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 |
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.