JP2010098485A - Proxy server connected to mobile terminal through communication link having unstable communication quality, and program and proxy connection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a proxy server, etc., that makes a generated difference in cumulative data amount of data transfer as small as possible between a mobile terminal connected through a communication link having unstable communication quality and a mobile terminal connected through a communication link having stable communication quality. <P>SOLUTION: The proxy server performs proxy transfer of data packets transmitted from a server to a mobile terminal which moves in a plurality of areas covered by an access point. The proxy server includes a communication disconnection continuance derivation unit which derives a continuance of communication disconnection from a mobile terminal, a buffer unit which temporarily stores data packets received from the server during the communication disconnection from the mobile terminal, a data transmission unit that transmits the data packets stored in the buffer means to the mobile terminal during communication connection with the mobile terminal, and a rate control unit that controls the rate of the data packets transmitted from the data transmitting means according to the continuance of the communication disconnection. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a proxy server connected to a mobile terminal, a program, and a proxy connection method.

  In recent years, with the development of wireless terminals typified by wireless LAN (Local Area Network) and wireless networks, the communication area is also expanding. On the other hand, it is necessary to further cope with a communication area where the communication link is unstable and disconnection is likely to occur. For example, it corresponds to a communication area such as a subway or a highway.

  In order to enable communication as much as possible even in such a communication area, there is a technology of DTN (Delay, Disruption, Disconnect Tolerant Network) (or Challenged Network) (see, for example, Non-Patent Document 1). This technique assumes that the applied communication link is not always available (often broken) and is unreliable. According to Non-Patent Document 1, DTN includes the meanings of a delay tolerant network and a communication failure tolerant network. Here, DTN is mainly used as a “link disconnection tolerant network”.

  FIG. 1 is a system configuration diagram in which a proxy server is interposed.

  According to FIG. 1, the proxy server 1 is interposed in the network between the mobile terminal 2 and the content server 3. The proxy server 1 performs proxy transfer of the data packet transmitted from the content server 3 to the mobile terminal 2 moving in a plurality of areas covered by the access point.

  According to FIG. 1, the proxy server 1 includes a communication interface unit 11, a transport protocol layer unit 12, and a DTN protocol unit 13. The DTN protocol unit 13 is mounted as an upper layer of the transport protocol layer unit 12. As the transport protocol layer unit 12, for example, existing TCP (Transmission Control Protocol), SCTP (Stream Control Transmission Protocol), UDP (User Datagram Protocol), DCCP (Datagram Congestion Control Protocol) or wireless TCP can be used.

  According to the DTN technology, as described above, a communication link is not always established with a communication partner device, so a so-called store-forward method is used. For this purpose, the DTN protocol unit 13 includes a data reception unit 131, a buffer unit 132, and a data transmission unit 133. The data receiving unit 131 receives a data packet to be transmitted from the content server 3 to the mobile terminal 2. The buffer unit 132 temporarily accumulates data packets received from the content server 3 during communication disconnection with the mobile terminal. The data transmission unit 133 transmits the data packets stored in the buffer unit 132 to the mobile terminal during communication connection with the mobile terminal.

  According to FIG. 1, the session is divided into two sessions of a first communication link between the mobile terminal 2 and the proxy server 1 and a second communication link between the proxy server 1 and the content server 3. Even if the first communication link through the communication link with unstable communication quality is interrupted, the second communication link remains connected. The proxy server 1 receives data packets destined for the mobile terminal 2 from the content server 3 and temporarily accumulates these data packets even when the first communication link is disconnected. Thereafter, when the first communication link is restored, the proxy server 1 transmits the temporarily accumulated data packet to the mobile terminal 2.

  As the first movement state of the mobile terminal, for example, the mobile terminal may be carried by a walking user and may be communicating with a wireless LAN access point. At this time, for the mobile terminal, although there is a possibility that the communication link may be momentarily interrupted due to blocking by a wall or the like, the duration during disconnection is shorter than the duration during communication connection.

  As the second movement state of the mobile terminal, for example, the mobile terminal may be present in a traveling vehicle and may be communicating with a wireless LAN access point having a road as a service area. At this time, the mobile terminal continues to receive data packets from the content server 3 via the proxy server 1 as long as the mobile terminal exists in the first service area covered by the first access point. When the mobile terminal leaves the first service area, the proxy server 1 receives a subsequent data packet from the content server 3. Further, after that, when the mobile terminal enters the second service area covered by the second access point, the proxy server 1 transmits to the mobile terminal 2 data packets temporarily stored during communication disconnection. To do. Thus, since the mobile terminal is moving at high speed, the time that exists in one service area is short. That is, the duration during communication disconnection is longer than the duration during communication connection.

  FIG. 2 is a graph showing the relationship between the accumulated accumulated data amount, the transfer rate, and the TCP window size according to the elapsed time.

  As long as the packet loss rate or the delay time variation is the same, the transport protocol layer unit 12 similarly controls the window size for controlling the transfer rate (transfer data amount per unit time). Therefore, the mobile terminal in the first movement state (low speed movement) and the mobile terminal in the second movement state (high speed movement) have the same transfer rate. On the other hand, as shown in FIG. 2, the duration of communication connection is different between the mobile terminal in the first movement state and the mobile terminal in the second movement state. Therefore, the accumulated data amount transferred within the predetermined time T is also different.

  According to the wireless TCP technology, a dedicated TCP window can be controlled between the proxy server and the terminal by dividing the end-to-end TCP session with the proxy server. However, as described above, even with this technique, as long as the packet loss rate or delay time variation is the same, the window size for controlling the transfer rate is similarly controlled.

J. Ott, D. Kutscher, “A Disconnection-Tolerant Transport for Drive-thru Internet Environments,” Infocom 2005, [online], [October 15, 2008 search], Internet <URL: http: // www .tzi.de / ~ dku / pub / infocom-2005-ott-kutscher.pdf>

  Normally, a user contracts for a service with a constant transfer rate regardless of the movement state of the mobile terminal. Therefore, the difference in transfer rate between different users who have subscribed to the same service according to the movement state of the mobile terminal will cause a difference in user satisfaction.

  Therefore, the present invention occurs in the accumulated data amount of data transfer between a mobile terminal connected via a communication link with unstable communication quality and a mobile terminal connected via a communication link with stable communication quality. It is an object of the present invention to provide a proxy server, a program, and a proxy connection method that can make the difference as small as possible.

According to the present invention, in a proxy server for proxy transfer of a data packet transmitted from a server to a mobile terminal moving in a plurality of areas covered by an access point,
Communication disconnection duration deriving means for deriving the duration during communication disconnection with the mobile terminal;
Buffer means for temporarily storing data packets received from the server during communication disconnection with the mobile terminal;
Data transmission means for transmitting data packets stored in the buffer means to the mobile terminal during communication connection with the mobile terminal;
And rate control means for controlling the rate of data packets transmitted from the data transmission means in accordance with the duration during communication disconnection.

  According to another embodiment of the proxy server of the present invention, it is also preferable that the rate control means controls the rate higher as the duration during disconnection becomes longer than the duration during communication connection.

  According to another embodiment of the proxy server of the present invention, the communication disconnection duration deriving means measures the duration during communication disconnection by a counter, increments the counter at a predetermined time interval during communication disconnection, and is in communication connection It is also preferable to decrement the counter at predetermined time intervals.

According to another embodiment of the proxy server of the present invention,
Further comprising terminal information receiving means for receiving terminal information including the duration of disconnection from the mobile terminal;
It is also preferable that the communication disconnection duration deriving means extracts the duration during communication disconnection included in the terminal information.

According to another embodiment of the proxy server of the present invention,
Terminal information receiving means for receiving terminal information including a communication quality value from the mobile terminal;
It is also preferable that the communication disconnection duration deriving means derives the duration during communication disconnection based on the communication quality value included in the terminal information.

According to another embodiment of the proxy server of the present invention,
The data transmission means transmits a data packet using TCP / IP (Transmission Control Protocol / Internet Protocol) or DCCP / IP (Datagram Congestion Control Protocol / Internet Protocol),
The rate control means also preferably controls the window size in TCP.

  According to another embodiment of the proxy server of the present invention, the data transmission means preferably establishes communication with the mobile terminal by DTN (Delay / Disruption / Disconnect Tolerant Network).

According to the present invention, in a program for a proxy server that causes a computer mounted on a device that performs proxy transfer of a data packet transmitted from a server to a mobile terminal that moves in a plurality of areas covered by an access point,
Communication disconnection duration deriving means for deriving the duration during communication disconnection with the mobile terminal;
Buffer means for temporarily storing data packets received from the server during communication disconnection with the mobile terminal;
Data transmission means for transmitting data packets stored in the buffer means to the mobile terminal during communication connection with the mobile terminal;
The computer is caused to function as a rate control unit that controls the rate of the data packet transmitted from the data transmission unit in accordance with the duration during which communication is disconnected.

According to the present invention, a mobile terminal that moves in a plurality of areas covered by an access point, a server that transmits a data packet to the mobile terminal, and a proxy that proxy-transfers the data packet transmitted from the server to the mobile terminal In a proxy transfer method in a system having a server,
The proxy server derives the duration of communication disconnection with the mobile terminal,
A first step of temporarily storing data packets received from a server during communication disconnection with a mobile terminal;
A second step of controlling a rate of the data packet according to a duration during disconnection when transmitting the accumulated data packet to the mobile terminal during communication connection with the mobile terminal It is characterized by.

  According to the proxy server, the program, and the proxy connection method of the present invention, between a mobile terminal connected via an unstable communication quality communication link and a mobile terminal connected via a stable communication quality communication link. The difference that occurs in the accumulated data amount of data transfer can be made as small as possible.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 3 is a functional configuration diagram of the proxy server in the present invention.

  According to FIG. 3, the proxy server 1 includes a communication state determination unit 134, a communication disconnection duration derivation unit 135, a rate control unit 136, and a terminal information reception unit 137 in addition to the functional configuration of FIG. . These functional components are realized by executing a proxy server program that causes a computer mounted on the server to function.

  The communication state determination unit 134 determines that the communication is disconnected when, for example, the confirmation message (ACK) is not received from the mobile terminal for a predetermined time or longer. Thereafter, when a line return notification message (or other message) is received from the mobile terminal, or when reception of the confirmation message is resumed, it is determined that the communication connection has been recovered.

  The terminal information receiving unit 137 receives terminal information including “duration during communication disconnection” or “communication quality value” from the mobile terminal 2. The total time interval with respect to “duration during communication disconnection” may be a predetermined time interval T, or may be the sum of durations by separately including “duration during communication connection”. The “communication quality value” is, for example, a radio wave reception intensity, a fluctuation amount of the intensity, a wireless system name, or a frequency band.

The communication disconnection duration deriving unit 135 derives the duration of communication disconnection with the mobile terminal by the following three methods.
[Method 1] Counter for measuring disconnection / communication of mobile terminal [Method 2] Duration of communication received from mobile terminal [Method 3] Communication quality value received from mobile terminal

[Method 1] Counter for Measuring Communication Disconnection / Communication Connection of Mobile Terminal The communication disconnection duration deriving unit 135 includes a “counter” indicating the duration of communication disconnection, and is countered at predetermined time intervals during communication disconnection. And the counter is decremented at predetermined time intervals during communication connection. The counter is provided for each transport session (for example, TCP session). The counter may have an upper limit. The counter is described as CNTs corresponding to the session S.

  The rate control unit 136 controls the transfer rate of the data packet transmitted from the data transmission unit 133 according to the counter CNTs. Here, the rate control unit 136 controls the transfer rate higher as the counter is larger.

According to the existing TCP, the window size increment for each RTT (Round Trip Time) when the window size is w is represented by the following three phases.
S (w): Slow start phase C (w): Congestion avoidance phase D (w): Window reduction phase
(When congestion is detected by duplicate ACK (or RTT increase)
Window reduction width)

At this time, the rate control unit 136 changes the window size using a function including the counter CNTs as a parameter. The function is provided for each phase as follows, for example.
Sdtn (w) = f (S (w), CNTs)
Cdtn (w) = g (C (w), CNTs)
Ddtn (w) = h (C (w), CNTs)
Here, for example, according to TCP Reno that changes the window size based on packet discard, S (w) = w, C (w) = 1, and D (w) = w / 2.

  FIG. 4 is a graph showing the relationship between the accumulated accumulated data amount, the transfer rate, and the TCP window size according to the elapsed time in the present invention.

  According to FIG. 4, the second movement state is different from that in FIG. 2. According to the second movement state of FIG. 4, the transfer rate (that is, the window size) in a short duration during communication connection is larger than the transfer rate in the case of FIG. Therefore, even if the duration of communication connection is short in the second movement state, the transferred accumulated data amount within a predetermined time is as much as possible in the first movement state and the second movement state. Can be approached.

  According to the window size in the second movement state of FIG. 4, the counter CNTs is greatly increased in the duration time during communication disconnection. Thereafter, after transferring the data packet during communication connection, the counter CNTs is decreased. As described above, the window size for controlling the transfer rate is changed according to the duration during which the communication is disconnected.

[Method 2] Duration during communication disconnection received from the mobile terminal The mobile terminal 2 may measure the duration during communication disconnection / communication connection and transmit the terminal information to the proxy server 1. . In this case, the DTN protocol unit 13 of the proxy server 1 can receive the terminal information from the mobile terminal 2 and extract the duration during which the communication is disconnected. The terminal information may be transmitted by the mobile terminal 2 independently or may be transmitted in response to a request from the proxy server 1. The terminal information may be included in the content request message or may be included in the line return message.

For example, the window size is changed using a function including RTs (for each session S) “duration during communication connection / predetermined time interval” as a parameter. The function is provided for each phase as follows, for example.
Sdtn (w) = f ′ (S (w), RTs)
Cdtn (w) = g ′ (C (w), RTs)
Ddtn (w) = h ′ (D (w), RTs)
Note that it is also preferable to return to the same window control algorithm as that of normal TCP after a predetermined time has elapsed.

[Method 3] Communication Quality Value Received from Mobile Terminal The communication disconnection duration deriving unit 135 predicts the time during which the mobile terminal is in the area (duration during communication connection) based on the communication quality value. The predicted duration of communication connection is shortened in the following cases, for example.
(1) The wireless system is a wireless system with a narrow cover area such as a wireless LAN.
(2) The received radio wave intensity is weak.
(3) The amount of fluctuation of the received radio wave intensity is large.
That is, in such a case, the duration during disconnection of communication becomes longer. The window size is controlled such that the longer the duration during communication disconnection, the greater the transfer rate after communication resumes.

  In the above-described embodiment, the transport protocol layer unit 12 has been described as being TCP. However, a protocol based on UDP such as DCCP or TRFC may be used. Further, when controlling the transfer rate, the redundancy of an error correction code such as FEC (Forward Error Correction) may be changed instead of changing the window size.

  As described above in detail, according to the proxy server, the program, and the proxy connection method of the present invention, the mobile terminal connected via the unstable communication quality communication link and the stable communication quality communication link are used. Thus, the difference in the accumulated data amount of data transfer can be reduced as much as possible between mobile terminals connected in this manner.

  According to the present invention, in order to keep the user satisfaction regarding the transfer rate constant, the transfer rate at the time of reconnection is changed according to the situation where the mobile terminal is placed. A normal transfer rate is applied to a mobile terminal having a long in-zone prediction time, that is, a short communication disconnection duration. On the other hand, a high transfer rate is applied to a mobile terminal having a short in-zone prediction time, that is, a long communication disconnection duration. As a result, the user satisfaction regarding the transfer rate can be kept constant according to the movement status of the mobile terminal.

  In the various embodiments of the present invention described above, various changes, modifications, and omissions in the scope of the technical idea and the viewpoint of the present invention can be easily made by those skilled in the art. The above description is merely an example, and is not intended to be restrictive. The invention is limited only as defined in the following claims and the equivalents thereto.

It is a system configuration diagram interposing a proxy server. It is a graph showing the relationship between the amount of accumulated data transferred according to the elapsed time, the transfer rate, and the TCP window size. It is a function block diagram of the proxy server in this invention. It is a graph showing the relationship of the amount of accumulated data transferred according to elapsed time, a transfer rate, and a TCP window size in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Proxy server 11 Communication interface part 12 Transport protocol layer part 13 DTN protocol part 131 Data receiving part 132 Buffer part 133 Data transmission part 134 Communication state determination part 135 Communication disconnection duration deriving part 136 Rate control part 137 Terminal information receiving part 2 Mobile terminal 3 Content server, destination server

Claims (9)

In a proxy server that proxy transfers data packets sent from the server to mobile terminals that move in multiple areas covered by the access point,
Communication disconnection duration deriving means for deriving a duration during communication disconnection with the mobile terminal;
Buffer means for temporarily storing data packets received from the server during communication disconnection with the mobile terminal;
Data transmission means for transmitting data packets stored in the buffer means to the mobile terminal during communication connection with the mobile terminal;
A proxy server comprising rate control means for controlling a rate of a data packet transmitted from the data transmission means in accordance with a duration during which the communication is disconnected.   2. The proxy server according to claim 1, wherein the rate control unit controls the rate to be higher as a duration time during the communication disconnection becomes longer than a duration time during the communication connection.   The communication disconnection duration deriving means measures a duration during the communication disconnection by a counter, increments the counter at a predetermined time interval during the communication disconnection, and decrements the counter at a predetermined time interval during the communication connection. The proxy server according to claim 1 or 2, characterized in that: Terminal information receiving means for receiving terminal information including the duration of the communication disconnection from the mobile terminal;
The proxy server according to claim 1, wherein the communication disconnection duration deriving unit extracts a duration during the communication disconnection included in the terminal information. Terminal information receiving means for receiving terminal information including a communication quality value from the mobile terminal;
The proxy server according to claim 1, wherein the communication disconnection duration deriving unit derives a duration during the communication disconnection based on the communication quality value included in the terminal information. The data transmission means transmits a data packet using TCP / IP (Transmission Control Protocol / Internet Protocol) or DCCP / IP (Datagram Congestion Control Protocol / Internet Protocol),
The proxy server according to claim 1, wherein the rate control unit controls a window size in TCP or DCCP.   7. The proxy server according to claim 1, wherein the data transmission unit establishes communication with the mobile terminal for DTN (Delay / Disruption / Disconnect Tolerant Network). 8. In a program for a proxy server that causes a computer mounted on a device that performs proxy transfer of a data packet transmitted from a server to a mobile terminal that moves in a plurality of areas covered by an access point,
Communication disconnection duration deriving means for deriving a duration during communication disconnection with the mobile terminal;
Buffer means for temporarily storing data packets received from the server during communication disconnection with the mobile terminal;
Data transmission means for transmitting data packets stored in the buffer means to the mobile terminal during communication connection with the mobile terminal;
A program for a proxy server, which causes a computer to function as a rate control unit that controls a rate of a data packet transmitted from the data transmission unit according to a duration during which the communication is disconnected. A system having a mobile terminal that moves in a plurality of areas covered by an access point, a server that transmits a data packet to the mobile terminal, and a proxy server that proxy-transfers the data packet transmitted from the server to the mobile terminal In the proxy transfer method in
The proxy server derives a duration during communication disconnection with the mobile terminal,
A first step of temporarily storing data packets received from the server during communication disconnection with the mobile terminal;
A second step of controlling a rate of the data packet according to a duration of the communication disconnection when transmitting the accumulated data packet to the mobile terminal during communication connection with the mobile terminal; A proxy transfer method comprising:

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