CN101631371A

CN101631371A - Zero delay switching method of wireless access points

Info

Publication number: CN101631371A
Application number: CN200910194639A
Authority: CN
Inventors: 徐昌庆; 滕劲; 刘大鹏; 查希; 周洲
Original assignee: Shanghai Jiao Tong University
Current assignee: Shanghai Jiao Tong University
Priority date: 2009-08-27
Filing date: 2009-08-27
Publication date: 2010-01-20

Abstract

The invention relates to a zero-delay switching method of a wireless access point in the field of communication technology, comprising the following steps: establishing multiple connections; after establishing multiple connections, the wireless network card can use any one of them as the main connection, Send data packets through the main connection, the other as a secondary connection, maintain the secondary connection in the background; perform switching when the quality of the primary connection declines, during the switching process, the control program modifies the MAC address of the destination AP in the MAC packet, without Delayed handover to another AP; after performing a MAC layer handover, AP scanning is performed in the background to re-establish and maintain a backup secondary connection. The invention solves the long-delay problem of MAC layer switching in the existing 802.11 wireless local area network protocol, overcomes the shortcomings of the existing fast switching method, such as high cost and difficult implementation, and only needs to modify the client program, and realizes it through multiple AP connection technology Switching with zero delay.

Description

Zero delay switching method of wireless access points

Technical field

What the present invention relates to is a kind of changing method of communication technical field, MAC layer Zero delay switching method in intensive 802.11 networks of particularly a kind of wireless access points AP.

Background technology

802.11 the communication radius of the AP in the WLAN (wireless local area network) is limited, its representative communication distance is generally below 100 meters.In order to cover a relatively large zone, just must lay a large amount of AP.Under many circumstances, because a wireless connections client has mobile needs, when the user broke away from the scope of a certain AP gradually, the portable terminal of he (she) (MS) should be connected to another AP in a short period of time and get on.This MS is called switching to the conversion of AP annexation.Switch and directly to determine user's communications service quality (QoS), because if can't finish switch or handoff delay long, the user's communications session, the particularly stronger session of some real-times will be affected, even is interrupted fully.MAC in the reality switches all can introduce level time-delay second, and solving the handover delay problem has very big meaning for 802.11 real-time Communication for Power Network.

Find by prior art documents, the author is V.Brik, " the Fliminating Handoff Latencies in 802.11 WLANs Using Multiple Radios:Applications; Experiences and Evaluation " of A.Mishra and S.Banerjee, ACM IMC, method with two network interface cards solution handoff delay problems has been proposed among the Oct.2005 (based on the method for handoff delay in reduction by 802.11 WLAN (wireless local area network) of many network interface cards: use, experience and assessment).This is a kind of method very intuitively---two network interface cards are all keeping and being connected of different AP, and standby each other.When the AP quality of using that network interface card inserted descended so that influences QoS, MS can switch to another quality network interface card preferably rapidly by changing the work network interface card, thereby has ensured QoS effectively.But it is very uneconomic on a MS two network interface cards being installed, and the mobility of MS has also proposed harsh requirement to its volume simultaneously, though so method tool learning value, practical value is not high.The author is S.Tsao, " the DualMAC:A Soft Handoff Mechanism for Real-time Communications inSecured WLANs " of P.Lo, in Computer Communications 30 (2007), p1785-1793 (two MAC: a kind of soft handoff mechanism of serving real time communication in the security wireless local area network) proposed on a network interface card, to utilize different MAC to realize the thought of two standby each other connections, but its application only limits to streaming media service, and do not provide concrete implementation method, so be still waiting to improve.

Summary of the invention

The objective of the invention is to overcome deficiency of the prior art, a kind of zero delay switching method of wireless access points is provided.The invention solves the long delay problem that the MAC layer switches in existing 802.11 protocol of wireless local area network and overcome shortcomings such as the cost height of existing fast switch over method, difficult realization, only need revise client-side program, by multiple AP interconnection technique, realized the zero propagation switching.

The present invention is achieved by the following technical solutions:

The present invention includes following steps:

Comprise the steps:

The first step: set up multiple connection, setting up in the process of wireless connections, set up the binding network interface card by the Socket function with AP, directly editor MAC wraps on application layer, network interface card authenticates and is connected or reconnects, and transmission of control network interface card and reception, connects with two AP;

Second step: after having set up a plurality of connections, wireless network card uses the wherein main connection of any one conduct, and by main connection transceive data bag, another is as less important connection, in the less important connection of background maintenance;

The 3rd step: carry out when the quality of main connection descends and switch, in handoff procedure, control program is revised the MAC Address of the purpose AP in the MAC bag, does not switch to another AP with having time-delay; After carrying out the switching of MAC layer, carry out AP scanning, rebulid and safeguard standby less important connection on the backstage.

The present invention is for most of practical application, only in intensive 802.11 networks of AP, discuss switch be only significant.The cavity can appear covering in 802.11 sparse or not dense wireless networks, and because the unsteadiness of wireless signal, a lot of temporary transient cavity or low-down zones of signal can occur, the direct result of this situation is exactly that the user can't normally be switched or frequently be switched, and has a strong impact on QoS.

The present invention proposes passes through the technological thought that Single NIC safeguards that multiple AP connects, and has overcome the shortcoming of existing 802.11 MAC Layer in Wireless fast switch over method, has realized a kind of simple and practical zero propagation MAC layer fast switching method, and following advantage is arranged:

1. reduce the MAC layer handoff delay of 802.11 WLAN (wireless local area network) greatly, be reduced to negligible degree by original level time-delay second.

2. do not change the network architecture, need not to increase hardware device, this method only need be revised the program of client.

3. method is independent of type of service, has pervasive characteristics.

Description of drawings

Many AP establishment of connection among Fig. 1 the present invention;

Main connection among Fig. 2 the present invention is connected with backup;

802.11MAC bag among Fig. 3 the present invention needs the field of modification;

The transmitting time and the ACK of UDP bag return the time spent among Fig. 4 embodiment.

Embodiment

Below in conjunction with accompanying drawing embodiments of the invention are elaborated: present embodiment has provided detailed execution mode and process being to implement under the prerequisite with the technical solution of the present invention, but protection scope of the present invention is not limited to following embodiment.

Multiple AP in the present embodiment connect be by revise the MAC head and and different AP finish the program realization of authentication/be connected.

Comprise the steps:

The first step: set up multiple connection.

Described multiple connection is to set up in the process of wireless connections with AP, sets up the binding network interface card by the Socket function, directly editor MAC wraps on application layer, network interface card authenticates and is connected or reconnects, and transmission of control network interface card and reception, connects with two AP.

Described network interface card sends and receives, and is that MS sends the authentication request mac frame to the AP that will insert, and AP beams back the authentication response mac frame; MS sends the connection request mac frame to AP, and AP beams back the connection response mac frame.

The essence that network interface card sends and receives is the management frames exchange of MS network interface card and AP network interface card, thereby promptly controlling wireless network card and a plurality of AP network interface card exchanges these management frames and realizes a plurality of establishment of connections, these are connected initial the time and set up, perhaps set up successively, even in MS and AP proper communication, as shown in Figure 1.

Second step: after having set up a plurality of connections, wireless network card uses the wherein main connection of any one conduct, and by main connection transceive data bag, another is as less important connection, in the less important connection of background maintenance, as shown in Figure 2.

Communication is finished by described main connection;

The MS maintenance is also upgraded described less important connection.

Maintenance is the beacon frame that the periodic AP that receives less important connection sends, and changes less important connection when being necessary again to guarantee the reliability of less important connection.Because the service action to less important connection is to carry out on the backstage, so can ignore the influence of main connection.

The 3rd step: carry out when the quality of main connection descends and switch, in handoff procedure, control program is revised the MAC Address of the purpose AP in the MAC bag, does not switch to another AP with having time-delay; After carrying out the switching of MAC layer, carry out AP scanning, rebulid and safeguard standby less important connection, as shown in Figure 3 on the backstage.

In the present embodiment, the wireless network card that makes notebook simultaneously and two AP (AP1 AP2) connects.1000 UDP bags are sent to the computer of a far-end by present embodiment control by these two AP then.After the UDP bag was received, far-end computer can return an ACK.Notebook passes next UDP bag again after receiving ACK.The implementation case is carried out in certain mansion office.Implement zone network situation more complicated, can receive the signal of 7-10 AP simultaneously, so be the intensive wireless network environment of AP.

At first only use an AP to send data (two subgraphs in top of accompanying drawing 4 are described), alternately send data then by these two AP.In other words, every packet is just finished an AP and is switched, and sees the below subgraph of explanation accompanying drawing 4.These experiments are simultaneously all finished at interval in very short time, can guarantee that substantially wireless environment stablizes constant.Note the transmitting time (seeing the abscissa of Fig. 4) of all UDP bag and corresponding ACK and return the time spent (Round TripTime, RTT see the ordinate of Fig. 4).The statistical value of these data is displayed in Table 1.

Table 1UDP bag ACK returns time spent statistics (unit is millisecond)

	The average time spent	The time spent standard deviation	The shortest time spent	The longest time spent
	The average time spent	The time spent standard deviation	The shortest time spent	The longest time spent	Only pass through AP1	??1.344	??0.663	??1.059	??9.115
Only pass through AP2	??1.585	??0.938	??1.056	??9.663	Only pass through AP1	??1.344	??0.663	??1.059	??9.115
Only pass through AP2	??1.585	??0.938	??1.056	??9.663	In turn by two AP	??1.319	??0.718	??1.057	??9.915

Fig. 4 and table 1 explanation, the quality of wireless connections is as broad as long substantially under these three kinds of situations of present embodiment.This has just illustrated to send packet and send packet by AP1 and AP2 in turn by AP1 or AP2 does not separately have essential distinction.This just so-called zero propagation switches---the variation of the imperceptible WAP (wireless access point) of user.

Claims

1. A zero-delay switching method for a wireless access point, characterized in that, comprising the steps of:

Step 1: Establish multiple connections. In the process of establishing a wireless connection with the AP, establish a bound network card through the Socket function, edit the MAC packet directly on the application layer, and perform authentication and connection or reconnection of the network card, and control the sending and receiving of the network card. , to establish a connection with two APs;

Step 2: After establishing multiple connections, the wireless network card uses any one of them as the main connection, sends and receives data packets through the main connection, and the other as the secondary connection, and maintains the secondary connection in the background;

Step 3: Perform switching when the quality of the main connection drops. During the switching process, the control program modifies the MAC address of the destination AP in the MAC packet, and switches to another AP without delay; after performing the MAC layer switching, in the background Perform an AP scan, re-establish and maintain alternate secondary connections.

2. The zero-delay switching method for wireless access points according to claim 1, characterized in that the sending and receiving of the network card is that the MS sends an authentication request MAC frame to the AP to be accessed, and the AP sends back an authentication request MAC frame. Response MAC frame; MS sends connection request MAC frame to AP, and AP sends back connection response MAC frame.

3. The zero-delay switching method for wireless access points according to claim 1, characterized in that the essence of sending and receiving by the network card is the exchange of management frames between the MS network card and the AP network card, that is, controlling the wireless network card and multiple AP network cards These management frames are exchanged to realize the establishment of multiple connections. These connections are established initially, or successively, even when the MS communicates with an AP normally.

4. The zero-delay handover method for a wireless access point according to claim 2 or 3, wherein the MS maintains and updates the secondary connection.

5. The zero-delay switching method of wireless access point according to claim 4, characterized in that the maintenance is to periodically receive the beacon frame sent by the AP connected to the secondary, and replace the secondary AP when necessary. connection to guarantee the reliability of the secondary connection.