CN103906152B

CN103906152B - Method for supporting UE quick recovery

Info

Publication number: CN103906152B
Application number: CN201310552962.3A
Authority: CN
Inventors: 许丽香; 王弘; 梁华瑞
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2012-12-24
Filing date: 2013-11-08
Publication date: 2022-02-25
Anticipated expiration: 2033-11-08
Also published as: CN103906152A

Abstract

The application discloses a method for supporting UE quick recovery, which comprises the following steps: when the UE is accessed to the service base station, the service base station carries out UE context synchronization on other base stations of the related small cell group; when the UE fails, the base station for the UE to perform Radio Resource Control (RRC) connection reestablishment performs RRC connection reestablishment on the UE according to the UE context stored in the synchronization process. The application also discloses another method for supporting the UE to recover quickly. By applying the technical scheme disclosed by the application, when the UE moves in a small cell scene, the UE can be quickly recovered under the condition of failure, so that the UE is prevented from returning to an idle mode, data loss is avoided, the service continuity is ensured, and the user experience is improved.

Description

Method for supporting UE quick recovery

Technical Field

The present application relates to wireless communication technologies, and in particular, to a method for supporting fast UE recovery.

Background

Modern mobile communications are increasingly tending to provide users with high-rate transmission multimedia services, as shown in fig. 1, which is a system architecture diagram of System Architecture Evolution (SAE). Wherein:

a User Equipment (UE) 101 is a terminal device for receiving data. An evolved universal terrestrial radio access network (E-UTRAN) 102 is a radio access network that includes macro base stations (eNodeB/NodeB) that provide access to a radio network interface for UEs. A Mobility Management Entity (MME) 103 is responsible for managing mobility context, session context and security information of the UE. Serving Gateway (SGW) 104 mainly provides the functions of the user plane, and MME103 and SGW104 may be in the same physical entity. A packet data network gateway (PGW) 105 is responsible for charging, lawful interception, etc., and may also be in the same physical entity as the SGW 104. A Policy and Charging Rules Function (PCRF) 106 provides quality of service (QoS) policy and charging criteria. The general packet radio service support node (SGSN) 108 is a network node device in the Universal Mobile Telecommunications System (UMTS) that provides routing for the transmission of data. The Home Subscriber Server (HSS) 109 is the home subsystem of the UE and is responsible for protecting user information including the current location of the user equipment, the address of the serving node, user security information, the packet data context of the user equipment, etc.

The 3GPP proposed the need for small cell enhancements in release 12 (Rel-12), the target scenarios for small cell enhancements including scenarios with and without macro cell coverage, indoor scenarios and outdoor scenarios, enhancements for ideal and non-ideal backhaul, as shown in fig. 2.

In the case of macro cell coverage, a technique is proposed that can apply carrier aggregation between different base stations. The macro cell and the small cell may operate in different frequency bands. In the case of no macro cell coverage, there is no specific solution on how to enhance the performance of the small cell.

Disclosure of Invention

The application provides a method for supporting UE quick recovery, when the UE moves in a small cell scene, the UE can be quickly recovered under the condition of failure, so that the UE is prevented from returning to an idle mode, data loss is avoided, service continuity is guaranteed, and user experience is improved.

The application provides a method for supporting UE quick recovery, which comprises the following steps:

A. when the UE is accessed to the service base station, the service base station carries out UE context synchronization on other base stations of the related small cell group;

B. when the UE fails, the base station for the UE to perform Radio Resource Control (RRC) connection reestablishment performs RRC connection reestablishment on the UE according to the UE context stored in the synchronization process.

Preferably, the UE accessing the serving base station is: the UE is switched from an idle mode to an active mode in the cell of the serving base station;

the UE context synchronization of the serving base station to other base stations of the relevant small cell group is: and the service base station sends the UE context of the UE to other base stations of the small cell group where the service base station is located, and the other base stations store the UE context.

Preferably, the method further comprises:

when the UE context needs to be updated, the service base station sends the updated UE context to other base stations of a small cell group where the service base station is located, and the other base stations store the updated UE context;

when the UE returns to the idle mode from the active mode in the cell of the serving base station, or when the UE moves out of the cell of the serving base station and the destination cell is not in the small cell group in which the serving base station is located, the serving base station sends a message releasing the UE context to the corresponding base station in the small cell group in which the serving base station is located, and the corresponding base station releases the corresponding UE context.

Preferably, the UE accessing the serving base station is: the UE is switched into a cell in the service base station;

the UE context synchronization of the serving base station to other base stations of the relevant small cell group is: synchronizing the UE context to the base station in the target small cell group, and releasing the UE context on the base station in the source small cell group;

wherein, the source small cell group means: the small cell group where the source base station of the handover is located; the target cell group means: the small cell group where the handover destination base station is located.

Preferably, before the step A, the method further comprises the following steps:

the first base station and the second base station exchange small cell group information during the X2 establishment;

or the first base station and the second base station exchange small cell group information through an S1 interface via the core network;

or the first base station broadcasts the small cell group information of the first base station, and the UE acquires the small cell group information of the first base station from the broadcast information of the first base station and sends the small cell group information of the first base station to the second base station;

or the first base station and the second base station exchange small cell group information during the X2 handover;

alternatively, the first base station and the second base station exchange small cell group information during the S1 handover;

the cell group information is: an identifier of the small cell group in which the base station is located or a list of base stations in the small cell group in which the base station is located; the base station list is a base station identification list, or a base station IP address list, or other lists of information capable of identifying base stations.

Preferably, the manners of synchronizing the UE context to the base station in the destination small cell group and releasing the UE context on the base station in the source small cell group include three manners, wherein:

the first mode is as follows: the target base station sends the UE context to other base stations in a target small cell group, and the other base stations store the UE context; the source base station sends a message for releasing the UE context to the base stations in the source small cell group, and the other base stations release the corresponding UE contexts;

the second way is: for base stations in both the source small cell group and the destination small cell group, the destination base station updates its UE context; for base stations in the target small cell group but not in the source small cell group, the target base station sends the UE context to it; for base stations in a source small cell group but not in a destination small cell group, the source base station sending it a message releasing the UE context;

the third mode is as follows: for base stations in both the source small cell group and the destination small cell group, the destination base station updates its UE context; for base stations in the target small cell group but not in the source small cell group, the target base station sends the UE context to it; for base stations in the source small cell group but not in the destination small cell group, the destination base station sends it a message releasing the UE context.

Preferably, the way in which the serving base station of the UE knows the other base stations in the small cell group in which the UE is located includes:

the service base station acquires other base stations in the small cell group where the service base station is located according to the configuration information;

or the serving base station determines a base station where a small cell around the cell is located according to the cell currently accessed by the UE, and takes the base station as another base station in the small cell group where the base station is located;

or, the serving base station determines the base station where the surrounding small cells are located according to the measurement report of the UE, and uses the base station as another base station in the small cell group where the serving base station is located;

or the serving base station acquires a group of small cell base stations according to the configuration information, and filters the configured group of small cell base stations according to the measurement report of the UE to obtain other base stations in the small cell group where the serving base station is located.

Preferably, the UE context includes a cell identity of an access cell of the UE serving the base station and a UE identity of the UE in the access cell;

the UE context further includes one or more of the following information: security context of the UE, ERAB information, information of the source MME, identification of the UE at the source MME, capability of the UE, a handover restriction list, and UE history information.

The application also provides a method for supporting the UE to recover quickly, which comprises the following steps:

the UE sends an RRC reestablishment request message to the second base station;

the second base station requests the UE context of the UE from the first base station; the first base station is a service base station before the UE fails;

the first base station sends the UE context of the UE to the second base station;

and the second base station reestablishes the RRC connection to the UE according to the received UE context.

Preferably, the UE context includes a cell identity of the UE in the cell where the UE failed to occur in the first base station and a UE identity of the UE in the cell where the UE failed to occur;

Preferably, the method further comprises:

and the first base station or the second base station carries out security check on the UE.

Preferably, the method further comprises:

and the first base station or the second base station performs access control check on the UE.

According to the technical scheme, when the UE moves in a small cell scene, the method for supporting the UE to recover quickly provided by the application enables the base station in the related small cell group to acquire the context of the UE by adopting different measures, so that the base station for the UE to reestablish the RRC connection acquires the context of the UE when the UE fails and reestablishes the RRC connection, the RRC reestablishment can be successful, the UE is prevented from returning to an idle mode, data loss is avoided, and the service continuity is ensured.

Drawings

FIG. 1 is a diagram of a conventional SAE system architecture;

figure 2 small cell enhanced deployment scenario;

FIG. 3 is a diagram illustrating a first method for supporting fast UE recovery according to the present application;

fig. 4 is a schematic diagram of a process for accessing a small cell by a UE according to the present application;

figure 5 is a schematic diagram of the process of synchronizing UE contexts in a small cell group according to the present application;

figure 6 is a schematic diagram of the process of updating UE context of other base stations in the small cell group;

figure 7 is a schematic diagram of a process of releasing UE context of other base stations in a small cell group according to the present application;

figure 8 is a schematic diagram of a method for a base station in a cell group of the present application to use a saved UE context;

figure 9 is a schematic diagram of the process of exchanging small cell group information between two base stations of the present application;

figure 10 is a schematic diagram of the process of two base stations exchanging small cell group information during an X2 handover process according to the present application;

figure 11 is a schematic diagram of the process of two base stations exchanging small cell group information during handover at S1;

FIG. 12 is a diagram illustrating a second method for supporting UE fast recovery according to the present application;

FIG. 13 is a diagram illustrating a base station of the present application acquiring a first UE context mode from another base station;

FIG. 14 is a diagram illustrating a second method for a base station to obtain UE context from another base station;

FIG. 15 is a diagram illustrating a third method for a base station of the present application to obtain UE context from another base station;

fig. 16 is a diagram illustrating a UE context acquiring manner four from another base station according to the present application.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is further described in detail below by referring to the accompanying drawings and examples.

When the UE moves in a small cell scene, failure may occur, and in order to enable the UE to be quickly recovered under the condition of failure, the application provides two methods for supporting the UE to quickly recover so as to prevent the UE from returning to an idle mode, avoid data loss and ensure service continuity. Wherein:

the main idea of the first method is that: when the UE is accessed to the service base station, the service base station accessed by the UE carries out UE context synchronization on other base stations in the related small cell group, so that when the UE fails and needs to reestablish RRC connection, the base station reestablished by the RRC connection stores the context information of the UE, and the RRC reestablishment can be successful.

The main idea of the second method is that: when the UE fails and needs to reestablish RRC connection, the base station reestablished by RRC connection requests the UE context from the current service base station of the UE, so that RRC reestablishment can be successful.

The two methods have the common points that: by adopting different measures, the base station for reestablishing the RRC connection obtains the context of the UE, so that the RRC reestablishment can be successful, the UE is prevented from returning to an idle mode, data loss is avoided, and the service continuity is ensured.

The two methods provided in the present application are described in detail below.

Fig. 3 is a diagram illustrating a first method for supporting UE fast recovery according to the present application.

Several base stations in which the Small Cell is located form a Small Cell Cluster (Small Cell Cluster). The small cell group may be composed of base stations where several small cells configured by the network according to the geographical location area are located, or may be composed of several small cell base stations around the base station where the small cell is located for different small cells accessed by the UE. When the UE accesses the base station of the small cell group, the service base station accessed by the UE sends the UE context to other base stations in the small cell group, and subsequently, when the UE context is updated or needs to be released, the service base station accessed by the UE informs the other base stations in the small cell group to update or release the UE context. For example: according to fig. 3, base station 1 synchronizes the UE context to base station 2 and base station 3.

In the first method, as shown in fig. 4, a procedure for a UE to access a small cell includes the following steps:

step 401: the UE accesses the base station 1.

Here, it is assumed that the base station 1 is a base station of a small cell, and the base station 1 is a base station in a small cell group.

The UE access base station 1 may be: the transition from Idle (Idle) mode to Active (Active) mode in the cell of base station 1 may also be a cell that accesses base station 1 by handover (in this case, base station 1 is the destination base station for the handover).

Step 402: base station 1 sends the UE context to other base stations in its small cell group, for example: shown are eNB2 and eNB 3.

Wherein the UE context includes one or more of the following information:

-a security context of the UE;

-ERAB information;

-information of the source MME;

-identity of the UE at the source MME;

-a capability of the UE;

-a list of handover restrictions;

-UE history information.

The UE context also includes a cell identity of the UE in the cell accessed by the base station 1 (i.e., the cell accessed by the UE in the base station 1), where the cell identity may be a Physical Cell Identity (PCI), and the UE context may also include frequency information of the UE in the cell accessed by the base station 1. The cell identity may also be an enhanced global cell identity (ECGI). The UE context also includes a UE identity of the UE in the cell accessed by the base station 1, where the UE identity may be a CRNTI. The UE context may also include other UE context information, which is not limited in this application.

Step 403: and the base station receiving the UE context saves the UE context information.

How the base station uses the saved UE context will be described in the embodiment of fig. 8.

In the following, taking the procedure of the base station 1 sending the UE context to the base station 2 as an example, the procedure of the first method, in which the base station 1 sends the UE context to other base stations in the small cell group where it is located, is described, as shown in fig. 5, including the following steps:

the process shown in fig. 5 may occur during the process of the UE switching from idle mode to active mode in the cell of the base station 1, or during the process of the UE accessing the base station 1 through a handover process.

Step 501: the base station 1 sends a UE context information send message to the base station 2.

Base station 2 and base station 1 are in the same small cell group. Wherein, the base station 1 can know whether the base station 2 is in the small cell group of the base station 1 according to the configuration (i.e. configuration information) of the operator; or the base station 1 may determine base stations of some small cells around the cell according to the currently accessed cell according to the difference of the UE accessed cells, and use these base stations as the base station 2 to send the UE context information sending message to the base station; or the base station 1 may determine base stations where a group of surrounding small cells are located according to the measurement report of the UE, and use these base stations as the base station 2 to send the UE context information sending message to them. It should be noted that the base station 1 determines the base stations included in the small cell group according to the measurement report of the current UE, or may determine the base stations included in the small cell group according to the measurement reports of some UEs accessing the current cell; or the base station 1 may obtain the base stations included in the small cell group of the base station 1 according to the configuration (i.e., configuration information) of the operator, and then filter the base stations according to the measurement report of the UE or a group of UEs, and determine the base station in the final small group. Of course, in practical applications, the base station in the small cell group may also be determined according to other factors, which is not limited in this application.

The content contained in the UE context information sending message is the same as that in step 402, and is not described herein again.

Step 502: the base station 2 stores the UE context information in the UE context information sending message.

Step 503: base station 2 sends a UE context information acknowledgement to base station 1.

The present application provides two ways for the base station 2 to respond to the base station 1, including: both the base station 2 sends the response message and the base station 2 does not send the response message, so step 503 is shown in dashed lines in fig. 5.

The base station 1 may send the UE context information to the base station 2 through an X2 interface, or may forward the UE context information to the base station 2 through an S1 interface.

When the base station 1 receives the UE context modification message from the MME, or when the base station 1 receives the ereb establishment message \ ereb modification message \ ereb release message, etc. from the MME for the UE, which needs to update the UE context, the base station 1 triggers the UE context update process to other base stations in the small cell group where the base station is located, as shown in fig. 6.

Step 601: the base station 1 sends a UE context information update message to the base station 2.

The UE context information update message includes updated UE context information, and includes a cell identifier of the UE in the access cell of the base station 1 and a UE identifier of the UE in the access cell of the base station 1, where the UE identifier of the UE in the access cell of the base station 1 may be CRNTI. The updated UE context information may include one or more of the UE context information described in step 402.

Step 602: the base station 2 saves the updated UE context information.

Step 603: base station 2 sends a UE context update acknowledgement to base station 1.

Here, the present application also provides two ways for the base station 2 to respond to the base station 1, including: both the response message is sent by base station 2 and the response message is not sent by base station 2, so step 603 is shown in dashed lines in fig. 6.

The base station 1 may send the updated UE context information to the base station 2 through an X2 interface, or may forward the updated UE context information to the base station 2 through a core network through an S1 interface.

When the UE returns from active mode to idle mode in the cell of base station 1, or when the UE moves out of the cell of base station 1 and the destination cell is not in the small cell group in which base station 1 is located, base station 1 triggers the process of releasing the UE context information to other base stations in its small cell group, as shown in fig. 7.

Step 701: base station 1 sends a UE context release request message to base station 2. The message includes a cell identifier of the UE in the access cell of the base station 1 and a UE identifier of the UE in the access cell of the base station 1, where the UE identifier of the UE in the access cell of the base station 1 may be CRNTI.

After receiving the UE context release request message, the base station 2 releases the UE context of the corresponding UE.

Step 702: the base station 2 sends a UE context release response message to the base station 1.

Here, the present application also provides two ways for the base station 2 to respond to the base station 1, including: both the base station 2 sends the response message and the base station 2 does not send the response message, so step 702 in fig. 7 is shown with a dashed line.

The base station 1 may send the UE context release request message to the base station 2 through an X2 interface, or may forward the UE context release request message to the base station 2 through an S1 interface.

As mentioned above, the base station in the small cell group will store the UE context transmitted by other base stations, and the following describes how the base station storing the UE context uses the stored UE context with reference to fig. 8, and as shown in fig. 8, the method includes the following steps:

step 801: when the UE fails in the cell of the base station 1, the UE sends an RRC reestablishment request message to the base station 2.

The RRC reestablishment request message may include a cell identifier of the UE in the cell where the failure occurs, where the cell identifier may be a PCI, and the RRC reestablishment request message may also include frequency information of the cell where the failure occurs. The cell identity may also be an ECGI. The message also contains the UE identification of the cell where the UE fails to occur, and the UE identification of the cell where the UE fails to occur can be CRNTI.

Step 802: since the base station 2 stores the security context information of the UE, the RRC reestablishment may be successful, and the base station 2 sends an RRC reestablishment message to the UE.

Step 803: the UE sends an RRC reestablishment complete message to the base station 2.

Step 804: the base station 2 sends a path switch request message to the MME serving the UE. Here, the base station 2 can know the MME serving the UE from the UE context information.

Wherein, step 802 and step 804 are both messages sent out by the base station 2, and the two messages have no absolute sequence.

Step 805: the MME sends a path switch request acknowledge message to the base station 2.

The above describes the procedure of the control plane, and the behavior of the user plane is not limited. Several operation modes of the user plane are described below, which can further reduce data loss and ensure service continuity.

The first method is as follows: when receiving the RRC reestablishment request message of step 801, the base station 2 allocates uplink and/or downlink TEIDs and transport layer addresses for data forwarding, and sends the TEIDs and the transport layer addresses to the base station 1.

For downlink data forwarding, if the base station 2 determines downlink data forwarding, the base station 2 allocates a TEID and a transport layer address for downlink data forwarding and sends the TEID and the transport layer address to the base station 1; for the uplink data forwarding, if the base station 2 requests the uplink data forwarding, the base station 2 allocates the TEID and the transport layer address for the uplink data forwarding and sends the TEID and the transport layer address to the base station 1, and the base station 1 determines whether to accept the uplink data forwarding. The base station 2 sends the identifier of the source cell (the service cell of the UE in the base station 1) where the UE is located and the identifier of the UE in the source cell to the base station 1; the base station 1 starts to forward the data of the UE to the base station 2 according to the cell identification received from the base station 2, the identification of the UE in the cell and the data forwarding user plane distributed by the base station 2. The base station 1 sends a data transmission context to the base station 2, the data transmission context comprising PDCP SN and HFN. The downlink PDCP SN indicates the SN needed for the next PDCD SDU. The uplink PDCP SN indicates the SN of the first missing PDCP SDU. The data transmission context may further include a reception state of an uplink PDCP SDU. The base station 2 may only request the radio link control protocol (RLC) to acknowledge the data forwarding of the bearer of the mode AM. To ensure the sequential transmission of data, the base station 2 may first transmit data received from the base station 1 to the UE, and then transmit data received from the core network to the UE.

The second method comprises the following steps: according to the measurement report of the UE, the base station 1 sends downlink data to the UE, and at the same time, sends the downlink data to the neighboring base station in the small cell group with a better signal, and sends corresponding data sending context information. When the UE re-accesses the base station 2, the base station 2 starts to send downlink data to the UE according to the data sending context information received from the base station 1, and sends a corresponding uplink data packet to the core network.

The third method comprises the following steps: the core network transmits data to a plurality of base stations in the small cell group simultaneously, so that the base station 2 receives the data transmitted from the core network synchronously with the base station 1.

Through the process shown in fig. 8, it can be ensured that the RRC connection of the UE is reestablished successfully, so that the UE does not return to the idle mode, data loss is reduced, and user experience is improved.

Several methods are provided for two base stations to exchange information about the cell groups in which they are located, as described in detail below.

Figure 9 is a schematic diagram of a first method for exchanging small cell group information between two base stations according to the present application, which includes:

step 901: the base station 1 sends an X2 establishment request message to the base station 2, wherein the X2 establishment request message includes information of the cell group in which the base station 1 is located.

The information of the small cell group contains a list of base stations in the small cell group in which the base station 1 is located, and the list of base stations may be a list of base station identifications or a list of base station IP addresses or a list of other information capable of identifying base stations. The information of the small cell group may also be an identification of the small cell group. The base station 2 stores the received information.

Step 902: the base station 2 sends an X2 establishment response message to the base station 1, wherein the X2 establishment response message includes information of the cell group in which the base station 2 is located.

The information of the small cell group contains a list of base stations in the small cell group in which the base station 2 is located, which may be a list of base station identities or a list of base station IP addresses or a list of other information that can identify base stations. The information of the small cell group may also be an identification of the small cell group. The base station 1 stores the received information.

The second method for exchanging the small cell group information between the two base stations is as follows:

when there is no X2 interface between the base station 1 and the base station 2, the base station 1 and the base station 2 transmit the small cell group information in the method shown in fig. 9 through the core network, i.e. through the S1 interface.

The method for exchanging the small cell group information between the two base stations comprises the following steps:

the base station 2 cell broadcasts the information of the cell group where it is, which is the same as described in step 902. The UE accesses the cell of the base station 1, reads the broadcast information of the cell of the base station 2, acquires the information of the small cell group where the base station 2 is located, and sends the information of the small cell group where the base station 2 is located to the base station 1. Through a similar procedure, the base station 2 can obtain information of the cell group in which the base station 1 is located.

The cell group in which base station 1 is located (cluster 1) and the cell group in which base station 2 is located (cluster 2) may be different, i.e. the base station included in the cell group in which base station 1 is located and the base station included in the cell group in which base station 2 is located may not be identical. By the above three methods, the base station 1 and the base station 2 already know the information of the small cell group where the opposite base station is located, when the UE is handed over from the base station 1 to the base station 2, the base station 2 needs to synchronize the UE context to the base station in cluster2, and the UE context not on the base station in cluster2 needs to be released. In the process of switching the UE from base station 1 to base station 2, base station 1 is the source base station of the handover, base station 2 is the destination base station of the handover, and the small cell group in which the source base station of the handover is located is hereinafter referred to as "source small cell group", i.e. cluster 1; the small cell group in which the handover destination base station is located is called the "destination small cell group", cluster 2. The present application specifically provides three ways of synchronizing UE contexts:

the first synchronization mode is as follows: base station 2 synchronizes the UE context to the other base stations in cluster2, i.e.: base station 2 performs the process shown in fig. 5 for the base station in cluster 2. Base station 1 releases the UE context on the base station in cluster1, i.e.: base station 1 performs the process shown in fig. 7 for the base station in cluster 1.

And a second synchronization mode: for base stations both in cluster1 and cluster2, base station 2 performs the process shown in fig. 6, sending UE context updates to the base stations. Corresponding to this method, in the handover preparation process, the source base station (e.g. base station 1) sends the UE identity in the cell of base station 1 and the UE identity in the cell of base station 1 to the destination base station (e.g. base station 2), and the base station 2 includes the cell identity and the UE identity in the message of updating the UE context request, so that the base stations in both cluster1 and cluster2 can update the corresponding UE context according to the request of base station 2. For base stations in cluster2 but not in cluster1, the base station 2 performs the process shown in fig. 5 to send UE context information to the base station. For base stations not in cluster2 in cluster1, base station 1 performs the procedure shown in fig. 7 to release the context of the UE at the base station.

A third synchronization mode: for base stations both in cluster1 and cluster2, base station 2 performs the process shown in fig. 6, sending UE context updates to the base stations. Corresponding to this method, in the handover preparation process, the source base station (e.g. base station 1) sends the UE identity in the cell of base station 1 and the UE identity in the cell of base station 1 to the destination base station (e.g. base station 2), and the base station 2 includes the cell identity and the UE identity in the message of updating the UE context request, so that the base stations in both cluster1 and cluster2 can update the corresponding UE context according to the request of base station 2. For base stations in cluster2 but not in cluster1, the base station 2 performs the process shown in fig. 5 to send UE context information to the base station. For the base station not in cluster2 in cluster1, the base station 2 executes the process shown in fig. 7 to release the context of the UE at the base station, and corresponding to this method, in the handover preparation process, the source base station (e.g. base station 1) sends the identity of the UE in the cell of base station 1 and the identity of the UE in the cell of base station 1 to the destination base station (e.g. base station 2), and the base station 2 includes the cell identity and the UE identity in the message of the request for releasing the UE context, so that the base station not in cluster2 in cluster1 can release the corresponding UE context according to the request of base station 2.

In addition to the above methods, small cell group information may be exchanged between two base stations in an X2 handover procedure or an S1 handover procedure, which will be described below with reference to fig. 10 and 11, respectively.

Fig. 10 is a method for two base stations to exchange small cell group information during handover of a UE from a source base station to a destination base station through X2, and the method includes the following steps.

Step 1001: the source base station sends a switching request message to the target base station. The message includes information of the small cell group where the source base station is located. The content included in the small cell group information is the same as in step 901, and is not described here again.

Step 1002: the target base station sends a switching request confirmation message to the source base station.

Optionally, the message may include information of the cell group in which the destination base station is located. The content included in the small cell group information is the same as that in step 902, and is not described here again.

Step 1003: existing handover execution procedures.

Step 1004: the existing handover completion procedure.

Step 1005: a context synchronization procedure of the UE in the new small cell group is performed. The target base station and the source base station synchronize the UE context information in other base stations according to the small cell group information exchanged in step 1001 and/or step 1002, and the specific synchronization manner is as described above and is not described herein again.

It should be noted that, the step 1005 may synchronize the UE context according to the information exchanged in steps 1001 and 1002, and is performed immediately after the handover is completed; in step 1002, the information of the small cell group in which the base station 2 is located may not be included, and after the handover is completed, the base station 2 may perform the measurement procedure on the UE again, obtain the information of the small cell group in which the base station 2 is located according to the measurement of the UE, and then perform the UE context synchronization procedure. If the process of synchronizing the UE context requires the base station 1 to participate, the base station 2 may send a message to the base station 1 to notify the base station 1 of the information of the small cell group in which the base station 2 is located after obtaining the information of the small cell group in which the base station 2 is located.

Fig. 11 is a method for two base stations to exchange small cell group information during handover of a UE from a source base station to a destination base station through S1, including the following steps:

step 1101: and the source base station sends a switching demand message to the MME. The message includes information of the small cell group where the source base station is located. The content included in the small cell group information is the same as in step 901, and is not described here again. The small cell group information may be contained in a transparent transmitter from the source base station to the destination base station.

Step 1102: and the MME sends a switching request message to the target base station. The message includes information of the small cell group where the source base station is located. The content included in the small cell group information is the same as in step 901, and is not described here again. The small cell group information may be contained in a transparent transmitter from the source base station to the destination base station.

Step 1103: and the target base station sends a switching request confirmation message to the MME.

Optionally, the message may include information of the cell group in which the destination base station is located. The content included in the small cell group information is the same as that in step 902, and is not described here again. The small cell group information may be contained in a transparent transmitter from the destination base station to the source base station.

Step 1104: and the MME sends a switching command message to the source base station.

If the handover request acknowledgement message of step 1103 includes information on the small cell group in which the target base station is located, the handover command message of this step will also include information on the small cell group in which the target base station is located. The content included in the small cell group information is the same as that in step 902, and is not described here again. The small cell group information may be contained in a transparent transmitter from the destination base station to the source base station.

Step 1105: an existing handover execution procedure is performed.

Step 1106: an existing handover completion procedure is performed.

Step 1107: a context synchronization procedure of the UE in the new small cell group is performed. The destination base station and the source base station synchronize the UE context information according to the small cell group information exchanged in step 1101 and step 1102, and/or step 1103 and step 1104, and the specific synchronization manner is as described above, and is not described herein again.

It should be noted that, the process of synchronizing the UE context in step 1107 may be executed immediately after the handover is completed according to the information exchanged in steps 1101 to 1104; in steps 1103 and 1104, the information of the small cell group in which the base station 2 is located is not included, and after the handover is completed, the base station 2 may perform the measurement procedure on the UE again, obtain the information of the small cell group in which the base station 2 is located according to the measurement of the UE, and then perform the UE context synchronization procedure. If the process of synchronizing the UE context requires the base station 1 to participate, the base station 2, after obtaining the information of the small cell group in which the base station 2 is located, may send a message to the base station 1 to notify the base station 1 of the information of the small cell group in which the base station 2 is located, where the message may be a message of an X2 interface or a message of an S1 interface.

The first method for supporting UE fast recovery according to the present application is described in detail above, and the second method for supporting UE fast recovery according to the present application is described in detail below with reference to fig. 12. The method shown in fig. 12 comprises the following steps:

step 1201: when the UE fails in the cell of the base station 1, the UE performs cell reselection, for example, selects the cell 2 of the base station 2, and sends an RRC reestablishment request message to the base station 2.

The RRC reestablishment request message may include a cell identifier of the UE in the cell where the failure occurs, where the cell identifier may be a PCI, and the RRC reestablishment request message may also include frequency information of the cell where the failure occurs. The cell identity may also be an ECGI. The message also contains the UE identification of the cell where the UE fails to occur, and the UE identification of the cell where the UE fails to occur can be CRNTI. The RRC reestablishment request message may further include a TAI in which the failure occurrence cell is located.

Step 1202: the base station 2 obtains the context of the UE from the base station 1, the base station 1 or the base station 2 performs access control check on the UE, and the base station 1 may also perform security check on the UE. Specifically, there are three ways for the base station 2 to acquire the context of the UE from the base station 1 and for the base station 1 or the base station 2 to perform the access control check on the UE, as shown in fig. 13, 14 and 15. The security check of the UE by the base station 1 will also be introduced in the description of fig. 13-15.

Subsequently, the base station 1 stops sending downlink data to the UE, and forwards the data to the base station 2.

As shown in fig. 13, the first method specifically includes the steps of: the base station 2 transmits a UE information request message to the base station 1 to request context information of the UE.

The message includes a cell identifier of the UE in the cell where the failure occurs (base station 1 cell), where the cell identifier may be a PCI, and may also include frequency information of the cell where the failure occurs. The cell identity may also be an ECGI or contain both a PCI and an ECGI. The message also includes an identifier of the UE in the cell where the UE failed, where the UE identifier of the cell where the UE failed may be CRNTI, and the UE identifier of the cell where the UE failed may also be eNB X2AP ID of the serving base station of the UE. The message also contains a short media access control identity, shortMACI.

The message also contains the cell identity PCI and/or ECGI of the re-established cell.

The message also includes the eNB UE X2AP ID assigned by eNB2 to the UE at the eNB1 and eNB2 interface.

Step 1302: the base station 1 performs security check and access check on the UE, and performs PLMN selection.

The specific way of the base station 1 to perform security check on the UE is as follows: the base station 1 performs security check on the UE by using the PCI or ECGI of the cell where the failure occurs and the CRNTI or shortMACI of the cell where the UE fails, which are received in step 1301. The base station 1 finds the cell where the failure occurs according to the PCI of the cell where the failure occurs, and in order to avoid PCI confusion, the base station 1 may find the cell where the failure occurs according to the ECGI or the PCI and the frequency information of the cell where the failure occurs, which are received in step 1301. The base station 1 finds the context of the UE according to the CRNTI of the cell where the UE fails. The base station 1 calculates shortMACI using the cell identity PCI of the reconstructed cell and the security context in the UE context, if the calculated value is the same as that received from the base station 1, the UE passes the security check, otherwise the UE does not pass the security check, and the eNB1 fails to send UE information to the eNB2 in step 1303.

The specific way for the base station 1 to perform access check on the UE is as follows: the base station 1 performs access check on the UE according to the cell identifier of the reconstructed cell and the access restriction list HRL of the UE. The base station 1 determines whether a PLMN broadcasted by the reestablished cell has a registration PLMN (rpplmn) or an equivalent PLMN (eplmn) of the UE, and the reestablished cell is not in a Tracking Area (TA) prohibited by the UE and is not in a Radio Access Technology (RAT) prohibited by the UE. The base station 1 may obtain the cell identifier, the supported TAC, and the PLMNID list of the cell of the base station 2 in the X2 establishing process, and then know the PLMN list and the located TA broadcast by the cell of the base station 2 according to the PCI or ECGI of the cell of the base station 2 received in step 1301 in combination with the information obtained in the X2 establishing process. The message in step 1301 may also include a TA (TAC or TAI) where the reconstructed cell is located and a broadcast PLMN ID list. If the PLMN ID broadcasted by the reestablishing cell does not have rPLMN or ePLMN of the UE, or the reestablishing cell is in a forbidden TA, or the reestablishing cell is in a forbidden RAT of the UE, the access check fails, otherwise the access check succeeds. The base station 1 knows the RAT to which the re-established cell belongs according to the frequency of the re-established cell or according to the configuration. If the access check fails, the eNB1 sends a UE information failure to the eNB2 in step 1303. In case the access check is successful, the base station 1 selects the serving PLMN for the UE among the PLMNs broadcasted by the re-establishing cell. The base station 1 uses the newly selected PLMN as the rPLMN, places the original rPLMN and other eplmns as the eplmns in the HRL, and sends the new HRL to the base station 2 in the message of step 1304.

In step 1303, according to the security check result and the access check result in step 1302, if both are successful, the eNB1 sends a UE information response to the eNB2, and if the security check or the access check is unsuccessful, the eNB1 fails to send the UE information to the base station 2.

The UE information response or UE information failure contains the eNB UE S1APID allocated by eNB2 for this UE. The UE information response may also contain the eNB UE X2AP ID assigned by the eNB1 for this UE. The UE information failure may also include a reason for the failure, such as a malicious UE or an access disallowance.

As another embodiment of the method, the eNB1 may also directly send the message of step 1304 when both the access check and the security check are successful. In case the check is unsuccessful, the eNB1 does not send a message to eNB 2. The eNB2 knows that the UE information request has failed according to a clock or the like, and transmits an RRC reestablishment reject message to the UE in step 1203.

In step 1304, the eNB1 sends a handover request message to the eNB 2. The message may contain the eNB UE X2AP ID assigned to the UE by eNB 2. The identification of the destination cell in the handover request message is the ECGI of the re-established cell received from the base station 2 in step 1301. The security information contained in the handover request message is calculated from the PCI and frequency of the re-established cell. The eNB1 may get the frequency of the re-established cell during the direct X2 establishment procedure of eNB1 and eNB2, or include the frequency of the re-established cell in step 1301.

In step 1305, the eNB2 sends a handover request acknowledge message to the eNB 1.

For reconstructing such a scenario, the transparent transmitter from the destination base station to the source base station may not be included in the handover request acknowledgement message.

Step 1305 and step 1203 are sent by base station 2, and there is no absolute sequence in the present invention, which is not limited in this respect.

It should be noted that, in the case that the base station 2 and the base station 1 do not have the X2 interface, the messages of the above steps 1301 to 1305 may be sent through the S1 interface. When the base station 2 sends the UE information request to the base station 1 through the MME using the S1 interface, the TAI and ECGI of the failure occurrence cell received from the UE in step 1201 are included, and the TAI is used for routing between core networks to find the MME to which the base station 1 is connected. The MME to which base station 1 is connected finds base station 1 with the ECGI of the failure occurrence cell.

The second method is shown in fig. 14, and specifically includes the steps of:

steps 1401 to 1402 are the same as steps 1301 to 1302, and are not described herein again. Note that, in the case where the access check or the security check in step 1402 fails, the base station 1 fails to transmit the UE information to the base station 2 in step 1403.

In step 1403, according to the security check result and the access check result of step 1402, the eNB1 sends a UE information response to the eNB2 if both are successful, and the eNB1 fails to send the UE information to the base station 2 if the security check or the access check is unsuccessful.

The UE information failure contains the eNB UE S1AP ID assigned by the eNB2 for this UE. The UE information failure may also include a reason for the failure, such as a malicious UE or an access disallowance.

The UE information response includes the eNB UE S1AP ID allocated by the eNB2 to the UE, and the UE information response may also include the eNB UE X2AP ID allocated by the eNB1 to the UE.

The UE information response message contains UE context information. Wherein the UE context information comprises one or more of the following information:

-a security context of the UE;

-ERAB information;

-information of the source MME;

-identity of the UE at the source MME;

-a capability of the UE;

-a list of handover restrictions;

-UE history information.

The ERAB information comprises an ERAB identifier, ERAB Qos information and ERAB uplink GTP TEID, and whether downlink data forwarding is needed or not.

The UE context information further includes a cell identifier of a cell where the UE fails in the base station 1, where the cell identifier may be a PCI, and the UE context information may further include frequency information of the cell where the UE fails. The cell identity may also be an ECGI. The UE context information further includes a UE identity of a cell where the UE fails in the base station 1, where the UE identity may be a CRNTI. The UE context information may also include other UE context information, which is not limited in this application.

The UE context information also comprises SN state information. The SN status information includes PDCP SN and HFN status information. Specifically, the method includes a receiving state of an uplink PDCP SDU of the ERAB that needs data forwarding and a COUNT value of an uplink and a downlink. The COUNT value refers to information of PDCP SN and HFN. The PDCPSN in the downlink indicates the SN needed for the next PDCD SDU. The uplink PDCP SN indicates the SN of the first missing PDCP SDU. The base station 2 may request only uplink data forwarding of the bearer of RLC acknowledged mode AM. To ensure the sequential transmission of data, the base station 2 may first transmit data received from the base station 1 to the UE, and then transmit data received from the core network to the UE. The base station 1 may transmit the SN status information to the base station 2 through the above-mentioned UE information response message, or may transmit the SN status information through another separate message.

The base station 1 stops sending downlink data to the UE.

In step 1404, the base station 2 allocates resources to the ERAB. Base station 2 sends a UE information indication to base station 1. The UE information indication may be an acknowledgement message of step 1403 or a separate indication message. The message contains the eNB UE X2AP IDs assigned by base station 1 and base station 2.

The message also contains a list of accepted ERABs. The received ERAB list contains uplink and/or downlink GTP TEIDs for data forwarding. The message may also contain a list of unaccepted ERABs.

After receiving the message, the base station 1 may start forwarding data to the base station 2.

Step 1404 and step 1203 are both sent by the base station 2, and there is no absolute sequence in the present invention, which is not limited in the present invention.

It should be noted that, in the case that the base station 2 and the base station 1 do not have the X2 interface, the messages of the above steps 1401 to 1404 may be transmitted through the S1 interface. When the base station 2 sends the UE information request to the base station 1 through the MME using the S1 interface, the TAI and ECGI of the failure occurrence cell received from the UE in step 1201 are included, and the TAI is used for routing between core networks to find the MME to which the base station 1 is connected. The MME to which base station 1 is connected finds base station 1 with the ECGI of the failure occurrence cell.

The third method is shown in fig. 15, and specifically includes the steps of:

step 1501 is the same as step 1301 and is not described further herein.

Step 1502, the base station 1 performs security check on the UE. The base station 1 performs security check on the UE by using the PCI or ECGI of the cell where the failure occurs and the CRNTI or shortMACI of the cell where the UE fails, which are received in step 1501. The base station 1 finds the cell where the failure occurs according to the PCI of the cell where the failure occurs, and in order to avoid PCI confusion, the base station 1 may find the cell where the failure occurs according to the ECGI or the PCI of the cell where the failure occurs and the frequency information received in step 1501. The base station 1 finds the context of the UE according to the CRNTI of the cell where the UE fails. The base station 1 calculates shortMACI using the cell identity PCI of the reconstructed cell and the security context in the UE context, if the calculated value is the same as that received from the base station 1, the UE passes the security check, otherwise the UE does not pass the security check, and the eNB1 fails to send UE information to the eNB2 in step 1303.

In case the security check is successful, the base station 1 transmits the handover request message of step 1503 to the base station 2.

In case the security check fails, the base station 1 does not transmit the message of step 1503. The eNB2 knows that the UE information request failed according to a clock or the like, and thus generates an RRC reestablishment reject message to the UE in step 1203.

As another implementation manner of the present invention, the security check may also be performed by the base station 2 after receiving the handover request message from the base station 1 in step 1504, so that this step may be skipped. In this way, the security context of the cell where the UE fails to occur needs to be included in the handover request message of step 1503. The base station 2 calculates shortMACI using the cell identity PCI of the re-established cell and the UE security context received from the base station 1, and if the calculated identity is the same as that received from the UE in step 1201, the UE passes the security check, otherwise the UE does not pass the security check. The base station 2 transmits an RRC reestablishment reject message to the UE in step 1203.

In step 1503, the eNB1 sends a handover request message to the eNB 2. The message may contain the eNB UE X2AP ID assigned to the UE by eNB 2. The identification of the destination cell in the handover request message is the ECGI of the re-established cell received from the base station 2 in step 1301. The security information contained in the handover request message is calculated from the PCI and frequency of the re-established cell. eNB1 may derive the frequency of the re-established cell during the direct X2 establishment procedure of eNB1 and eNB 2. Or in step 1301 includes the frequency of the re-established cell.

The base station 1 transmits HRL information of the UE to the base station 2.

Step 1504, the base station 2 performs access check on the UE. And the base station 2 performs access check on the UE according to the cell identifier of the reconstructed cell and the access restriction list HRL of the UE. The base station 2 determines whether the PLMN broadcasted by the reestablished cell has the rPLMN or the ePLMN of the UE, and the reestablished cell is not in the TA prohibited by the UE and is not in the RAT prohibited by the UE. If the PLMN ID broadcasted by the reestablishing cell does not have the rPLMN or the ePLMN of the UE, or the reestablishing cell is in the forbidden TA, or the reestablishing cell is in the radio access technology RAT forbidden by the UE, the access check fails. Otherwise the access check is successful. If the access check fails, the eNB2 sends a handover preparation failure to the eNB1 in step 1505. In case the access check is successful, the base station 2 selects the serving PLMN for the UE among the PLMNs broadcasted by the re-establishing cell. The base station 2 takes the newly selected PLMN as rPLMN and puts the original rPLMN and other eplmns as eplmns in the HRL. The base station 2 includes the newly selected PLMN ID in the TAI and transmits it to the MME in step 1206.

In step 1505, the eNB2 sends a handover request acknowledge message to the eNB 1. The eNB2 sends a handover request confirm message to eNB1 if the access check is successful, or the access check and the security check are successful.

Step 1505 and step 1203 are both sent from the base station 2, and there is no absolute sequence in the present invention, which is not limited in the present invention.

It should be noted that, in the case that the base station 2 and the base station 1 do not have an X2 interface, the messages of the above steps 1501 to 1505 can be sent through an S1 interface. When the base station 2 sends the UE information request to the base station 1 through the MME using the S1 interface, the TAI and ECGI of the failure occurrence cell received from the UE in step 1201 are included, and the TAI is used for routing between core networks to find the MME to which the base station 1 is connected. The MME to which base station 1 is connected finds base station 1 with the ECGI of the failure occurrence cell.

The fourth embodiment is shown in fig. 16, and specifically includes the steps of:

in step 1601, the base station 2 transmits a radio link failure indication message to the base station 1. The message includes the PCI of the cell where the failure occurred, the C-RNTI of the cell where the UE failed, the shortMAC-I received from the RRC reestablishment request message, and the ECGI of the cell to be reestablished. The message may also contain the ECGI of the cell in which the failure occurred. The message also contains an indication of whether the base station 2 requests UE context. The base station 2 includes in the message an indication requesting the UE context without the UE context information. The base station 2 does not transmit the RRC re-establishment rejection message to the UE for the moment when it contains an indication requesting the UE context information. The message of step 1203 is sent to the UE after receiving the message of step 1603, or the RRC re-establishment reject message is sent to the UE if the message of step 1603 is not received.

Step 1602, the base station 1 performs security check and access check on the UE, and performs PLMN selection.

When the received radio link failure indication message includes an indication requesting a context of the UE, the base station 1 performs security check and access check on the UE, and performs PLMN selection.

The base station 1 obtains the PCI, the supported PLMN ID(s), the TAC, and the frequency information of the reestablished cell by using the ECGI, the PCI, the supported PLMN ID(s), and the TAC of the serving cell of the base station 2 obtained in the establishing process of the X2 according to the ECGI of the reestablished cell received from the base station 2 in step 1601.

The specific way of the base station 1 to perform security check on the UE is as follows: the base station 1 performs security check on the UE by using the PCI or ECGI of the cell in which the failure occurs and the CRNTI or shortMAC-I of the cell in which the UE fails, which are received in step 1601. The base station 1 finds the cell where the failure occurs according to the PCI of the cell where the failure occurs, and in order to avoid PCI confusion, the base station 1 may find the cell where the failure occurs according to the ECGI or the PCI of the cell where the failure occurs and the frequency information received in step 1601. The base station 1 finds the context of the UE according to the CRNTI of the cell where the UE fails. The base station 1 calculates shortMAC-I by using the cell identity PCI of the reconstructed cell and the security context in the UE context, if the calculated value is the same as that received from the base station 1, the UE passes the security check, otherwise, the UE does not pass the security check.

The specific way for the base station 1 to perform access check on the UE is as follows: the base station 1 performs access check on the UE according to the cell identifier of the reconstructed cell and the access restriction list HRL of the UE. The base station 1 determines whether the plmn id broadcasted by the reestablished cell includes a registration plmn (rpplmn) or an equivalent plmn (eplmn) of the UE, and the reestablished cell is not in a Tracking Area (TA) prohibited by the UE and is not in a Radio Access Technology (RAT) prohibited by the UE. The base station 1 may obtain the cell identifier, the supported TAC, and the PLMN ID list of the cell of the base station 2 in the X2 establishing process, and then learn the PLMN ID list broadcast by the cell of the base station 2 and the TA where the PLMN ID list is located according to the PCI or ECGI of the cell of the base station 2 received in step 1601 in combination with the information obtained in the X2 establishing process. The message in step 1601 may also include a TA (TAC or TAI) where the reconstructed cell is located and a broadcast PLMN ID list. If the PLMN ID broadcasted by the reestablishing cell does not have rPLMN or ePLMN of the UE, or the reestablishing cell is in a forbidden TA, or the reestablishing cell is in a forbidden RAT of the UE, the access check fails, otherwise the access check succeeds. The base station 1 knows the RAT to which the re-established cell belongs according to the frequency of the re-established cell or according to the configuration. In case the access check is successful, the base station 1 selects the serving PLMN for the UE in the PLMN ID broadcasted by the re-establishing cell. The base station 1 uses the newly selected PLMN as rPLMN, places the original rPLMN and other eplmns as eplmns in the HRL, and sends the new HRL to the base station 2 in the message of step 1603.

In case the security check and the access check are successful, the base station 1 sends the handover request message of step 1603 to the base station 2.

In case of failure of the security check or failure of the access check, the base station 1 does not transmit the message of step 1603. The eNB2 knows that the UE context request failed according to a clock or the like, and then sends an RRC reestablishment reject message to the UE in step 1203.

As another implementation manner of the present invention, the security check may also be performed by the base station 2 after receiving the handover request message from the base station 1 in step 1603, so that the security check of this step can be skipped. In this way, the security context of the cell where the UE fails to occur needs to be included in the handover request message of step 1603. The base station 2 calculates shortMAC-I using the cell identity PCI of the re-established cell and the UE security context received from the base station 1, if the calculated identity is the same as that received from the UE in step 1201, the UE passes the security check, otherwise the UE does not pass the security check. The base station 2 transmits an RRC reestablishment reject message to the UE in step 1203.

In step 1603, the eNB1 sends a handover request message to the eNB 2.

In another method according to the present invention, the message in step 1601 may not include an indication of the context of the requesting UE. If the message in step 1601 includes an RRC connection setup indication indicating that the radio link failure indication is due to an RRC connection setup trigger, the base station 1 does not need to send the message in this step. If the radio link failure indication is triggered by an RRC re-establishment request and base station 1 has not made a handover preparation to base station 2 for the re-established cell, base station 1 may trigger the procedure of this step.

The identifier of the destination cell in the handover request message is the ECGI of the reconstructed cell received from the base station 2 in step 1601. The security information contained in the handover request message is calculated from the PCI and frequency of the re-established cell. The eNB1 may get the frequency of the re-established cell during the direct X2 establishment procedure of eNB1 and eNB2, or include the frequency of the re-established cell in step 1301.

The base station 1 transmits HRL information of the UE to the base station 2.

In step 1604, the eNB2 sends a handover request acknowledge message to the eNB 1. In case the eNB2 resources are not sufficient or other abnormalities, the base station 2 may send a handover preparation failure message to the base station 1, in which case an RRC reestablishment reject message is sent to the UE in step 1203.

Step 1604 and step 1203 are both sent by the base station 2, and there is no absolute sequence in the present invention, which is not limited in the present invention.

It should be noted that, in the case that the base station 2 and the base station 1 do not have the X2 interface, the messages of the above steps 1601 to 1604 may be sent through the S1 interface. When the base station 2 sends the radio link failure indication to the base station 1 through the MME using the S1 interface, the TAI and ECGI of the failure occurrence cell received from the UE in step 1201 are included, and the TAI is used for routing between core networks to find the MME to which the base station 1 is connected. The MME to which base station 1 is connected finds base station 1 with the ECGI of the failure occurrence cell.

Step 1203: the base station 2 sends an RRC re-establishment message to the UE. If the access check or security check for the UE fails in step 1202, in this step, the base station 2 sends an RRC reestablishment reject message to the UE.

In step 1204, the UE sends an RRC reestablishment complete message to the base station 2. In step 1203, when the RRC reestablishment message is received, the UE sends an RRC reestablishment complete message to the base station 2.

Step 1205, perform RRC connection reconfiguration procedure between the base station 2 and the UE. The base station 2 sends an RRC connection reconfiguration message to the UE, and the UE sends an RRC connection reconfiguration completion message to the base station 2.

Step 1206: the base station 2 sends a path switching request message to the MME serving the UE, requesting the core network to switch the downlink user plane. Here, the base station 2 learns the MME serving the UE from the UE context information received from the base station 1 in step 1202.

Step 1207: the MME sends a downlink path switch response message to the base station 2.

Step 1206 and step 1203 are all messages sent by the base station 2, and the two messages themselves have no absolute sequence, which is not limited in the present invention.

Step 1208: the base station 2 requests the base station 1 to release resources. The method provided by the invention comprises the steps and the methods without the steps. If the step is not executed, the base station 1 releases the resources allocated to the UE and the UE context after no data which can be forwarded is available and the last data mark (end marker) from the MME is received; if this step is performed, the base station 1, upon receiving the message and no forwardable data, releases the resources allocated to the UE and the UE context after receiving the last data flag from the MME.

This concludes the method flow shown in fig. 12.

The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A method performed by a second base station in a wireless communication system, the method comprising:

receiving a radio resource control, RRC, reestablishment request message from a user equipment, UE, wherein the RRC reestablishment request message includes an identity of the UE and the identity of the UE is allocated by a first base station that last served the UE before the UE selects a second base station to make an RRC connection;

transmitting a message for requesting a UE context of the UE to the first base station;

receiving a response message including a UE context of the UE from the first base station;

according to the response message, sending a path switching request message to a mobile management entity serving the UE;

receiving a path switching response message from the mobility management entity; and

sending a UE context release message to the first base station according to the path switching response message,

wherein the message for requesting UE context of the UE comprises a base station UE Application Protocol (AP) identity of the second base station allocated at the interface between the first base station and the second base station,

the response message including the UE context of the UE includes a base station UE AP identification of the first base station allocated at the interface between the first base station and the second base station, information associated with the old mobility management entity, an identification of the UE at the old mobility management entity, and E-UTRAN radio access bearer (ERAB) information,

the ERAB information comprises ERAB quality of service (Qos) information and ERAB uplink General Packet Radio Service (GPRS) tunnel protocol GTP Tunnel Endpoint Identification (TEID).

2. The method of claim 1, wherein:

the message for requesting a UE context further includes at least one of: the UE identifies C-RNT in the cell radio network of the first base station, the cell identification of the cell of the second base station, the physical cell identification PCI of the failed cell and the short media access control identification shortMACI.

3. The method according to claim 1 or 2, characterized in that: the response message including the UE context of the UE further comprises at least one of a base station UE AP identification allocated by the second base station, the security context of the UE, the capability of the UE and a switching restriction list.

4. The method according to claim 1 or 2, characterized in that the method further comprises:

the resources and UE context allocated at the first base station for the UE are released based on the UE context release message.

5. The method of claim 1, further comprising:

and sending an RRC reestablishment message to the UE.

6. The method of claim 1, further comprising:

sending RRC connection reconfiguration information to the UE;

and receiving an RRC connection reconfiguration complete message sent by the UE.

7. A method performed by a first base station in a wireless communication system, the method comprising:

receiving a message for requesting a UE context of a User Equipment (UE) from a second base station, wherein the Radio Resource Control (RRC) reestablishment request message is received by the second base station from the UE, wherein the first base station is a base station that last serves the UE before the second base station is selected by the UE for RRC connection, and the RRC reestablishment request message includes an identity of the UE allocated by the first base station; and

transmitting a response message including the UE context of the UE to the second base station to: the second base station sends a path switching request message to a mobility management entity serving the user equipment according to the response message, receives a path switching response message from the mobility management entity, and sends a UE context release message to the first base station according to the path switching response message,

8. The method of claim 7, wherein:

the message for requesting a UE context further includes at least one of: the method comprises the steps that a cell radio network temporary identifier C-RNTI of UE in a first base station, a cell identifier of a cell of a second base station, a cell radio network temporary identifier CRNTI of the UE in the first base station, a physical cell identifier PCI of a failed cell and a short media access control identifier shortMACI.

9. The method according to claim 7 or 8, wherein the response message including the UE context of the UE further includes at least one of a base station UE AP identity allocated by the second base station, a security context of the UE, a capability of the UE, and a handover restriction list.

10. The method of claim 7 or 8, further comprising:

and receiving a UE context release message, and releasing the UE context and the resources allocated to the UE.

11. The method of claim 7, wherein:

the RRC connection reconfiguration message is sent to the UE by the second base station;

the RRC connection reconfiguration complete message is sent by the UE to the second base station.