the scheme in Figure 8.

[0136] According to the implementation, in order to process the associated RCM mechanism, each CPE non-AP station can process an RCM state variable that can take the following values: • RCM Idle: FA parameters will not change until the next EDP Epoch transition.

[0137] • RCM Ready: Changes to FA parameters occur within a specific time period (called dot11EpochStartTimeMargin).

[0138] • RCM Transition: A change in FA parameters has just occurred, and both the current and old FA parameters may be used according to specific rules.

[0139] In practice, the back margin is ignored, and therefore the RCM idle state corresponds to the state after the epoch transition (including the back margin and RCM Done) that persists until the next RCM Ready state begins.

[0140] For the purposes of describing this state machine, we will refer to dot11EpochStartTimeMargin as the duration of the RCM Ready state (identified as the forward margin above), and dot11EpochTransitionTime as the maximum duration of the RCM transition state.

[0141] The two duration values ​​mentioned above can be stored as Management Information Base (MIB) variables in the internal memory of each device. These values ​​can be transmitted by the AP during the association process or in a beacon, or set up using predefined default values.

[0142] The default value for RCM State is RCM Idle.

[0143] To account for clock drift, all CPE non-AP MLDs registered in an EDP Epoch Sequence can enter the RCM Ready state by dot11EpochStartTimeMargin before the start of the next EDP Epoch start time in the sequence.

[0144] For all non-CPE AP MLDs that have registered an EDP epoch sequence, they can be considered to be in the RCM Ready state at a point in time equal to dot11EpochStartTimeMargin before the start of the next EDP epoch in the sequence.

[0145] In the RCM Ready state, each CPE non-AP MLD registered in the EDP Epoch sequence can accept reception from its AP-MLD: • Any frame using the FA parameter set configured for the current EDP Epoch.

[0146] • Individually addressed frames using the FA parameter set established for the next EDP Epoch.

[0147] In the RCM Ready state, a CPE non-AP MLD can send or retransmit only frames using the FA parameters associated with the current EDP Epoch.

[0148] An AP-MLD, in the RCM Ready state, can accept reception from its associated non-AP MLD: • Any frame using the FA parameter set configured for the current EDP Epoch.

[0149] • Individually addressed frames using the FA parameter set established for the next EDP Epoch.

[0150] The CPE AP MLD can use the FA parameters associated with the current EDP Epoch to send or retransmit only frames to non-AP MLDs that are in the RCM Ready state.

[0151] In the RCM Ready state, a CPE non-AP MLD may switch to the RCM Transition state at the start of the next EDP Epoch of its registered EDP Epoch Sequence for the maximum duration of dot11EpochTransitionTime.

[0152] CPE AP MLDs can consider all non-AP MLDs registered in the EDP Epoch sequence during the RCM Transition state at the start time of the next EDP Epoch of the sequence.

[0153] In the RCM Transition state, non-AP MLDs can be accepted: • Any frame received using the current FA parameter set.

[0154] • Frames individually addressed using the FA parameter set associated with the immediately preceding EDP epoch within a registered EDP epoch sequence.

[0155] In the RCM Transition state, a non-AP MLD must not send frames using different FA parameters in a single TXOP.

[0156] Non-AP MLDs can retransmit frames using the FA parameter set originally associated with the previous EDP Epoch.

[0157] Non-AP MLDs can send new frames using the FA parameter set associated with the current EDP Epoch.

[0158] At dot11EpochTransitionTime after entering the RCM Transition state, a non-AP MLD can use any FA parameter set different from the current FA parameter set to flush all remaining buffered traffic for transmission or retransmission and enter the RCM Idle state.

[0159] In the RCM Idle state, any non-AP MLD can only accept, transmit, or retransmit frames using the current FA parameter set.

[0160] AP-MLD can only accept frames that use the current FA parameter set from a non-AP MLD in the RCM Idle state.

[0161] AP-MLD can use the current FA parameter set to send or retransmit only frames to non-AP MLDs in the RCM Idle state.

[0162] Figure 9 shows an embodiment in which RCM(n-1) is completed and both RCM(n) preparation events are set simultaneously (effectively in the middle of the period in this example). In this embodiment, there are always at least two RA MAC addresses on the station side that are valid for receiving from the AP. On the AP side, there are always at least two TA MAC addresses that are valid for receiving from the station.

[0163] It should be noted that three or more simultaneous MAC addresses are possible. For example, by setting the station to prepare RCM(n) at the start of period n-1 and complete RCM(n) at the end of period n, three RA MAC addresses can be enabled upon reception.

[0164] This embodiment is easy to implement because the forward and backward margins (RCM ready and RCM completed) do not need to be precisely determined based on clock drift. Only a sufficiently large margin (larger than the worst case) needs to be considered. Also, two MAC addresses are considered simultaneously (either the RA on the station side or the TA on the AP side), but the MAC addresses are deterministically obtained and are known to belong to the correct station to which the AP is associated. Therefore, there is no risk of accepting frames that are not received from or intended to be received from the correct target station.

[0165] Figure 10 schematically shows an example of a communication device that may correspond to any of the stations of a wireless network described with reference to Figure 1, configured to carry out at least some embodiments of the present invention. The communication device referred to as 1000 may preferably be a device such as a microcomputer, workstation, or lightweight portable device. The communication device 1000 may include a communication bus 1013 to which it can be connected: - A central processing unit 1001, such as a processor, called a CPU, - A memory 1003 called MEM for storing executable code of a method or step of a method according to an embodiment of the present invention, and registers adapted for recording variables and parameters necessary to carry out the method, - At least two communication interfaces 1002 and 1002' connected via a transmitting antenna 1004 and a receiving antenna 1004' respectively to a wireless communication network, such as a communication network conforming to one of the IEEE 802.11 standard families, It is equipped with.

[0166] Preferably, the communication bus 1013 may be included in or connected to the communication device 1000 to provide communication and interoperability between various elements. The representation of the bus is not limited, and in particular, the central processing unit may be operated to communicate instructions directly to any element of the communication device 1000 or through another element of the communication device 1000.

[0167] Executable code can be stored in memory, which may be read-only, a hard disk, or a removable digital medium such as a disk. According to an optional modification, the executable code of a program can be received by a communication network via interface 1002 or 1002' in order to be stored in the memory 1003 of communication device 1000 before execution.

[0168] In some embodiments, the communication device 1000 may be a programmable device that uses software to carry out embodiments of the present invention. However, alternatively, some embodiments of the present invention may be implemented in whole or in part in hardware (for example, in the form of an application-specific integrated circuit or ASIC).

[0169] Embodiments of the present invention can also be realized by a computer of a system or device that reads and executes computer-executable instructions (e.g., one or more programs) recorded on a storage medium (which may be more fully referred to as a “non-temporary computer-readable storage medium”), which includes one or more circuits (e.g., application-specific integrated circuits (ASICs)) for performing one or more functions of the embodiments described above, and / or by controlling one or more circuits for performing one or more functions of the embodiments described above, for example, by the computer of the system or device. The computer may comprise one or more processors (e.g., a central processing unit (CPU), a microprocessor unit (MPU)), and may include a separate computer or a network of separate processors for reading and executing computer-executable instructions. Computer-executable instructions may be provided to the computer from, for example, a network or a storage medium. Storage media may include, for example, one or more of the following: hard disks, random access memory (RAM), read-only memory (ROM), storage devices for distributed computing systems, optical discs (e.g., compact discs (CDs), digital multipurpose discs (DVDs), etc.), flash memory devices, and memory cards.

[0170] The expressions “comprise,” “include,” “incorporate,” “contain,” “is,” and “have” shall be interpreted in a non-exclusive manner when interpreting this specification and the related claims. That is, they shall be interpreted in a manner that allows for the coexistence of other items or components that are not expressly defined. Singular references shall be interpreted as plural references, and vice versa.

[0171] Those skilled in the art will readily understand that the various parameters disclosed in the description may be modified, and that the various embodiments disclosed may be combined without departing from the scope of the invention.

Claims

1. A method of communication between a first station and a second station, wherein the first station is capable of changing the identifier from the current identifier to a new identifier, and the method, during a margin period, at the first station, Setting the set of identifiers, including the current identifier and the new identifier, as a valid identifier for the first station to receive frames, Setting either the current identifier or the new identifier as a valid identifier for the first station that sends out the frame, A method that includes this.

2. The method according to claim 1, wherein the set of valid identifiers is applied to the receiver address (RA) field in the received frame.

3. The method according to claim 1, wherein the one identifier is applied to the transmitter address (TA) field in the transmitted frame.

4. A method of communication between a first station and a second station, wherein the first station is capable of changing an identifier from the current identifier to a new identifier, and the method, during a margin period, at the second station, Setting the set of identifiers, including the current identifier and the new identifier, as a valid identifier for the first station to receive frames, Setting either the current identifier or the new identifier as a valid identifier for the first station that sends out the frame, A method that includes this.

5. The method according to claim 1, wherein the set of valid identifiers is applied to the transmitter address (TA) field in the received frame.

6. The method according to claim 1, wherein the one identifier is applied to the receiver address (RA) field in the transmitted frame.

7. The method according to any one of claims 1 to 6, further comprising determining the start time of a usage period in which the identifier of the first station changes from the current identifier to the new identifier.

8. The method according to claim 7, wherein the margin period is a forward margin period that begins before the start of the usage period.

9. The method according to claim 8, further comprising shifting the start time of the usage period or subsequent usage periods forward based on the time difference between the reception of the frame and the determined start time of the usage period, in response to the reception of a frame addressed to the first station using the new identifier during the forward margin period.

10. The method according to claim 7, wherein the margin period is a backward margin period that ends after the start of the usage period.

11. The method according to claim 10, further comprising: if a frame addressed to the first station having the current identifier is received during the backward margin period, the start time of the subsequent usage period is shifted backward based on the time the frame was received.

12. The method according to any one of claims 1 to 11, wherein the first station is a non-access point (AP) station and the second station is an AP station.

13. The method according to any one of claims 1 to 12, wherein the station identifier is a MAC address.

14. It is a station, A means for changing the identifier of the first station from the current identifier to a new identifier, Means for setting a set of identifiers, including the current identifier and the new identifier, as a valid identifier for the first station during a margin period for receiving frames, Means for setting one of the current identifier or the new identifier as a valid identifier for the first station during the margin period in order to transmit a frame, A station equipped with these features.

15. A non-temporary computer-readable medium for storing a program that, when executed by a microprocessor or computer system within a wireless device, causes the wireless device to perform the method according to claim 1 or 4.

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