CN107333307B

CN107333307B - Method and equipment for switching access points in wireless local area network

Info

Publication number: CN107333307B
Application number: CN201610289641.2A
Authority: CN
Inventors: 叶苏昌; 季标; 王云贵; 张�林
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2016-04-29
Filing date: 2016-04-29
Publication date: 2020-06-16
Anticipated expiration: 2036-04-29
Also published as: WO2017186059A1; CN107333307A

Abstract

A method and device for switching access points in a wireless local area network are used for enabling an STA in a power saving mode to perform AP switching. The method comprises the following steps: the method comprises the steps that a first AP determines that an STA connected with the first AP is in a power-saving mode, wherein the first AP provides services for the STA on the basis of a BSSID corresponding to the STA, and the BSSID corresponding to the STA is different from BSSIDs corresponding to any other STAs in the same ESS with the STA; the first AP determines a second AP in the same ESS as a target AP connected after the STA is switched; a first AP sends a wakeup frame to the STA, wherein the wakeup frame is used for indicating that the STA is in an awake state when a second AP sends a beacon frame based on BSSID corresponding to the STA; and the first AP sends a switching instruction to the second AP, wherein the switching instruction is used for instructing the second AP to provide service for the STA based on the BSSID corresponding to the STA.

Description

Method and equipment for switching access points in wireless local area network

Technical Field

The present invention relates to the field of communications technologies, and in particular, to a method and an apparatus for switching an access point AP in a wireless local area network WLAN.

Background

In a Wireless Local Area Network (WLAN) system, a terminal needs to connect to an Access Point (AP) and receive and transmit data through the AP. During communication, signals between the terminal and the currently connected AP may be degraded, for example, as the distance between the terminal and the currently connected first AP becomes longer, the signals between them are degraded. When the signal quality between the terminal and the first AP currently connected is lower than the threshold, the terminal will initiate an association request to the second AP with better signal, and switch from connecting with the first AP to connecting with the second AP, which may be referred to as roaming of the terminal.

The terminal usually enters a power save mode when there is no data to be transmitted or received, and after entering the power save mode, the terminal only periodically turns on the rf module to transmit or receive data. During the period that the radio frequency module of the terminal is closed, the terminal cannot actively initiate roaming. When the terminal opens the radio frequency module, the link between the terminal and the originally connected AP may have been degraded to fail to communicate normally, and the terminal can only be associated with the AP in the WLAN again, which not only delays the communication requirement of the terminal, but also causes data loss because the STA cannot receive the data when the originally connected AP caches the data for the terminal.

Disclosure of Invention

The application provides a method and equipment for switching access points in a wireless local area network, which are used for enabling a terminal in a power saving mode to successfully switch the access points.

In a first aspect, the present application provides a method for switching an AP in a WLAN, where in a WLAN system applied by the method, each STA in an Extended Service Set (ESS) is assigned a Basic Service Set Identifier (BSSID), BSSIDs assigned to different STAs in the same ESS are different, and an AP in the ESS provides services for the STAs based on the BSSIDs assigned to the STAs. After determining that the STA connected to the first AP is in a power-saving mode and that the STA in the power-saving mode needs to be switched to a second AP in the same ESS, the first AP transmits an awake frame to the STA on the one hand, and indicates that the STA is in an awake state when the second AP transmits a beacon frame based on the BSSID allocated to the STA. On the other hand, the first AP sends a handover instruction to the second AP instructing the second AP to provide service to the STA based on the BSSID allocated to the STA. The first AP stops providing service to the STA after sending the wakeup frame to the STA and sending the switch instruction to the second AP.

The process of switching the AP connected with the STA is executed by the AP, so that even if the STA is in a power-saving mode and the radio frequency module is closed, the AP switching of the STA can be normally carried out, the STA can be ensured to communicate through the AP in the ESS after the radio frequency module is opened, and the STA can switch the AP with better connection signals, so that the communication quality of the STA is better

In an optional implementation, after determining that the STA is in the power saving mode and that the STA needs to be connected to the second AP, the first AP first determines whether the beacon frame transmission time of the first AP is synchronized with the beacon frame transmission time of the second AP, and if the beacon frame transmission time of the first AP is synchronized with the beacon frame transmission time of the second AP, the first AP may omit the step of transmitting the wakeup frame to the STA and directly transmit the switching instruction to the second AP. Under the condition that the beacon frame sending time of the first AP is not synchronous with the beacon frame sending time of the second AP, the first AP sends an awakening frame to the STA and sends a switching instruction to the second AP, the STA is ensured to be in an awakening state when the second AP sends the beacon frame based on the BSSID allocated to the STA, and the STA can receive the beacon frame sent by the second AP. The method and the device can reduce the sending of the wake-up frame when the first AP and the second AP send the beacon frame in time synchronization, save transmission resources and reduce the time consumption of AP switching.

In one optional implementation, the wakeup frame includes a first beacon frame including a field to instruct the STA to adjust the wakeup time to a time at which the second AP transmits a beacon frame based on the BSSID allocated for the STA. For example, a timestamp field included in the first beacon frame may be used to instruct the STA to synchronize the local time with the time of the second AP, such that the STA's wake-up time is synchronized with the beacon frame transmission time of the second AP, enabling the STA to receive the beacon frame transmitted by the second AP to the STA based on the BSSID assigned to the STA.

In an optional implementation, before transmitting the wakeup frame including the field for instructing the STA to adjust the wakeup time to the time when the second AP transmits the beacon frame based on the BSSID allocated to the STA, the first AP determines a time interval between the beacon frame transmission time of the first AP and the beacon frame transmission time of the second AP, where the time interval may be determined by: the first AP determines the time of receiving a second beacon frame sent by a second AP; and the first AP determines the time interval between the beacon frame sending time of the first AP and the beacon frame sending time of the second AP according to the beacon frame sending time of the first AP and the time of receiving the second beacon frame. After determining the time interval, the first AP determines the field for updating the STA awake time according to the time interval.

In an alternative implementation, the wakeup frame includes a third beacon frame including a field to indicate that the STA remains awake. Wherein the STA being in the awake state may be that the STA is in the active mode, or that the STA is in the power-save mode and enters the awake state (e.g., enters according to the listening interval). The STA in the awake state turns on its radio frequency module. For example, the field of the data pending indication message (DTIM) in the third beacon frame is set to 1, in some embodiments, the AP and the STA agree, and after receiving the beacon frame with the field of the DTIM 1, the STA switches from the power saving mode to the active mode. In other embodiments, the AP and the STA agree that the STA continues to be in the power saving mode but remains in the awake state after receiving the beacon frame with DTIM field set 1.

In an alternative implementation, the STA receives the third beacon frame, the DTIM field in the third beacon frame is set to 1, the STA sends an election (english: poll) frame to the first AP, the first AP receives the poll frame, but does not send data to the STA, and the STA keeps an awake state until receiving the data sent by the connection AP or the beacon frame.

In an alternative implementation, after sending the third beacon frame indicating that the STA is in the awake state to the STA, the first AP sends 1 or more data frames to the STA, where the data frames may be null data frames containing no transmission data. For example, when the STA is in the awake state in the power saving mode, the first AP receives the poll frame sent by the STA, sends 1 or More Data frames to the STA, sets a "More Data" field of each Data frame to 1, maintains the awake state after the STA receives the Data frame, and sends the poll frame to the first AP again. For another example, when the STA is in the active mode, the first AP transmits a data frame to the STA, and after receiving the data frame, the STA will count down again to enter the power saving mode, so that the STA can maintain the active mode.

In an alternative implementation, the first AP may include a null data frame in a plurality of data frames transmitted to the STA to maintain the STA in the awake state after transmitting the beacon frame indicating that the STA is in the awake state. Even if the first AP does not buffer the Data frame of the STA, the first AP may send a null Data frame to the STA, and the "More Data" field of the null Data frame is set to 1, indicating that the first AP buffers the Data frame of the STA, to trick the STA into keeping the awake state.

In an optional implementation, after confirming that the connection with the STA is successful, the second AP sends a handover success message to the first AP, and after receiving the handover success message, the first AP stops sending the wakeup frame to the STA.

In a second aspect, the present application provides an apparatus for switching an AP in a WLAN, where the apparatus is configured to perform the method in the first aspect or any possible implementation of the first aspect. In particular, the apparatus comprises means for performing the method of the first aspect described above or any possible implementation of the first aspect.

In a third aspect, the present application provides an apparatus for switching an AP in a WLAN, where the apparatus is configured to perform the method in the first aspect or any possible implementation of the first aspect. In particular, the apparatus includes a processor and a transceiver, the processor coupled with the transceiver. The transceiver is configured to communicate with other network elements in the WLAN, and the processor is configured to perform the method of the first aspect or any possible implementation of the first aspect by the transceiver.

In a fourth aspect, the present application provides a computer-readable medium for storing a computer program comprising instructions for performing the method of the first aspect or any possible implementation of the first aspect.

The invention can be further combined to provide more implementations on the basis of the implementations provided by the above aspects.

Drawings

In order to more clearly illustrate the technical solutions in the present application, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.

Fig. 1 is a schematic diagram of one possible implementation of a communication system in an embodiment of the invention;

FIG. 2 is a flowchart illustrating a method for switching APs according to an embodiment of the present invention;

FIG. 3 is a schematic flow chart illustrating a method for switching APs according to an embodiment of the present invention;

fig. 4 is a schematic structural diagram of an apparatus for switching an AP in a WLAN according to an embodiment of the present invention;

fig. 5 is a schematic structural diagram of another apparatus for switching an AP in a WLAN according to an embodiment of the present invention.

Detailed Description

The technical solution of the present invention is explained in detail by the accompanying drawings and the specific embodiments. The embodiments and specific features in the embodiments of the present invention are described in detail for the technical solution of the present invention, and are not limited to the technical solution of the present invention. The embodiments of the present invention and the technical features in the embodiments may be combined with each other without conflict.

In WLAN communication, a STA needs to connect with an AP, and the connected AP is responsible for data forwarding for the STA. When the signal between the STA and the currently connected AP is poor, the STA needs to switch to the AP with a better signal, so as to ensure normal data communication of the STA. Roaming is usually initiated by the STA after detecting that the link with the AP has degraded to a certain extent, so as to perform AP handover.

However, after the STA enters the power saving mode, the STA turns off the rf module, and only turns on the rf module periodically to transmit and receive data. During the period that the radio frequency module of the STA is closed, the STA cannot actively initiate roaming. When the radio frequency module is opened by the STA, the link between the STA and the AP connected originally may be degraded to prevent normal communication, the STA can only be associated with the AP in the WLAN again, the communication requirement of the STA is delayed, and when the AP connected originally caches data for the STA, the STA cannot receive the data, so that data loss is caused.

In order to solve the problem that the STA in the power saving mode is difficult to perform AP switching, embodiments of the present invention provide an AP switching method, where when the STA is in the power saving mode, the AP is responsible for switching the AP to which the STA is connected, so that even when the STA turns off the radio frequency module, the AP to which the STA is connected can still be switched.

In the embodiment of the present invention, when an STA associates with an AP in an Extended Service Set (ESS) for the first time, the STA is assigned a Basic Service Set Identifier (BSSID), and any AP in the ESS connected to the STA provides services for the STA based on the BSSID. That is, the AP in the ESS simulates an AP whose BSSID allocated to the STA is the BSSID, and transmits and receives a frame of the STA. That is, when the AP in the ESS communicates with the STA, the BSSID is used as the radio Medium Access Control (MAC) address of the AP. Because different APs provide services for the STA based on the same BSSID, the STA does not perceive the AP switch after the AP to which the STA is connected switches. On the other hand, BSSIDs allocated by any two STAs in the ESS are different, so that a situation that packet forwarding is disordered after the STAs perform AP switching in the ESS can be avoided.

The assignment method of the BSSID corresponding to the STA includes multiple implementation methods. For example, after the STA initiates an association request to the AP in the ESS, the AP receiving the STA association request allocates a BSSID to the STA, and notifies other APs in the ESS of the BSSID, so that when the STA connects with other APs in the ESS, the AP to which the STA connects can provide a service for the STA based on the BSSID allocated to the STA. For another example, in the communication system shown in fig. 1, after an STA initiates an association request to an AP in an ESS, a roaming controller in the WLAN allocates a BSSID to the STA, and notifies the AP in the ESS to provide a service to the STA based on the BSSID allocated to the STA.

In the embodiment of the present invention, when the WLAN includes the roaming controller, the roaming controller may have a plurality of implementation manners, for example, the roaming controller may be used as an Access Controller (AC) in a Control and provisioning of Wireless Access Points (CAPWAP) protocol, and correspondingly, the AP may be used as a Wireless termination Point (wap) in the CAPWAP protocol. In addition, the roam controller may be implemented by one independent device, or may be implemented by a cluster of a plurality of distributed devices.

In the embodiment of the present invention, after the STA reaches the roaming threshold, the AP to which the STA is connected switches the STA to another AP in the same ESS.

The AP to which the STA is connected may determine whether the STA reaches the roaming threshold, or the roaming controller shown in fig. 1 may determine whether the STA reaches the roaming threshold. Specifically, the AP connected to the STA monitors a signal indicator of the STA, such as a Received Signal Strength Indication (RSSI), a packet loss rate, and the like. When the monitoring value of the AP connected with the STA on the signal index of the STA is degraded to a preset value, the STA can be determined to reach the roaming threshold. When the roaming controller determines whether the STA reaches the roaming threshold, the AP to which the STA is connected needs to send the monitoring value of the signal index of the STA to the roaming controller.

The determination method of the target AP to which the STA needs to connect may be: and the AP or the roaming controller connected with the STA determines the target AP from the APs which are not connected with the STA according to the monitoring values of the AP which is not connected with the STA on the signal index of the STA in the same ESS. For example, the AP not connected to the STA in the same ESS transmits the monitored value of the signal indicator of the STA to the AP or the roaming controller connected to the STA, and the AP or the roaming controller connected to the STA determines the AP with the best detected signal indicator as the target AP.

Generally, after an STA sends a message to a connected AP, the STA can receive the message as well as the physical layer of another AP to which the STA is not connected, and calculate signal indicators such as RSSI, and then the Media Access Control (MAC) layer of the AP determines whether the message is sent to itself, and if the message is not sent to itself, discards the message. However, in the embodiment of the present invention, after determining that the packet is not sent to the AP, the MAC layer still stores the signal indicators of the packet, such as RSSI, in the memory, so that the AP can obtain the signal indicators of the STAs which are not connected to the AP. The AP may also use other technical means in the prior art to monitor the signal indicator of the STA that is not connected to the AP, and the embodiment of the present invention is not described in detail.

Typically, the times at which different APs transmit beacon frames are not synchronized. For example, the beacon intervals for different APs are different. For example, one AP transmits a beacon frame at 0 milliseconds (ms), 100ms, 200ms …, and another AP transmits a beacon frame at 0ms, 110ms, 220ms …. Alternatively, although the beacon intervals of different APs are the same, the phases of the transmitted beacon frames are different. For example, one AP transmits beacon frames at 0ms, 100ms, 200ms …, and another AP transmits beacon frames at 30ms, 130ms, 230ms … …. When the STA is in an active mode, the STA is always in an awake state, and the STA can receive a beacon frame sent by the second AP after the switch, and synchronize its own time with the time of the second AP according to a field for synchronizing the time included in the beacon frame sent by the second AP.

When the STA is in the power saving mode, the STA is in a doze state (doze state) and enters an awake state to receive the selected beacon frame according to a listen interval (listen interval). The listening interval is typically an integer multiple of the beacon interval. Therefore, the STA turns on the radio frequency module only at the time when the first AP before the handoff transmits the beacon frame, and receives the beacon frame. However, since the times of sending the beacon frames by the first AP and the second AP are usually not synchronized, the STA in the power saving mode may not receive the beacon frame sent by the second AP in the short time when entering the awake state, so that the STA cannot synchronize its local time with the time of the second AP after switching according to the beacon frame sent by the second AP. In this way, although the second AP has already provided the STA with service in place of the first AP, the STA cannot synchronize the local time with the time of the second AP because the STA cannot receive the beacon frame transmitted by the second AP, and cannot transmit and receive data through the second AP.

In order to solve the problem, embodiments of the present invention provide a method for switching an AP in a WLAN and an AP, where a first AP before switching sends an awake frame to an STA, so that the STA can be in an awake state at a time when a second AP after switching sends a beacon frame, and further can receive the beacon frame sent by the second AP, and synchronize a local time with a time of the second AP according to the beacon frame sent by the second AP.

With reference to fig. 2, the following describes in detail an AP switching method provided in an embodiment of the present invention, taking an example that a first AP switches a first STA connected to the first AP to a second AP, where the AP switching method includes the following steps:

step 101: the first AP determines that a first STA connected with the first AP is in a power saving mode, and determines that a second AP in an ESS where the first AP is located is a target AP to which the first STA needs to be connected.

Specifically, the connection of the first AP and the first STA means that the first STA is connected to the WLAN through the first AP, and the first AP provides service for the first STA, for example, the first AP forwards data for the first STA; for another example, when the first STA enters the power saving mode, the first STA buffers data for the first STA.

The first AP may determine that the first STA enters the power saving mode according to the locally stored record.

In step 101, the first AP may obtain the roaming threshold of the first AP according to the manner described above, and obtain that the second AP in the same ESS is the target AP to which the first AP needs to connect.

Step 102: the first AP sends a wakeup frame to the first STA, wherein the wakeup frame is used for indicating that the first STA is in an awake state when the second AP sends a beacon frame to the first STA based on the first BSSID allocated to the first STA.

Wherein the STA being in the awake state may be that the STA is in the active mode, or that the STA is in the power-save mode and enters the awake state (e.g., enters according to the listening interval). The STA in the awake state turns on its radio frequency module.

The wake-up frame in step 102 may be implemented in a variety of ways, including but not limited to any of the following:

in mode 1, the wakeup frame is a beacon frame, and the beacon frame includes a field for updating the wakeup time of the first STA, where the field for updating the wakeup time of the first STA is used to instruct the first STA to adjust the wakeup time to a time when the second AP transmits the beacon frame based on the first BSSID.

In general, the beacon frame transmitted by the first AP to the first STA based on the first BSSID includes a field for indicating that the first STA synchronizes the awake time with the time at which the first AP transmits the beacon frame. However, in this embodiment of the present invention, in order to ensure that the first STA can receive the beacon frame sent by the second AP, the first AP may use a value of the field for updating the awake time of the first STA in the beacon frame sent to the first STA, where the modified field is used to instruct the first STA to synchronize the awake time with the time when the second AP sends the beacon frame, and the beacon frame including the field for instructing the first STA to adjust the awake time to the time when the second AP sends the beacon frame based on the first BSSID may be used as the awake frame in this embodiment of the present invention.

Wherein the first AP determines that the field includes an instruction for the first STA to adjust the awake time to a time at which the second AP transmits the beacon frame based on the first BSSID, in order to determine a difference between its beacon frame transmission time and a beacon frame transmission time of the second AP. Since the first AP and the second AP are adjacent, the first AP may receive a beacon frame transmitted by the second AP, which may be a conventional beacon frame, that is, a beacon frame transmitted by the second AP based on the BSSID of the second AP itself. The first AP determines the local time of the first AP when receiving the beacon frame of the second AP, calculates a time difference (T _ offset) between the time when the first AP sends the next beacon frame and the time when the first AP receives the beacon frame of the second AP, and then determines the value of the field for updating the wakeup time of the first STA according to the time difference. If the period of the beacon frame transmitted by the second AP is different from the period of the beacon frame transmitted by the first AP, the difference between the periods of the beacon frame transmitted by the two APs can be considered when calculating the time difference. Optionally, the time difference may be calculated by taking into account a time delay between a time when the first AP receives the beacon frame transmitted by the second AP and a time when the second AP actually transmits the beacon frame.

For example, a timestamp field in the beacon frame is the field for updating the STA awake time, and the timestamp field is used for synchronizing the local time of the STA with the time of the AP. If the first STA does not need to perform AP switching, the timestamp field of the beacon frame sent by the first AP to the first STA at time T1 has a value of a; however, when the first STA needs to be switched to the second AP, the value of the timestamp field of the beacon frame sent by the first AP to the first STA at time T1 is adjusted to (a-T _ offset), so that after the first STA performs time synchronization according to (a-T _ offset), although the time of the first STA and the time of the first AP are not synchronized, the next wakeup time of the first STA and the time of the beacon frame sent by the second AP can be synchronized.

Also for example, the field for updating the wake-up time of the STA in the beacon frame may be a beacon interval (beacon interval) or a listening interval field. The beacon interval field is the interval of the AP sending the beacon frame, and the listening interval field is an integer multiple of the beacon interval field, indicating the interval of the STA receiving the beacon frame. If the first STA does not need to switch the AP, the first AP sets the value of the beacon interval field to B, the value of the listening interval field to k × B, and k is a positive integer in the beacon frame sent to the first STA by the first AP at time T1; in the case that the first STA needs to be switched to the second AP, the beacon interval field of the beacon frame sent by the first AP to the first STA at time T1 has a value of (B-D), and the listening interval field has a value of k × B-D, where k × D is T _ offset, so that the first STA enters the next wake-up time after k × (B-D) duration according to the listening interval l field, and the time is exactly the time when the second AP sends the beacon frame.

By means of the above mode 1, after determining to switch the first STA to the second AP, the first AP sends a beacon frame to the first STA, where a field used for updating the wakeup time of the first STA in the beacon frame points to the time when the second AP sends the beacon frame, but not to the time when the first AP sends the beacon frame. In this way, after the first STA receives the beacon frame, the wake-up time after the first STA is adjusted to a time synchronized with the beacon frame transmitted by the second AP, so that the first STA can receive the beacon frame transmitted by the second AP.

It should be noted that, in the method 1, the wakeup time of the first STA is synchronized with the beacon frame transmission time of the second AP, which means that the set of wakeup times of the first STA is a subset of the set of beacon frame transmission times of the second AP, and the two sets may be equal, but are not necessarily equal.

Mode 2, the wakeup frame includes a beacon frame including a field indicating that the first STA remains awake in the power save mode.

In general, a first STA in power save mode enters an awake state from a doze state, receives a beacon frame transmitted by a first AP connected, and switches back from the awake state to the doze state if the beacon frame does not include a field for the first STA to maintain the awake state. If the beacon frame includes the field for keeping the first STA in the wake-up state, the first STA keeps the wake-up state after receiving the beacon frame.

For example, the field of the beacon frame for waking up the first STA may be a data pending indication message (DTIM) field.

Generally, after buffering a data frame or a management frame for a first STA connected to the first AP, the first AP informs the first STA of a cacheable unit (BU) to be acquired, in a DTIM field of a beacon frame sent to the first STA, where the DTIM field corresponds to a position 1 of the first STA. And the first STA in the power saving mode turns on a radio frequency module at the wakeup time, receives the beacon frame and keeps the wakeup state according to the DTIM field in the beacon frame. And sending a election (poll) frame to the first AP, and the first AP sending the data packet buffered for the first STA to the first STA after receiving the poll frame.

In the embodiment of the present invention, when the first STA in the power saving mode needs to be switched to the second AP, even if the first AP does not buffer the data frame or the management frame for the first STA, the first AP still adds a field (for example, a DTIM field with a bit corresponding to the first STA being set to 1) for keeping the first STA in the awake state to the beacon frame sent by the first STA, so that the first AP keeps the awake state, and further can receive the beacon frame sent by the second AP.

Optionally, after receiving the third beacon frame sent by the first AP, the first STA sends a poll frame to the first AP, and after receiving the poll frame, the first AP does not send the cacheable unit BU to the first STA. And the first STA will keep awake state because it cannot receive the cacheable unit sent for the poll frame, until it receives the cacheable unit sent by the first AP for the poll frame, or until the beacon frame sending time of the first STA comes.

Mode 3 is different from mode 2 in that a beacon frame transmitted by the first AP to the first STA includes a field indicating that the first STA switches from the power save mode to the active mode.

In specific implementation, the following two cases exist between the modes 2 and 3:

in case 1, in the mode 2, a beacon frame sent by the first AP to the first STA includes a field a, where the field a is used to indicate that the first STA keeps an awake state; in the mode 3, the beacon frame transmitted by the first AP to the first STA includes a field B, which is used to instruct the first STA to switch from the power saving mode to the active mode. The fields a and B are two different fields.

In case 2, a beacon frame sent by the first AP to the first STA in the mode 2 includes a field a, and in an application scenario in which the mode 2 is located, the first AP makes an agreement with the first STA, where the field a is used to indicate that the first STA keeps an awake state. In the mode 3, the beacon frame sent by the first AP to the first STA also includes a field a, but in an application scenario in which the mode 3 is located, the first AP and the first STA agree that the field a is used to instruct the first STA to switch from the power saving mode to the active mode. For example, in one possible implementation, the first STA does not exit the power saving mode and remains awake after receiving the beacon frame of DTMI position 1; in another possible implementation manner, after receiving the beacon frame in DTMI position 1, the first STA sends a record of exiting the power saving mode to the connected AP, exits the power saving mode, and enters the active mode.

It should be noted that, regardless of whether the first STA keeps the awake state without exiting the power saving mode in the mode 2 or the first STA switches from the power saving mode to the active mode in the mode 3, the radio frequency module of the first STA is in the working state and can receive the beacon frame transmitted by the second AP based on the first BSSID.

Mode 4, in combination with mode 2, after sending a beacon frame indicating that the first STA keeps the awake state to the first STA, the first AP sends at least one data frame to the first STA, where the data frame includes a field indicating that the first STA continues to keep the awake state.

In the embodiment of the present invention, the data frame may be a data frame including transmission data, or may be a null data frame not including transmission data.

Specifically, after receiving the third beacon frame sent by the first AP, the first STA sends a poll frame to the first AP, and after receiving the poll frame, the first AP sends at least one Data frame (including a null Data frame) to the first STA, where a "More Data" field of each of the at least one Data frame is set to 1, which indicates that the first STA continues to maintain an awake state and continues to send the poll frame to the first AP, and the first AP continues to set a "More Data" field to 1 in the Data frame sent to the first STA. Thus, the first STA will remain awake until the first AP does not set the "MoreData" field in the data frame sent to the first STA to 1.

Mode 5, in combination with mode 3, the first AP transmits at least one data frame to the first STA after transmitting a beacon frame to the first STA instructing the first STA to switch from the power save mode to the active mode.

The first STA may remain in the active mode for a duration after switching from the power save mode to the active mode, which may be determined by the first STA, the first AP, or a negotiation of both. If the duration of the keep-alive mode is short, the first STA may switch back from the active mode to the power-saving mode before the beacon frame transmission time of the second AP, so that the first STA cannot receive the beacon frame transmitted by the second AP based on the first BSSID.

In order to solve this problem, in the embodiment of the present invention, after transmitting a beacon frame to the first STA to instruct the first STA to switch from the power save mode to the active mode, the first AP further transmits 1 or more data frames (including a case of a null data frame) to the first STA. The first STA may remain in the active mode for a period of time after receiving each data frame, and thus, the first STA may remain in the active mode if data frames are transmitted without interruption.

For example, assume that the power save policy of the first STA is set to: and if the first STA does not transmit or receive data for more than the time length S in the active mode, switching from the active mode to the power saving mode. The first STA receives a beacon frame including a field for instructing the first AP to switch from the power save mode to the active mode, which is transmitted by the first AP at time T1, switches from the power save mode to the active mode, and enters the power save mode again at time (T1+ S) if the first STA does not transceive data. To avoid this, in the embodiment of the present invention, the first AP transmits a null data frame to the first STA at a time (T1+ S-m) before the time (T1+ S), and the first STA maintains the active mode for a time period from (T1+ S-m) to (T1+2S-m) after receiving the null data frame. By analogy, before the active mode of the first STA is ended, the first AP sends a null data frame (which may also be a data frame containing transmission data) to the first STA again, so that the first STA continues to maintain the active mode.

In the above-described modes 4 and 5, the first AP maintains the awake state of the first STA by transmitting the plurality of data frames to the first STA after transmitting the third beacon frame to the first STA, and further enables the first STA to receive the beacon frame transmitted by the second AP.

It should be noted that, in the case of no collision, any two or More of the above-mentioned modes 1 to 5 may be used in combination, for example, the first AP sends to the first STA both a beacon frame for synchronizing the local time with the time of the second AP, and a plurality of null Data frames, where a "More Data" field in these null Data frames is set to 1, indicating that the first STA maintains the awake state.

In addition, in the above mode 1, the fact that the awake time of the first STA is synchronized with the beacon frame transmission time of the second AP means that the set of awake times of the first STA is a subset of the set of beacon frame transmission times of the second AP, and the two sets may be equal, but are not necessarily equal.

Step 103: the first AP sends a switching instruction to the second AP, wherein the switching instruction is used for instructing the second AP to provide service for the first STA based on the first BSSID.

Specifically, the handoff instruction includes an identifier of the first STA, and is used to instruct the second AP to provide a service for the first STA. Optionally, if the first AP or the roaming controller does not immediately notify the second AP of the mapping between the first STA and the first BSSID after allocating the first BSSID to the first STA, the handover instruction sent by the first AP to the second AP may further include the first BSSID allocated to the first STA, so that the second AP can provide service for the first STA based on the first BSSID.

Step 104: and the first STA receives the wake-up frame and keeps in the wake-up state at the beacon frame sending time of the second AP.

The specific implementation manner that the second AP keeps the awake state at the beacon frame transmission time of the second AP according to the awake frame in step 104 has been described in step 102, and is not repeated here. In addition, in step 104, the first STA keeping the awake state at the beacon frame transmission time of the second AP means that the first STA keeps the awake state at any one (or any plurality of) beacon frame transmission times of the second AP.

Step 105: the second AP receives the handoff instruction and provides service to the first STA based on the first BSSID assigned to the first STA.

Specifically, after receiving the handover command, the second AP is responsible for providing services to the first STA. The service provision includes: the second AP transmits a beacon frame to the first STA based on the first BSSID to enable the first STA to maintain a link with the second AP according to the beacon frame.

The second AP obtains the mapping between the first STA and the first BSSID, and may be implemented as follows: after the roaming controller allocates the first BSSID to the first STA, the roaming controller sends a mapping between the first STA and the first BSSID to each AP in the ESS, and the second AP can further learn the first BSSID allocated to the first STA by the roaming controller. Or after receiving the switching instruction sent by the first AP, the second AP requests the roaming controller to send the BSSID corresponding to the first STA to the second AP, and the second AP can further acquire the first BSSID. Or, when the first AP transmits the handover command to the second AP, the first AP transmits the first BSSID corresponding to the first STA to the second AP.

Step 106: the first AP stops serving the first STA.

Specifically, the first AP stops providing service for the first STA, which means that the first AP no longer uses the first STA as a STA that needs to provide normal WLAN service, for example, no longer sends a beacon frame based on its BSSID, forwards data, buffers data, and so on for the first STA.

In combination with any one of manner 2 to manner 5 in the foregoing various implementations of step 102, after performing step 102 and step 103, the first AP may continue to transmit the wakeup frame to the first STA, indicating that the first STA maintains the awake state at the beacon frame transmission time of the second AP. In the action of the first AP sending the wakeup frame to the first STA, the first AP does not provide the first STA with normal WLAN service, so that the first AP stops providing the first STA with service in step 106, and does not collide with the first AP continuing to send the wakeup frame to the first STA after performing steps 102 and 103.

Before and after the AP switching, the IP address used by the STA does not change. From the perspective of the STA, the BSSID of the AP to which the STA is connected is unchanged, and the STA still uses the same IP address for data transmission and reception, so in the embodiment of the present invention, the STA cannot perceive that the AP has been handed over at all.

In the above technical solution of the embodiment of the present invention, a first STA in the ESS is assigned a unique first BSSID, and an AP in the ESS, which is connected to the first STA, provides a service for the first STA based on the first BSSID. When the first AP determines that a first STA connected with the first AP reaches a roaming threshold and the first STA is in a power-saving mode, a switching instruction is sent to a second AP to which the first STA needs to be connected on one hand, and the second AP is indicated to provide service for the first STA based on a first BSSID; on the other hand, the first AP sends an awake frame to the first STA, and indicates that the first STA keeps an awake state at the beacon frame sending time of the second AP, so that the first STA can receive the beacon frame sent by the second AP, and can maintain a link with the second AP according to the beacon frame sent by the second AP, thereby ensuring that the first STA can receive services provided by the second AP. The switching process of the STA connecting the AP is executed by the AP side, so even if the first STA is in the power saving mode and the radio frequency module is turned off, the AP switching of the first STA can be performed normally, it is ensured that the first STA can communicate through the AP in the ESS after the radio frequency module is turned on, and the communication quality of the first STA is better because the first STA can switch the AP with better connection signal.

Moreover, when the first AP caches the data for the first STA, the first AP also hands over the data cached for the first STA to the second AP, and the second AP sends the cached data to the first STA, thereby avoiding data loss.

In a possible implementation manner, referring to fig. 3, before step 102, the following steps are further included:

step 107: the first AP determines whether the beacon frame transmission time of the first AP is synchronized with the beacon frame transmission time of the second AP, if yes, step 102 is skipped, and step 103 is directly performed, and if not, step 102 and step 103 are performed.

Specifically, after determining that the first STA needs to be switched to the second AP, the first AP first determines whether the beacon frame transmission times of the second AP and the first AP are synchronized, and if so, the first STA which can receive the beacon frame transmitted by the first AP can receive the beacon frame transmitted by the second AP, and the first AP may not perform step 102, but directly perform step 103.

If the second AP is not synchronized with the beacon frame transmission time of the first AP, the first AP performs step 102, so that the wakeup time of the first STA is the beacon frame transmission time of the second AP.

In the above technical solution, the first AP determines whether the time for sending the beacon frame by the first AP and the second AP is synchronous, and when the two are synchronous, the first AP does not need to send the wakeup frame for adjusting the time for the first AP to be in the wakeup state to the first STA, and only when the two are not synchronous, the first AP sends the wakeup frame to the first STA, which not only can ensure that the first STA can receive the beacon frame sent by the second AP, but also can reduce the sending of the wakeup frame when the time for sending the beacon frame by the first AP and the second AP is synchronous, thereby saving transmission resources.

In another possible implementation, after determining that the connection with the first STA is successful, the second AP sends a handover success message to the first AP, so that the first STA knows that the first STA has successfully handed over to the second AP, and after receiving the handover success message, the second AP may stop sending the wake-up frame in step 102 to the first STA.

The method for the second AP to determine that the connection with the first STA is successful includes:

in the mode A, the second AP sends a frame needing the first STA to return a message to the first STA, the first STA returns a message to the second AP, and the second AP receives the returned message, so that the successful connection establishment with the first STA can be determined.

The frame that requires the first STA to return the packet may have various implementation manners, for example, the frame is a data frame, and the first STA returns an ACK frame to the second AP after receiving the data frame sent by the second AP. Because the ACK frame sent by the first STA to the second AP includes the identifier of the second AP, the second AP provides service to the first STA based on the first BSSID, and the second AP uses the first BSSID as its own BSSID only when providing service to the first STA, the second AP can determine that the ACK frame is sent by the first STA according to the first BSSID in the received ACK frame, and further determine that the connection with the first STA has been successfully established.

Optionally, because the first STA may keep in the awake state for a short time after receiving the beacon frame sent by the second AP, the second AP may send, to the first STA, the frame for determining whether the second AP determines to be successfully connected with the first STA in the short time after sending the beacon frame to the first STA, so that the first STA can receive the frame and return the packet according to the frame.

In the method B, the first STA in the power saving mode may actively send messages to the connected AP, and after receiving the messages, the second AP may determine that the connection is successfully established with the first STA.

For example, when the first STA closes the power saving mode, it may send a record of closing the power saving mode to the connected AP, and the second AP may determine that the connection is successfully established with the first STA by receiving the message including the record.

In the above technical solution, the second AP can determine to establish a connection with the first STA according to the received message sent by the first STA, and send a handover success message to the first AP, so that the first STA knows that the first STA has successfully handed over to the second AP. The first AP may send a wakeup frame to the first STA before receiving the handover success message, so as to ensure that the first STA can receive the beacon frame sent by the second AP, and after receiving the wakeup frame, the first AP stops sending the wakeup frame to the first STA.

The embodiment of the present invention further provides an AP switching device 200, where the AP switching device 200 is used as an AP in a WLAN. Fig. 4 is a schematic structural diagram of the apparatus 200, the apparatus 200 including: a processor 201 and a transceiver 202.

Wherein, the processor 201 is configured to: determining that a STA connected to the device 200 is in a power save mode, wherein the device 200 provides services for the STA based on a BSSID corresponding to the STA, and the BSSID corresponding to the STA is different from BSSIDs corresponding to any other STAs in the same ESS as the STA; determining a second AP in the ESS as a target AP, wherein the target AP is an AP connected after the STA is switched; generating a wakeup frame, where the wakeup frame is used to indicate that the STA is in an awake state when the second AP sends a beacon frame based on the BSSID corresponding to the STA; generating a switching instruction, wherein the switching instruction is used for instructing the second AP to provide service for the STA based on the BSSID corresponding to the STA;

a transceiver 202, coupled to the processor 201, for: sending the wakeup frame to the STA; and sending the switching instruction to the second AP.

In the embodiment of the present invention, the processor 201 and the transceiver 202 may be two separate components, and are connected through a bus; in addition, the processor 201 and the transceiver 202 may also be integrated, and the embodiment of the present invention is not limited thereto.

The processor 201 may be a single processing element or may be a combination of multiple processing elements. For example, the processor may be a Central Processing Unit (CPU), an Application Specific Integrated Circuit (ASIC), or one or more integrated circuits configured to implement embodiments of the present invention.

The transceiver 202 includes an antenna and a radio frequency module connected to the antenna. Optionally, when the device 200 communicates with the second AP through a wired network such as an optical fiber network, the transceiver 202 further includes a data transceiver of a wired communication type, such as an ethernet data transceiver, in addition to the radio frequency module and the antenna.

In one possible implementation, the processor 201 is configured to: before generating the wake-up frame, further configured to: it is determined that the beacon frame transmission time of the device 200 is not synchronized with the beacon frame transmission time of the second AP.

In one possible implementation, the wakeup frame includes a first beacon frame, and the first beacon frame includes a field for updating the STA wakeup time, where the field for updating the STA wakeup time is used to instruct the STA to adjust the wakeup time to a time when the second AP sends a beacon frame based on the BSSID corresponding to the STA.

In one possible implementation, the transceiver 202 is further configured to: receiving a second beacon frame sent by a second AP;

the processor 201 is further configured to: determining the time when the transceiver receives the second beacon frame, and determining a time interval between the beacon frame transmission time of the device 200 and the beacon frame transmission time of the second AP according to the beacon frame transmission time of the device 200 and the time when the transceiver receives the second beacon frame; and determining a field for updating the STA wake-on time according to the time interval.

In one possible implementation, the wakeup frame includes a third beacon frame including a field indicating that the STA remains awake.

In one possible implementation, the wake-up frame further includes: at least one data frame transmitted after the third beacon frame, the at least one data frame for maintaining the STA in an awake state.

In one possible implementation, the at least one data frame comprises a null data frame.

In one possible implementation, the device 200 further includes a memory 203, and the memory 203 may be configured to: store data sent by connected STAs, store data sent by other network elements to STAs, store status records of STAs (e.g., whether in power save mode), store instructions sent by other network elements to device 200, and so on.

Optionally, the memory 203 may further store executable instructions, and the processor 201 reads and executes the executable instructions in the memory 203 to implement the functions of the device 200 in the embodiment of the present invention.

The memory 203 may be a single memory element or a combination of multiple memory elements, and is used for storing executable program codes or parameters, data, and the like required by the device to operate. The memory 203 may include a random-access memory (RAM), a non-volatile memory (NVM), and so on.

It should be noted that the memory 203 and the ethernet data transceiver in fig. 4 are represented by dashed boxes, which indicate that they are not modules necessary for the AP to implement its functions in the embodiment of the present invention. Typically, the AP also has functions other than those described in the embodiments of the present invention, which need to be implemented based on the memory 203 and/or the ethernet data transceiver.

The specific implementation manner of the operations executed by the constituent modules included in the device 200 may refer to corresponding steps executed by the first AP in the embodiments corresponding to fig. 2 and fig. 3, and no further details are given in the embodiments of the present invention.

The embodiment of the invention also provides equipment for switching the AP, and the equipment can be used as the AP in the WLAN. The apparatus comprises: a processor and a transceiver.

The transceiver is configured to receive a handover instruction sent by the first AP, where the handover instruction includes an identifier of the first STA.

A processor, coupled to the transceiver, to: the controlling AP provides service to the first STA based on the first BSSID generated for the first STA.

In one possible implementation, the transceiver is further configured to: receiving any message sent by a first STA;

the processor is further configured to: after the transceiver receives any message sent by the first STA, a switching success message is generated;

the transceiver is further configured to: and sending a switching success message to the first STA.

In one possible implementation, the processor is further configured to: after the transceiver receives the switching instruction, generating a frame requiring the first STA to return a message;

the transceiver is further configured to: and sending the frame needing the first STA to return the message to the first AP.

The specific implementation manner of the operation performed by each component module included in the AP may refer to the corresponding step performed by the second AP in the embodiment corresponding to fig. 2, and the embodiment of the present invention is not described again.

The embodiment of the invention also provides a communication system which comprises a plurality of APs and a plurality of STAs.

Wherein a first AP of the plurality of APs is to: determining that a first STA connected with a first AP is in a power-saving mode, and determining that the first STA needs to switch to be connected with a second AP in the same ESS; sending a wakeup frame to the first STA, wherein the wakeup frame is used for enabling the first STA to be in a wakeup state at the time when the second AP sends the beacon frame; sending a switching instruction to the second AP, wherein the switching instruction is used for enabling the second AP to provide service for the first STA based on the first BSSID distributed for the first STA;

a first STA of the plurality of STAs to: receiving the wakeup frame, and keeping the wakeup state at the time of sending the beacon frame by the second AP according to the wakeup frame;

a second AP of the plurality of APs is to: receiving a switching instruction sent by a first AP, wherein the switching instruction comprises an identifier of a first STA; and provides services to the first STA based on the first BSSID.

In one possible implementation, before the first AP sends the STA the wakeup frame, it is determined that the beacon frame sending time of the first AP is not synchronized with the beacon frame sending time of the second AP.

In one possible implementation, the wakeup frame includes a first beacon frame including a field for updating the wakeup time of the first STA, where the field is used to instruct the first STA to adjust the wakeup time to a time when the second AP sends a beacon frame based on the first BSSID corresponding to the first STA.

In one possible implementation, the first AP determines a time to receive a second beacon frame transmitted by the second AP before transmitting the wakeup frame to the first STA; determining a time interval between the beacon frame sending time of the first AP and the beacon frame sending time of the second AP according to the beacon frame sending time of the first AP and the time of determining the second beacon frame sent by the second AP; determining the field for updating the first STA wake-on time according to the time interval.

In one possible implementation, the wake-up frame further includes: at least one data frame transmitted after the third beacon frame, the at least one data frame to maintain the first STA in an awake state.

In one possible implementation, the second AP is further configured to: after receiving any message sent by the first STA, sending a switching success message to the first STA;

the first AP is further configured to: and receiving the switching success message and stopping sending the wake-up frame to the first STA.

In one possible implementation, the communication system further includes a roaming controller for assigning a unique BSSID to each STA in the same ESS, so that an AP to which each STA is connected provides services to the STA based on the BSSID assigned to the STA.

In one possible implementation, the first AP and the second AP are further configured to: reporting a monitoring value of a signal index of the first STA to a roaming controller;

the roaming controller is further configured to: determining that the first STA reaches a roaming threshold according to the monitoring value, determining that the second AP is a target AP, and sending a switching trigger instruction to the first AP;

the first AP is used for: determining that the first STA reaches the roaming threshold and that the second AP is the target AP, comprising: and receiving a switching trigger instruction, determining that the first STA reaches a roaming threshold according to the switching trigger instruction, and determining that the second AP is a target AP.

The specific implementation manner of the operation executed by each device included in the above system may refer to corresponding steps in the embodiments corresponding to fig. 2 and fig. 3, and the embodiments of the present invention are not described again.

The embodiment of the invention also provides a device for switching the AP in the WLAN, and the WLAN comprises a plurality of APs and a plurality of STAs. Referring to fig. 5, the apparatus includes:

a first determining module 301, configured to determine that a STA connected to the apparatus is in a power saving mode, where the apparatus provides a service for the STA based on a BSSID corresponding to the STA, and the BSSID corresponding to the STA is different from BSSIDs corresponding to any other STAs in the same ESS as the STA;

a second determining module 302, configured to determine that a second AP in the ESS is a target AP, where the target AP is an AP connected after the STA is switched;

a first sending module 303, configured to send a wakeup frame to the STA, where the wakeup frame is used to indicate that the STA is in an awake state when the second AP sends a beacon frame based on a BSSID corresponding to the STA;

a second sending module 304, configured to send a switching instruction to the second AP, where the switching instruction is used to instruct the second AP to provide a service for the STA based on the BSSID corresponding to the STA;

a service stop module 305, configured to stop providing services for the STA after the second sending module sends the switching instruction.

In one possible implementation, the apparatus further comprises:

a third determining module 306, configured to determine, before the first sending module sends the wakeup frame, a time when a second beacon frame sent by the second AP is received; determining a time interval between the beacon frame transmission time of the device and the beacon frame transmission time of the second AP according to the beacon frame transmission time of the device and the time of receiving the second beacon frame; and determining the field for updating the STA wake-on time according to the time interval.

The specific implementation manner of the operations executed by the constituent modules included in the apparatus may refer to corresponding steps executed by the first AP in the embodiments corresponding to fig. 2 and fig. 3, and the embodiments of the present invention are not described again.

As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-readable storage media (including, but not limited to, disk storage, optical storage, and the like) having program code embodied therein.

The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims.

Claims

1. A method for switching Access Points (APs) in a Wireless Local Area Network (WLAN), the method comprising:

a first AP determines that a station STA connected with the first AP is in a power-saving mode, wherein the first AP is one of a plurality of APs, the first AP provides services for the STA based on a Basic Service Set Identifier (BSSID) corresponding to the STA, and the BSSID corresponding to the STA is different from BSSIDs corresponding to any other STAs in the same Extended Service Set (ESS) with the STA;

the first AP determines that a second AP in the ESS in the plurality of APs is a target AP, and the target AP is an AP connected after the STA is switched;

the first AP sends a wakeup frame to the STA, wherein the wakeup frame is used for indicating that the STA is in an awake state when the second AP sends a beacon frame based on the BSSID corresponding to the STA;

the first AP sends a switching instruction to the second AP, wherein the switching instruction is used for instructing the second AP to provide service for the STA based on the BSSID corresponding to the STA;

and after the first AP sends the switching instruction, stopping providing service for the STA.

2. The method of claim 1, wherein the wakeup frame comprises a first beacon frame, the first beacon frame comprising a field to update the STA wakeup time, the field to update the STA wakeup time to instruct the STA to adjust the wakeup time to a time at which the second AP sends a beacon frame based on the BSSID to which the STA corresponds.

3. The method of claim 2, wherein prior to the first AP sending a wakeup frame to the STA, the method further comprises:

the first AP determines the time of receiving a second beacon frame sent by the second AP;

the first AP determines a time interval between the beacon frame sending time of the first AP and the beacon frame sending time of the second AP according to the beacon frame sending time of the first AP and the time of receiving the second beacon frame;

the first AP determines the field for updating the STA wake-on time according to the time interval.

4. The method of claim 1, wherein the wakeup frame comprises a third beacon frame comprising a field indicating that the STA remains awake.

5. The method of claim 4, wherein the wakeup frame further comprises: at least one data frame transmitted after the third beacon frame, the at least one data frame for maintaining the STA in an awake state.

6. The method of claim 5, wherein the at least one data frame comprises a null data frame.

7. An apparatus for switching an AP in a WLAN, the apparatus serving as an AP in the WLAN, the apparatus comprising:

a first determining module, configured to determine that a STA connected to the device is in a power saving mode, where the device provides a service for the STA based on a BSSID corresponding to the STA, and the BSSID corresponding to the STA is different from BSSIDs corresponding to any other STAs in the same ESS as the STA;

a second determining module, configured to determine that a second AP in the ESS is a target AP, where the target AP is an AP to which the STA is connected after being switched;

a first sending module, configured to send a wakeup frame to the STA, where the wakeup frame is used to indicate that the STA is in an awake state when the second AP sends a beacon frame based on a BSSID corresponding to the STA;

a second sending module, configured to send a switching instruction to the second AP, where the switching instruction is used to instruct the second AP to provide a service for the STA based on a BSSID corresponding to the STA;

and the service stopping module is used for stopping providing service for the STA after the second sending module sends the switching instruction.

8. The apparatus of claim 7, wherein the wakeup frame comprises a first beacon frame, the first beacon frame comprising a field to update the STA wakeup time, the field to update the STA wakeup time to instruct the STA to adjust wakeup times to times at which the second AP sends beacon frames based on the BSSID to which the STA corresponds.

9. The apparatus of claim 8, wherein the apparatus further comprises:

a third determining module, configured to determine, before the first sending module sends the wakeup frame, a time when a second beacon frame sent by the second AP is received; determining a time interval between the beacon frame transmission time of the device and the beacon frame transmission time of the second AP according to the beacon frame transmission time of the device and the time of receiving the second beacon frame; and determining the field for updating the STA wake-on time according to the time interval.

10. The apparatus of claim 7, wherein the wakeup frame comprises a third beacon frame comprising a field to indicate that the STA remains awake.

11. The device of claim 10, wherein the wake-up frame further comprises: at least one data frame transmitted after the third beacon frame, the at least one data frame for maintaining the STA in an awake state.

12. The apparatus of claim 11, wherein the at least one data frame comprises a null data frame.

13. An apparatus for switching an AP in a WLAN, the apparatus serving as an AP in the WLAN, the apparatus comprising:

a processor to: determining that a STA connected with the device is in a power-saving mode, wherein the device provides services for the STA based on a BSSID corresponding to the STA, and the BSSID corresponding to the STA is different from BSSIDs corresponding to any other STAs in the same ESS with the STA; determining a second AP in the ESS as a target AP, wherein the target AP is an AP connected after the STA is switched; generating a wakeup frame, where the wakeup frame is used to indicate that the STA is in an awake state when the second AP sends a beacon frame based on the BSSID corresponding to the STA; generating a switching instruction, wherein the switching instruction is used for instructing the second AP to provide service for the STA based on the BSSID corresponding to the STA;

a transceiver, coupled to the processor, to: sending the wakeup frame to the STA; and sending the switching instruction to the second AP.

14. The apparatus of claim 13, wherein the wakeup frame comprises a first beacon frame, the first beacon frame comprising a field to update the STA wakeup time, the field to update the STA wakeup time to instruct the STA to adjust the wakeup time to a time at which the second AP sends a beacon frame based on the BSSID to which the STA corresponds.

15. The device of claim 14, wherein the transceiver is further to: receiving a second beacon frame sent by a second AP;

the processor is further configured to: determining a time when the transceiver receives the second beacon frame, and determining a time interval between a beacon frame transmission time of the device and a beacon frame transmission time of the second AP according to a beacon frame transmission time of the device and the time when the transceiver receives the second beacon frame; and determining the field for updating the STA wake-on time according to the time interval.

16. The apparatus of claim 13, wherein the wakeup frame comprises a third beacon frame comprising a field to indicate that the STA remains awake.

17. The device of claim 16, wherein the wake-up frame further comprises: at least one data frame transmitted after the third beacon frame, the at least one data frame for maintaining the STA in an awake state.

18. The apparatus of claim 17, wherein the at least one data frame comprises a null data frame.