KR100943077B1 - Packet forwarding method for non-loss handover between base stations - Google Patents

Abstract

The present invention relates to a packet forwarding method for lossless handover between base stations, wherein the source base station stops splitting and assembling a packet at the start of handover and fills an extra field of a packet that was being split and assembled with 0 bits. In the case of handover between base stations, it is not necessary to transmit scheduling information and data already divided and assembled through the signaling message to the target base station by forwarding the downlink packet from the time point at which the splitting and assembling is stopped to the target base station. The packet forwarding complexity can be reduced, thereby improving handover performance.

Mobile communication, base station, handover, packet forwarding

Description

Packet forwarding method for non-loss handover between base stations {Packet forwarding method for non-loss handover between base stations}

The present invention relates to a packet forwarding method for lossless handover between base stations. The present invention relates to a packet forwarding technique for preventing downlink packet loss of a user terminal that may occur during handover between base stations in a mobile communication system.

The present invention is derived from the research conducted as part of the IT new growth engine core technology development project of the Ministry of Information and Communication and the Ministry of Information and Communication Research and Development. [Task Management Number: 2005-S-404-23, Project Name: 3G Evolution Access System] .

When a user equipment (UE) performs a handover from a source base station to a target base station, the user terminal does not receive data during the time for performing the handover. In DL, downlink packets are likely to be lost.

To prevent this, the source base station forwards data that is likely to be lost to the target base station, which is called packet forwarding. The target base station receiving the forwarded packets from the source base station transmits it to the user terminal to prevent the loss of downlink packets that are likely to be lost during the time of handover.

However, since the packet is divided, assembled and transmitted according to protocol unit data of each layer during packet transmission, in the past, when a handover occurs during packet transmission, a signaling message is used to process the divided data that could not be transmitted. Since scheduling information has to be transmitted to the target base station, and data that has already been divided and assembled has to be transmitted to the target base station, it has become a factor of increasing the complexity of packet forwarding.

Accordingly, the present inventors have studied a packet forwarding technique capable of minimizing the packet forwarding complexity performed during handover between base stations.

The present invention has been invented under the above-described object, and an object thereof is to provide a packet forwarding method for lossless handover between base stations, which can reduce the packet forwarding complexity performed during inter-base station handover.

According to an aspect of the present invention for achieving the above object, the present invention, the source base station stops dividing and assembling the packet at the start of performing the handover, and fills the extra field of the packet that was being divided and assembled with zero bits Characterized in that the transmission to the terminal.

The present invention stops splitting and assembling a packet at the start of the handover of the source base station, and transmits an extra field of a packet that was being split and assembled to zero bits to send to the user terminal. By forwarding the link packet to the target base station, it is not necessary to transmit the scheduling information through the signaling message and the data already divided and assembled to the target base station, thereby reducing the packet forwarding complexity performed during handover between base stations, thereby improving handover performance. Has a useful effect that can be improved.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily understand and reproduce the present invention.

1 is a diagram illustrating an example of a user plane protocol stack of a mobile communication system, and is a user plane protocol stack of 3G Generation Long Term Evolution (LTE).

The 3G LTE mobile communication system includes a user equipment (UE), a base station (ENB: Evolved Node B), and an access gateway (AGW).

The base station ENB serves as an access point for the user terminal UE to access the network, and performs radio resource allocation and management for the user terminal UE. In this case, from the standpoint of the user terminal (UE), the base station currently being accessed may be defined as a source base station, and the base station to be handed over may be defined as a target base station.

The Access Gateway (AGW) is largely divided into Mobility Management Entity (MME) and User Plane Entity (UPE) .The MME is responsible for authentication, bearer management, NAS signaling control, and UPE is the Packet Data Convergence Protocol (PDCP) and GTP. (GPRS Tunneling Protocol), through which packet transmission, packet filtering, etc. are performed, and in particular, packet switching (routing) during handover.

Define a transmission / reception route for the wireless section between the UE and the base station ENB as an Xu interface, and define a data transmission / reception route between the access gateway AGW and the base station ENB as an S1 interface, Define the route for forwarding as the X2 interface.

In the 3G LTE mobile communication system, when the UE performs a handover to the target base station, the UE does not receive data during the handover time, and thus is transmitted from the access gateway (AGW) to the source base station during this period. There is a possibility of data being lost.

To prevent this, the source base station forwards lost data to the target base station through the X2 interface, which is responsible for RLC (Radio Link Control) in the source base station.

2 is a schematic diagram of packet processing of RLC (Radio Link Control). Radio Link Control (RLC) provides a radio link establishment and release service, and performs segmentation and concatenation of service data unit (SDU) downlink packets transmitted from a higher layer. .

Radio Link Control (RLC) divides a Service Data Unit (SDU) packet, assembles it into a Protocol Data Unit (PDU) packet, and transmits it to a Media Access Control (MAC) layer.

The protocol data unit (PDU) packet is transmitted to the user terminal (UE) via the MAC layer and the physical (PHY) layer, and the RLC does not successfully transmit the packet when an acknowledgment message is received from the user terminal (UE). It is prescribed by.

In addition, the RLC forwards service data unit (SDU) packets that may occur in a transmission / reception interval due to handover from a source base station to a target base station.

3 is a diagram illustrating a forwarding scheme of divided and assembled packets. If the handover is started in the n th service data unit (SDU) packet, the source base station should forward all the service data unit (SDU) packets from the n th present in the buffer to the target base station.

In this case, the n th service data unit (SDU) packet is divided into a k th protocol data unit (PDU) packet and a k + 1 th protocol data unit (PDU) packet through a partitioning process. Assuming that the packet has already been transmitted to the terminal, the protocol data unit (PDU) packet is received from the middle portion (bit not transmitted) of the nth service data unit (SDU) packet after the RLC of the target base station receives the forwarded packet. In order to be able to configure, the RLC of the source base station should transmit the scheduling information for this to the target base station through a signaling message.

This causes the complexity of the packet forwarding method in the handover in the mobile communication system.

In addition, if the handover is started in the process of partitioning and assembling the n + 2th service data unit (SDU) packet, the n + 2nd service data unit (SDU) packet is a k + 1th protocol data unit (PDU) packet. As a result, the K + 1th protocol data unit (PDU) packet cannot be transmitted to the user terminal (UE) and handover is performed.

Accordingly, the target base station receives all service data unit (SDU) packets including the n-th and n + 1-th service data unit (SDU) packets, which are already divided and assembled, which constitute the k + 1th protocol data unit (PDU) packet. Must be forwarded to

That is, among the service data unit (SDU) packets constituting the k + 1th protocol data unit (PDU), there are n-th and n + 1-th service data unit (SDU) packets that have already been divided and assembled. There is a burden of transmitting a signaling message including scheduling information to a target base station.

In order to improve the complexity of packet forwarding during handover of the mobile communication system as illustrated above, in the present invention, the source base station stops dividing and assembling the packet at the start of performing the handover. Fill the extra field with 0 bits to send to the user terminal, and forward the scheduling information of the source base station to the target base station by forwarding service data unit (SDU) packets transmitted from the access gateway (AGW) to the target base station until the handover is completed. Since there is no need to transmit, the complexity of performing packet forwarding can be reduced during handover.

4 is a flowchart according to an embodiment of a packet forwarding method for lossless handover between base stations according to the present invention. A packet forwarding procedure for a lossless handover between base stations according to the present invention will be described with reference to FIG. 4.

When a handover is performed, first, in step S110, a protocol data unit (PDU) packet is added to a service data unit (SDU) packet, which is being split and assembled at the start of the handover. The remaining fields of the corresponding PDU packet are filled with 0 bits.

In step S120, the source base station transmits the protocol data unit (PDU) packet processed by step S110 to the user terminal.

Thereafter, in step S130, the source base station forwards the service data unit (SDU) packets transmitted from the mobile communication system side to the target base station until the handover is completed.

That is, the source base station stops dividing and assembling packets at the start of handover and transmits the extra fields of the packets being divided and assembled to 0 bits by using zero-bit padding. After that, since the downlink packet transmitted from the mobile communication system side is forwarded to the target base station until the handover is completed, the source base station does not need to transmit scheduling information through a signaling message to the target base station, It only needs to buffer the downlink packet of the service data unit (SDU) and transmit it to the target base station, thereby reducing the complexity of performing packet forwarding by eliminating the need for generating, transmitting, and processing scheduling information for synchronization of the interrupted packet. To achieve the object of the present invention set out above It is possible.

An example of the 0 bit process by step S110 is shown in Figs. 5A to 5C. 5A to 5C are diagrams illustrating an example of downlink packet 0 bit processing in a packet forwarding method for lossless handover between base stations according to the present invention.

As shown in FIG. 5A, if the handover is determined during the partitioning and combining of the n th service data unit (SDU) packet, the k + 1 th protocol data unit (PDU) up to the n th service data unit (SDU) packet is determined. The packet is included in the packet, 0 bits are processed for the remaining fields, and then transmitted to the UE, and packet forwarding is performed from the n + 1 th service data unit (SDU) packet to the target base station.

As shown in FIG. 5B, if the handover is determined during the division and combining of the n + 1 th service data unit (SDU) packet, the k + 1 th protocol data up to the n + 1 th service data unit (SDU) packet is determined. It is included in a unit (PDU) packet, 0 bits are processed for the remaining fields, transmitted to the user terminal (UE), and packet forwarding from the n + 2 th service data unit (SDU) packet to the target base station.

As shown in FIG. 5C, if it is determined that handover is performed during the partitioning and combining of the n + 2 th service data unit (SDU) packet, the k + 1 th protocol data up to the n + 2 th service data unit (SDU) packet. It is included in a unit (PDU) packet, 0 bits are processed for the remaining fields, transmitted to the user terminal (UE), and packet forwarding from the n + 3 th service data unit (SDU) packet to the target base station.

Meanwhile, according to an additional aspect of the present invention, the packet forwarding method for lossless handover between base stations according to the present invention may be implemented such that the source base station drives a timer at the start point of handover in step S110. . This timer may be a time point at which packet forwarding is performed upon termination.

On the other hand, the step S130 may be made of the following detailed process.

First, in step S131, the source base station stops dividing and assembling a service data unit (SDU) packet, and buffers service data unit (SDU) packets transmitted from the mobile communication system.

If the acknowledgment (Ack) message for all transmitted protocol data unit (PDU) packets are received from the user terminal (UE) or the timer expires, in step S132 the source base station to the target base station in step S131 Forward the service data unit (SDU) packets buffered by.

Therefore, the source base station buffers the downlink packets of the service data unit (SDU) transmitted from the mobile communication system from the time point at which the handover is determined, and after a specific time elapses (receiving a signal from the user terminal or ending the timer). By forwarding the downlink packets of the buffered service data unit (SDU) to the target base station, the source base station needs to transmit scheduling information through a signaling message to the target base station or transmit data that has already been divided and assembled to the target base station. Therefore, the complexity of packet forwarding performed during handover between base stations can be reduced.

On the other hand, according to an additional aspect of the present invention, in step S130, when a resource release command is received from a target base station, the source base station terminates forwarding of a service data unit (SDU) packet in step S133 It is preferable to further include.

That is, after the source base station transmits a handover command message to the user terminal (UE) in the handover process, if the user terminal (UE) successfully connected to the target base station and the path is changed, the target base station is the source A resource release command is transmitted to the base station. Then, the source base station receiving the resource release command ends the packet forwarding. Subsequent packet processing is performed between the target base station and the user terminal (UE).

An example of applying the packet forwarding method for lossless handover between base stations according to the present invention having the above configuration to a 3G LTE mobile communication system will be described with reference to FIG. 6.

If it is determined in S210 that a handover is performed in the source ENB, a radio link control (RLC) of the source eNB drives a timer (S220), and an access gateway (AGW) currently being split and assembled. The service data unit (SDU) packet received from the PDU packet is included in the protocol data unit (PDU) packet, and the remaining fields of the corresponding protocol data unit (PDU) packet are filled with 0 bits. (S230).

After that, the radio link control (RLC) of the source base station stops dividing and assembling the service data unit (SDU) packet received from the access gateway (AGW) (S240) and moves down to the user terminal (UE). The transmission of the link packet is stopped and the buffering of the service data unit (SDU) packet transmitted from the access gateway (AGW) is started (S250).

Acknowledgment (Ack) message for all downlink packets transmitted from the user terminal (UE), or wait until the timer end is detected, acknowledgment (Ack) message for all downlink packets transmitted from the user terminal (UE) When receiving the timer or detecting the timer termination (S260), the RLC of the source base station forwards a service data unit (SDU) packet buffered to the target ENB through the X2 interface (S270).

If the handover procedure is successful and a resource release command is transmitted from the target base station (S280), the source base station terminates packet forwarding (S290). Accordingly, the present invention does not need to forward a service data unit (SDU) packet, which has been divided or assembled, to a target base station, thereby reducing load, and dividing or splitting a service data unit (SDU) packet. Since the scheduling information related to the assembly does not have to be transmitted to the target base station, it is possible to reduce the complexity of packet forwarding during handover between base stations.

While the invention has been described with reference to the preferred embodiments, which are referred to by the accompanying drawings, it is apparent that various modifications are possible without departing from the scope of the invention within the scope covered by the following claims from this description. .

The present invention can be industrially used in the field of packet forwarding technology and its application technology for preventing downlink packet loss of a user terminal that may occur during a handover between base stations in a mobile communication system.

1 is a diagram illustrating an example of a user plane protocol stack of a mobile communication system;

2 is a schematic diagram of packet processing in RLC (Radio Link Control)

3 shows an overview of forwarding of split and assembled packets.

4 is a flowchart according to an embodiment of a packet forwarding method for lossless handover between base stations according to the present invention.

5A to 5C illustrate an example of downlink packet 0 bit processing of a packet forwarding method for lossless handover between base stations according to the present invention.

6 is a diagram illustrating an application example of a packet forwarding method for lossless handover between base stations according to the present invention;

Claims (4)

In the packet forwarding method during handover between a source base station and a target base station, a) In the protocol data unit (PDU) packet, the source base station includes a service data unit (SDU) packet, which is being split and assembled at the time of performing the handover, and includes the corresponding protocol data unit (PDU) packet. Filling the remaining fields of with 0 bits; b) sending, by the source base station, a protocol data unit (PDU) packet processed by step a) to the user terminal; c) forwarding, by the source base station, service data unit (SDU) packets transmitted from an access gateway (AGW: Access Gateway) of the mobile communication system to the target base station after step b) until the handover is completed; Packet forwarding method for lossless handover between base stations comprising a. The method of claim 1, In step a): A packet forwarding method for lossless handover between base stations, wherein the source base station drives a timer at the start time of performing the handover. The method of claim 2, Step c) above: c1) The source base station stops dividing and assembling a service data unit (SDU) packet and buffers service data unit (SDU) packets transmitted from an access gateway (AGW) of a mobile communication system. ); c2) when an acknowledgment (Ack) message for all transmitted protocol data unit (PDU) packets is received from the user terminal (UE) or the timer is expired, the source base station is sent to the target base station by step c1). Forwarding buffered service data unit (SDU) packets; Packet forwarding method for lossless handover between base stations comprising a. The method of claim 3, wherein Step c) above: c3) when the Resource Release command is received from the target base station, ending the forwarding of a service data unit (SDU) packet by the source base station; Packet forwarding method for lossless handover between base stations further comprising.

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