WO2011026391A1 - Load reallocation method for serving gateway, system and serving gateway - Google Patents

Abstract

A load reallocation method for serving gateway is disclosed in the present invention, and the method includes: a Serving Gateway(SGW) sends a load reallocation indication message to a mobility management unit when load reallocation is required; and the mobility management unit chooses other serving gateway than the said serving gateway as a new serving gateway, and transfers part or the whole of users on the said serving gateway to the chosen new gateway. The corresponding system, serving gateways and mobility management unit are also disclosed in the present invention. With the present invention, part or the whole of users on the serving gateway can be transferred to a new SGW, and load reallocation for SGW can be realized so that the SGW is able to achieve the goal of load balance.

Description

 Service redistribution method, system and service gateway of service gateway

Technical field

 The present invention relates to the field of communications, and in particular, to a load redistribution method, system, and service gateway of a service gateway.

Background technique

 With the emergence of the World Interoperability for Microwave Access (WiMax) technology, the third generation of mobile communication systems must maintain their competitiveness in the field of mobile communications, and must improve their network performance and reduce network construction and operation. cost. Therefore, the Standardization Working Group of the 3rd Generation Partnership Project (3GPP) is currently working on the Packet Switch Core (PS Core) and the Global Mobile Telecommunications System Wireless Access Network (Universal Mobile). Evolution of the Telecommunication System Radio Access Network, UTRAN. The research topic is called System Architecture Evolution (SAE). The purpose is to enable Evolved Packet Core (EPC) to provide higher transmission rate, shorter transmission delay, and optimized packetization. And mobility management between evolved UTRAN (Evolved UTRAN, E-UTRAN), UTRAN, Wireless Local Area Network (WLAN) and other non-3GPP access networks.

 The current SAE architecture is shown in Figure 1, where the evolved radio access network (Evolved Radio)

The network element included in the Access Network (E-RAN for short) is an Evolved NodeB (eNodeB), which is used to provide radio resources for user access; Packet Data Network (PDN) It is a network that provides services to users; EPC provides lower latency and allows more wireless access systems to access, including the following network elements:

The Mobility Management Entity (MME) is a control plane function entity that temporarily stores user data. It is responsible for managing and storing the context of user equipment (User Equipment, UE for short) (such as user identity, mobility management status, and user). a security parameter, etc.), assigning a temporary identifier to the user, and when the UE is camped on the tracking area or the network, is responsible for authenticating the user; processing all non-access stratum messages between the MME and the UE; Page of SAE. The MME is a mobility management entity of the SAE system. In the Universal Mobile Telecommunications System (UMTS), the mobility management entity is a serving general packet radio service (GPRS) support node (Serving GPRS Support Node). , referred to as SGSN).

 The Serving Gateway (SGW) is a user plane entity responsible for user plane data routing processing and terminating downlink data of UEs in idle (ECM_IDLE) state. Manage and store the SAE bearer context of the UE, such as IP bearer service parameters and network internal routing information. The SGW is the anchor point of the internal user plane of the 3GPP system. A user can only have one SGW at a time.

 The Packet Data Network Gateway (PDN Gateway, PGW for short) is the gateway responsible for the UE accessing the PDN, and assigns the user IP address. It is also the mobility anchor of the 3GPP and non-3GPP access systems. The PGW functions include policy implementation and accounting. stand by. Users can access multiple PGWs at the same time. The Policy and Charging Enforcement Function (PCEF) is also located in the PGW.

 Policy and Charging Rules Function (referred to as Policy and Charging Rules Function)

PCRF), responsible for providing policy control and charging rules to PCEF.

 The Home Subscriber Server (HSS) is responsible for permanently storing user subscription data. The content stored in the HSS includes the International Mobile Subscriber Identification (IMSSI) of the UE and the IP address of the PGW.

 Physically, the SGW and the PGW may be unified, and the EPC system user plane network element includes the SGW and

PGW.

In an actual network, the load of the SGW is basically balanced. However, when the SGW needs to be upgraded, some or all users of the SGW that are being upgraded and upgraded are migrated to other SGWs to ensure continuity of user services. When a new SGW is added, the newly added SGW needs to be able to quickly reach a certain load state. In this case, some users of other SGWs in the network need to be migrated to the newly added SGW. However, there is currently no processing mechanism for implementing user migration on the SGW. Summary of the invention

 The technical problem to be solved by the present invention is to provide a load redistribution method and system for a service gateway, which implements migration of some or all users on the SGW.

 In order to solve the above problem, the present invention provides a load redistribution method for a service gateway, including:

 The serving gateway sends a load reassignment indication message to the mobility management unit when load redistribution is required;

 The mobility management unit selects other service gateways other than the serving gateway as a new service gateway, and migrates some or all of the users on the serving gateway to the selected new serving gateway.

 The service gateway needs to perform load re-allocation: the service gateway needs to migrate the user when maintaining or upgrading, or knowing that the service gateway is newly added in the network;

 When the mobility management unit selects the new serving gateway, the mobility management unit selects a lower-loaded gateway or the newly added serving gateway among the other service gateways in the network.

 Before the load re-allocation indication message is sent to the mobility management unit, the serving gateway carries the number of users to be migrated in the load re-distribution indication message;

 In the migrating step, the mobility management unit selects a corresponding number of users to migrate to the new serving gateway according to the number of users. The migration is performed according to the state of the user; the user in the idle state is directly migrated to the new service gateway; and the user in the connected state is first transitioned from the connected state to the idle state, and then migrated to the On the new service gateway.

 The mobility management unit preferentially selects the user in the idle state when selecting the corresponding number of users for migration.

The step of the mobility management unit converting the user in the connection state to the idle state includes: the mobility management unit sending a user context release instruction message to the base station of the user, where the user context release instruction message carries a specific cause value , redistributing the service gateway load to indicate the release reason; Sending, by the base station, a radio resource connection release request message to the user, where the radio resource connection release request message carries the specific cause value;

 After the user completes the release of the user context according to the radio resource connection release request message, the user transitions from the connected state to the idle state.

 The method also includes the step of reconverting the user transitioning to an idle state to a connected state,

 The step of re-converting the user transitioning to the idle state to the connected state includes: reinitiating an indication of the tracking area update request;

 And the base station includes, in the sent radio resource connection release request message, an indication that the user re-initiates a tracking area update request;

 And the user sends a tracking area update request to the mobility management entity according to the indication; and after the mobile management entity receives the tracking area update request, if the user is confirmed to be valid in the current tracking area, the user is Send tracking area update accept message.

 The method also includes the step of reconverting the user transitioning to an idle state to a connected state,

 The step of re-converting the user that is converted to the idle state to the connected state includes: the mobility management entity initiating a paging message to a base station in the tracking area list to which the user belongs;

 The base station in the tracking area list initiates a paging message to the user; after receiving the paging message, the user sends a service request message to the mobility management entity;

 The mobility management entity sends an initial context setup request message to the base station; the base station sends a radio bearer setup request message to the user;

 The user establishes a radio bearer according to the radio bearer setup request message, and returns a radio bearer setup response message to the base station.

 The method further includes:

After the user migrates to the new serving gateway, the new serving gateway sends packet data The network gateway sends a modify bearer request message;

 And after the packet data network gateway updates the context of the user according to the received modify bearer request message, sending a modify bearer response to the new serving gateway.

 In addition, the present invention further provides a load redistribution system of a service gateway, including a service gateway and a mobility management unit, the service gateway includes a load redistribution indication module, and the mobility management unit includes a load redistribution execution module, The load redistribution execution module includes a gateway selection unit and a user migration unit, where:

 The load redistribution indication module is configured to: send a load reassignment indication message to the gateway selection unit and the user migration unit when the service gateway needs to maintain the upgrade, or if the service gateway is newly added in the network;

 The gateway selection unit is configured to: after receiving the load re-distribution indication message, select to send another service gateway other than the load re-allocation indication message as a new service gateway;

 The user migration unit is configured to: after receiving the load reassignment indication message, select some or all users on the serving gateway, and migrate the selected user to a new service gateway selected by the gateway selection unit. on.

 The load re-allocation indication module is further configured to: carry the number of users that need to be migrated in the load re-distribution indication message;

 The user migration unit is configured to: select a corresponding number of users on the service gateway according to the number of users, and migrate the selected user to the new service gateway.

 The gateway selection unit is configured to: when selecting the new service gateway, select a gateway with a lower load in the network or a new service gateway in the network.

 The user migration unit is configured to: when migrating the user to the new service gateway, perform migration according to the state of the user as follows: for the user in the idle state, directly migrate to the new On the service gateway, for the user in the connection state, after the connection state is changed to the idle state, the user in the connection state is migrated to the new service gateway.

 The user migration unit is configured to: preferentially select a user in an idle state when selecting a corresponding number of users for migration.

The service gateway further includes a context update module; The context update module is configured to: after the user on the other gateway migrates to the serving gateway, send a modify bearer request message to the packet data network gateway, requesting the packet data network gateway to update the context of the user.

 A service gateway, where the service gateway includes a load redistribution indication module,

 The load redistribution indication module is configured to: send a load reassignment indication message to the gateway selection unit and the user migration unit when the service gateway needs to maintain the upgrade, or if the service gateway is newly added in the network;

 The gateway selection unit and the user migration unit belong to a load re-allocation execution module of the mobility management unit; after receiving the load re-distribution indication message, the gateway selection unit selects to send other services than the load re-allocation indication message. The gateway serves as a new service gateway. After receiving the load re-distribution indication message, the user migration unit selects some or all users on the service gateway, and migrates the selected user to the gateway selection unit. On the new service gateway.

 The load re-allocation indication module is further configured to: carry the number of users that need to be migrated in the load re-distribution indication message;

 The user migration unit selects a corresponding number of users on the service gateway according to the number of users, and migrates the selected user to the new service gateway.

 The service gateway further includes a context update module;

 The context update module is configured to: after the user on the other gateway migrates to the service gateway, send a modify bearer request message to the packet data network gateway, requesting the packet data network gateway to update the context of the user.

 A mobility management unit, the mobility management unit includes a load redistribution execution module, and the load redistribution execution module includes a gateway selection unit and a user migration unit, where:

The gateway selection unit is configured to: after receiving the load re-allocation indication message, select to send another service gateway other than the load re-allocation indication message as a new serving gateway; the load re-allocation indication message is heavy by the load The allocation indication module sends to the gateway selection unit and the user migration unit when the service gateway needs to maintain the upgrade, or learns to newly add the service gateway in the network; the user migration unit is configured to: receive the load redistribution After indicating the message, selecting some or all users on the service gateway, and migrating the selected user to the gateway selection list The yuan is selected on the new service gateway.

 The user migration unit is configured to: select a corresponding number of users on the service gateway according to the number of users, and migrate the selected user to the new service gateway; the load redistribution indication module is The load redistribution indication message carries the number of users that need to be migrated.

 The gateway selection unit is configured to: when selecting the new service gateway, select a gateway with a lower load in the network or a new service gateway in the network.

 The user migration unit is configured to: when migrating the user to the new service gateway, perform migration according to the state of the user as follows: for the user in the idle state, directly migrate to the new On the service gateway, for the user in the connection state, after the connection state is changed to the idle state, the user in the connection state is migrated to the new service gateway.

 The user migration unit is configured to: preferentially select a user in an idle state when selecting a corresponding number of users for migration.

With the above implementation, some or all users on the SGW can be migrated to the new SGW, which can implement load redistribution of the SGW and achieve the purpose of load balancing. BRIEF abstract

 1 is a schematic structural diagram of a SAE in the prior art;

 2 is a flowchart of migrating a user in an embodiment of the present invention;

 3 is a flowchart of migrating an idle state user in an embodiment of the present invention;

 4 is a flowchart of changing a user state in an embodiment of the present invention;

 FIG. 5 is a flowchart of a user in a migration connection state according to an embodiment of the present invention; FIG.

 6 is a flowchart of a user in a migration connection state according to another embodiment of the present invention;

 FIG. 7 is a structural block diagram of a load redistribution system of a service gateway according to an embodiment of the present invention.

Preferred embodiment of the invention

The invention provides a load redistribution method for a service gateway, and adopts the following technical solutions: If the SGW needs to perform load redistribution because of maintenance upgrade or other reasons (such as when the system newly adds the SGW), the mobile management unit is notified that the mobile management unit needs to migrate the user, and the mobility management unit selects the user to perform the migration;

 The mobility management unit selects a new SGW, sends a session establishment request message to the selected new SGW, and migrates the UE to the new SGW;

 After the migration of the UE is completed, the user context is updated between the new SGW and the PGW. The mobile management unit stores the current state of the user, and the user selected by the mobility management unit may be an idle state user or a connected state user. For the UE in the idle state, the mobility management unit directly migrates to the new SGW; for the UE in the connected state, it needs to be released by the mobility management unit to make it idle, and then the UE in the idle state. Perform the migration.

 Further, the mobility management unit performs migration according to other SGWs with lower load in the load state network of the SGW in the network, and when the SGW is newly added in the network, the mobility management unit migrates some users on the original SGW to the newly added SGW.

 Further, the mobility management unit sends the SI of the specific cause value (the interface between the MME and the eNodeB is an S1-MME, collectively referred to as an S1 interface) /Iu (the interface of the RNC to the SGSN) Release procedure, and changes the UE from the connected state to In the idle state, the cause value may be "SGW load balancing Tracking Area Update (TAU) / Routing Area Update (RAU) request (required),,".

 Further, the mobility management unit includes: an MME, an SGSN, and the like.

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clearly, the implementation of the technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

 The method for migrating a user in the embodiment of the present invention, as shown in FIG. 2, mainly includes the following steps: Step 201: The SGW sends a load re-allocation indication message to the mobility management unit to notify the mobility management unit to migrate the user because of maintenance upgrade or other reasons. The number of migrated users can be carried in the message;

The load re-allocation indication message may be carried by using an existing message, such as a bearer update. Equivalent; a separate indication message can also be used.

 Step 202: The mobility management unit selects a corresponding number of users to perform migration, selects a new SGW for the user, and migrates the user to the new SGW.

 In this embodiment, the mobility management unit randomly selects a specified number of users for migration according to the load reassignment message, and the migrated user may include both an idle state user and a connection state user. For idle state users, the mobility management unit can directly migrate it to the new SGW; for the connection state user, the mobility management unit first releases its wireless resources, turns the user into an idle state, and then migrates it to the new SGW. on.

FIG. 3 shows a flow of service gateway load redistribution in the embodiment of the present invention. As shown in FIG. 3, the method mainly includes the following steps:

 Step 301: The SGW1 sends a load re-allocation indication message to the mobility management unit (such as the MME), and the indication message may carry the number of users that need to be migrated.

 Step 302: The MME selects a user in an idle state to perform migration.

 In this embodiment, the MME preferentially selects the user in the idle state to perform migration.

 Step 303: The MME selects a new SGW (SGW2) for the UE, and sends a session establishment request message to the new SGW, requesting to migrate the UE to the new SGW, where the request message carries the control plane address and tunnel of the IMSL MME. Endpoint Identifier (TEID), Bearer ID, and Quality of Service (Bearer QoS). Step 304: The new SGW sends a modify bearer request message to the PGW, requesting to update the context, and carrying the request message. Control plane address and TEID of the new SGW, bearer ID, downlink user plane address and TEID of the new SGW;

 Step 305: The PGW returns a modify bearer response message to the new SGW.

 Step 306, the new SGW returns a session establishment response message to the MME, where the message carries the control plane address and TEID of the new SGW;

Step 307: The MME sends a release session request to the original SGW (SGW1), and the original SGW releases the context of the UE. Step 308, the original SGW returns a release session response to the MME.

 It should be noted that this embodiment is also applicable to the case where the UE accesses the SGSN.

FIG. 4 shows a process in which the MME needs to change the user state and change the UE from the connected state to the idle state in the embodiment of the present invention. As shown in FIG. 4, the method includes the following steps:

 Step 401: The MME sends an access bearer release request message to the SGW, requesting the SGW to release the user plane address and the TEID.

 Step 402: The SGW returns an access bearer release response message to the MME.

 Step 403: The MME sends a user context release command message to the eNodeB, where the command message carries a specific cause value, which is used to indicate that the release cause is caused by SGW load re-allocation, and the UE needs to re-initiate the TAU process.

 Step 404: The eNodeB sends a radio resource connection (RRC) connection release request message to the UE, where the request message carries a specific cause value, which is used to indicate that the release cause is caused by SGW load re-allocation, and the UE needs to re-initiate TAU. Process

 Step 405: The UE returns an RRC connection release response message to the eNodeB.

 Step 406: The eNodeB returns a user context release complete message to the MME.

 At this point, the UE transitions from the connected state to the idle state.

 It should be noted that this embodiment is also applicable to the case where the UE accesses the SGSN.

FIG. 5 is a flowchart of a service gateway load redistribution according to another embodiment of the present invention. As shown in FIG. 5, the method includes the following steps:

 Step 501: The SGW sends a load re-allocation indication message to the MME, where the SGW can carry the number of users that need to be migrated.

 Step 502: The MME selects a corresponding number of users to perform migration.

 In this embodiment, the MME selects a user in the connection state to perform migration.

The operations of steps 503-508 are similar to the operations of steps 401-406 in FIG. 4, and details are not described herein again. Step 509: The UE sends a tracking area update request to the MME, where the request message carries the Globally Unique Temporary Identity (GUTI) allocated by the MME for the UE; the operations of steps 510-515 and the operations of steps 303-308 in FIG. Similar, it will not be repeated here. Step 516: If the MME confirms that the UE is valid in the current tracking area, send a tracking area update accept message to the UE.

 At this point, the UE re-transitions to the connected state.

 Step 517: If the MME allocates a new GUTI identifier to the UE through the TAU procedure, the UE returns a trace area update complete message to the MME for confirmation.

 It should be noted that this embodiment is also applicable to the case where the UE accesses the SGSN.

FIG. 6 is a flowchart showing a process of reassigning a service gateway load according to another embodiment of the present invention. As shown in FIG. 6, the method includes the following steps.

 Step 601: The SGW sends a load re-allocation indication message to the MME, where the SGW can carry the number of users that need to be migrated.

 Step 602: The MME selects a corresponding number of connection state users to perform migration.

 Step 603, the MME needs to change the user state, and the UE is changed from the connection state to the idle state, and the MME sends an access bearer release request message to the SGW, requesting the SGW to release the user plane address and the TEID;

 Step 604: The SGW returns an access bearer response message to the MME.

 Step 605: The MME sends a user context release command message to the eNodeB, where the command message carries a specific cause value, which is used to indicate that the release is caused by SGW load redistribution;

 Step 606: The eNodeB sends a Radio Resource Connection (RRC) connection release request message to the UE, where the command message carries a specific cause value, which is used to indicate that the release is caused by SGW load redistribution;

 Step 607: The UE returns an RRC connection release response message to the eNodeB.

 Step 608: The eNodeB returns a user context release complete message to the MME.

The operations of steps 609-614 are similar to the operations of steps 303-308 in FIG. 3, and details are not described herein again. Step 615: The MME initiates a paging message to the eNodeB of the tracking area list (TA list) to which the UE belongs.

 Step 616, the eNodeB initiates a paging message.

 Step 617: The UE sends a service request (Service Request) message to the MME. Step 618: The MME sends an initial context setup request message to the eNodeB, where the request message carries the user plane address and TEID of the SGW, the Bearer QoS, and the security context.

 Step 619: The eNodeB initiates a radio bearer setup request message to the UE, requesting to establish a radio bearer.

 Step 620: The UE returns a radio bearer setup response message to the eNodeB.

 At this point, the UE re-transitions to the connected state.

 Step 621: The eNodeB sends an initial context setup complete message to the MME, where the response message carries the user plane address and the TEID of the eNodeB.

 Step 622: The MME sends a modify bearer request message to the SGW, where the request message carries the user plane address and the TEID of the eNodeB.

 Step 623: The SGW returns a modify bearer response message to the MME.

 It should be noted that the embodiment is also applicable to the case where the UE accesses the SGSN.

As shown in FIG. 7, the present invention further provides a load redistribution system of a service gateway, including a service gateway and a mobility management unit, where the service gateway includes a load redistribution indication module, and the mobility management unit includes load redistribution execution. The module, the load redistribution execution module further includes a gateway selection unit and a user migration unit, and each module/unit functions as follows:

 The load re-allocation indication module is configured to: when the service gateway needs to maintain and upgrade, or learn to newly add a service gateway in the network, send a load re-allocation indication message to the gateway selection unit and the user migration unit; the gateway selection unit is configured to receive the load After reassigning the indication message, select another service gateway;

The user migration unit is configured to: after receiving the load reassignment indication message, select some or all users on the service gateway, and migrate the selected user to another new service selected by the gateway selection unit. On the gateway.

 Further, the load re-allocation indication module is further configured to: carry the number of users that need to be migrated in the load re-distribution indication message;

 The user migration unit is configured to select a corresponding number of users on the service gateway according to the number of users, and migrate the selected users to the new service gateway.

 Further, when selecting a new serving gateway, the gateway selecting unit selects a gateway with a lower load in the network or a new service gateway in the network.

The state is migrated, and the user in the idle state is directly migrated to the new service gateway; for the user in the connected state, it is first changed from the connected state to the idle state, and then migrated to the new one. On the service gateway.

 The user migration unit may change the user in the connected state to the idle state in the manner of the foregoing embodiment, and the specific operation procedure is not described herein.

 Further, when the user migration unit selects a corresponding number of users for migration, the user in the idle state is preferentially selected.

 Further, the service gateway further includes a context update module, configured to: after the user on the other gateway migrates to the serving gateway, send a modify bearer request message to the packet data network gateway, requesting the packet data network gateway to update the context of the user. .

 The present invention also provides a service gateway, where the service gateway includes a load redistribution indication module, and the load redistribution indication module is configured to: when the service gateway needs to be upgraded, or when the service gateway is newly added in the network Sending a load re-allocation indication message to the gateway selection unit and the user migration unit;

The gateway selection unit and the user migration unit belong to a load re-allocation execution module of the mobility management unit; after receiving the load re-distribution indication message, the gateway selection unit selects to send other services than the load re-allocation indication message. The gateway serves as a new service gateway. After receiving the load re-distribution indication message, the user migration unit selects some or all users on the service gateway, and migrates the selected user to the gateway selection unit. On the new service gateway. The load redistribution indication module is further configured to: carry the number of users that need to be migrated in the load re-distribution indication message;

 The user migration unit selects a corresponding number of users on the service gateway according to the number of users, and migrates the selected user to the new service gateway.

 The service gateway further includes a context update module;

 The context update module is configured to: after the user on the other gateway migrates to the service gateway, send a modify bearer request message to the packet data network gateway, requesting the packet data network gateway to update the context of the user.

The present invention also provides a mobility management unit, the mobility management unit includes a load redistribution execution module, and the load redistribution execution module includes a gateway selection unit and a user migration unit, where:

 The gateway selection unit is configured to: after receiving the load re-allocation indication message, select to send another service gateway other than the load re-allocation indication message as a new serving gateway; the load re-allocation indication message is heavy by the load The allocation indication module sends to the gateway selection unit and the user migration unit when the service gateway needs to maintain the upgrade, or learns to newly add the service gateway in the network; the user migration unit is configured to: receive the load redistribution After the message is indicated, some or all of the users on the service gateway are selected, and the selected user is migrated to the new service gateway selected by the gateway selection unit.

 The user migration unit is configured to: select a corresponding number of users on the service gateway according to the number of users, and migrate the selected user to the new service gateway; the load redistribution indication module is The load redistribution indication message carries the number of users that need to be migrated.

 The gateway selection unit is configured to: when selecting the new service gateway, select a gateway with a lower load in the network or a new service gateway in the network.

The user migration unit is configured to: when migrating the user to the new service gateway, perform migration according to the state of the user as follows: for the user in the idle state, directly migrate to the new On the service gateway, for the user in the connection state, after the connection state is changed to the idle state, the user in the connection state is migrated to the new service gateway. The user migration unit is configured to: preferentially select a user in an idle state when selecting a corresponding number of users for migration.

The above is only the preferred embodiment of the present invention and is not intended to limit the scope of the present invention. The invention may be embodied in various other forms and modifications without departing from the spirit and scope of the invention.

Industrial applicability

 With the above implementation, some or all users on the SGW can be migrated to the new SGW, which can implement load redistribution of the SGW and achieve the purpose of load balancing.

Claims

Claim A load redistribution method for a service gateway, the method comprising:  The serving gateway sends a load reassignment indication message to the mobility management unit when load redistribution is required;  The mobility management unit selects other service gateways other than the serving gateway as a new service gateway, and migrates some or all of the users on the serving gateway to the selected new serving gateway.  2. The method of claim 1 wherein  The service gateway needs to perform load re-allocation: the service gateway needs to migrate the user when maintaining or upgrading, or knowing that the service gateway is newly added in the network;  When the mobility management unit selects the new serving gateway, the mobility management unit selects a lower-loaded gateway or the newly added serving gateway among the other service gateways in the network.  3. The method of claim 2, wherein  Before the load re-allocation indication message is sent to the mobility management unit, the serving gateway carries the number of users to be migrated in the load re-distribution indication message;  In the migrating step, the mobility management unit selects a corresponding number of users to migrate to the new serving gateway according to the number of users.  4. The method according to claim 3, comprising: performing migration according to the state of the user; directly migrating to the new service gateway for the user in the idle state; After the connection state transitions to the idle state, it is migrated to the new service gateway.  5. The method of claim 4, wherein  The mobility management unit preferentially selects the user in the idle state when selecting the corresponding number of users for migration.  6. The method of claim 4, wherein The step of the mobility management unit converting the user in the connected state to the idle state includes: The mobility management unit sends a user context release instruction message to the base station of the user, where the user context release command message carries a specific cause value to indicate that the release reason is a service gateway load redistribution;  Sending, by the base station, a radio resource connection release request message to the user, and carrying the specific cause value in the radio resource connection release request message;  After the user completes the release of the user context according to the radio resource connection release request message, the user transitions from the connected state to the idle state.  7. The method of claim 6 further comprising the step of reconverting said user transitioning to an idle state to a connected state,  The step of re-converting the user transitioning to the idle state to the connected state includes: reinitiating an indication of the tracking area update request;  And the base station includes, in the sent radio resource connection release request message, an indication that the user re-initiates a tracking area update request;  And the user sends a tracking area update request to the mobility management entity according to the indication; and after the mobile management entity receives the tracking area update request, if the user is confirmed to be valid in the current tracking area, the user is Send tracking area update accept message.  8. The method of claim 6, further comprising the step of re-converting the user transitioning to an idle state to a connected state, the step of re-converting the user transitioning to an idle state to a connected state The steps include:  The mobility management entity initiates a paging message to a base station in a tracking area list to which the user belongs;  The base station in the tracking area list initiates a paging message to the user; after receiving the paging message, the user sends a service request message to the mobility management entity;  The mobility management entity sends an initial context setup request message to the base station; the base station sends a radio bearer setup request message to the user; The user establishes a radio bearer according to the radio bearer setup request message, and sends the radio bearer to the base station Returns the radio bearer setup response message.  9. The method of any of claims 1 to 8, the method further comprising:  After the user migrates to the new serving gateway, the new serving gateway sends a modify bearer request message to the packet data network gateway;  And after the packet data network gateway updates the context of the user according to the received modify bearer request message, sending a modify bearer response to the new serving gateway.  A load reassignment system of a service gateway, the system includes a service gateway and a mobility management unit, the service gateway includes a load redistribution indication module, and the mobility management unit includes a load redistribution execution module, where the load is heavy The allocation execution module includes a gateway selection unit and a user migration unit, where:  The load redistribution indication module is configured to: send a load reassignment indication message to the gateway selection unit and the user migration unit when the service gateway needs to maintain the upgrade, or if the service gateway is newly added in the network;  The gateway selection unit is configured to: after receiving the load re-distribution indication message, select to send another service gateway other than the load re-allocation indication message as a new service gateway;  The user migration unit is configured to: after receiving the load reassignment indication message, select some or all users on the serving gateway, and migrate the selected user to a new service gateway selected by the gateway selection unit. on.  11. The system of claim 10, wherein  The load re-allocation indication module is further configured to: carry the number of users that need to be migrated in the load re-distribution indication message;  The user migration unit is configured to: select a corresponding number of users on the service gateway according to the number of users, and migrate the selected user to the new service gateway.  12. The system of claim 10, wherein  The gateway selection unit is configured to: when selecting the new service gateway, select a gateway with a lower load in the network or a new service gateway in the network. 13. The system of claim 10, 11 or 12, wherein The user migration unit is configured to: when migrating the user to the new service gateway, perform migration according to the state of the user as follows: for the user in the idle state, directly migrate to the new On the service gateway, for the user in the connection state, after the connection state is changed to the idle state, the user in the connection state is migrated to the new service gateway.  14. The system of claim 13 wherein  The user migration unit is configured to: preferentially select a user in an idle state when selecting a corresponding number of users for migration.  15. The system of claim 14 wherein  The service gateway further includes a context update module;  The context update module is configured to: after the user on the other gateway migrates to the service gateway, send a modify bearer request message to the packet data network gateway, requesting the packet data network gateway to update the context of the user.  16. A service gateway, where the service gateway includes a load redistribution indication module,  The load redistribution indication module is configured to: send a load reassignment indication message to the gateway selection unit and the user migration unit when the service gateway needs to maintain the upgrade, or if the service gateway is newly added in the network;  The gateway selection unit and the user migration unit belong to a load re-allocation execution module of the mobility management unit; after receiving the load re-distribution indication message, the gateway selection unit selects to send other services than the load re-allocation indication message. The gateway serves as a new service gateway. After receiving the load re-distribution indication message, the user migration unit selects some or all users on the service gateway, and migrates the selected user to the gateway selection unit. On the new service gateway.  17. The service gateway according to claim 16, wherein  The load re-allocation indication module is further configured to: carry the number of users that need to be migrated in the load re-distribution indication message;  The user migration unit selects a corresponding number of users on the service gateway according to the number of users, and migrates the selected user to the new service gateway. 18. The service gateway of claim 16, the service gateway further comprising a context update module; The context update module is configured to: after the user on the other gateway migrates to the serving gateway, send a modify bearer request message to the packet data network gateway, requesting the packet data network gateway to update the context of the user.  19. A mobility management unit, the mobility management unit includes a load redistribution execution module, and the load redistribution execution module includes a gateway selection unit and a user migration unit, where:  The gateway selection unit is configured to: after receiving the load re-allocation indication message, select to send another service gateway other than the load re-allocation indication message as a new serving gateway; the load re-allocation indication message is heavy by the load The allocation indication module sends to the gateway selection unit and the user migration unit when the service gateway needs to maintain the upgrade, or learns to newly add the service gateway in the network; the user migration unit is configured to: receive the load redistribution After the message is indicated, some or all of the users on the service gateway are selected, and the selected user is migrated to the new service gateway selected by the gateway selection unit.  20. The mobility management unit of claim 19, wherein  The user migration unit is configured to: select a corresponding number of users on the service gateway according to the number of users, and migrate the selected user to the new service gateway; the load redistribution indication module is The load redistribution indication message carries the number of users that need to be migrated. 21. The mobility management unit of claim 19, wherein  The gateway selection unit is configured to: when selecting the new service gateway, select a gateway with a lower load in the network or a new service gateway in the network.  22. The mobility management unit of claim 19, wherein  The user migration unit is configured to: when migrating the user to the new service gateway, perform migration according to the state of the user as follows: for the user in the idle state, directly migrate to the new On the service gateway, for the user in the connection state, after the connection state is changed to the idle state, the user in the connection state is migrated to the new service gateway.  23. The mobility management unit of claim 22, wherein  The user migration unit is configured to: preferentially select a user in an idle state when selecting a corresponding number of users for migration.