CN108495347B

CN108495347B - Seamless roaming method

Info

Publication number: CN108495347B
Application number: CN201810178538.XA
Authority: CN
Inventors: 杨磊; 陈其银; 章程; 张胜利; 杨俊文
Original assignee: Jiangsu Creatcomm Electronic Co ltd
Current assignee: Jiangsu Creatcomm Electronic Co ltd
Priority date: 2018-03-05
Filing date: 2018-03-05
Publication date: 2021-01-12
Anticipated expiration: 2038-03-05
Also published as: CN108495347A

Abstract

The invention discloses a seamless roaming method, which comprises the following specific steps: a. configuring same-frequency networking, b, accessing same-frequency networking, c, quitting same-frequency networking, d, exception handling, and e, providing roaming user data service by same-frequency networking. Through the method for seamless roaming provided by the invention, the switching time delay is further reduced so that the STA cannot even sense the switching of the AP, and the application with strict requirements on the switching time delay, such as VoIP or real-time video transmission service in the wireless roaming process, is met.

Description

Seamless roaming method

Technical Field

The invention relates to the field of wireless communication technology, in particular to a seamless roaming method.

Background

At present, wireless AP products based on 802.11 standards are widely deployed in places such as shopping malls, office buildings, airports, railway stations and the like, and provide convenient wireless access Internet services for users. However, for real-time audio and video transmission application in the roaming process, the common AP product is not careful. Generally, the coverage of APs is limited, and clients (STAs) often switch from one AP to another AP during roaming. Most clients need to disconnect the wireless connection with the current serving AP during the handover process, then scan the signal strength of the neighboring APs, and finally select the AP wireless association with the best signal strength. The process causes the disconnection of the wireless access service for hundreds of milliseconds or even seconds, and the requirement of real-time audio and video transmission application cannot be met.

The 802.11r standard specifies a fast handoff mechanism of the WLAN, which implements key management and resource allocation before wireless reassociation or during reassociation, reduces time delay caused by handoff, and reduces the impact of wireless access service interruption on real-time services caused by handoff. However, the 802.11r standard-based device still has a handover delay of about 50 ms, which is still not suitable for some services with high delay requirements, such as VoIP.

A new wireless roaming method is therefore needed to further reduce handover latency.

Disclosure of Invention

The invention mainly solves the technical problem of providing a seamless roaming method, further reducing the switching time delay to ensure that the STA can not even sense the switching of the AP, and meeting the application with strict requirement on the switching time delay, such as VoIP or real-time video transmission service in the wireless roaming process.

In order to solve the technical problems, the invention adopts a technical scheme that: the method for seamless roaming is provided, and comprises the following specific steps:

a. configuring a same-frequency networking, wherein the same-frequency networking comprises a plurality of APs, and an AC wireless controller and a client which are connected with the APs, wherein all the APs use the same channel, SSID, BSSID, encryption mode and channel width, and the AC wireless controller is also provided with a CC central controller;

b. accessing the same-frequency networking, wherein a client scans an SSID in the same-frequency networking, after the scanning is finished, the client sends an AUTH frame and an AP for authentication, and after the authentication is finished, an ASSOC process is initiated by the client;

c. during the quitting process of the same-frequency networking, if the same-frequency networking quits normally, the client sends a DisassationRequest management frame to the current service APs, and the current service APs replies the DisassationResponse management frame after receiving the DisassationRequest management frame and informs the CC central controller of the MAC address of the client; if the client exits abnormally, the current service APs start a Wireless Local Area Network (WLAN) wireless drive kickoff flow after not receiving ack response of the client to a keepalive frame of the client for a long time, and simultaneously inform the CC central controller of an Media Access Control (MAC) address of the client so that the CC central controller can immediately delete the relevant information of the client;

d. exception handling, the CC central controller detects that the AP is off-line through overtime of an Echo Request message, deletes the AP, switches all client sides associated with the AP to adjacent AP, and the adjacent AP with the maximum RSSI in an RSSI data structure of the client side becomes a new service AP of the client side;

e. the co-frequency networking provides roaming user data service, the CC central controller concerns the change of service APs of the client and the RSSI of a client signal reported by an adjacent APn at all times, and once the change of the RSSI triggers a switching process, the CC central controller switches the client to a new service AP.

In a preferred embodiment of the invention, the client also uses the same channel as the connected AP.

In a preferred embodiment of the present invention, all the APs are in the same lan, and all the APs are configured and managed by the AC wireless controller in a unified manner.

The invention has the beneficial effects that: the seamless roaming method of the invention further reduces the switching time delay so that the STA can not even sense the switching of the AP, thereby meeting the application with strict requirement on the switching time delay, such as VoIP or real-time video transmission service in the wireless roaming process.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without inventive efforts, wherein:

fig. 1 is a flowchart of AP handover in the method of seamless roaming according to the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The embodiment of the invention comprises the following steps:

a method for seamless roaming includes the following steps:

The invention introduces a special AP same-frequency networking scheme. The special same-frequency networking enables a plurality of APs to work just like one AP, so that a client cannot be disconnected when freely switching from one AP to another AP during movement, and any packet drop or communication interruption does not exist. The special same-frequency networking is Zero-switching (ZHO for short) same-frequency networking. ZHO co-channel networking requires that all APs use the same channel and SSID. In addition, all AP-connected wireless clients also use the same channel. The architecture of the same-frequency networking network is shown in fig. 1. All the APs are in the same local area network and are uniformly configured and managed by the AC wireless controller. Unlike the conventional AC, the AC of the same-frequency networking not only needs to configure all APs with the same BSSID, SSID, frequency, encryption scheme and channel width, but also needs to determine the most suitable physical AP for each client to provide wireless access service.

The invention focuses on the architecture design and switching algorithm of the same-frequency networking. The present invention will not be described in detail with respect to the configuration and management functions between the conventional AC and the AP.

There are 3 basic procedures for a terminal in a WLAN wireless network: access, user data service and exit. Assuming that M APs constitute an intra-frequency network, the AC has configured APx (X = 1-M) to the same channel ch, the same SSID and BSSID, and the same encryption scheme and channel width. Thus, for the client, only one virtual AP provides it with wireless access services. There should also be a Central Controller (CC) on the AC for executing the handover algorithm and completing the access and exit procedure of the client in cooperation with the AP.

1. Wireless access procedure

During the access process, the client will scan only one SSID in this on-channel network. After the scanning is finished, the client sends the AUTH frame and the AP for authentication, and after the authentication is finished, the client initiates an ASSOC process. Since the client needs to be assigned a network-wide unique ASSOC ID in the ASSOC procedure, the ASSOC ID cannot be assigned by each physical APx, but only by the CC. Each physical APx does not assign an ASSOC ID immediately after receiving the Association Request management frame. But forwards the Association Request management frame and the RSSI corresponding thereto to the CC. The WLAN wireless driver requires the client to receive the Association Response within a certain time, for example, 30ms, after sending the Association Request management frame, otherwise, the client will retransmit the Association Request management frame. The CC side then proposes to collect Association Request management frames for a small amount of time, e.g., 10 ms. After the ASSOC ID is allocated to the CC, selecting the APx with the largest RSSI, only enabling the APx to be associated with the client, and only enabling the APx to send an Association Response management frame carrying the ASSOC ID information to the client. The EAPOL four-way handshake communication of the following CC with the client is also only completed by this APx. The key information contained in EAPOL is generated by Hostapd module on CC, and APx is responsible for forwarding. In the above access procedure, the CC determines the service APx of the client. After the access procedure is successfully completed, the serving APx determines that the neighboring APn is also determined, after which AP handover will occur. Before this or if the access is unsuccessful, no AP handover will occur since the serving APx is not certain. The CC will continue to select the service APx of the client until the access procedure is successfully completed.

2. Exit and exception handling

In the exiting process, if the exiting is normal, the client sends a Disassocination Request management frame to the current service APs (the APs and the APx in the above-mentioned accessing process may be the same physical AP or different). After receiving the Disassailability Request management frame, the APs replies a Disassailability Response management frame and informs the CC central controller of the MAC address of the client. Therefore, both the CC and the current service APs can delete the relevant information of the client. If the system is abnormal exit (such as power-off of the client), the current service APs start the self-contained kiskoff process of the WLAN wireless drive after not receiving ack response of the client to the keepalive frame for a long time. And simultaneously, the APs inform the CC client of the MAC address. As with the normal exit, both the CC and the current serving APs may delete the relevant information for the ue.

If the AP is abnormally restarted or powered off, the CC detects that the AP is off-line through overtime of an Echo Request message. The CC deletes the AP and switches all clients associated under the AP to neighboring APs according to the switching flow of fig. 1. The neighboring AP with the highest RSSI in the client RSSI data structure will become the new serving AP for the client. If the client, such as iphone, has its keep-alive function, it can detect the AP abnormality and re-initiate the association process, in which case it processes according to the radio access procedure.

3. User data service

During the user data service, the client is roaming all the time. Although it does not feel the change of the physical AP in the same-frequency networking, the central controller CC needs to pay attention to the change of the RSSI of the received client signals reported by the serving APs and the neighboring APs all the time. In addition, since the serving APs may be neighboring APs for other clients, the physical APs in the same-frequency networking need to provide not only data access services, but also monitoring services similar to wireless probes. And the wireless driving software collects all the detected MAC address information and RSSI of the client under the same frequency operation and reports the information and RSSI to the CC. Since the RSSI is greatly affected by the transmission rate and bandwidth, the reported RSSI should report the RSSI of the management frame and the control frame as much as possible. These 802.11 frames are sent at a fixed rate and fixed bandwidth, comparable. If the RSSI of the data frame is reported, the RSSI is added with the power back-off caused by the sending rate and the sending bandwidth. After receiving the client address information and RSSI reported by the physical AP, the CC shall store the receiving timestamp TSr and the smoothly filtered RSSI in the following data structure. The smoothing filter coefficient is related to the difference value of the timestamp of the current time when the CC receives the information of the client reported by the AP. The larger the difference is, the larger the weight the current RSSI occupies in the smoothing process, i.e. RSSI = arsicur + (1-a) RSSIpre (0< a <1, a is the weight of the current RSSI in the smoothing process). For the neighboring AP, if the RSSI reported by it after smoothing is greater than RSSI + RSSIh of the serving APs (RSSIh is RSSI hysteresis, positive, preventing switching ping-pong effect), the CC also needs to record the current timestamp TSg, otherwise TSg is set to 0.

STA RSSI data structure table:

STA MAC

service APs address/RSSI/TSr

Adjacent AP1 Address/RSSI/TSr/TSg

Adjacent AP2 Address/RSSI/TSr/TSg

……

Adjacent APn address/RSSI/TSr/TSg

Although the number of physical APs in the same-frequency networking is not limited, the data structure is not infinite. Since the number of neighboring APs is not so large for a STA. The more distant AP does not receive the STA's signal. We can limit the maximum value of n to 32. When more than n neighboring APs report the RSSI information of the STA, the information reported by the oldest neighboring AP is overwritten by the new information. After each data structure update, the CC operates as shown in fig. 1. Like RSSIh, TSh is a time lag, positive, to eliminate unnecessary handovers caused by sudden changes in RSSI.

The central controller CC decides that the client needs to switch to the next AP, it first sends a switch request message to the new serving AP. The switching request message contains the MAC address and the encryption information of the client. The new service AP firstly associates the client, then sets the encryption information, and finally sends a switching response message to the CC. And the CC sends a disassociation request message to the old serving AP after receiving the switching response message. The disassociation request message includes the MAC address of the client. The old serving AP disassociates the client first and then sends a disassociation response message to the CC. The CC re-initializes the client RSSI data structure after receiving the disassociation response message.

In summary, the method for seamless roaming of the present invention further reduces the handover delay so that the STA cannot even perceive the handover of the AP, and meets the application that has a very strict requirement on the handover delay, such as VoIP or real-time video transmission service in the wireless roaming process.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by the present specification, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims

1. A method for seamless roaming is characterized by comprising the following specific steps:

c. during the quitting process of the same-frequency networking, if the same-frequency networking quits normally, the client sends a DisassationRequest management frame to the current service APs, and the current service APs replies the DisassationResponse management frame after receiving the DisassationRequest management frame and informs the CC central controller of the MAC address of the client; if the client exits abnormally, the current service APs start a Wireless Local Area Network (WLAN) wireless drive kickoff flow after not receiving ack response of the client to a keepalive frame of the client for a long time, and simultaneously inform a central control unit (CC) of an Media Access Control (MAC) address of the client so that the central control unit (CC) can delete relevant information of the client immediately;

e. the method comprises the steps that a roaming user data service is provided by the co-frequency networking, a CC central controller constantly pays attention to changes of service APs of a client and a client signal RSSI reported by an adjacent APn, once the change of the RSSI triggers a switching process, the CC central controller switches the client to a new service AP, and after the CC receives client address information and the RSSI reported by a physical AP, a receiving timestamp TSr and the RSSI after smooth filtering are stored in an RSSI data structure of the client; for the neighboring AP, if the RSSI reported by the neighboring AP after smoothing is greater than RSSI + RSSIh of the serving APs, where RSSIh is RSSI hysteresis, the CC needs to record the current timestamp TSg, otherwise TSg is set to 0; the method comprises the steps that a Central Controller (CC) determines that a client needs to be switched to a next AP, the central controller firstly sends a switching request message to a new service AP, the new service AP firstly associates the client, then sets encryption information, and finally sends a switching response message to the CC; after receiving the switching response message, the CC sends a disassociation request message to the old service AP; the disassociation request message contains the MAC address of the client, the old service AP disassociates the client and then sends a disassociation response message to the CC; the CC re-initializes the client RSSI data structure after receiving the disassociation response message.

2. The method of seamless roaming according to claim 1, wherein the client also uses the same channel as the connected AP.

3. The method of seamless roaming according to claim 2, wherein all the APs are in the same lan, and all the APs are configured and managed by the AC wireless controller in a unified manner.