WO2012159399A1

WO2012159399A1 - Cross-enb handover method and evolved nodeb

Info

Publication number: WO2012159399A1
Application number: PCT/CN2011/080028
Authority: WO
Inventors: 叶凌云; 王达菲; 张瑞霞
Original assignee: 中兴通讯股份有限公司
Priority date: 2011-05-25
Filing date: 2011-09-22
Publication date: 2012-11-29
Also published as: CN102802208A

Abstract

Provided are a cross-eNB handover method and an evolved NodeB. The handover method includes: the user plane of a target side eNB receiving a handover indication message and then judging whether or not a sequence number status transfer (SN Status Transfer) message is received before receiving the handover indication message (S302); and if it is not received, then caching the handover indication message and processing same until the SN Status Transfer message is received and processed (S304). In the present invention, the handover indication message of the user plane which arrives first is cached and processed until an SN Status Transfer message is received and processed, thereby ensuring the accuracy of the PDCP sequence number information when the user side of the target eNB processes the downlink message of the PDCP layer, reducing packet loss due to inconsistency of PDCP sequence number information, and thus achieving the effects of lossless data transmission during handover and improving user experience.

Description

The present invention relates to the field of communications, and in particular to a method for handover between base stations and an evolved base station. BACKGROUND OF THE INVENTION Handover is a basic function for ensuring user mobility in a mobile communication system. Among them, ensuring lossless transmission of data during handover is a key technical problem. The following takes the X2 handover as an example to describe the problems existing in the prior art. The cross-base station handover in other scenarios has the same problem. FIG. 1 is a schematic flow chart of an existing X2 handover. The specific processing of the handover scenario includes: Step S102: The user equipment UE reports a measurement report (Measure Report) to the source side eNB. Step S104: The source side eNB sends a handover request (Handover Request) message to the target side eNB. Step S106: After the target eNB control plane (RNLC) receives the handover request message, the user plane (RNLU) creates a new UE instance according to the configuration information of the control plane, and the new configuration takes effect immediately. After successful, the control returns a Handover Request Ack message to the source side eNB control plane. Steps S108-S112: After receiving the handover request response message, the source-side eNB control plane sends a handover command (HandoverCommand) message to the UE, and notifies the UE to perform handover. At the same time, the source side eNB user plane is notified to start data forwarding. After the data backhaul is completed, the source side eNB sends a sequence number state transmission (SN Status Transfer) message to the target side eNB. Step S114: After receiving the handover command, the UE performs operations such as corresponding configuration, reset, and re-establishment. After successful, the UE synchronizes with the target cell, and sends a Handover Confirm message to inform the target eNB that the air interface link has been established. At this time, the UE starts transmitting uplink data to the target side eNB. Steps S116-S120, the target side eNB delivers the uplink data and then delivers the data to the S-GW. After receiving the Handover Confirm message, the target side eNB starts to send downlink data. The target eNB sends a Path Switch Request message to the MME. After the MME performs a series of configurations, it returns a Path Switch Request Ack message to the target eNB. So far, both the UE and the S-GW switch to the target side e B, and the uplink and downlink data can be transmitted through the target side eNB. 2 is a processing flow of a user plane of a target side eNB in an existing X2 handover, where the user plane RLC is an acknowledge mode (AM, Acknowledged Mode). Step S202: The user plane of the target side eNB creates a new UE instance according to the configuration message sent by the control plane, and the new configuration takes effect immediately. The serial number (SN) information of the PDCP is initialized according to the protocol, and the PDCP SN (Next_PDCP_TX_SN) of the next expected transmission message is initialized to 0, and the super frame number (TX HFN) of the next expected transmission message is initialized to 0, the next expectation. The PDCP SN (Next PDCP RX SN) of the received message is initialized to 0, the superframe number (RX_HFN) of the next expected received message is initialized to 0, and the last PDCP SN ( Last Submitted PDCP RX SN) successfully delivered to the upper layer message. ) Initialized to 4095. Step S204: The target side eNB user plane receives the packet that is forwarded by the source side eNB, and includes two parts: a PDCP SDU that has been processed by the PDCP layer but has not been successfully sent, and the backhaul message carries the PDCP SN; The PDCP layer does not carry the PDCP SN. Step S206: The target side eNB receives the sequence number status transmission message sent by the source side eNB, and the user plane PDCP layer updates the PDCP sequence number information according to the message (Next_PDCP_TX_SN/TX HFN/Next PDCP RX SN/RX HFN/ Last Submitted PDCP RX SN). S208: After receiving the handover confirmation message, the user plane of the target side eNB constructs a handover indication message, and after the user plane upper layer receives the handover indication message, the PDCP starts processing the downlink data. The PDCP SN is used for the backhaul packet carrying the PDCP SN. The PDCP sequence information is used for the backhaul packet that does not carry the PDCP SN and the new packet that is sent by the SI interface. Both the existing protocol and the implementation assume that the SN Status Transfer message (step S112 in Fig. 1) precedes the HandoverConfirm message (step S114 in Fig. 1), assuming that there is no problem; but in the process of handover between base stations, the two messages are successively The order cannot be guaranteed. It is possible that the HandoverConfirm message precedes the SN Status Transfer message. If the HandoverConfirm message precedes the SN Status Transfer message, the PDCP sequence number information is still the initial value when the PDCP performs downlink data processing. For the backhaul message that does not carry the PDCP SN and the new packet of the S1 port, the PDCP processing is filled. The PDCP SN information is incorrect. As a result, the UE cannot receive the packet correctly, resulting in downlink packet loss. SUMMARY OF THE INVENTION A primary object of the present invention is to provide a handover method for a cross-base station and an evolved base station e B to at least solve the above-mentioned handover process, in which the sequence of the HandoverConfirm message and the SN Status Transfer message cannot be guaranteed. Lost bag problem. According to an aspect of the present invention, a handover method for a cross-base station is provided, including: after receiving a handover indication message, the user plane of the target side e B determines whether the sequence number status transmission SN Status has been received before receiving the handover indication message. The Transfer message; if not, the handover indication message is buffered until the handover indication message is processed after receiving and processing the SN Status Transfer message. Preferably, after receiving the handover indication message, the user plane of the target side eNB determines whether the sequence number status transmission SN Status Transfer message has been received before receiving the handover indication message, including: after the user plane receives the handover indication message, setting the first The flag indicates that the handover indication message has been received; whether the SN Status Transfer message has been received according to the second flag, wherein the second flag is set to indicate whether the SN Status Transfer message has been received. Preferably, the handover indication message is buffered, and the handover indication message is processed after receiving and processing the SN Status Transfer message, including: the user plane buffers the handover indication message; after receiving the SN Status Transfer message, the user plane sets the second flag to Instructing that the SN Status Transfer message has been received; the user side processes the SN Status Transfer message, and determines whether the handover indication message has been received according to the first flag; if yes, the user plane processes the buffered handover indication message, and clears the first flag and The second sign. Preferably, the user plane processes the SN Status Transfer message, including: updating the sequence information of the packet data convergence layer PDCP of the user plane according to the information carried in the SN Status Transfer message, and constructing and transmitting the status report of the PDCP layer if required Status report of the PDCP layer. Preferably, the user plane processes the buffered handover indication message, including: the PDCP layer of the user plane processes the downlink packet, and if the PDCP layer status report is required, constructs and sends a PDCP layer status report, preferably, if the user plane After receiving the handover indication message, it is determined that the sequence number status transmission SN Status Transfer message has been received before, and the handover indication message is directly processed. According to another aspect of the present invention, an evolved base station eNB is provided, including: a determining module, configured to determine, after receiving a handover indication message, a user plane of the eNB, whether the sequence number status has been received before receiving the handover indication message Transmitting the SN Status Transfer message; the cache module is set to be determined not to be received by the judging module In the case of the SN Status Transfer message, the switching instruction indication message is cached; and the execution module is configured to process the switching indication message buffered by the cache module if the SN Status Transfer message is received and processed by the user plane. Preferably, the determining module includes: a first flag setting sub-module, configured to: after the user plane receives the switching indication message, set a first flag to indicate that the switching indication message has been received; and the second flag determining sub-module is set according to the first The second flag determines whether the SN Status Transfer message has been received, wherein the second flag is set to indicate whether the SN Status Transfer message has been received. Preferably, the execution module comprises: a second flag setting sub-module, configured to set a second flag to indicate that the SN Status Transfer message has been received after the user plane receives the SN Status Transfer message; the first flag determining sub-module is set to be After processing the SN Status Transfer message, the user plane determines whether the handover indication message has been received according to the first flag. The execution submodule is configured to process the buffer if the first flag determination submodule determines that the handover indication message has been received. The switching indication message; the flag clearing sub-module is configured to clear the first flag and the second flag after the execution sub-module processes the switching indication message. Preferably, the execution module is further configured to directly process the handover indication message if the determination module determines that the SN Status Transfer message has been received. By means of the invention, the switching indication message of the first arrival of the buffer is adopted until the SN Status is received and processed.

After the transfer message is processed, the handover indication message is processed to ensure the correctness of the PDCP sequence number information when the user plane of the target side e B processes the PDCP layer downlink message, and the PDCP sequence number maintained between the eNB and the UE is reduced. Packet loss caused by inconsistent information, which in turn achieves lossless transmission of data during handover and improves user experience. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are set to illustrate,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, In the drawings: FIG. 1 is a schematic flowchart of X2 handover according to the related art; FIG. 2 is a flowchart of processing of a user plane of a target side eNB when X2 handover according to the related art; FIG. 3 is a cross diagram according to Embodiment 1 of the present invention. FIG. 4 is a flowchart of processing a user facing a handover indication message according to Embodiment 2 of the present invention; 5 is a flowchart of processing a user facing an SN Status Transfer message according to Embodiment 3 of the present invention; FIG. 6 is a schematic structural diagram of an evolved base station according to Embodiment 4 of the present invention; FIG. 7 is an evolved type according to Embodiment 5 of the present invention; Schematic diagram of the base station structure. BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the embodiments in the present application and the features in the embodiments may be combined with each other without conflict. FIG. 3 is a flowchart of a cross-base station handover method according to the first embodiment of the present invention. As shown in FIG. 3, the method includes the following steps: Step S302: After receiving the handover indication message, the user plane of the target side e B determines to receive Whether the sequence number status transmission (SN Status Transfer) message has been received before the handover indication message; Step S304, if no, the handover indication message is buffered until the handover indication message is processed after receiving and processing the SN Status Transfer message. In this embodiment, the handover indication message of the first arrival is used, and the handover indication message is processed after the SN Status Transfer message is received and processed, so that the user plane of the target side eNB is processing the PDCP layer downlink report when the handover is performed across the base station. The correctness of the PDCP sequence number information in the text reduces the packet loss caused by the inconsistency of the PDCP sequence number information maintained between the eNB and the UE, thereby achieving the lossless transmission of data during handover and improving the user experience. In the above embodiment, the receiving status of the SN Status Transfer message and the handover indication message by the user may be determined by setting a flag. If the SN Status Transfer message arrives at the user plane earlier than the handover indication message, the user plane processes the SN Status Transfer message and processes the handover indication message according to the order in which the signaling arrives; if the handover indication message arrives at the user plane earlier than the SN Status Transfer message, The user plane first receives the handover indication message, but only caches the message first, does not process it, and processes the handover indication message after the SN Status Transfer message is processed. For the scenario where the handover indication message arrives at the user plane before the SN Status Transfer message, the user plane receives the handover indication message, and sets a flag that the handover indication message has been received; at this time, the SN Status Transfer message has not been received, so The handover indication message is processed, and only the handover indication message is saved. When SN Status When the Transfer message arrives at the user plane, it sets a flag that the SN Status Transfer message has received, and processes the SN Status Transfer message; at this time, the handover indication message has been received, so the handover indication message is processed. In this embodiment, the SN Status Transfer message processing includes: updating the serial number information of the PDCP according to the information carried in the message (Next_PDCP_TX_SN/TX_HFN/Next_PDCP_RX_SN/RX_HFN/Last_Submitted_PDCP

_RX_SN), if a status report is required, construct a status report. In this embodiment, the handover indication message processing includes: the PDCP layer starts processing the downlink message, and if the PDCP layer status report is required, constructs and sends the status report. Because the SN Status Transfer message has been processed before the handover instruction message is processed in the invention, the PDCP sequence number information and the status information have been updated, and the PDCP message can be correctly processed, thereby ensuring the target side eNB user plane PDCP when switching across base stations. After the sequence number information is obtained, the downlink data processing is started, and the packet loss caused by the inconsistency of the PDCP sequence number information maintained by the target eNB and the UE is effectively reduced. Embodiment 2 This embodiment describes a process for a user to face a handover indication message when the handover indication message arrives at the target side eNB user plane earlier than the SN Status Transfer message in the RLC acknowledge mode for the cross-base station handover mode, as shown in FIG. 4 . The method includes the following steps: Step 402: After receiving the HandoverConfirm message sent by the UE, the target eNB sends a handover indication message to the upper layer, and the user plane receives the handover indication message. Step 404: The user plane sets a flag for indicating that the handover indication message has been received. Step 406, judging by setting a flag indicating whether the SN Status Transfer message has been received.

Whether the SN Status Transfer message has been received. Step 408: In this scenario, the user plane does not receive the SN Status Transfer message, so the user plane only saves the handover indication message, and does not process the message. Step 410: If the user plane has received the SN Status Transfer message before the handover indication message, the handover indication message is directly processed. Embodiment 3 The present embodiment describes the processing flow of the user facing the SN Status Transfer message when the handover indication message arrives at the target side eNB user plane earlier than the SN Status Transfer message in the RLC acknowledge mode for the cross-base station handover mode, as shown in FIG. 5, including The following steps are as follows: Step 502: The control plane of the source side eNB sends a SN Status Transfer message to the control plane of the target eNB, and the control plane sends the message to the user plane, and the user plane receives the SN Status Transfer message; Step 504: User Setting a flag to indicate that the SN Status Transfer message has been received; Step 506: The user plane PDCP processes the SN Status Transfer message, including: updating the serial number information of the PDCP according to the information carried in the message (Next_PDCP_TX_SN/TX_HFN/Next_PDCP_RX_SN/ RX_HFN/ Last_Submitted_PDCP _RX_SN), if a status report is required, construct a status report. Step 508: The user plane determines whether the handover indication message has been received. Step 510: In this scenario, because the handover indication message has been received before, the user plane performs the processing of the handover indication message. The method includes: clearing the indication that the handover indication message and the SN Status Transfer message are received, the PDCP layer starts processing the downlink message, and if the PDCP layer status report is required, constructs and sends the status report. In this embodiment, the SN Status Transfer message has been processed before the handover instruction message is processed, and the PDCP sequence number information and the status information have been updated, so that the target side eNB user plane PDCP can obtain the correct sequence number information. Start processing downstream packets to reduce packet loss. Embodiment 4 FIG. 6 is a schematic structural diagram of an evolved base station according to Embodiment 4 of the present invention. As shown in FIG. 6, the method includes: a determining module 10, a cache module 20, and an executing module 30. They are connected in turn. The determining module 10 is configured to determine whether the sequence number status transmission SN Status Transfer message has been received before receiving the handover indication message after the user plane of the eNB receives the handover indication message; the cache module 20 is configured to determine at the determining module 10 that If the SN Status Transfer message is not received, the switching instruction indication message is cached; the execution module 30 is configured to process the switching indication buffered by the cache module 20 in the case that the SN Status Transfer message is received and processed by the user plane. In this embodiment, the handover indication message that is cached first is used, and the handover indication message is processed after receiving and processing the SN Status Transfer message, so as to ensure the user plane of the target side eNB when switching across the base station. The correctness of the PDCP sequence number information when processing the downlink packets of the PDCP layer reduces the packet loss caused by the inconsistency of the PDCP sequence number information maintained between the e B and the UE, thereby achieving the lossless transmission of data during handover and improving the user experience. Embodiment 5 FIG. 7 is a schematic structural diagram of an evolved base station according to Embodiment 5 of the present invention. As shown in FIG. 7, the embodiment includes each functional module in Embodiment 4. The judging module 10 includes: a first flag setting sub-module 101 and a second flag judging sub-module 102. The first flag setting sub-module 101 is configured to set a first flag to indicate that the switching indication message has been received after the user plane receives the switching indication message; the second flag determining sub-module 102 is configured to determine whether the second flag is received according to the second flag. The SN Status Transfer message, wherein the second flag is set to indicate whether the SN Status Transfer message has been received. The execution module 30 includes: a second flag setting sub-module 301, a first flag determining sub-module 302, an executing sub-module 303, and a flag clearing sub-module 304. The second flag setting sub-module 301 is configured to: after the user plane receives the lj SN Status Transfer message, set a second flag to indicate that the SN Status Transfer message has been received; the first flag determining sub-module 302 is set to be processed at the user plane. After the SN Status Transfer message, it is determined whether the handover indication message has been received according to the first flag. The execution sub-module 303 is configured to: when the first flag determination sub-module 302 determines that the handover indication message has been received, the processing cache is switched. The indication message; the flag clearing sub-module 304 is configured to clear the first flag and the second flag after the execution sub-module 303 processes the handover indication message. The execution module 30 is further configured to directly process the handover indication message if the determination module 10 determines that the SN Status Transfer message has been received. In the foregoing embodiments of the present invention, the handover indication message is first cached, and the handover indication message is processed after receiving and processing the SN Status Transfer message, so as to ensure that the user plane of the target side eNB is processed when switching across the base station. The correctness of the PDCP sequence number information in the downlink packets of the PDCP layer reduces the packet loss caused by the inconsistency of the PDCP sequence number information maintained between the eNB and the UE, thereby achieving the lossless transmission of data during handover and improving the user experience. Obviously, those skilled in the art should understand that the above modules or steps of the present invention can be implemented by a general-purpose computing device, which can be concentrated on a single computing device or distributed over a network composed of multiple computing devices. Alternatively, they may be implemented by program code executable by the computing device, such that they may be stored in the storage device by the computing device and, in some cases, may be different from The steps shown or described are performed sequentially, or they are separately fabricated into individual integrated circuit modules, or a plurality of modules or steps thereof are fabricated into a single integrated circuit module. Thus, the invention is not limited to any specific combination of hardware and software. The above is only the preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes can be made to the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and scope of the present invention are intended to be included within the scope of the present invention.

Claims

Claim

A method for switching between base stations, including:

After receiving the handover indication message, the user plane of the target side eNB determines whether the sequence number status transmission SN Status Transfer message has been received before receiving the handover indication message;

If not, the handover indication message is buffered until the handover indication message is processed after receiving and processing the SN Status Transfer message.

The method according to claim 1, wherein, after receiving the handover indication message, the user plane of the target side eNB determines whether the sequence number status transmission SN Status Transfer message has been received before receiving the handover indication message, including: After receiving the handover indication message, the user plane sets a first flag to indicate that the handover indication message has been received;

Determining, according to the second flag, whether the SN Status Transfer message has been received, wherein the second flag is set to indicate whether the SN Status Transfer message has been received.

The method according to claim 2, wherein: the switching indication message is cached, and the switching indication message is processed after receiving and processing the SN Status Transfer message, including:

The user plane caches the handover indication message;

After receiving the SN Status Transfer message, the user plane sets the second flag to indicate that the SN Status Transfer message has been received;

The user plane processes the SN Status Transfer message, and determines, according to the first flag, whether the handover indication message has been received;

If yes, the user plane processes the buffered handover indication message and clears the first flag and the second flag.

4. The method according to claim 3, wherein the processing, by the user plane, the SN Status Transfer message comprises:

Updating the sequence number information of the packet data convergence layer PDCP of the user plane according to the information carried in the SN Status Transfer message, and constructing and transmitting the status report of the PDCP layer if the status report of the PDCP layer is required .

The method according to claim 3 or 4, wherein the user plane processing the buffering the indication indication message comprises:

The PDCP layer of the user plane processes the downlink packet, and constructs and sends a status report of the PDCP layer if the status report of the PDCP layer is required.

6. The method according to claim 1, wherein, if so, the handover indication message is directly processed.

7. An evolved base station e B, comprising:

The determining module is configured to: after receiving the handover indication message on the user plane of the eNB, determine whether the sequence number status transmission SN Status Transfer message has been received before receiving the handover indication message;

a cache module, configured to cache the handover indication message if the determining module determines that the SN Status Transfer message is not received;

And an execution module, configured to process, when the user plane receives and processes the SN Status Transfer message, the handover indication message buffered by the cache module.

The evolved base station according to claim 7, wherein the determining module comprises:

a first flag setting submodule, configured to: after the user plane receives the handover indication message, set a first flag to indicate that the handover indication message has been received;

The second flag determining submodule is configured to determine, according to the second flag, whether the SN Status Transfer message has been received, wherein the second flag is set to indicate whether the SN Status Transfer message has been received.

The evolved base station according to claim 8, wherein the execution module comprises:

a second flag setting submodule, configured to set the second flag to indicate that the SN Status Transfer message has been received after the user plane receives the SN Status Transfer message;

a first flag determining sub-module, configured to determine, according to the first flag, whether the handover indication message has been received after the user plane finishes processing the SN Status Transfer message;

The executing submodule is configured to process the buffered handover indication message if the first flag determining submodule determines that the handover indication message has been received;

The flag clearing submodule is configured to clear the first flag and the second flag after the execution submodule processes the switching indication message.

The evolved base station according to claim 7, wherein the execution module is further configured to directly process the handover indication message if the determining module determines that the SN Status Transfer message has been received.