JP2003047037A - Communication system and handover control method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To prevent packet loss during a handover, to reduce the amount of packets buffered in a network, and to eliminate the misordering of packets after a handover. SOLUTION: A mobile communication terminal 11 detects the start of handover from an area of a source base station 12 to an area of a destination base station 13, and buffers packet data in response to the detection. The buffered packet data is transmitted to the mobile communication terminal 11 after the end of the handover for the mobile communication terminal. This prevents packet loss during handover from the source base station area to the destination base station area for mobile communication terminals, reduces the amount of network buffer required for that purpose, and prevents out-of-order packets after handover. it can.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system and a handover control method, and more particularly to a communication system and a handover control method for transmitting packet data from a packet transmission source to a mobile communication terminal via a base station.

[0002]

2. Description of the Related Art In mobile communication, it is known that the communication environment changes greatly at the time of a handover in which a terminal moves between base stations, such as a packet loss and a large change in the arrival interval of packets. Therefore, flow control technology and QoS guarantee technology are important. Here, TCP (Transmission Control), which is a flow control function used for data communication, is used.
Protocol) and RSVP (Resource)
Reservation Protocol), Dif
QoS guarantee technology such as fServ is generally known. Further, as a handover method for preventing packet loss during handover by buffering packets in the network instead of terminals during handover, IET
F (Internet Engineering Ta)
sk force) Internet draft, HAWAII, Smooth handof
f etc. are known.

[0003]

Since the above-mentioned conventional flow control technology and QoS guarantee technology do not perform control in consideration of handover, bursty packet loss may occur during handover. In order to prevent this packet loss, a function of buffering on the network side instead of the terminal at the time of handover and forwarding them to the terminal after the handover is required. As a result, a large buffer is required on the network side.

Further, after the handover, there are two paths at the same time, that is, the path where the packet is forwarded from the buffer source to the terminal and the path where the packet is originally transmitted from the packet source. Since the packets are forwarded to the terminal simultaneously from the two paths that exist at the same time, the buffered packet and the new packet forwarded from the source of the packet are mixed to the terminal. arrive. Then, the packet may be out of order.

When such packet out-of-order occurs, the terminal receiving the packet needs a large buffer capacity for rearrangement, or requires a longer time for rearrangement. There is a case.
In particular, in order to correct the packet misordering, the terminal is required to have a larger buffer capacity than in the case where the packet misordering does not occur.

The present invention has been made to solve the above-mentioned drawbacks of the prior art, and its purpose is to prevent packet loss during handover and to make the flow control function and the QoS technology aware of the handover so that the terminal after the handover is completed. In addition, by notifying the number of buffered packets to the communication system, it is possible to reduce the number of buffered packets in the network during handover and prevent the packets from being out of order,
And to provide a handover control method.

[0007]

A communication system according to claim 1 of the present invention is a communication system for transmitting packet data from a packet transmission source to a mobile communication terminal via a base station, wherein the mobile communication terminal is mobile. The mobile communication terminal includes buffering means for buffering the packet data in response to detection of the start of handover from the source base station area to the destination base station area, and the packet data buffered by the buffering means. Is transmitted to the mobile communication terminal in response to the detection of the end of the handover. By buffering the packet data from the start of the handover and transmitting the buffered packet data to the mobile communication terminal after the handover, it is possible to eliminate the packet loss during the handover.

A communication system according to claim 2 of the present invention comprises:
In claim 1, further comprising means for instructing the packet source to limit transmission of the packet data in response to detection of the start of the handover. Immediately after the detection of the start of handover, the packet transmission of the transmission source can be stopped by using the flow control technology or the QoS guarantee technology, so that the buffer capacity required in the network can be reduced.

A communication system according to claim 3 of the present invention comprises:
3. The method according to claim 1, further comprising means for transmitting a packet forwarding request for forwarding the packet buffered by the buffering means to the source base station in response to detection of the end of the handover. Is characterized by. A communication system according to claim 4 of the present invention is the communication system according to any one of claims 1 to 3, wherein a buffering number indicating how many packets are buffered is set to the mobile communication terminal which has issued the packet forwarding request. The method further includes: context transmitting means for notifying, and means for resuming packet transmission to a packet source when a final buffered packet is received according to the buffering number notified by the context transmitting means. Is characterized by. After all buffered packets have been received, a communication restart message is sent to the packet source, which prevents the packets from being out of order and reduces the receive buffer capacity required by the packet receiving terminal. .

A communication system according to claim 5 of the present invention comprises:
5. The buffer according to any one of claims 1 to 4, wherein buffering by the buffering means is performed in a base station in a source area of the mobile communication terminal, and the buffered packet data is further transferred to a destination of the mobile communication terminal. It is characterized in that the information is transmitted to the mobile communication terminal via a base station in the area.

A communication system according to claim 6 of the present invention comprises:
In any one of Claims 1-5, the start of the said hand-over is detected in the said mobile communication terminal. A communication system according to claim 7 of the present invention is characterized in that, in any one of claims 1 to 5, the start of the handover is detected in the base station.

A handover control method according to claim 8 of the present invention is a handover control method in a communication system for transmitting packet data from a packet source to a mobile communication terminal via a base station, the handover for the mobile communication terminal. Detecting the packet, buffering the packet to be received by the mobile communication terminal on the network side, instructing the packet transmission source to limit the transmission of the packet, and buffering after detecting the end of the handover. Sending a packet transfer request first, notifying the mobile communication terminal of the number of packets buffered by the buffering destination that received the packet transfer request, and transmitting the packet when the packet forwarding is completed. To restart packet transmission Characterized in that it comprises the step of sending a. By buffering packets during handover in the packet switching network on the network side, packet loss during handover can be eliminated. Moreover, since the packet transmission of the transmission source can be stopped immediately after the detection of the handover, the buffer capacity required in the network can be reduced. Further, after the handover, the buffering source notifies the mobile communication terminal of the number of buffered packets, and after the mobile communication terminal receives all the buffered packets, the communication restart message is sent to the transmission source of the packet. It is possible to prevent the packets from being out of order and reduce the receiving buffer capacity required for the packet receiving terminal.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. In each drawing referred to in the following description, the same parts as those in the other drawings are denoted by the same reference numerals. This communication system detects the start of a handover from a source base station area to a destination base station area for a mobile communication terminal, buffers packet data in response to this detection, and stores the buffered packet. Operates to send data to the mobile communication terminal after the handover for the mobile communication terminal is completed. This prevents packet loss during handover from the source base station area to the destination base station area for mobile communication terminals, reduces the amount of network buffer required for that purpose, and prevents packet misordering after handover. it can.

The present communication system can be applied to a mobile communication terminal-oriented handover and a base station-oriented handover, respectively. Hereinafter, a mobile communication terminal-oriented handover and a base station-oriented handover will be described separately for each item. (Handover by Mobile Communication Terminal Orientation) First, a terminal-oriented handover in which the terminal side has a handover prediction function and the base station has a packet buffering function will be described with reference to FIGS.
Will be described with reference to. It should be noted that in this example, description will be made assuming that TCP, which is widely used in data communication on the Internet, is provided as a flow control function between a packet transmission source and a packet reception destination terminal. .

As shown in FIG. 1A, the base station in the communication system of the present example receives a packet buffering request 204 from the terminal and outputs a filtering instruction 205 to receive a packet buffering request. In response to the filtering instruction 205 from the unit 21 and the packet buffering request receiving unit 21, the packet filtering unit 22 that filters the received data packet 200 and the packet forward request 208 from the terminal are received, and the context generation instruction 209 is received. Packet forward request message receiving unit 23 that outputs a context generation instruction 209 and a context generation unit 24 that outputs a context and packet forward 212.
And a forward unit 26 for transmitting context and packet data 213 to the terminal, and a buffer 25 for buffering the data packet 200 filtered by the packet filter unit 22. Note that the buffer 25 is monitored by the context generation unit 24 by the buffer monitoring signal 210, and
Packet forwards the buffered packet 21
It is output to the context generation unit 24 as 1.

Further, as shown in FIG. 1B, the mobile communication terminal in the communication system of this example predicts the movement of its own terminal based on the external signal 201 and outputs the movement detection notification 202. The terminal movement detection unit 27, the ACK generation unit 29 that receives the movement detection notification 202 and transmits the ACK 203 to the packet transmission source, and the movement detection notification 202 that receives the packet buffering request 20 from the movement source base station.
4 and the connection detection unit 30 that detects a connection with a new base station based on the external signal 206 and outputs a connection notification 207; and the connection source 207 that receives the connection notification 207. A packet forward request unit 31 that transmits a packet forward request 208 to the base station, and context and packet data 213 from the source base station are received, and ACK is received according to the context.
A context receiving unit 33 that outputs a generation instruction 214,
An ACK transmission unit 32 that outputs ACKs 215 and 216 returned to the packet transmission source is included. In addition, A
ACKs 215 and 216 output from the CK transmission unit 32
Is returned to the packet sender via the context receiver 33.

A handover control method of the present system including the base station and the mobile communication terminal having the above-mentioned configuration will be described with reference to FIG. The figure shows steps (1) to (7) of the terminal-oriented handover control method. (1) The movement of the mobile communication terminal 11 from the currently registered base station (BS) 12 to a new base station 13 is detected by the external signal 101. The following methods can be considered as the detection method. Method of using information of Link Layer (change of electric field strength, etc.) Ping is transmitted to peripheral base stations at regular intervals and RT
Method of calculating T (Round Trip Time) Base station layout and GPS (Global Position)
(2) When the mobile communication terminal 11 decides to move, in order to control the flow from the receiving side to the transmitting side with respect to the packet source 14, the mobile communication terminal 11 controls the flow from the receiving side to the transmitting side. ACK20 with window size 0
Returns 3. The window field is originally used to prevent a buffer overflow on the receiving side. ACK20 of window field 0
By returning 3, the source 14 of the packet cannot send any data packet other than the packet for which the emergency flag (URG) is set. During this time, the timeout timer (time out timer) is not calculated, so that the timeout does not occur. (3) The mobile communication terminal 11 sends the buffering request 204 to the source base station 12 at the same time as sending the ACK 203 in step (2) described above. The source base station 12 that has received the buffering request 204 creates a filter for the terminal and buffers the packet addressed to the terminal. At this time, if the terminal 11 has a plurality of sessions, it is necessary to further determine the sessions after the destination is determined. For example, the following methods can be considered. Method of determining upper layer header after judging from packet header destination. In advance, upper layer information is embedded in the packet header at the packet destination (for example, using option, IPv6 (Internet). Protoc
ol version 6), a flow label is used), and a method for determining the destination after determining the destination. In advance, a different address (Mobile) is used for each session.
A method of allocating a care-of address in IP and making a determination based on the address (4) The mobile communication terminal 11 immediately moves from the source base station 12 to the destination base station 13 Then, a forward request 208 for the buffered packet data is transmitted. (5) The packet data 213 buffered by the buffering request 204 is forwarded to the mobile communication terminal 11 ′ after moving.

At the same time, the number of packets buffered in the source base station 12, that is, the number of buffered packets is notified to the terminal by the context. The context is realized as follows, for example. Method of creating a new message for notifying the terminal Method of utilizing the option of the IP header (indicate in the header option of the last data packet forwarded from the source base station that it is the last packet). (6) When the forwarded packet is received while the packet is being forwarded from the base station 12, the ACK 215 of the window field 0 is returned to the transmission source 14 of the packet, or the ACK 215 is not returned. In TCP, basically, it is necessary to return ACK to all received packets, but by delaying the return of ACK for a certain period of time, a plurality of packets can be transmitted as one A packet.
It is also allowed to respond with CK. (7) When the last buffered packet is sent from the source base station 12, the mobile communication terminal 1
1'returns the original value in the window field as the ACK 216 for the packet. When the packet destination receives this message, the communication can be restarted without causing the packets to be out of order.

By carrying out the terminal-oriented handover as in steps (1) to (7) described above, the packet loss is prevented during the handover, the network buffer amount required for that purpose is reduced, and the packet after the handover is Out-of-order prevention can be realized. When performing the terminal-oriented handover as described above, since no change is made to the communication partner, there is a great merit that the existing Web server can be used. Further, as for the packet forward request message transmitted after the handover, instead of creating a dedicated message, the location update message (for example, Mobile IP binding update message) transmitted after the handover should be piggybacked on it. Therefore, it is possible to suppress the consumption of the wireless link.

Further, in the case of the above-mentioned terminal orientation, there is no need to change the configuration of the base station, so that the present system can be realized simply. As the demand for privacy on the Internet increases in the future, when it is expected that advanced cryptographic techniques will be used, it is expected that the layer portion related to only the terminal above the IP layer will be encrypted. Even in such a case, the above-mentioned terminal-oriented method that does not require the interpretation of the cipher by a relay node such as a proxy can realize the present system in the simplest manner. (Base Station Oriented Handover Part 1) Next, a base station oriented handover in which the base station side has a handover prediction function and a packet buffering function will be described with reference to FIGS. 3 and 4.

As shown in FIG. 3A, the base station in the communication system of this example predicts the movement of its own terminal based on the external signal 401 and outputs a movement detection notification 402 to detect the terminal movement. Unit 35, receiving the movement detection notification 402, outputting a filtering instruction 205, and receiving the filtering instruction 205, the packet filter unit 2 for filtering the received data packet 200
2, a proxy ACK unit 36 that returns an ACK for the first packet addressed to a specific terminal that has passed through the packet filter unit 22, a buffer 25 that buffers the data packet 200 filtered by the packet filter unit 22, and a terminal Packet forward request 20 from
8 and outputs a context generation instruction 209, a packet forward request message reception unit 23, a context generation instruction 209, and a context generation unit 24 that outputs a context and packet forward 212, and a context and packet data to a terminal. 213
And a forward unit 26 for transmitting the. Note that the buffer 25 is monitored by the context generation unit 24 by the buffer monitoring signal 210, and
Packet forwards the buffered packet 21
It is output to the context generation unit 24 as 1.

Also, the mobile communication terminal in the communication system of this example detects a connection with a new base station based on the external signal 206 and issues a connection notification 207, as shown in FIG. 3 (b). Connection detection unit 30 for outputting and connection notification 20
7, the packet forward request unit 31 that transmits the packet forward request 208 to the source base station.
And a context receiving unit 33 that receives the context and packet data 213 from the source base station and outputs an ACK generation instruction 214 according to the context, and outputs ACKs 215 and 216 returned to the packet source 14.
The CK transmission unit 32 is included. In addition, AC
The ACKs 215 and 216 output from the K transmission unit 32 are
It is returned to the packet transmission source 14 via the context receiving unit 33.

A handover control method of the present system including the base station and the mobile communication terminal having the above-mentioned configuration will be described with reference to FIG. The figure shows steps (1) to (6) of the terminal-oriented handover control method. (1) The movement of the mobile communication terminal 11 is detected by the external signal 401 in the movement-source base station 12. The following methods can be considered as the detection method. Method of receiving a trigger when a terminal moves from Link Layer in the base station 12 Method of checking TCP ACK in the base station 12 and confirming by Ping when it does not return for a certain period Method of confirming periodically by Ping in the base station 12 (2) When the movement of the mobile communication terminal 11 is confirmed, the movement-source base station 12 thereafter filters all packets addressed to the movement-destination mobile communication terminal 11 ′ that reach the movement-source base station 12 and buffers them. At the same time, the source base station 12
Is a proxy for the terminal 11 for the first packet received,
ACK 404 with window size 0 is returned. By returning the ACK 404 of the window field 0, the transmission source 14 of the packet cannot transmit any data packet other than the packet for which the emergency flag (URG) is set. During this time, the timeout timer is not calculated either, so no timeout occurs.

When a plurality of sessions are set up in the terminal when performing buffering, it is necessary to further determine the session after determining the destination. For example, the following methods can be considered. How to determine up to the higher layer header after judging from the packet header destination, the destination of the packet is determined beforehand by incorporating the upper layer information into the packet header at the destination of the packet. A method to determine that part later. In advance, a different address (Mobile
A method of allocating a care-of address in IP and deciding by the address (3) The mobile communication terminal 11 ′ is buffered in the source base station 12 as soon as it arrives in the area of the destination base station 13. Packet data forward request 208
To send. For this forward request 208, for example, an option is used or, in the case of IPv6, a flow label is used. (4) In response to the packet data forward request 208, the packet data 213 buffered in the source base station 12 is forwarded to the mobile communication terminal 11 ′. At the same time, the number of packets buffered in the source base station 12 is notified to the mobile communication terminal 11 ′ by the context. The context transfer is realized as follows, for example. Method of creating a new message for notifying the mobile communication terminal 11 'Method of using the IP header option (in the header option of the last data packet forwarded from the source base station 12, the last packet is (5) While the packet is being forwarded from the source base station 12, when the forwarded packet is received, the ACK 215 of the window field 0 is returned to the source of the packet or the ACK is sent. Does not return. (6) When the last buffered packet is sent from the source base station 12, the original value is input to the window field and returned as ACK 216 for the packet. When the packet transmission source 14 receives this message, communication can be restarted without causing the packet to be out of order.

By performing the base station-oriented handover as in steps (1) to (6) described above,
It is possible to prevent packet loss during handover, reduce the amount of network buffer required for that purpose, and prevent out-of-order packets after handover. (Handover based on base station No. 2) Different from the above-described handover based on base station, there is no configuration to be added to the terminal, and a base having a packet buffering function on the source base station side and the destination base station side Station-oriented handover will be described with reference to FIGS. 5 and 6.

The source base station in the communication system of the present example, as shown in FIG.
The movement detection notification 40 predicts the movement of the own terminal based on 1.
2. Terminal movement detection unit 35 that outputs 2 and movement detection notification 40
In response to 2, the filtering instruction 205 is output 34
A packet filter unit 22 that receives the filtering instruction 205 and filters the received data packet 200; and a proxy ACK unit 36 that returns an ACK for the first packet addressed to a specific terminal that has passed through the packet filter unit 22. , And a buffer 25 that buffers the data packet 200 filtered by the packet filter unit 22.

Further, the source base station receives the packet forward request 208 from the terminal and outputs the context generation instruction 209, as shown in FIG. When,
Upon receiving the context generation instruction 209, the context generation unit 24 that outputs the context and packet forward 212, and the buffering request 21 to the movement-destination base station
9 is included in the packet buffering request unit 36, and the packet buffering request 218 and the forward unit 26 that sends the context and packet data 213 to the movement-destination base station are included. The buffer 25 is monitored by the context generation unit 24 by the buffer monitoring signal 210 and outputs the buffered packet to the context generation unit 24 as the packet forward 211.

Also, the mobile communication terminal in the communication system of this example detects a connection with a new base station based on the external signal 206 and issues a connection notification 207, as shown in FIG. 5B. Connection detection unit 30 for outputting and connection notification 20
7 and a packet forward request unit 31 for transmitting a packet forward request 208 to the source base station.

The destination base station in the communication system of this example receives the packet buffering request 218 from the source base station and outputs the filtering instruction 205, as shown in FIG. 5 (c). The packet buffering request receiving unit 21, the packet filtering unit 205 that receives the filtering instruction 205 from the packet buffering request receiving unit 21, receives the context from the source base station, and receives the context from the source base station. , The context receiving unit 33 that controls the buffer 38 to buffer the data packets up to the last packet indicated by, the buffer 38 that buffers the data packets filtered by the packet filter unit 22, and the buffer 3
8 and the forwarding unit 37 that forwards the packet 217 buffered to 8 to the terminal.

A handover control method of the present system including the base station and the mobile communication terminal having the above-mentioned configurations will be described with reference to FIG. The figure shows steps (1) to (6) of the terminal-oriented handover control method. (1) The movement of the mobile communication terminal 11 is detected by the external signal 401 in the movement-source base station 12. The following methods can be considered as the detection method. Method of receiving a trigger when a terminal moves from Link Layer in the base station 12 Method of checking TCP ACK in the base station 12 and confirming by Ping when it does not return for a certain period Method of confirming periodically by Ping in the base station 12 (2) When the movement of the mobile communication terminal 11 is confirmed, the movement-source base station 12 thereafter filters all packets addressed to the movement-destination mobile communication terminal 11 ′ that reach the movement-source base station 12 and buffers them. At the same time, the source base station 12
Is a proxy for the terminal 11 for the first packet received,
ACK 404 with window size 0 is returned. By returning the ACK 404 of the window field 0, the transmission source 14 of the packet cannot transmit any data packet other than the packet for which the emergency flag (URG) is set. During this time, the timeout timer is not calculated either, so no timeout occurs.

When a plurality of sessions are set up in the terminal when performing buffering, it is necessary to further determine the session after determining the destination. For example, the following methods can be considered. Method to determine up to higher layer header after determining from packet header destination. Incorporate upper layer information into the packet header in advance at the packet destination (for example, option Use, if IPv6, use flow label), method to determine the part after determining the destination. In advance, a different address (Mobile) is used for each session.
A method of allocating a care-of address in IP and deciding by the address (3) The mobile communication terminal 11 ′ is buffered in the source base station 12 as soon as it arrives in the area of the destination base station 13. Packet data forward request 208
To send. (4) In response to the packet data forward request 208, the packet data 213 buffered in the source base station 12 is forwarded to the destination base station 13. At the same time, the number of packets buffered in the source base station 12 is notified to the destination base station 13 by the context. The context transfer is realized as follows, for example. Method of creating a new message for notifying to the base station 13 Method of using the option of IP header (The header packet of the last data packet forwarded from the source base station 12 must be the last packet. All packets addressed to the mobile communication terminal 11 are buffered in the movement-destination base station 13 until the forwarding of the packet from the movement-source base station 12 is completed. (5) The packet 217 buffered in the base station 13 is forwarded to the terminal 11 ′ after the last buffered packet indicated by the context arrives from the movement-destination base station 13. (6) When the packet is forwarded from the movement-destination base station 13, the terminal automatically inputs and returns the original value in the window field as an ACK 216 for these packets. When the packet transmission source 14 receives this message, communication can be restarted without causing the packet to be out of order.

By performing the base station-oriented handover as in steps (1) to (6) described above,
It is possible to prevent packet loss during handover, reduce the amount of network buffer required for that purpose, and prevent out-of-order packets after handover. In the case of performing the base station-oriented handover as described above, since no change is made to the communication partner, there is a great advantage that the existing Web server can be used. Further, as for the packet forward request message transmitted after the handover, instead of creating a dedicated message, the location update message (for example, Mobile IP binding update message) transmitted after the handover should be piggybacked on it. Therefore, it is possible to suppress the consumption of the wireless link.

In the case of base station orientation, in the terminal orientation, the terminal side judges the radio wave state and the base station is provided with a buffering function so that the radio wave state may change depending on the sudden radio environment change such as entering a tunnel. It is possible to deal with a lack of communication. In addition, in the case of "handover based on base station No. 2" described above, there is a great merit that no change is required to the existing terminal. (Summary) By the way, in TCP adopted in the communication system of the present example, since the timeout is not calculated while the window field 0 is notified, the increase of the delay time caused by the handover processing in this system is increased. Does not matter. In TCP, if a packet is output and ACK is not returned for a certain period,
It determines that packet loss has occurred, reduces the throughput, and retransmits the lost packet. According to this system, the influence of handover on communication can be minimized.

By the way, in the communication system described above, the following handover control method is realized. That is, it is a handover control method in a communication system for transmitting packet data from a packet source to a mobile communication terminal via a base station, the step of detecting a handover for the mobile communication terminal, and the mobile communication terminal to receive Buffering packets on the network side, instructing the packet transmission source to restrict transmission of the packets, sending a packet transfer request to the buffering destination after detecting the end of handover, and the packet transfer request The handover control includes a step of notifying the mobile communication terminal of the number of packets buffered by the buffering destination that has received the packet, and a step of sending a packet transmission restart instruction to the transmission source of the packet when the forwarding of the packet is completed. Method realized It has been.

If such a control method is adopted, the following effects can be obtained. That is, the packet loss during the handover can be eliminated by buffering the packet under the handover in the packet switching network on the network side. In addition, it is possible to immediately stop the packet transmission of the transmission source after the detection of handover,
The buffer capacity required in the network can be reduced. Further, after the handover, the buffering source notifies the mobile communication terminal of the number of buffered packets, and after the mobile communication terminal receives all the buffered packets, the communication restart message is sent to the transmission source of the packet. It is possible to prevent the packets from being out of order and reduce the receiving buffer capacity required for the packet receiving terminal. Especially in TCP, throughput may be reduced because packet misordering may be treated as packet loss, but this system does not reduce packet throughput because it prevents packet misordering.

With respect to the description of the claims, the present invention can have the following aspects. (1) Detecting a handover in a network configuration in which a packet transmission source and a packet receiving terminal are equipped with a flow control technology and a QoS guarantee technology and have a buffering function in the network,
A handover control method comprising a function of transmitting a packet transmission restriction message to a packet transmission source by using a flow control technology or a QoS guarantee technology and prohibiting further flow control packet transmission.

(2) The handover control method according to (1), further comprising a function of transmitting a packet transmission restriction message to a packet transmission source and simultaneously transmitting a buffering request to the network. (3) The handover control method according to (2), further including a function of transmitting a request for forwarding the buffered packet to the source base station, triggered by the connection to the destination base station.

(4) The handover control method according to (3), further including a context transmission function of notifying how many packets are buffered to the terminal which has issued the packet forwarding request. (5) When the buffered final packet notified by the context is received, the packet transmission source is further provided with a function of restarting packet transmission by using a flow control function or a QoS guarantee technology. (4) The handover control method according to (4).

[0039]

As described above, according to the present invention, the packet loss during the handover can be eliminated by buffering the packet during the handover in the packet switching network on the network side. Further, since the packet transmission of the transmission source can be stopped immediately after the detection of the handover by using the flow control technique or the QoS guarantee technique, there is an effect that the buffer capacity required in the network can be reduced. Further, after the handover, the buffering source notifies the mobile communication terminal of the number of buffered packets, and after the mobile communication terminal receives all the buffered packets, the communication restart message is sent to the transmission source of the packet. It is possible to prevent the packets from being out of order and reduce the receiving buffer capacity required for the packet receiving terminal. In TCP, the packet misordering may be treated as a packet loss, which may reduce the throughput. However, according to the present invention, the packet misordering can be prevented, and thus the throughput cannot be reduced. There is no.

[Brief description of drawings]

1A is a block diagram showing a configuration example of a base station in a communication system according to the present invention, and FIG. 1B is a block diagram showing a configuration example of a mobile communication terminal in a communication system according to the present invention.

FIG. 2 is a schematic diagram showing a handover operation when the communication system according to the present invention is configured to be oriented to mobile communication terminals.

FIG. 3 (a) is a block diagram showing another configuration example of a base station in a communication system according to the present invention, and FIG. 3 (b) is a block diagram showing another configuration example of a mobile communication terminal in the communication system according to the present invention. Is.

FIG. 4 is a schematic diagram showing a handover operation in the case where the communication system according to the present invention is configured to be base station oriented.

FIG. 5 (a) is a block diagram showing another configuration example of a source base station in a communication system according to the present invention, FIG.
Is a block diagram showing another configuration example of the mobile communication terminal in the communication system according to the present invention, and FIG. 11C is a block diagram showing another configuration example of the movement-destination base station in the communication system according to the present invention.

FIG. 6 is a schematic diagram showing a handover operation in the case where the communication system according to the present invention is configured with a base station oriented.

[Explanation of symbols]

11, 11 'mobile communication terminal 12, 13 Base station 14 sender 21 Packet buffering request receiver 22 Packet filter section 23 Packet Forward Request Message Receiver 24 Context generator 25,38 buffers 26, 37 Forward section 27 Terminal movement detector 28,36 Packet buffering request unit 29 ACK generation unit 30 Connection detector 31 Packet Forward Request Unit 32 ACK transmitter 33 Context receiver 34 Packet Filtering Management Unit 35 terminal movement detector

Claims (8)

[Claims] 1. A communication system for transmitting packet data from a packet source to a mobile communication terminal via a base station, wherein handover of the mobile communication terminal from a source base station area to a destination base station area is started. To the mobile communication terminal in response to detection of handover end for the mobile communication terminal, including buffering means for buffering the packet data in response to detection of the packet data. A communication system characterized in that the transmission is performed. 2. The communication system according to claim 1, further comprising means for instructing the packet source to limit transmission of the packet data in response to detection of the start of the handover. 3. The apparatus further comprises means for transmitting a packet forwarding request to forward the packet buffered by the buffering means to the source base station in response to the detection of the end of the handover. The communication system according to claim 1 or 2. 4. A context transmitting means for notifying a mobile communication terminal which has issued the packet forwarding request, of a buffering number indicating how many packets are buffered, and a buffer notified by the context transmitting means. The communication according to any one of claims 1 to 3, further comprising means for restarting packet transmission to a packet source when a final buffered packet is received according to the ring number. system. 5. The buffering by the buffering means is performed in a base station in a source area of the mobile communication terminal, and the buffered packet data is stored in a base station in a destination area of the mobile communication terminal. The communication system according to any one of claims 1 to 4, wherein the communication is transmitted to the mobile communication terminal via the mobile communication terminal. 6. The start of the handover is detected in the mobile communication terminal.
The communication system according to any one of 1. 7. The communication system according to claim 1, wherein the base station detects the start of the handover. 8. A handover control method in a communication system for transmitting packet data from a packet source to a mobile communication terminal via a base station, the method comprising: detecting a handover for the mobile communication terminal; Buffering a packet to be received on the network side, instructing the packet transmission source to limit the transmission of the packet, and sending a packet transfer request to the buffering destination after detecting the end of handover, A step of notifying the mobile communication terminal of the number of packets buffered by a buffering destination that has received the packet transfer request; and a step of sending a packet transmission restart instruction to the source of the packet when the forwarding of the packet is completed. A hand characterized by including Over control method.