CN1324924C - Method for realizing mobile node switching in mobile IP - Google Patents

Abstract

The invention discloses a method for handover of a mobile node in mobile IP. The key is: the mobile node compares the currently detected selected physical layer channel information with the set trigger condition, and judges whether the base station meeting the trigger condition belongs to the mobile network. The subnet where the node is currently located to determine whether to trigger a network layer handover, and if so, send a handover instruction to the network layer. And, establish a dual link for each mobile node, after the network layer receives the switching instruction, only disconnect one of the currently established dual links, and establish a new connection; then, the mobile node uses the newly established connection to the home network Register and switch over the network layer; after the registration is completed, disconnect another link, and also establish a new connection between the mobile node and the new subnet. The method can not only enable the lower layer to actively and accurately trigger the network layer to start switching, and improve the switching speed; moreover, it can ensure that the communication is not interrupted during the switching process, and the packet loss rate during the switching process can be reduced.

Description

The Method of Mobile Node Handover in Mobile IP

technical field

The invention relates to mobile IP switching technology, in particular to a method for realizing switching of mobile nodes in mobile IP.

Background technique

With the rapid popularization of the Internet, the extensive use of portable devices, the rapid development of wireless communication devices, and the increase in people's dependence on the network, mobile users hope to access the corporate network anytime, anywhere in a more flexible way. Resources and Internet resources, that is to say, the user has a demand for the mobility of the host, hoping that the host does not need to interrupt the existing communication connection when changing its location. For this reason, the Internet Engineering Task Force (IETF) has defined Mobile IP (Mobile IP). Mobile IP is a network layer solution that supports host mobility. On the basis of hardware, it provides a location tracking and IP data message forwarding mechanism. When a host moves, the IP data message sent to the host can be safely forwarded to the current location of the host.

Mobile IP is a scheme that provides mobile functions on the global Internet, so that mobile nodes (MN) can still maintain ongoing communication when switching links. The IP routing mechanism provided by mobile IP enables mobile nodes to connect to any link with a permanent IP address.

The introduction of mobile IP technology enables mobile users to continue to use all resources in the original network without modifying the original IP address of the computer during cross-network movement and roaming. It shields users from changes in IP access networks during movement the impact. Simply put, Mobile IP is to realize the smooth movement and roaming functions of mobile users in the network.

Fig. 1 is the basic network topological structure figure that each entity is formed in the mobile IP, and the mobile node 10 shown in the figure refers to a mobile computer or router, also can be referred to as mobile host (MH), this mobile node 10 still remains after moving. The original IP address can be used for communication; the correspondent (CN) 11 shown in the figure is a computer communicating with the mobile node 10, and can also be called a correspondent host (CH). 1, for the mobile node 10, the home network of the mobile node 10 is called a home network (HN), and the network where the mobile node 10 is in a roaming state is called a foreign network (FN). foreign network. The permanent IP address assigned to mobile node 10 is called home address (Home Address), and this address does not change with the change of node position; In the home network, the link of mobile node 10 home network is called home link (HL); The router running on the home network of the mobile node 10 is called the home agent (HA, HomeAgent) 12, which is responsible for saving the current location information of the mobile node, and is also responsible for intercepting the message sent to the mobile node, and forwarding the message in a tunnel mode to the current location of the mobile node. In the foreign network, the link of the foreign network where the mobile node 10 is located is called a foreign link (FL); the router running on the foreign network is called a foreign agent (FA), which is the agent for the mobile node to send messages in the foreign network. The default router also provides tunnel decapsulation service sometimes, and Fig. 1 includes foreign agent 13 and foreign agent 14 belonging to foreign network 1 and foreign network 2 respectively.

When the mobile node A roams from the home network to the foreign network or roams from the foreign network 1 to the foreign network 2, according to the standard mobile IP protocol, the handover process of the mobile node A includes the following steps:

a. After mobile node A discovers that he has entered a new network, it first disconnects the original link connection, and establishes a new link connection with the base station and agent of the new network; then mobile node A obtains a care-of address from the foreign agent, The care-of-address may be a foreign-agent care-of-address obtained from an agent broadcast message, or a configured care-of-address obtained according to a certain configuration procedure. The following foreign agent care-of-address is taken as an example.

b. The mobile node A sends a registration request message to the current foreign agent, which contains the obtained care-of address, and the foreign agent checks the validity of the registration request message. The request is forwarded to the home agent of mobile node A; if the check fails, the foreign agent directly returns a registration response message to mobile node A, indicating that the registration failed, and the current process ends.

c. After the home agent of mobile node A receives the registration request message, it performs a validity check. If the message is valid, the home agent binds the home address of mobile node A with the care-of address, and returns a registration response message, indicating that the registration is successful. And start to prepare the packet sent to the mobile node A as the tunnel entry encapsulation; if the message is invalid, then send back a registration response message indicating that the registration failed.

d. After the foreign agent receives the registration response message, it will perform a validity check. If the check is passed, the foreign agent will update the list of visited mobile nodes, forward the registration response message to mobile node A, and start preparing to unpack and send it to the mobile node as the tunnel exit message from node A; if the check fails, the foreign agent forwards the registration response message to mobile node A, indicating that the registration failed.

e. After the mobile node A receives the registration response message, if the registration is successful, it starts to work normally; otherwise, it can re-initiate the registration request after adjusting according to the error information.

After the above handover process, all messages sent to mobile node A are routed to the home network of mobile node A. After the home agent intercepts the message, it uses the care-of address registered by mobile node A as the tunnel exit, and its The address is used as the tunnel entrance, and the packet is encapsulated and sent. After the foreign agent receives the message and unpacks it, it checks its own visiting mobile node list, and if the mobile node A exists in the list, it forwards the message to the mobile node A according to the care-of address.

It can be seen from the above handover process that only after the handover of the mobile node in the lower layer is completed, the network layer handover starts. More specifically, the network layer switching can only be performed after the physical layer and the link layer disconnect the original network connection and establish a new connection. Before the network layer switching, the original connection has been broken, but the network layer does not Therefore, this switching process will inevitably interrupt communication, cause switching delay and prolong the cycle of overall communication recovery, and then lead to packet loss. Moreover, if the communication interruption time is too long, it will affect applications with high real-time requirements, making roaming opaque to upper-layer applications and affecting the use effect of mobile IP.

In order to shorten the handover delay and reduce packet loss, the industry has proposed many different solutions. It mainly includes: a scheme to realize fast switching, such as cellular IP, etc.; a scheme to realize smooth switching, such as a packet buffering and forwarding mechanism; and a method combining Layer 2 and Layer 3 switching. However, in the above solutions, no matter whether it is to realize fast switching or smooth switching, it is limited to the improvement of the processing process of network layer switching, and cannot completely solve the problem that the network layer switching can only be performed after the low-level switching is completed, so simply shorten the switching of the network layer The effect of time on increasing the overall switching speed is not obvious.

Therefore, some research institutes propose to combine the link layer and the network layer handover, and use the link layer to trigger the network layer to perform pre-registration, so that the layer 3 handover is also completed when the layer 2 handover is completed, thereby realizing fast handover. This kind of scheme mainly includes: An Internet draft proposed by Ericsson - "Fast Switching in Mobile IPv4". The main idea of this scheme is: when the mobile node is in the overlapping area, register in advance, and use the original link to register with the new foreign agent. However, since the implementation of this solution is still based on a single link, the time coordination between the Layer 3 handover and the Layer 2 handover is very important. If the original link is disconnected before the network layer handover is completed, the communication will still be interrupted. causing packet loss.

Contents of the invention

In view of this, the main purpose of the present invention is to provide a kind of method that mobile node realizes handover in Mobile IP, not only can make lower layer trigger network layer to start handover actively and accurately, improve handover speed; Interruption, reducing the packet loss rate during switching.

In order to achieve the above object, technical solution of the present invention is achieved in that way:

A kind of method that mobile node realizes switching in mobile IP, the key is, set up two link connections that carry out communication with current subnet for each mobile node, and this method also includes the following steps:

a. The current mobile node detects the selected physical layer channel information of all currently discovered base stations;

b. Judging whether the detected selected physical layer channel information satisfies the set trigger condition, if not, then return to step a; if yes, then judge whether the base station that currently satisfies the trigger condition belongs to the current location of the mobile node Subnet, if it does not belong to, send a switching instruction to the network layer; otherwise return to step a;

c. After the network layer receives the handover instruction, it disconnects one of the two links established between the current mobile node and the base station of the atomic network, and establishes a new link between the current mobile node and the target base station to be handed over to link connection;

d. The current mobile node registers with the home agent through the newly created link in step c, and performs network layer handover;

e. After the registration is completed, disconnect another link connection between the current mobile node and the base station of the atomic network, and establish another new link connection between the current mobile node and the target base station to be handed over to.

The method further includes: the current mobile node obtains and stores all the base station information of the current subnet, and obtains the base station information of all the currently discovered base stations in real time; The current subnet of the mobile node is: the current mobile node matches the base station information of the base station that currently satisfies the trigger condition with the base station information of all base stations stored in itself. If they do not match, the base station that meets the trigger condition does not belong to the current mobile node. Otherwise, it belongs to the subnet where the current mobile node is currently located.

In the above scheme, when the mobile node switches from the home network to the foreign network, the network layer switching described in step d specifically includes:

d11. The mobile node obtains a new care-of address through the link connection established with the target base station;

d12. The mobile node establishes a tunnel, and sends a registration request to the home agent through the newly established link;

d13. After receiving the registration request, the home agent establishes a tunnel leading to the care-of address, sends a registration response, and sends an agent address resolution protocol ARP message;

Then the completion of the registration described in step e is: the mobile node receives the registration response sent by the home agent.

When the mobile node is handed over from a foreign network to another foreign network, the network layer handover described in step d specifically includes:

d21. The mobile node obtains a new care-of address through the link connection established with the target base station;

d22. The mobile node establishes a tunnel after obtaining the care-of address, and sends a registration request to the home agent through the newly established link, and the registration request carries an instruction to retain the original care-of address;

d23. After receiving the new registration request, the home agent retains the original care-of address, stores the new care-of address carried in the registration request, and sends a registration response to the mobile node;

d24. After receiving the registration response, the mobile node sends a deregistration request from the link reserved between the mobile node and the original base station;

d25. After receiving the deregistration request, the home agent deletes the original care-of address and sends a registration response to the mobile node;

Then the completion of the registration in step e is: the mobile node receives the registration response sent by the home agent after deleting the original care-of address.

When the mobile node switches back to the home network from the foreign network, the network layer switching described in step d specifically includes:

d31. The mobile node sends a gratuitous ARP message in the home network, and sends a deregistration request to the home agent;

d32. After receiving the deregistration request, the home agent deletes the care-of address and tunnel of the mobile node, and returns a registration response to the mobile node;

Then the completion of the registration in step e is as follows: the mobile node deletes the tunnel established with the foreign agent after receiving the registration response sent by the home agent.

In the above solution, during the handover process, after receiving duplicate data sent from different links, the mobile node filters a piece of duplicate data according to the existing protocol.

In the above solution, before the handover of the mobile node or after the handover is completed, the two links established by the mobile node and the current base station are in the same network and share a care-of address.

In the above solution, the trigger time caused by the set trigger condition is earlier than the time of automatic switching of the physical layer. The set trigger condition is a preset threshold value of the selected physical layer channel information to be detected. The selected physical layer channel information is received signal strength or signal-to-noise ratio.

In the above solution, the base station information is the base station ID, or the SSID of the subnet to which the base station belongs, or the MAC address of the base station. Then, the obtaining of all base station information of the current subnet by the mobile node specifically includes: the mobile node sends a registration request message to an agent of the current subnet, and the registration request information carries a request to obtain all base stations of the current subnet Indication of information: the agent receiving the registration request returns a registration response message carrying information of all base stations of the current subnet to the mobile node that initiates the registration request. Wherein, the indication of requesting to acquire information of all base stations of the current subnet is placed in the extension field of the registration request message; the information of all base stations of the current subnet is placed in the extension field of the registration response message.

The method that mobile node realizes switching in Mobile IP provided by the present invention has the following advantages and characteristics: 1) the present invention utilizes the relevant information of the physical layer channel that detects as the triggering condition of network layer switching, and network layer switching is ahead of schedule Low-level switching can shorten the time for network layer switching judgment, fundamentally improve switching speed, and effectively reduce packet loss.

2) The present invention introduces the concept of dual links in the mobile IP handover, that is: each mobile node maintains the communication of two wireless links simultaneously, when the mobile node enters the overlapping network coverage area that may be handed over, in the original network still When it is available, it is judged whether a network layer switch is required. If necessary, one link is used to establish a connection with the new network, and the other link is used to maintain the connection with the original network, so that before the original network is unavailable, Realize the simultaneous access of the original network and the new network, so that the communication can be guaranteed to be uninterrupted during the switching process, thereby reducing the packet loss rate.

3) The present invention combines the use of physical layer channel information to trigger network layer switching and the establishment of dual-link technology at the same time, fundamentally improving the switching speed and effectively reducing packet loss. It is an effective way to realize seamless switching in mobile IP .

4) When the mobile node in the present invention utilizes the physical layer channel information as a trigger condition, it judges whether itself switches between different subnets according to the information of all base stations in the current wireless subnet, so that not only improves the accuracy of handover judgment , and avoid blind switching of the network layer due to frequent triggering of low-level switching information.

5) In the present invention, when the mobile node is in the non-handover stage, two links can be used in parallel, so that hardware resources can be fully utilized, bandwidth can be increased, and the purpose of load balancing can be achieved.

6) The present invention is an extension to the standard mobile IP protocol, only slightly changes the existing processing, and is fully compatible with the standard mobile IP system, therefore, it is simple and convenient to realize, and is easy to carry out function expansion on the existing mobile IP system.

Description of drawings

Fig. 1 is the basic network topology structure chart that each entity in the mobile IP is formed;

Fig. 2 is the processing flowchart that the present invention realizes;

Fig. 3 is a schematic diagram of triggering timing of physical layer channel information when the mobile node is handed over as defined in the present invention;

Fig. 4 is a schematic diagram of the handover process of the mobile node moving from the home network to the foreign network in the present invention;

FIG. 5 is a schematic diagram of a handover process in which a mobile node moves between two foreign networks in the present invention;

6 is a schematic diagram of the handover process of the mobile node returning to the home network from the foreign network in the present invention;

FIG. 7 is a network topology diagram of a specific embodiment of the present invention.

Detailed ways

The core idea of the present invention is: the mobile node uses the relevant information of the physical layer channel as a trigger condition, and combines the base station information of the current network to judge whether it needs to trigger the network layer handover. Moreover, a dual link is established for each mobile node, and when the mobile node is in the non-handover state, the mobile node uses the established dual links to communicate in parallel; when the mobile node is in the handover state, only disconnect the One, that is, use one link to maintain the original connection, and use another link to establish a new connection at the same time. New connections between subnet base stations.

The premise that the present invention realizes is: select a physical layer channel information in advance as a trigger parameter, and set trigger conditions for the selected physical layer channel information, here, the selected physical layer channel information is to judge from the mobile node whether to perform physical Select from the physical layer parameter information used for layer handover; and establish a dual link for communication between the mobile node and the base station of the subnet where the mobile node is currently located. Based on this, the realization process of the present invention is referring to shown in Figure 2, comprises the following steps:

Step 201: the mobile node detects in real time the selected physical layer channel information of all currently discovered base stations.

Wherein, the physical layer channel information is the physical layer parameter information used by the mobile node to judge whether to perform physical layer handover, including the ID of the base station to which it is currently connected, the list of available basic service sets, the received signal strength, and the signal-to-noise ratio etc.; any one of the above parameter information can be selected as the selected physical layer channel information, usually the received signal strength or signal-to-noise ratio can be selected. For example, using the signal-to-noise ratio as the channel information of the selected physical layer, the mobile node detects the signal-to-noise ratios of all base station signals currently discovered in real time.

Step 202: the mobile node judges whether the detected selected physical layer channel information satisfies the set trigger condition, if so, executes step 203; otherwise, returns to step 201.

Here, the trigger condition may be a preset threshold of selected physical layer channel information, such as: the selected signal-to-noise ratio is the selected physical layer channel information, and the trigger condition is to set the signal-to-noise ratio threshold as SIR1, then, if The trigger condition is met if the current SNR value of the mobile node is greater than SIR1. The set trigger condition must ensure that the trigger time caused by using this trigger condition is ahead of the time of link layer automatic switching, as shown in Figure 3, time 32 is the starting time for network layer switching in the prior art, time 31 It is the triggering moment of the network layer switching set in the present invention.

Steps 203-204: the mobile node judges whether the base station meeting the trigger condition belongs to the new subnet, if not, returns to step 201, and if so, sends a handover instruction to the network layer.

Here, the mobile node can determine whether the base station meeting the trigger condition belongs to the subnet where it is currently located by comparing the base station information. In this case, in step 201, the mobile node also obtains base station information of all currently discovered base stations at the same time; moreover, the mobile node also needs to periodically search, obtain and store all base station information of the subnet it is currently in. Wherein, the base station information refers to information that can identify the subnet to which each base station belongs, that is, identification information of which subnet the current base station belongs to, such as: base station ID, service set identifier (SSID) of the subnet to which the base station belongs, and the like. The time period of the regular search can be set arbitrarily according to the actual situation, for example: set according to the moving speed of the mobile node; if the time period is set to zero, real-time search will be performed.

Then, the judgment is: the mobile node matches the base station information of all base stations satisfying the trigger condition with the information of all base stations in the current subnet stored by the mobile node. If they can match, it means that none of the base stations satisfying the trigger condition Belong to the new subnet, then return to step 201, if they do not match, it means that there is a base station that meets the trigger condition and belongs to the new subnet, then the network layer handover is actively triggered, that is, a handover instruction is sent to the network layer.

The reason for further judging whether the base station that satisfies the trigger condition belongs to the new subnet, that is, the reason why it is necessary to combine the information of the base station to determine whether to perform network layer switching is because: if only relying on the selected physical layer channel information for triggering, there is It may only complete the handover between different base stations in the same subnet. That is to say, if the handover of the network layer is only triggered according to this trigger condition, it may cause many unnecessary handovers, which seriously affects network performance and consumes system resources. Therefore, it is determined in this step that the base station of the new wireless subnet appears before starting the network layer handover, otherwise the network layer handover will not be performed, thus reducing unnecessary handover.

There are many ways for a mobile node to obtain base station information, and the two commonly used ways are:

a) Because the definition of the registration message in the standard mobile IP protocol has extended domains, as shown in Table 1 and Table 2, Table 1 is the message format of the registration request message, and Table 2 is the message format of the registration response message. Therefore, the foreign agent The transfer of information about the base station to and from the mobile node can utilize the extended field of the registration message. 0 1 2 3 type S B D. m G R T x Lifetime Home Address Home Agent Care-of Address Description Extensions...

Table I 0 1 2 3 type Code Lifetime Home Address Home Agent Extensions...

Table II

In this case, the process for the mobile node to obtain the base station information in the current network is: the mobile node sends a registration request message to the agent of the current network, and the registration request carries an indication of requesting to transfer the information of all base stations in the current network. Placed in the extension field of the registration request message; after the agent of the network where the mobile node is currently located receives the registration request, it sends back a registration response message carrying information of all base stations in the current network to the mobile node. Similarly, all base station information is also placed in the registration response in the extension field of the message.

Then, the specific extension method of the registration message is: add an item in the extension field of the registration request message, and set a specific value for the item, representing the mobile node to request the foreign agent to transmit the information of the base station in the subnet, for example: set A type item, and define the type value as 39, as shown in Table 3. Of course, if a mobile node is in the home network, it can also send a registration request carrying a specific type of value to the home agent. 0 type

Table 3

Correspondingly, an item is added to the extension field of the registration response message to carry the information of all base stations in the current subnet, as shown in Table 4. 0 1 2 3 type Bytes quantity Flag information of base station 1 Flag information of base station 2 ... Flag information of base station n

Table 4

In Table 4, the type indicates that the registration response message carries base station information, and the type value is the same as that in the registration request message, for example: the type value is 39; the quantity indicates the number of base stations in the subnet; the number of bytes indicates a The number of bytes required for base station information is assumed to be four bytes in Table 4; the logo information of base station 1 to base station n is base station information, which can be the ID, MAC address, etc. of the base station, as long as it can uniquely identify a certain base station information is available.

In order to prevent the number of base stations in the current network from changing, for example: shutting down a base station, adding a new base station, etc., in addition to the regular update of the foreign agent, the mobile node can also periodically request the foreign agent to transmit the information of all base stations in the current subnet . Since the registration request in the standard mobile IP protocol is also sent periodically, the timing registration request can be directly used to request base station information regularly.

Once the mobile node enters a new foreign network, the base station information of the original foreign network will be replaced by the information of the new foreign network. But for the base station information of the home network, the mobile node must keep it all the time, because for the network layer, there is a difference between returning home and switching between different foreign networks.

b) Configure different SSIDs for adjacent wireless networks, for example: if network 1 is adjacent to network 2, configure the SSID of network 1 as Ssid1 and the SSID of network 2 as Ssid2. During the interaction process with the base station, the mobile node extracts the SSID of the subnet it belongs to from the message delivered by the base station.

Of course, in practical applications, the manners for the mobile node to acquire base station information are not limited to the above two methods.

Step 205: After the network layer receives the switching instruction from the lower layer, the system releases the current connection of a link, that is, disconnects the original connection of any link in the dual link, and the other link assumes the responsibility of the current subnet. All communications, while the broken link is used to establish a connection with the base station in the new wireless subnet.

Step 206: After the connection with the new base station is established, the mobile node registers with the home agent through the newly established connection, and performs network layer handover. Specifically, the mobile node establishes a connection with the agent in the new subnet and registers with the home agent. Here, if the mobile node enters a new foreign network, then the agent in the new subnet is the new foreign agent; if the mobile node returns to the home network, then the agent in the new subnet is the home agent.

Taking entering a new foreign network as an example, after the mobile node establishes a connection with the new foreign agent, it registers with the home agent through the new foreign agent. The registration process includes: first, the mobile node obtains a new handover from the new foreign agent. address, and then register with the home agent, and send the new care-of address to the home agent; after the home agent receives the registration of the new care-of address, it does not immediately delete the original care-of address, but keeps the two registrations bound, and will Every data packet sent to the mobile node is sent to each care-of address of the mobile node through the tunnel. In this case, the mobile node will receive duplicate data through the dual link, then the mobile node will filter a piece of duplicate data according to the processing method for duplicate data in the existing protocol.

Step 207: After the new link is formed stably and the registration of the mobile node is completed, the system releases the original connection of the other link, and connects between the mobile node and the base station of the new wireless subnet, and between the mobile node and the new wireless subnet Another link connection is established between the agents of the network, and then the normal communication process is resumed.

The handover of the mobile node can be divided into three situations: the mobile node moves from the home network to the foreign network, the mobile node moves between different foreign networks, and the mobile node returns to the home network from the foreign network.

When the mobile node leaves the home network for handover, it uses one link to register and another link to communicate during the handover process. As shown in FIG. 4 , link 40 is a link for maintaining the original connection to continue communication, and link 41 is a link for disconnecting the original connection and establishing a new connection with the foreign agent for registration. The handover process when the mobile node moves from the home network to the foreign network includes the following steps:

a1. When the mobile node moves out of the home network and enters a foreign network, the mobile node connects any one of the two links established by itself to the foreign network. When a new connection is established, the mobile node passes this connection Obtain the care-of address in the new network, for example: use the link 41 to obtain the care-of address.

b1. A tunnel is established between the mobile node and the foreign agent, and a registration request is sent to the home agent through the newly established link, that is, the mobile node registers with the home agent through links 41, paths 42, 43, and 44.

c1. After receiving the registration request, the home agent establishes a tunnel leading to the care-of address, sends a registration response, and sends an Agent Address Resolution Protocol (ARP) message. Here, the purpose of sending the ARP message is to indicate that the mobile node has left the home network, and all data packets sent to the mobile node will be received and forwarded by the home agent.

d1. After the mobile node receives the registration response from the home agent, indicating that the new connection has been formed stably, it disconnects the other link that maintains the original connection in the home network, reconnects to the foreign network, and completes the handover.

When the mobile node leaves a foreign network and enters another foreign network, the home agent adopts multiple binding methods during the handover process, that is, it stores two care-of addresses for the mobile node and binds two routes at the same time. Referring to Fig. 5, the handover process when the mobile node moves between different foreign networks includes the following steps:

a2. When the mobile node roams from foreign network 1 to foreign network 2, it disconnects one of the two links established with foreign network 1 and connects to foreign network 2. After a new connection is established, the mobile node The node obtains the care-of address in the new network through this connection.

b2. The mobile node establishes a tunnel after obtaining the care-of address, and sends a registration request to the home agent through the newly established link. It should be noted that: at this time, the registration request needs to set the "S" bit. The format of the registration request message stipulated in the standard mobile IP protocol is shown in Table 1, wherein, the S bit represents the binding information at the same time, if S is set, it means that the mobile node requires the home agent to retain its previous binding information.

c2. Since the mobile node has already registered a care-of address on the home agent, the home agent does not delete the original care-of address after receiving a new registration request, but just adds another one, and sends a registration response to the mobile node. Thereafter, the home agent sends each data packet received and sent to the mobile node to each care-of address of the mobile node through the tunnel.

d2. After receiving the registration response, the mobile node sends a deregistration request message from the original link.

e2. The home agent receives the deregistration request, deletes the original configured care-of address, and sends a registration response. Thereafter, the home agent forwards data only to the new care-of address.

f2. After receiving the registration response, the mobile node also disconnects the other link that maintains the original connection with the foreign network 1, reconnects to the foreign network, and completes the handover.

When the mobile node returns to the home network from the foreign network, the handover process adopts a link registration, and the other link continues to communicate through the foreign network. As shown in Figure 6, the handover process when the mobile node returns to the home network from the foreign network includes the following steps:

a3. When the mobile node returns to the home network from the foreign network, it disconnects one of the two links established with the foreign network and connects to the home network. When the new connection is established, the mobile node is in the home network Send a gratuitous ARP message and send a deregistration request to the home agent.

Here, the purpose of sending the ARP message is to inform the mobile node that it has returned to the home network.

b3. After receiving the deregistration request, the home agent deletes the care-of address and tunnel of the mobile node, and returns a registration response to the mobile node.

c3. After the mobile node receives the registration response sent by the home agent, it deletes the tunnel established with the foreign agent, and disconnects the other link that maintains the original connection in the foreign network, and reconnects to the home network. Complete the switch.

In FIG. 4 , FIG. 5 , and FIG. 6 , dotted lines represent one-way tunnels, solid lines represent registration messages, dotted lines represent normal communication data, and rectangles on solid lines represent tunnels.

Before the handover of the mobile node or after the handover is completed, if the mobile node is in a foreign network, the home agent only binds the care-of address of the network where the mobile node is located, so all data packets sent to the mobile node are forwarded to the on the care-of address. At this time, the two links established by the mobile node are in the same subnet and share a care-of address. Although there are two links, a virtual link layer can be used to make them use one IP address for communication, so that the upper layer application cannot realize the existence of dual links. In practical applications, the two links of the mobile node can be realized through two network cards respectively. From the perspective of the upper layer application of the mobile node, the mobile node has only one IP address, but the datagram it sends is transmitted through two links. of. When using which link to send, you can choose according to the busy or idle status of the link. For example, when you need to choose, first judge the busy or idle status of the two links, and use the link with the light load to send, so that both It can improve bandwidth and realize load balancing.

Referring to FIG. 7 and in conjunction with specific embodiments, the handover process of establishing a dual link and actively triggering network layer handover at the lower layer will be described in detail. FIG. 7 is a network topology diagram of the mobile IP system where the mobile node 70 is located. As shown in Figure 7, the mobile IP system is a wireless local area network using the 802.11 protocol, and the wireless local area network includes three subnets: home network, foreign network 1 and foreign network 2. The three subnets are connected by a router, and each subnet includes an agent, namely: home agent, foreign agent 1 and foreign agent 2. Each subnet includes two base stations, ie, access points AP1-AP6. The six dashed circles in FIG. 7 represent the coverage areas of AP1-AP6 respectively. Wherein, the access points AP1 and AP2 belong to the home network, the access points AP3 and AP4 belong to the foreign network 1 , and the access points AP5 and AP6 belong to the foreign network 2 . The dotted line in FIG. 7 represents the moving trajectory of the mobile node 70. It can be seen that the mobile node 70 starts from the home network, roams to the foreign network 1 first, and then roams from the foreign network 1 to the foreign network 2. The moving process includes three steps. Types of handover: handover from home network to foreign network, handover between two foreign networks, and handover from foreign network back to home network.

In this embodiment, the mobile node 70 selects two 802.11 wireless network cards to simulate dual links, and the network layer switching is actively triggered by the lower layer according to the detected physical channel information.

The mobile node 70 is initially located in the home network, and when the mobile node 70 moves to the overlapping coverage area 71 of AP2 and AP3, the second-layer trigger starts to notify the network layer that the mobile node 70 will move from the home network to the foreign network 1, triggering the network layer to start handover . At this time, the mobile node 70 disconnects one of the two links established with AP2, and establishes a connection with AP3; while the other link remains connected with AP2. After the link between the mobile node 70 and AP3 is established, the mobile node 70 obtains the care-of address 1 in the foreign network 1 through this connection; and establishes a tunnel according to the care-of address 1, and sends a registration request to the home agent through the link with AP3.

After the home agent receives the registration request, it sets up a tunnel leading to the care-of address 1, and sends a registration response to the mobile node 70, and sends a proxy ARP message at the same time; It is also disconnected, and the link is connected to AP3 as the second link between the mobile node 70 and AP3. In this way, the entire handover process from the home network to the foreign network 1 is completed.

Taking the signal-to-noise ratio as the selected physical layer channel information and the base station information as the MAC address of the AP as an example, the specific process of the two-layer trigger start is: the mobile node 70 enters the junction of the home network and the foreign network 1, that is, from the AP2 When moving into AP3, as the distance from AP3 gets closer, mobile node 70 will find that the signal-to-noise ratio of AP3 has met the set trigger condition, that is, reaches the preset signal-to-noise ratio threshold; at the same time, mobile node 70 searches and obtains The MAC address of AP3 compares the MAC address of AP3 with the MAC addresses of all APs in the current subnet that it currently saves. At this time, what the mobile node 70 itself saves is the MAC addresses of AP1 and AP2, so find the MAC address of AP3 If it does not match the MAC addresses of all the APs currently saved by itself, it can be determined that AP3 belongs to a new subnet, so the mobile node 70 actively triggers a network layer handover.

When the mobile node 70 moves to the overlapping coverage area 72 of AP4 and AP6 along the moving track, the layer 2 trigger starts, notifies the network layer that the mobile node 70 is about to enter a new foreign network, and triggers the network layer to start switching. Mobile node 70 disconnects a link connection in the two links established between AP4, and establishes connection with AP6, but still maintains a link and connects with AP4; Care-of address 2 in network 2. The mobile node 70 establishes a tunnel, and sends a registration request to the home agent through the link with AP6. At this time, the registration request needs to set the "S" bit. Here, if the signal-to-noise ratio is used as the selected physical layer channel information and the base station information is the MAC address of the AP, the specific process of the two-layer trigger start is similar to the handover from the mobile node 70 to AP3.

Although the mobile node 70 has registered a care-of address 1 on the home agent, the home agent does not delete the care-of address 1 after receiving a new registration request with the S bit set, but adds the care-of address 2 to the binding table, and send a Registration Reply to the mobile node 70. Thereafter, the home agent sends each data packet sent to the mobile node 70 to the two care-of addresses 1 and 2 through the tunnel. After receiving the registration response, the mobile node 70 sends a deregistration request to the home agent through the link with AP4. After receiving the deregistration request, the home agent deletes the care-of address 1, and returns a registration response to the mobile node 70, indicating that the care-of address 1 has been deleted. After that, the home agent only forwards data to care-of address 2. After receiving the registration response, the mobile node 70 disconnects the link with AP4, and inserts the link into AP6 as the second link between the mobile node 70 and AP6. The entire switching process from network 1 to foreign network 2.

When the mobile node 70 moves to the overlapping coverage area 73 of AP5 and AP2 along the moving track, the layer 2 trigger starts, notifies the network layer that the mobile node 70 will return to the home network from the foreign network 2, and triggers the network layer to start switching. At this time, the mobile node 70 disconnects one of the two links established with AP5, establishes a connection with AP2, and maintains the other link connection with AP6. Here, if the signal-to-noise ratio is used as the selected physical layer channel information and the base station information is the MAC address of the AP, the specific process of the two-layer trigger start is similar to the handover from the mobile node 70 to AP3.

After the link with AP2 is established, the mobile node 70 sends a free ARP message in the home network through the connection established with AP2, indicating that it has returned to its hometown, and sends a deregistration request. After receiving the deregistration request, the home agent deletes the care-of address 2 and the tunnel of the mobile node 70, and sends a registration response to the mobile node 70. After the mobile node 70 receives the registration response, it deletes the tunnel, disconnects the link connection with AP5, and connects to AP2 on the home network as the second link between the mobile node 70 and AP2. The entire switching process from the foreign network 2 back to the home network.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention.

Claims (13)

1, the method that mobile node realize to switch among a kind of mobile IP is characterized in that, sets up two for each mobile node and is connected with link that current sub network communicates, and this method is further comprising the steps of:

A. current mobile node detects the selected physical layer channel information of all base stations of current discovery;

B. judge that whether detected selected physical layer channel information satisfies the trigger condition of setting, if do not satisfy, then returns step a; If satisfy, judge again then whether current base station of satisfying trigger condition belongs to the current place of described mobile node subnet, if do not belong to, then send and switch indication to network layer; Otherwise return step a;

C. after network layer is received and switched indication, disconnect in two links having set up between current mobile node and the former subnet base station, and between current mobile node and the target BS that will switch to, set up a new link and be connected;

D. current mobile node is registered by chain road direction home agent newly-built among the step c, and carries out the network layer switching;

E. after registration is finished, disconnect current mobile node and be connected, and between current mobile node and the target BS that will switch to, set up another new link and be connected with another link between the former subnet base station.

2, method according to claim 1 is characterized in that, this method further comprises: current mobile node obtains and stores all base station informations of current subnet of living in, and obtains the base station information of current all base stations of finding in real time;

Judge described in the step b then whether current base station of satisfying trigger condition belongs to the current place of described mobile node subnet and be: current mobile node mates the base station information of all base stations of the base station information of current base station of satisfying trigger condition and self storage, if all do not match, the base station of then satisfying trigger condition does not belong to the current place of current mobile node subnet, otherwise belongs to the current place of current mobile node subnet.

3, method according to claim 1 is characterized in that, when mobile node switched to field network from home network, steps d is described carried out network layer and switch and specifically comprise:

D11. mobile node by with target BS between the link set up be connected and obtain new Care-of Address;

D12. mobile node is set up the tunnel, sends register requirement by newly-built chain road direction home agent;

D13. after home agent is received register requirement, set up and lead to the tunnel of this Care-of Address, send registration reply, and send Proxy Address Resolution Protocol ARP message;

Then the described registration of step e finish for: mobile node is received the registration reply that home agent is sent.

4, method according to claim 1 is characterized in that, when mobile node switched to another field network from a field network, steps d is described carried out network layer and switch and specifically comprise:

D21. mobile node by with target BS between the link set up be connected and obtain new Care-of Address;

D22. mobile node is set up the tunnel after obtaining Care-of Address, sends register requirement by newly-established chain road direction home agent, and carries the indication that keeps former Care-of Address in this register requirement;

D23. home agent keeps former Care-of Address after receiving new register requirement, stores the new Care-of Address that carries in the register requirement simultaneously, and sends registration reply to mobile node;

D24. after mobile node is received registration reply, send the cancel register request from the link that keeps between mobile node and the former base station;

D25. after home agent is received the cancel register request, delete former Care-of Address, and send registration reply to mobile node;

Then the described registration of step e is finished and is received home agent for: mobile node and delete the registration reply of sending behind the former Care-of Address.

5, method according to claim 1 is characterized in that, mobile node switches when going back home network from field network, and steps d is described carries out network layer and switch and specifically comprise:

D31. mobile node sends gratuitous ARP message in home network, and sends the cancel register request to home agent;

D32. after home agent is received the cancel register request, delete the Care-of Address and the tunnel of mobile node, and return registration reply to mobile node;

Then the tunnel of setting up between deletion and the Foreign Agent is finished to after: mobile node receives the registration reply that home agent sends in the described registration of step e.

According to each described method of claim 1 to 5, it is characterized in that 6, in handoff procedure, mobile node filters a repeating data according to existing protocol after receiving the repeating data that sends over from different links.

7, according to each described method of claim 1 to 5, it is characterized in that, before mobile node switches or switch finish after, two links that mobile node and current base station are set up are in the consolidated network, and a public Care-of Address.

8, method according to claim 1 and 2 is characterized in that, the triggered time that the trigger condition that sets causes is in advance in the time that physical layer automaticallyes switch.

9, method according to claim 1 and 2 is characterized in that, the trigger condition of described setting is the threshold value of selecting the physical layer channel information that will detect that sets in advance.

10, method according to claim 1 and 2 is characterized in that, described selected physical layer channel information is received signal intensity or is signal to noise ratio.

11, method according to claim 2 is characterized in that, described base station information is Base Station Identification ID or is the service set SSID of subnet under the base station or the MAC Address of base station.

12, method according to claim 2, it is characterized in that, all base station informations that described mobile node obtains current subnet of living in specifically comprise: mobile node sends login request message to the agency of current subnet of living in, and described registration information carries the indication of all base station informations of the described current subnet of living in of acquisition request; Receive that the agency of described register requirement returns the registration reply message of all base station informations that carry described current subnet of living in to the mobile node of initiating register requirement.

13, method according to claim 12 is characterized in that, the indication that described request is obtained all base station informations of current subnet of living in is positioned in the extension field of login request message; All base station informations of described current subnet of living in are positioned in the extension field of registration reply message.

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