JP2003224619A - Mobile communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a decrease in the use efficiency of a communication line resulting from resending control. <P>SOLUTION: During a TCP session, a mobile machine 1 sends a segment to which an RTO value variation request is added to a web server 4. The web server 4 varies an RTO value according to the RTO value variation request and sets it to a resending timer. Consequently, resending control over a TCP is carried out with the best RTO value for a bearer in use to prevent the use efficiency of the communication line from decreasing. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to retransmission control when data is transferred using a transport control protocol (TCP) in a mobile communication system.

[0002]

2. Description of the Related Art Conventionally, a transport control protocol (hereinafter referred to as "T") has been used as a network protocol used for communication in a network.
CP ”. )It has been known. This TCP is the OS
It is a protocol located in the fourth layer (transport layer) in the I (Open Systems Interconnection) reference model and performing flow control, retransmission control, and the like. TCP is a standard network for communication on the Internet.
It is used as a protocol. Also, this TCP
Is also used when connecting from a mobile terminal such as a mobile phone to the Internet via a mobile communication network including a wireless communication line for communication.

FIG. 4 shows an example of a sequence of connection establishment processing and data transmission when a client in a network requests a TCP connection from a server for communication. T
In the CP connection establishment process, as shown in FIG.
The client 101 requesting the connection of P transmits the segment 1 with the SYN flag turned on to the server 100. The server 100 receiving the segment 1 turns on the SYN flag and transmits the segment 2 of ACK for SYN to the client. The client receiving this segment 2 sends the ACK segment 3 for SYN to the server 10
Send to 0. As a result, the TCP connection has been established between the client 101 and the server 100. Such connection establishment is called a 3-way handshake. When the connection is established, for example, as shown in FIG. 4, the client 101 transmits the segment 4 requesting the data to the server 100, and the server 100 returns the segment 5 of the ACK for this segment 4 to the client 101, and Then, the response data (not shown) for the request is transmitted. In this way
The client 101 can obtain the predetermined data from the server 100.

Also, if the ACK corresponding to the transmitted segment does not return for a fixed time, the client 101, which is the transmission source, retransmits the segment. This fixed time is called a retransmission timeout time (RTO), and the RTO is based on a round trip time (RTT: Round Trip Time) from the client 101 transmitting a segment to the server 100 until receiving an ACK segment from the server 100. It is calculated according to the line quality at that time. For example,
As shown in FIG. 5, the client sends data 1 (DATA
It is assumed that, when the segment 4 of 1) is transmitted to the server 100, the segment 4 disappears halfway and the server cannot receive it. In this case, the server 100 did not receive ACK because segment 4 could not be received. When the client 101 transmits the segment 4, the retransmission timer in which the RTO value is set is activated, and when the retransmission timer times out, as shown in FIG.
Retransmit K segment 10. If the server 100 receives this retransmitted segment 4, the server 100
Returns the segment 11 of the ACK for the segment 10 to the client 101, and the client 101 receiving this ACK knows that the data of the segment 10 has been normally received. By performing such retransmission control, the reliability of communication using TCP can be improved. In the retransmission control, retransmission is repeated for several times until ACK is returned.

[0005]

In the mobile communication system, an intermediate node is generally provided between the wireless communication line side and the wire communication line side to absorb the difference between the communication lines. Server 2 in this case
FIG. 6 shows a sequence diagram showing an example of retransmission control when data is transferred from 00 to the mobile device 201 using TCP. In FIG. 6, between the server 200 and the intermediate node 202, retransmission control is performed by TCP located in the fourth layer (transport layer). That is, the server 200 sets the RTO value calculated based on the RTT in the retransmission timer, and the retransmission is performed when the retransmission timer times out. On the other hand, the intermediate node 202
Between the mobile station 201 and the mobile device 201, the second OSI reference model
Retransmission control is performed in the layer (data link layer). The retransmission control performed in the second layer is generally performed in a shorter time than the TCP retransmission control performed in the fourth layer.

[0006] In particular, since the wireless communication line has poor line quality as compared to the wired communication line and its quality is not constant, the round trip time RTT from the transmission of a segment to the reception of an ACK segment in the wireless communication line. It tends to be long. Therefore, in the communication network including the wireless communication line, there is a possibility that the segment is retransmitted based on the elapse of the retransmission timeout time RTO even though no packet is lost on the communication line. This retransmission is retransmitted from the server 200 by the TCP retransmission control, and is also retransmitted from the intermediate node 202 by the second layer retransmission control. In this way, if the TCP retransmission control and the second layer retransmission control compete with each other or the retransmission segment is erroneously retransmitted, useless packets will be present on the communication line, and the communication line utilization efficiency will be improved. It will decrease. That is,
The data segment of the wireless line is used by the retransmission segment, which causes a problem that the band of the wireless line is compressed.
Since the band is narrow in the case of a wireless line, it is a big problem that the data band is wasted by the retransmission segment.

Therefore, in order to solve this, when establishing communication using TCP between the mobile terminal and the server, the server is given the information of the retransmission timeout time held in the mobile terminal, It was proposed that the retransmission control be performed according to the given information on the retransmission timeout time. According to such retransmission control, it is possible to prevent the bandwidth of the wireless line due to the retransmission control from being uselessly used, and to suppress a decrease in utilization efficiency of the communication line. However, the intermediate node may support the circuit-switched bearer and the packet-switched bearer, and the circuit-switched bearer (packet-switched bearer) used until then when the mobile terminal performs the handover is the packet-switched bearer (circuit-switched bearer). ) Occurs when it is changed to. In such a case, it is preferable to set a retransmission timeout time (RTO value) suitable for the changed bearer.

Therefore, an object of the present invention is to provide a mobile communication system capable of changing the retransmission timeout time even during a TCP session.

[0009]

In order to achieve the above object, a mobile communication system of the present invention provides a transport control protocol (TC) between a mobile terminal in a radio access network and a server in a core network.
P) is a mobile communication system capable of transferring data, and has an option to change a retransmission timeout time during a session using the transport control protocol between the mobile terminal and the server. By sending the segment to the server,
The server controls change of the retransmission timeout time based on the option.

In the mobile communication system of the present invention, when the mobile terminal is handed over and a protocol subordinate to the transport control protocol is changed, the mobile terminal is changed to the server. You may make it transmit the segment which added the option which changes into the retransmission timeout time suitable for the said protocol.

According to the present invention as described above, during the session using the transport control protocol, by sending the segment to which the option for changing the retransmission timeout time is added to the server, the server can control the change of the retransmission timeout time. It can be done during a TCP session. For this reason, the server can control the change of the retransmission timeout time while communicating with the mobile device,
Since it is possible to set the optimum retransmission timeout time, it is possible to prevent the utilization efficiency of the communication line from decreasing. That is, it is possible to prevent the band of the wireless line from being wasted. In particular, even when the protocol located under TCP is changed when the mobile device is handed over, it is possible to make the retransmission timeout time optimal for the changed protocol. Further, since the TCP retransmission control is performed between the mobile terminal and the server, it is possible to omit an intermediate node for absorbing the difference between the TCP retransmission control and the second layer retransmission control.

[0012]

FIG. 1 shows a schematic configuration of a mobile communication system according to an embodiment of the present invention. In FIG.
The mobile device 1 is a mobile terminal including a mobile phone as an information terminal device, and is capable of performing data communication with a web server 4 on the Internet via a mobile communication network. The mobile communication network is composed of a radio access network (RAN) including a radio communication line between the mobile device 1 and the base station 2, and a core network including a wire communication line provided with various nodes. When the mobile device 1 accesses the web server 4, the browser is launched and the URL of the web server 4 (Unifor
m resource locators) is specified and transmitted, so that HTML files and image files can be sent to the web server 4
From the mobile device 1 to the mobile device 1 and displayed on the browser screen of the mobile device 1. The transmission and reception of HTML files and image files are performed by HTTP (Hypertext Transfer) located in the fifth layer (session layer) or higher of the OSI reference model.
Protocol).

In this case, the End-to-End between the mobile device 1 and the web server 4 is connected by the transport control protocol (TCP) located in the fourth layer (transport layer). In addition, between the mobile device 1 and the base station 2, and
The base station 2 and the exchange 3 are connected to each other by a circuit switched bearer that supports circuit switching or a packet bearer that supports packet switching located in the second layer (data link layer). Further, the exchange 3 and the web server 4 are connected by a wired line such as Ethernet (registered trademark) located in the second layer (data link layer).

Next, features of the mobile communication system according to the embodiment of the present invention will be described with reference to the sequence diagram shown in FIG. In the sequence diagram shown in FIG. 2, the mobile device 1 in the mobile communication system is connected to the web server 4 and the TCP.
It is said that the sequence is during the session after the connection is established. The mobile device 1 is connected by a circuit switching bearer or a packet switching bearer located in the lower layer of TCP, and the current bearer is shown as bearer A. That is, the current TCP session is performed using bearer A. Here, it is assumed that the mobile device 1 moves and is handed over. At this time, the base station in which the mobile device 1 is located is changed from the base station 2 to another base station. Therefore, as shown in the figure, the bearer used is changed from the bearer A to the other bearer B. The optimum value of the retransmission timeout time RTO differs depending on the type of bearer, that is, the circuit switched bearer or the packet switched bearer.

Therefore, when the mobile device 1 detects that the bearer has been changed, it adds a request for changing the value of the retransmission timeout time RTO to the segment using the option area and sends it to the web server 4. This segment is the ACK segment of the segment in the TCP session (bearer A) in the example shown in FIG.
The segment is not limited to this, and any segment may be used as long as the segment is transmitted by the mobile device 1 during the session. When the web server 4 receives the ACK segment 1 to which the option of the RTO value change request is added, the RTO value is changed so that the bearer changed according to the RTO change request has the optimum RTO value. Next, the web server 4 transmits an ACK segment 2 indicating that the RTO value change request has been received, to the mobile device 1. This allows subsequent TCP
Bearer B changed in session (bearer B)
The retransmission control based on the optimum RTO value is performed.

The data structure of the TCP segment is shown in FIG. In the TCP segment shown in FIG. 3, up to options are TCP headers. The TCP header includes a transmission source port number (16 bits), a destination port number (16 bits), and a sequence number (3
2 bits), acknowledgment number (ACK number: 32 bits 9), header length (HLen: 4 bits), and reserve (6 bits) fields.In addition, an emergency flag (URG), an ACK flag, Includes 6-bit flag bit consisting of PSH flag, RST flag, SYN flag, and FIN flag, where ACK is valid when ACK flag is "1" and SYN flag is "1". When it is ", it means that the sequence number field has an initial value. When the FIN flag is" 1 ", it means that there is no more data to send. Furthermore, a window field (16 bits) for indicating the amount of buffer to the other party, a checksum field (16 bits) used for detecting an error in the header and data, and an urgent pointer file. Field (16 bits) and an optional field that sets the RTO value during the session in the present invention.
The fields following the header are data fields.

By the way, when the transmission source is the web server 4 and the destination is the mobile device 1, if the ACK corresponding to the segment transmitted from the web server 4 is not returned from the mobile device 1, the web server 4 The segment is retransmitted when the RTO value set in the retransmission timer of 1 times out. This RTO value is the TCP described above.
It is set according to the RTO value change request transmitted from the mobile device 1 to the web server 4 during the session. Since the set RTO value is the optimum RTO value for the mobile communication system and the bearer to be used, it is possible to set the optimum retransmission timeout time, which reduces the utilization efficiency of the communication line. Can be prevented. In addition, as a mobile communication system, PDC (Person
al DigitalCellular), WCDMA (Wideband Code Di)
vision Multiple Access) GSM (global system for
mobile communication), PHS (Personal Handy-pho
neSystem) and other mobile communication systems.

If the source is the mobile device 1 and the destination is the web server 4, and the ACK corresponding to the segment transmitted from the mobile device 1 is not returned from the web server 4, the mobile device 1 The segment is retransmitted when the RTO value set in the retransmission timer of 1 times out. Since this RTO value is a fixed RTO value held in the mobile device 1 and is an optimum RTO value according to the mobile communication system and the bearer used, erroneous retransmission is prevented. This can be prevented as much as possible, and the use efficiency of the communication line can be prevented from being lowered. As described above, even if the TCP retransmission control is performed in the End-to-End between the mobile device 1 and the web server 4, it is possible to prevent the utilization efficiency of the communication line from being lowered. It becomes possible to omit the intermediate node for absorbing the difference from the retransmission control of the second layer (data link layer).

In the above explanation, the segment to which the RTO value change request is added is sent during the TCP session when the bearer is changed. However, the segment to which the RTO value change request is added when the RTO value is to be changed May be sent. Further, the RTO value change request may be information to instruct the RTO value to be set or the RTO value to be set. For example, since the retransmission control mechanism is different for each bearer type, the optimum RTO value differs depending on the bearer type. Then, this optimum value can be set in advance in a table or the like as an RTO value for each bearer type. Therefore, instead of the RTO value, information designating a specific RTO value on the table may be sent.

The En between the mobile device 1 and the web server 4
The TCP retransmission control may be performed in d-to-End, while the retransmission control may be performed in the circuit switched bearer or packet bearer located in the second layer (data link layer). Also, the AC for the retransmitted segment
When the K number is not returned, the retransmission is performed again, but the retransmission timeout time in this case is the fixed RTO value set in the retransmission timer. That is, for example, it takes 10 seconds until the preset maximum time is reached.
Retransmission is repeated every time. However, the initial RTO value is 10se in consideration of when there is a failure.
If it is c, the second RTO value is 20 sec, 3
An exponential backoff of 40 seconds may be incorporated in the second time. Further, the RTO value may be increased by adding a predetermined value to the RTO value each time it times out.

In the above description, the retransmission timeout time RTO held by the mobile device 1 is set to 10 sec, but the present invention is not limited to this. This retransmission timeout time RTO is a round trip time (R) in the radio access network for each bearer used.
It is preferable to set the optimum value based on the transmission characteristics such as TT). In the above description, TCP is used as the protocol of the fourth layer (transport layer) between the mobile device 1 and the web server 4, but transaction type T / TCP is used instead of TCP. Is also good. Furthermore, the mobile terminal is not limited to a mobile phone, and may be a mobile information terminal or the like, and the server is not limited to a web server on the Internet and may be a server on a network.

[0022]

As described above, according to the present invention, during the session using the transport control protocol, the server changes the retransmission timeout time by sending the segment to which the option for changing the retransmission timeout time is added. The control can be performed during the TCP session. Therefore, the server can control the change of the retransmission timeout time during the communication with the mobile device, and can set the optimal retransmission timeout time, so that the use efficiency of the communication line can be prevented from being lowered. it can. That is, it is possible to prevent the band of the wireless line from being wasted. In particular, even when the protocol located under TCP is changed when the mobile device is handed over, it is possible to make the retransmission timeout time optimal for the changed protocol. Further, since the TCP retransmission control is performed between the mobile terminal and the server, it is possible to omit an intermediate node for absorbing the difference between the TCP retransmission control and the second layer retransmission control.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a mobile communication system according to an embodiment of the present invention.

FIG. 2 is a sequence diagram showing characteristic points in the mobile communication system according to the exemplary embodiment of the present invention.

FIG. 3 is a diagram showing a data structure of a TCP segment in the mobile communication system according to the exemplary embodiment of the present invention.

FIG. 4 is a sequence diagram showing a conventional connection establishment process and data transmission process using TCP.

FIG. 5 is a sequence diagram showing a retransmission control process using conventional TCP.

FIG. 6 is a sequence diagram showing retransmission control in a conventional mobile communication system.

[Explanation of symbols]

1 mobile unit, 2 base station, 3 exchange, 4 web server, 100 server, 101 client, 200
Server, 201 mobile, 202 intermediate node

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5K034 EE03 EE11 HH65 MM03                 5K067 AA21 BB04 CC08 DD11 EE02                       EE10 EE16 FF02 FF32 HH22                       KK15

Claims (2)

[Claims] 1. A mobile communication system in which data can be transferred between a mobile terminal in a radio access network and a server in a core network by using a transport control protocol (TCP), wherein the mobile terminal and the During the session between the servers using the transport control protocol, by sending the segment to which the option for changing the retransmission timeout time is added to the server, the server controls the change of the retransmission timeout time based on the option. A mobile communication system characterized by the above. 2. When the mobile terminal is handed over and a protocol subordinate to the transport control protocol is changed, the mobile terminal transfers to the server.
The mobile communication system according to claim 1, wherein the segment to which the option of changing the retransmission timeout time suitable for the changed protocol is added is sent.