CN100518376C - Method to speed up terminal switching - Google Patents

Abstract

The method comprises: in terminal switching process, the service network side sends the context session messages of its maintained terminals to the destination network side where said terminals will be switched into.

Description

Method to speed up terminal switching

technical field

The invention relates to the communication field, in particular to a method for accelerating terminal switching.

Background technique

IEEE (Institute of Electrical and Electronics Engineers) 802.16 defines the wireless metropolitan area network standard of BWA (Fixed Broadband Wireless Access). The standard defines different physical layer technologies for different frequency bands. The scope of application of the standard is mainly for the residential, small office/home office, teleworker and SME (small business users) markets.

IEEE 802.16MAC (Media Access Control Layer) has strong adaptability to the user environment, can cope with the application environment where there may be hundreds of users on each channel, and supports different business volumes such as continuous and burst . It has an ATM (Asynchronous Transfer Mode) convergence sublayer and a packet convergence sublayer. After being processed by the convergence sublayer, multiple high-level data units are encapsulated into a MAC PDU (Media Access Control Layer Protocol Data Unit) for transmission, which can realize Protocol transparency for ATM, IP (Internet Protocol) and Ethernet traffic.

The IEEE 802.16e air interface protocol can support the mobility of terminals. Due to the mobility of terminals and the diversity of connection relationships in the network structure, the handover scenarios of terminals have diverse characteristics. A schematic diagram of a switching process of a terminal in a centralized control mode is shown in FIG. 1 .

As shown in Figure 1, the switching process requires the following three steps:

1. The MS (Mobile Station) communicates with the serving BS (base station) through the air interface, and the serving BS communicates with the serving ASN-GW (Access Service Network Gateway) 1, and the ASN-GW. As a logical entity, it usually includes functional modules such as Authenticator (authenticator), mobile IP client, FA (foreign agent), PC (paging controller) and SFA (service flow authorization), corresponding to physical entities, these functions A logical entity may exist within one or more physical entities.

2. After the handover of the MS, the MS communicates with the target BS. When both the target BS and the serving BS communicate with the same ASN-GW1, only the R6 interface is migrated, and the R3 interface does not need to be migrated. When the target BS and the serving BS do not communicate with the same ASN-GW1, for example, the target BS communicates with the target ASN-GW2, the original R6 and R3 interfaces must be migrated.

3. After the handover of the MS is completed, the signaling interface with the core network is completely migrated to the target BS and the target ASN-GW.

A method of accelerating terminal handover in the prior art is as follows: According to the handover process given by the NWG (Network Working Group of Wimax Forum) standard draft, as shown in Figure 2, it includes the following steps:

Step 2-1. The MS periodically scans and measures neighboring BSs within the scanning interval, obtains the signal quality of the neighboring BSs, and performs initial search and synchronization with the neighboring BSs.

Step 2-2. When the terminal finds that the signal quality of the current serving BS is not as good as the signal quality of the adjacent BS, or the bit error rate of the signal currently received by the terminal is very high, the terminal sends MOB_MSHO_REQ (handover request message) to the serving BS to trigger handover process.

Step 2-3: After the serving BS receives the handover request message from the MS, the serving BS sends a HO_Request (handover request) message to the serving ASN-GW, requesting to obtain a list of target BSs.

Step 2-4, the serving ASN-GW judges whether the handover is cross-ASN-GW, if it is cross-ASN-GW, the serving ASN-GW will notify the target ASN-GW through the HO_Request message;

Step 2-5, the target ASN-GW sends a HO_Response (handover response) message to the serving ASN-GW, and the message carries a recommended target BS list.

Step 2-6: The serving ASN-GW sends the received HO_Response message to the serving BS.

Step 2-7, the serving BS sends a MOB_MSHO_RSP (terminal handover response) message to the MS, and the message carries a suggested target BS list.

Step 2-8, MS selects a target BS from the suggested target BS list sent by the serving BS, then starts the handover process, and sends a MOB_HO_IND (Mobile Terminal Handover Instruction) message to the serving BS, indicating that the handover starts, and the message will carry Information about the handover target BS finally selected by the MS.

Step 2-9, the serving BS sends the backbone network message HO_Indication (handover indication) to the ASN-GW, indicating that the MS is officially handing over, and at the same time sends a message to the target BS, notifying the target BS to be ready, and confirming the target BS, indicating that the terminal is finally This BS is selected as the target BS.

In step 2-10, the MS starts the network re-entry process. If the target BS does not obtain the relevant Session (session) information of the MS when the target BS receives the MS's network re-entry request, the target BS will communicate with the target ASN-GW through the session information request/response (session information request/response) message If the target ASN-GW does not obtain the information, the target ASN-GW will further request it through the serving ASN-GW or the serving BS.

Step 2-11. After the network reentry process is completed, the target BS starts to establish one or more data paths with the target ASN-GW for the MS; the target ASN-GW will also start to establish one or more data paths with the anchor ASN-GW. Multiple data paths for the MS.

In step 2-12, the anchor ASN-GW sends a data path establishment response message to the target ASN-GW, indicating that the service of the MS can now be forwarded to the new base station.

The disadvantage of the above method of accelerating terminal handover is: when the terminal re-enters the network with the target BS, if the target BS does not obtain the relevant session information of the MS, the target BS needs to actively request the information from the target ASN-GW. At the same time, the target ASN-GW may also request the information from the serving ASN-GW and the serving BS. This process will significantly slow down the handover process. At the same time, this method does not clearly describe the specific process of session information transmission.

Another method for accelerating terminal handover in the prior art is: when the target ASN-GW or the serving ASN-GW selects a target BS list for the terminal, send a handover pre-notification message carrying the above session information to the relevant neighboring BSs.

The disadvantage of the above-mentioned method for accelerating terminal handover is that the final choice of which target BS to perform handover is determined by the MS, and the serving BS is notified in the handover instruction message. Therefore, this method transmits the session information of the MS to neighboring BSs before that, and when these neighboring BSs are not finally selected as target BSs by the MS, this method not only wastes bandwidth resources, but also does not guarantee information transmission. pertinence. At the same time, the MS session information carried is incomplete, which is not enough to speed up a complete switching process.

Contents of the invention

In view of the above-mentioned problems in the prior art, the purpose of the present invention is to provide a method for accelerating terminal switching, so as to ensure the rapidity of the terminal switching process.

The purpose of the present invention is achieved through the following technical solutions:

A method of speeding up terminal switching, comprising:

A. After receiving the air interface handover request and/or handover indication message sent by the terminal, the serving base station BS transmits the session information of the terminal to the serving access service network gateway ASN-GW;

B. After the serving ASN-GW receives the session information of the terminal delivered by the serving BS, it judges whether the target BS and the serving BS belong to the same ASN-GW jurisdiction, and if so, directly transfers the session information of the terminal Forward it to the target BS; otherwise, pass the session information of the terminal to the target BS through the target ASN-GW.

The session information of the terminal includes:

The network access identifier NAI information of the terminal;

and / or,

IP address information of the terminal;

and / or,

The remaining life cycle information of the IP address of the terminal;

and / or,

MAC address information of the media access control layer of the terminal;

and / or,

The terminal's anchor service access service network gateway Anchor ASN GW information, including anchor paging controller, and/or anchor authenticator, and/or anchor agent mobile node, and/or anchor foreign agent, and/or anchor data Channel function body information;

and / or,

Terminal related service flow information, including service flow classifier, service flow quality of service parameters, service flow CID and data path information corresponding to the service flow;

and / or,

Terminal related R3 link information, including IP address of home agent, CoA, dynamic host configuration protocol server information, AAA server information and R3 link status information;

and / or,

Relevant security information of the terminal, including AK and AK context, and/or SAID, and/or TEK, and/or credential information between the proxy mobile node and the home agent;

and / or,

The mobile IP capability information of the terminal, the mobile IP capability information includes: IP version negotiation result, simple IP and mobile IP support capability negotiation result, multi-IP address capability support negotiation result, The negotiation result of the reverse tunnel service capability and/or the negotiation result of the route optimization capability.

Described step A specifically comprises:

After receiving the air interface handover request or handover indication message sent by the terminal, the serving BS sends the handover request or handover indication message carrying the session information of the terminal maintained by the serving BS to the serving ASN-GW.

The transfer of the session information of the terminal to the target BS through the target ASN-GW specifically includes:

The serving ASN-GW adds the session information it maintains in the received session information of the terminal delivered by the serving BS, and transfers the processed session information to the target ASN-GW;

After receiving the session information delivered by the serving ASN-GW, the target ASN-GW retains the session information maintained by it in the message, and transfers the remaining session information maintained by the target BS to the target BS. The method also includes:

C. After the serving BS receives the air interface switching instruction message sent by the terminal, the target BS also receives the access request message sent by the terminal. If the target BS has obtained the session information of the terminal, the session information obtained through the air interface management message will be Pass it to the terminal; otherwise, execute step D;

D. The target BS sends a request message to the target ASN-GW, obtains the session information of the terminal through the target ASN-GW, and transmits the obtained session information to the target BS.

Described step D specifically comprises:

D1. After the target ASN-GW receives the request message sent by the target BS, if the target ASN-GW has obtained the session information of the terminal, then transfer the session information to the target BS, otherwise, perform step D2;

D2. The target ASN-GW sends a request message to the serving ASN-GW. If the serving ASN-GW has obtained the session information of the terminal, it transmits the session information to the target ASN-GW, and the target ASN-GW keeps the information in the message that it maintains session information, transfer the remaining session information maintained by the target BS to the target BS; otherwise, perform step D3;

D3. The serving ASN-GW forwards the received request message to the serving BS, the serving BS transfers the session information of the terminal maintained by the serving BS to the serving ASN-GW, and the serving ASN-GW adds the session information maintained by it to the session information , transfer the processed session information to the target ASN-GW, the target ASN-GW retains the session information maintained by itself, and forwards the remaining session information maintained by the target BS to the target BS.

The method also includes:

When there is an interface between the serving BS and the target BS, the serving BS directly transfers the session information it maintains to the target BS through the interface, and the serving ASN-GW passes the session information it maintains through the interface between ASN-GW The target ASN-GW transfers the session information of the terminal that the target BS should know to the target BS after the target ASN-GW retains the information that should be saved.

The method also includes:

If the authenticator is located in the serving ASN-GW, the serving ASN-GW generates new key information for the terminal according to the information of the target BS and the information of the terminal before delivering the session information it maintains.

The method also includes:

If the authenticator is located in the anchor ASN-GW, the serving ASN-GW will notify the anchor ASN-GW to generate new key information for the terminal according to the information of the target BS and the information of the terminal before delivering the session information it maintains , transfer the key information to the target BS directly or indirectly.

The method also includes:

After the target BS and the target ASN-GW receive the session information of the terminal they should maintain, they update the session information according to their own policies and algorithms, and then, during the reentry process between the terminal and the target BS network, the updated The session information is passed to the terminal through the air interface message.

It can be seen from the above-mentioned technical solution provided by the present invention that the present invention clearly describes the transfer process of the MS session information during the terminal switching process, thereby ensuring the rapidity of the terminal switching process and the continuity of terminal services. The present invention also considers multiple scenarios, and defines a clear handover process, as well as the backbone network interaction process and related message formats involved in the handover process.

Description of drawings

FIG. 1 is a schematic diagram of a switching process of a terminal in a centralized control mode;

Fig. 2 is the handover flowchart given by the NWG standard draft in the prior art;

Fig. 3 is the specific processing flowchart of the implementation 1 of the method of the present invention;

Fig. 4 is a specific processing flowchart of implementation 2 of the method of the present invention.

Detailed ways

The present invention provides a method for accelerating terminal switching. The core of the present invention is: during the terminal switching process, the service network side transmits the context session information of the terminal maintained by it to the target network side for the terminal switching. Specifically, after the terminal sends a MOB_HO_IND message to the serving BS to indicate that the handover officially starts, the serving BS will transfer the session information of the MS to the target BS selected during the handover.

Describe the present invention in detail below in conjunction with accompanying drawing, the present invention provides 3 embodiments of the method of the present invention, wherein the specific processing flow of embodiment 1 is as shown in Figure 3, comprises the following steps:

Step 3-1: After receiving the MOB_HO_IND message sent by the terminal, the serving BS sends a handover indication message carrying the session information of the MS to the serving ASN-GW.

The present invention mainly improves the flow shown in FIG. 2 . After the serving BS receives the MOB_HO_IND message sent by the terminal, the serving BS obtains the session information of the MS. The main content of the session information is as follows:

1. NAI (Network Access Identity) information of the MS;

2. The MAC address information of the MS, and the home IP address information obtained by the MS, the remaining life cycle information of the IP address can be included in the process;

3. Anchor ASN GW (Anchor Service Access Service Network Gateway) information of MS, including Anchor PC (Anchor Paging Controller), Anchor Authenticator (Anchor Authenticator), AnchorFA (Anchor External Agent Information) and Anchor Data Path Function (anchor data channel function body);

4. MS-related service flow information: including SFID (service flow classifier), service flow QOS (quality of service) parameters, CID (connection identifier), and corresponding data path information, such as Data path (data path) type, data path ID, etc.;

5. MS-related R3 link information: including IP address of HA (home agent), CoA (care-of address), DHCP (Dynamic Host Configuration Protocol) server, AAA (Authentication Authentication Authorization) server, R3 link status ( normal, disconnected) information;

6. MS-related security information: including AK (Authentication Key) and AK context, SAID (Security Association Identity), TEK (Service Encryption Key), and the certificate of trust between the agent mobile node and HA .

7. The content of the mobile IP capability information negotiated by the MS before. The mobile IP capability information includes the IP version negotiation results, the negotiation results of simple IP and mobile IP support capabilities, the negotiation results of supporting multiple IP addresses, and the support of multiple mobile IP addresses. One or more of the negotiation result of registration capability, the negotiation result of supporting reverse tunnel service capability, and the negotiation result of supporting route optimization capability.

According to the content and process of the present invention, the above MS context transfer process may occur in the handover execution stage, that is, after the serving BS receives the MS's air interface handover instruction message, it may also occur in the handover request process and handover preparation process. The following takes the transfer process occurring in the handover execution stage as an example for illustration.

In terms of specific implementation, the message element: MS Session Information can be added to the handover indication message transmitted on the backbone network defined in the current protocol draft. The MS Session Information includes Session information, as shown in Table 1. (type length value) is stored in MS Session Information.

Table 1:

Primitives From->To Message Content HO Indication ASN GW-＞ASN GWBS-＞ASN GWASN-GW-＞BS MS ID, Target BS ID, MS Session Information

Some of the session information of the above MS is maintained by the BS, and some are maintained by the ASN-GW.

The serving BS then sends the HO_Indication message carrying the obtained MS session information to the serving ASN-GW. The MS session information carried includes the MS session information maintained and known by the serving BS, such as the MS's NAI, MAC address, and IP address And the CID, SFID, SAID, TEK and other information related to the air interface service flow.

Step 3-2, whether the target BS and the serving BS belong to the jurisdiction of the same ASN-GW.

After the serving ASN-GW receives the HO_Indication message carrying the session information of the MS sent by the serving BS, it judges whether the target BS and the serving BS belong to the same ASN-GW jurisdiction. If yes, perform steps 3-4; otherwise, perform steps 3-3.

Step 3-3: The serving ASN-GW sends a handover indication message carrying the session information of the MS to the target ASN-GW.

If the target BS and the serving BS are not under the jurisdiction of the same ASN-GW, the serving ASN-GW will send a HO_Indication message to the target ASN-GW. In addition to carrying the session information delivered by the serving BS, the HO_Indication message will also carry The session information of the MS maintained by the serving ASN-GW. The session information of the MS maintained by the serving ASN-GW is as follows:

1. Information about the Anchor ASN-GW of the MS retained by the service ASN-GW, including Anchor PC, Anchor Authenticator, Anchor FA and other information;

2. MS-related R3 link information, including HA's IP address, CoA, DHCP server and AAA server information, and R3 link status information (normal, disconnected) and other information;

3. MS-related security information, such as AK and AK context information, including the credential information between the agent mobile node and HA; because according to the IEEE 802.16e protocol definition, the terminal switches to a different BS, AK and AK context need Regenerated, so this part of information needs to be regenerated by the Authenticator in the serving ASN-GW and passed to the target BS as part of the session information; if the serving ASN-GW and Anchor ASN-GW are not the same physical entity during the handover process, then The serving ASN-GW needs to notify the Anchor ASN-GW where the Authenticator that maintains the key information of the MS is located to regenerate and send it to the target BS;

4. MS-related service flow information, including SFID, service flow classifier, service flow QOS parameters, CID, and corresponding data path information, such as Data path type, data path ID, etc.

Execute steps 3-5.

Step 3-4: The serving ASN-GW forwards the received HO_Indication message to the target BS.

If the target BS and the serving BS belong to the same ASN-GW jurisdiction, the serving ASN-GW directly forwards the handover indication message carrying the session information of the MS sent by the serving BS to the target BS. During the forwarding process, operations such as addition and deletion are not performed on the session message carried in the handover indication message.

Step 3-5: The target ASN-GW sends a handover indication message carrying the session information of the MS to the target BS.

After the target ASN-GW receives the handover indication information sent by the serving ASN-GW, it retains the session information maintained by itself in the message, and partially updates the parameters of the retained session information according to its own local policy, and then sends the message to the target BS A handover instruction message carrying the MS session information that the remaining target BS should maintain.

After receiving the handover indication message sent by the target ASN-GW, the target BS retains the session information maintained by itself in the message, such as RNG_RSP, SBC_RSP, and REG-RSP messages. Because the value of the CID and SAID in the session information may be repeated in different BSs, the target BS needs to properly update the reserved session information according to its own actual situation.

Then, when the terminal re-enters the network with the target BS, the target BS transmits the reserved session information to the terminal through an air interface management message, thereby ensuring normal communication between the terminal and the base station.

The session information of the MS maintained by the BS and ASN-GW described in this embodiment, if the logical functions of the BS and the ASN-GW are placed in the same physical entity when implemented, then the above-mentioned MS session information The session information is maintained by the same physical entity, so the transfer process of the above MS session information is attributed to the transfer between the BS or the ASN-GW.

The MS session information maintained by the BS and ASN-GW described in this embodiment, if the logical function mapping of the BS and ASN-GW is changed when the logical functions are implemented, then the above-mentioned BS and ASN-GW The MS session information maintained by the GW also changes accordingly.

The specific processing flow of embodiment 2 of the method of the present invention is as shown in Figure 4, comprises the following steps:

Step 4-1. The serving base station BS receives the air interface switching indication message sent by the terminal, and the target BS receives the access request message sent by the terminal.

When the serving base station BS receives the air interface switching instruction message sent by the terminal, the terminal quickly performs an access request operation with the target BS, and then sends an access request message to the target BS.

Step 4-2, the target BS judges whether the session information of the terminal has been obtained.

After receiving the access request message sent by the terminal, the target BS judges whether it has obtained the session information of the terminal, and if so, executes step 4-4; otherwise, executes step 4-3.

Step 4-3, the target BS sends the MS session information request message to the target ASN-GW.

If the target BS has not obtained the session information of the terminal, the target BS actively asks the target ASN-GW for the session information of the MS, and sends a MS-Session-information-Request (MS session information request) message to the target ASN-GW.

Execute steps 4-5.

In step 4-4, the target BS transmits the reserved session information to the terminal through an air interface management message.

If the target BS has obtained the session information of the terminal, the target BS transfers the reserved session information to the terminal through an air interface management message.

Step 4-5: The target ASN-GW sends the obtained session information of the MS to the target BS.

After the target ASN-GW receives the MS-Session-information-Request message, it judges whether it has obtained the session information of the MS, and if it has obtained it, returns to the target BS the MS-Session-information-Reposnse (MS session information response) message.

If the target ASN-GW has not obtained the session information of the MS, it forwards the MS-Session-information-Request message to the serving ASN-GW, and the serving ASN-GW judges whether it has obtained the session information of the MS, and if so, sends The target ASN-GW returns an MS-Session-information-Response message carrying the learned session information of the MS.

If the serving ASN-GW has not obtained the session information of the MS, the serving ASN-GW forwards the received MS-Session-information-Request message to the serving BS. After receiving the message, the serving BS responds to the serving ASN-GW with a MS-Session-information-Response message, which carries the session information of the MS well-known by the serving BS. After receiving the message, the serving ASN-GW further adds the above-mentioned session information belonging to the MS it maintains to the obtained MS session information,

The serving ASN-GW forwards the processed MS-Session-information-Response message to the target ASN-GW. After the target ASN-GW receives the MS-Session-information-Response message, it retains the session information it should manage and maintain, and partially updates the parameters of the reserved session information according to its own local policy, and then contains the remaining The MS-Session-information-Response message of the session information that the target BS should maintain is forwarded to the target BS.

After receiving the handover indication message sent by the target ASN-GW, the target BS retains the session information maintained by itself in the message, such as RNG_RSP, SBC_RSP, and REG-RSP messages. Because the value of the CID and SAID in the session information may be repeated in different BSs, the target BS needs to properly update the reserved session information according to its own actual situation.

Then, the target BS transmits the reserved session information to the terminal through an air interface management message, thereby ensuring normal communication between the terminal and the base station.

The specific processing flow of Embodiment 3 of the method of the present invention is as follows: after the serving BS receives the MOB_HO_IND message sent by the terminal, when there is an interface between the serving BS and the target BS, the serving BS sends the session of the MS maintained by it to The information is directly transmitted to the target BS through this interface, and the serving ASN-GW transmits the session information of the MS maintained by it to the target ASN-GW through the interface between the ASN-GWs. After the target ASN-GW retains the information that should be saved, Then the session information of the MS that the target BS should know is delivered to the target BS.

In the processing flow of Embodiment 1, Embodiment 2, and Embodiment 3 above, if the authenticator is located in the serving ASN-GW, the serving ASN-GW will, according to the information of the target BS and the Terminal information, to generate new key information for the terminal.

If the authenticator is located in the anchor ASN-GW, the serving ASN-GW will notify the anchor ASN-GW to generate new key information for the terminal according to the information of the target BS and the information of the terminal before delivering the session information it maintains , transfer the key information to the target BS directly or indirectly.

According to the process described in the present invention above, before or after the terminal switches to the target BS and sends an access request to the target BS, the target BS can obtain the relevant session information of the MS, thereby ensuring the continuity of terminal services and the terminal switching process the rapidity.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present invention can easily think of changes or Replacement should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (10)

1. A method for speeding up terminal switching, comprising: A. After receiving the air interface handover request and/or handover indication message sent by the terminal, the serving base station BS transmits the session information of the terminal to the serving access service network gateway ASN-GW; B. After the serving ASN-GW receives the session information of the terminal delivered by the serving BS, it judges whether the target BS and the serving BS belong to the same ASN-GW jurisdiction, and if so, directly transfers the session information of the terminal Forward it to the target BS; otherwise, pass the session information of the terminal to the target BS through the target ASN-GW. 2. The method according to claim 1, wherein the session information of the terminal includes: The network access identifier NAI information of the terminal; and / or, IP address information of the terminal; and / or, The remaining life cycle information of the IP address of the terminal; and / or, MAC address information of the media access control layer of the terminal; and / or, The terminal's anchor service access service network gateway Anchor ASN GW information, including anchor paging controller, and/or anchor authenticator, and/or anchor agent mobile node, and/or anchor foreign agent, and/or anchor data Channel function body information; and / or, Terminal related service flow information, including service flow classifier, service flow quality of service parameters, service flow CID and data path information corresponding to the service flow; and / or, Terminal related R3 link information, including IP address of home agent, CoA, dynamic host configuration protocol server information, AAA server information and R3 link status information; and / or, Relevant security information of the terminal, including AK and AK context, and/or SAID, and/or TEK, and/or credential information between the proxy mobile node and the home agent; and / or, The mobile IP capability information of the terminal, the mobile IP capability information includes: IP version negotiation result, simple IP and mobile IP support capability negotiation result, multi-IP address capability support negotiation result, The negotiation result of the reverse tunnel service capability and/or the negotiation result of the route optimization capability. 3. The method according to claim 1, wherein said step A specifically comprises: After receiving the air interface handover request or handover indication message sent by the terminal, the serving BS sends the handover request or handover indication message carrying the session information of the terminal maintained by the serving BS to the serving ASN-GW. 4. The method according to claim 1, 2 or 3, wherein the transfer of the session information of the terminal to the target BS through the target ASN-GW specifically includes: The serving ASN-GW adds the session information it maintains in the received session information of the terminal delivered by the serving BS, and transfers the processed session information to the target ASN-GW; After receiving the session information delivered by the serving ASN-GW, the target ASN-GW retains the session information maintained by it in the message, and transfers the remaining session information maintained by the target BS to the target BS. 5. The method according to claim 1, further comprising: C. After the serving BS receives the air interface switching indication message sent by the terminal, the target BS also receives the access request message sent by the terminal. If the target BS has obtained the session information of the terminal, the session information obtained through the air interface management message will be Pass it to the terminal; otherwise, execute step D; D. The target BS sends a request message to the target ASN-GW, obtains the session information of the terminal through the target ASN-GW, and transmits the obtained session information to the target BS. 6. The method according to claim 5, wherein said step D specifically comprises: D1. After the target ASN-GW receives the request message sent by the target BS, if the target ASN-GW has obtained the session information of the terminal, then transfer the session information to the target BS, otherwise, perform step D2; D2. The target ASN-GW sends a request message to the serving ASN-GW. If the serving ASN-GW has obtained the session information of the terminal, it transmits the session information to the target ASN-GW, and the target ASN-GW keeps the information in the message that it maintains session information, transfer the remaining session information maintained by the target BS to the target BS; otherwise, perform step D3; D3. The serving ASN-GW forwards the received request message to the serving BS, the serving BS transfers the session information of the terminal maintained by the serving BS to the serving ASN-GW, and the serving ASN-GW adds the session information maintained by it to the session information , transfer the processed session information to the target ASN-GW, the target ASN-GW retains the session information maintained by itself, and forwards the remaining session information maintained by the target BS to the target BS. 7. The method according to claim 1, further comprising: When there is an interface between the serving BS and the target BS, the serving BS directly transfers the session information it maintains to the target BS through the interface, and the serving ASN-GW passes the session information it maintains through the interface between ASN-GW The target ASN-GW transfers the session information of the terminal that the target BS should know to the target BS after the target ASN-GW retains the information that should be saved. 8. The method according to claim 1, further comprising: If the authenticator is located in the serving ASN-GW, the serving ASN-GW generates new key information for the terminal according to the information of the target BS and the information of the terminal before delivering the session information it maintains. 9. The method according to claim 1, further comprising: If the authenticator is located in the anchor ASN-GW, the serving ASN-GW will notify the anchor ASN-GW to generate new key information for the terminal according to the information of the target BS and the information of the terminal before delivering the session information it maintains , transfer the key information to the target BS directly or indirectly. 10. The method according to claim 1, further comprising: After the target BS and the target ASN-GW receive the session information of the terminal they should maintain, they update the session information according to their own policies and algorithms, and then, during the reentry process between the terminal and the target BS network, the updated The session information is passed to the terminal through the air interface message.

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