JP2002204255A - Device and method for controlling transmission rate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize unbroken medium transmission with a TCP(Transmission Control Protocol) by securing the connectability to the current TCP without changing the framework of the current TCP. SOLUTION: A band estimating part 101 for estimating a transmission band where a communication path between a transmitting terminal 103 and a receiving terminal 104 can be used, a band managing part 102 for setting the upper limit of a use band in each TCP session by allocating the available transmission band to respective TCP sessions between the terminals 103 and 104, and a transmission rate managing part 105 for limiting the transmission rate of data related to each TCP session according to the set upper limit of the use band are added to a TCP controlling part 106 being a well-known transmission processing system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission rate control device and a transmission rate control method for controlling a data transmission rate between a transmitting terminal and a receiving terminal in accordance with a congestion state of a transmission line. .

[0002]

2. Description of the Related Art On an IP (Internet Protocol) network such as an intranet or the Internet, a usable transmission band varies with time. In order to provide stable transmission quality using such a network, a maximum value of a transmission band that can be secured in a communication path is estimated (referred to as band estimation). It is necessary to change the data transmission rate (referred to as transmission rate control). In particular, U
Data transmission using a DP (User Datagram Protocol) packet is performed using TCP (Transmission Control Protocol).
Since flow control is not performed in the transport layer unlike the transport layer, it is necessary to control the data transmission rate in the application layer. As a protocol for managing time on an application basis, RTP (Real Tim
e Transport Protocol) / RTCP (RTP Control Prot)
ocol) is known.

Here, conventional techniques will be described with respect to (1) band estimation and (2) transmission rate control.

(1) Prior Art of Band Estimation The prior art of band estimation is roughly divided into path (path).
(char) system and a pair packet (Pair Packet) system. Hereinafter, the pathchar method and the Pair Packet method will be described respectively.

(I) pathchar method: One of the methods for estimating the bandwidth in a communication path is pathchar by V. Jacobson.
Is well known (ftp://ftp.ee.lbl.gov/pathchar/
msri-talk.pdf). This is, like traceroute, TTL (T
By sending a packet with the “ime To Live” field set to n, ICMP (In) is sent to the nth router on the route.
TTL Exp of Internet Control Message Protocol) packet
By transmitting an ired message, a round trip time (RTT) between each router is measured (AB Downey et al., "Using pathchar to e").
stimate Internetlink characteristics ", ACM SIGCOMM
'99).

In band estimation using pathchar, many RTs
The bandwidth is estimated from the T data by statistical processing. BA
By further devising this statistical processing method, Mar's Peacher (pchar) can calculate the reliability of the estimated band along with improving the accuracy (http: //www.ca.sandia.g
ov / bmah / Software / pchar).

(Ii) Pair Packet method: Band estimation by the Pair Packet method is performed as follows. That is,
The transmitting terminal continuously transmits the band estimation packet (survey packet) to the receiving terminal. Due to the difference in the packet processing speed of the link, an interval occurs between the packets after the band estimation packet has passed through the bottleneck link. This interval is measured, and the bandwidth of the bottleneck link is calculated using the size of the bandwidth estimation packet (RL Carter e
t al., "Measuring Bottleneck Link Speed inPacket-S
witched Networks ", Technical Report BU-CS-96-006,
Computer Science Department, Boston University, Ma
rch 1996).

(2) Conventional Technique of Transmission Rate Control As an example of conventional transmission rate control, DAA (Direct Adj)
ustment algorithm) (D. Si
salem et al., "The Direct Adjustment Algorithm: AT
CP-Friendly Adaptation Scheme ", Technical Report G
MD-FOKUS, August 1997. Available from http: //www.f
okus.gmd.dc / usr / sisalem). In the DAA system, information such as data RTT and data loss rate is
Is used to feed back from the receiving terminal to the transmitting terminal, and the data transmission rate is changed based on the information.

[0009] Further, it is assumed that there is one virtual buffer on the communication path from the transmitting terminal to the receiving terminal, and the transmission rate is controlled so that the amount of data remaining in the virtual buffer approaches the target buffer amount. (Japanese Patent Application Laid-Open No. 11-308271).

[0010]

The RTP / RTCP is
Although this protocol is suitable for transmitting media data requiring real-time properties such as video and audio, the transmission rate control has been left to the application designer. On the other hand, TCP is an attractive protocol for application designers because transmission rate control is automatically performed on the system side. Therefore, it is desired to realize media transmission by TCP while securing connectivity with the existing TCP without largely changing the existing TCP framework.

[0011] However, in the conventional transmission rate control of TCP, the transmission rate may be increased beyond the physically usable transmission band. As a result, packet loss occurs due to congestion and data transmission fails. Deterioration of transmission quality has been a problem.

An object of the present invention is to realize media transmission without failure by TCP.

[0013]

According to the present invention, there is provided a transmission rate control apparatus for controlling a data transmission rate between a transmitting terminal and a receiving terminal.
A band estimating unit for estimating a usable transmission band of a communication path between the transmitting terminal and the receiving terminal; and a transmission available for each TCP session between the transmitting terminal and the receiving terminal. By allocating the bandwidth, each TC
A bandwidth management unit for setting an upper limit of the used bandwidth for the P session;
A transmission rate management unit for limiting the transmission rate of data related to the CP session is provided.

Further, the present invention relates to a transmission rate control method for controlling a data transmission rate between a transmitting terminal and a receiving terminal, the method comprising the steps of: Estimating a bandwidth, and allocating the available transmission bandwidth to each of the TCP sessions between the transmitting terminal and the receiving terminal,
Setting an upper limit of the used band for each TCP session, and setting each TC according to the set upper limit of the used band.
Limiting the transmission rate of data related to the P session.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration example of a transmission rate control device according to the present invention. In the transmitting terminal 103 shown in FIG. 1, a new TCP control unit 106 is generated every time a session is established with the receiving terminal, and the corresponding TCP control unit 106 is deleted each time the session processing ends. It has become. Here, a session refers to one or more logical transmission paths generated on a physical transmission path between transmitting and receiving terminals.

Each of the generated TCP control units 106
It is a known transmission processing system based on TCP, and includes a working buffer 107, a window management unit 108, a retransmission timer unit 109, and a transmission buffer 110, and stores encoded video / video data. Not only audio data but also video / audio real-time encoded data can be transmitted. More specifically, the TCP control unit 106
In accordance with the reception response of the transmitted data, the transmission amount (window size) is controlled as in the case of normal TCP. The window management unit 108 increases the window size when a reception response is correctly returned from the reception side. Conversely, if a reception response is not correctly returned, retransmission is performed and the window size is reduced. Whether the reception response has been returned correctly is set in the retransmission timer unit 109 together with the data transmission and a timer. If the reception response is returned within the set timer value, it is determined that the transmission was successful. However, it is not always necessary to adopt transmission amount control using a window. Instead of the window management unit 108, for example, the transmission terminal 103
The transmission amount may be controlled based on the RTT between the receiver and the receiver. The transmission format and retransmission method are the same
May be the same as

The transmitting terminal 103 shown in FIG.
When a request for establishing a TCP session between the transmission terminal 103 and the transmission terminal 103 is made,
And a bandwidth estimating unit 101 for estimating a usable transmission band of a communication path between the transmitting terminal 103 and the transmitting terminal 103 and a receiving terminal 104. A bandwidth management unit 102 for setting an upper limit of the bandwidth used for each TCP session;
It further includes a transmission rate management unit 105 for limiting the transmission rate of data related to each TCP session according to the set upper limit of the used bandwidth, and these constitute a transmission rate control device for the TCP control unit 106 .
The band estimation unit 101 may use a conventional band estimation technique. For example, the above-mentioned pathchar method and Pair Packet method are mentioned.

FIG. 2 shows the operation of the transmission rate control device shown in FIG. The transmitting terminal 103 accepts a TCP session establishment request by the band management unit 102 (step 201). The session establishment request is made based on the IP address and port number of the other party. The bandwidth management unit 102 manages the IP addresses and port numbers of all the reception terminals logically connected to the transmission terminal 103, and generates a new TCP control unit 106 every time a session establishment request is received. Each time the session process ends, the corresponding TCP control unit 106 is deleted. Next, it is checked whether or not the bandwidth between the transmitting terminal 103 and the receiving terminal 104 relating to the requested session has already been estimated (step 202). If the band estimation has not been performed, the band estimation unit 101
Estimate a physically usable transmission band of a communication path between the communication terminal 3 and the receiving terminal 104 (step 203). The band management unit 102 receives the estimation result from the band estimation unit 101, and records the estimation result so that it can be reused (step 204). For example, as the estimation result, a result that 10 Mbps can be used between the transmitting terminal 103 and the receiving terminal 104 is recorded. Further, the bandwidth management unit 102
Is calculated based on the estimation result and the current number of TCP sessions existing between the transmitting terminal 103 and the receiving terminal 104.
The upper limit of the transmission band that can be used in one session of P is calculated, and the result is notified to the transmission rate management unit 105 (step 205). For example, the transmitting terminal 103 and the receiving terminal 1
If there are two sessions between the server and the server 04, it is calculated that 5 Mbps per session is the upper limit of the used bandwidth. The transmission rate management unit 105 limits the maximum transmission rate of each TCP session according to the upper limit of the used band (step 206). That is, the transmission rate management unit 105
The transmission rate is given to the transmission buffer 110 from the transmission buffer 110, and the transmission rate management unit 105 receives the feedback of the transmission amount from the transmission buffer 110, whereby the transmission amount from the transmission buffer 110 to the transmission path can be suppressed.

As described above, by managing a plurality of TCP sessions by a single band management unit 102, a plurality of
This makes it possible to suppress the deterioration of transmission quality due to the exchange of bandwidth between P sessions, and to make the available bandwidth fair among multiple TCP sessions. However, when a plurality of TCP sessions are established for the same receiving terminal 104, the bandwidth management unit 102 assigns a TCP to the transmission bandwidth in accordance with the type of data to be transmitted, the type of protocol, the port number, and the user request. Weighting may be performed between sessions. As described with reference to FIG. 2, it is not always necessary to perform band estimation for the same receiving terminal 104 for the second and subsequent times. This is because the result estimated in the first time may be used. By not performing estimation after the second time, it is possible to reduce processing overhead due to bandwidth estimation that occurs for each session and increase in network load.

Regardless of the configuration of the TCP control unit 106, it is preferable not to use the TCP slow start (set the transmission rate at the start of transmission low). Generally, slow start is not suitable for media transmission. The timeout interval of the retransmission timer unit 109 and the number of retransmissions may be specified by the application user, or the retransmission timer value may be set based on the value of the RTT between the transmitting terminal 103 and the receiving terminal 104. .

FIG. 3 shows the effect of the transmission rate control device shown in FIG. According to the conventional example, an attempt is made to increase the transmission rate beyond the upper limit of the transmission band that can be used in the TCP session. When data is transmitted at a transmission rate exceeding the upper limit in this way, congestion occurs, and as a result, packet loss occurs (transmission is broken). Therefore,
The transmission rate drops sharply, and the transmission quality deteriorates significantly. On the other hand, according to the present invention, data is not transmitted beyond the upper limit of the used bandwidth of each TCP session, and transmission does not fail. That is, according to the configuration of FIG.
By adding the band estimation unit 101, the band management unit 102, and the transmission rate management unit 105 to the known TCP control unit 106, stable media transmission without failure can be realized by TCP.

In the above example, the transmission band that can be used in each TCP session is managed. However, even if the overall transmission band at the transmitting terminal 103 including the UDP session is managed by the band management unit 102. Good.

[0024]

As described above, according to the present invention, the media transmission without any failure is ensured by the TCP by securing the connectivity with the conventional TCP without largely changing the existing TCP framework. It can be realized.

The present invention is not limited to TV telephones, video-on-demand, music distribution, etc., but can also be applied to broadcasting systems.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of a transmission rate control device according to the present invention.

FIG. 2 is a flowchart showing an operation of the transmission rate control device shown in FIG. 1;

FIG. 3 is a diagram illustrating the effect of the transmission rate control device shown in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Band estimation part 102 Band management part 103 Transmission terminal 104 Reception terminal 105 Transmission rate management part 106 TCP control part 107 Work buffer 108 Window management part 109 Retransmission timer part 110 Transmission buffer

Continuing on the front page (72) Inventor Junichi Sato 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 5K030 HA08 KA01 KA03 LA01 LC03 LC05 LC09 5K034 DD01 HH01 HH02 HH06 HH21 HH63 HH65

Claims (2)

[Claims] 1. A transmission rate control device for controlling a data transmission rate between a transmitting terminal and a receiving terminal, wherein a usable transmission band of a communication path between the transmitting terminal and the receiving terminal is provided. A bandwidth estimating unit for estimating the maximum transmission bandwidth for each TCP session by allocating the available transmission bandwidth to each of the TCP sessions between the transmitting terminal and the receiving terminal. A transmission rate control device comprising: a band management unit; and a transmission rate management unit for restricting a transmission rate of data related to each TCP session according to the set upper limit of the used band. 2. A transmission rate control method for controlling a data transmission rate between a transmitting terminal and a receiving terminal, wherein a usable transmission band of a communication path between the transmitting terminal and the receiving terminal is provided. Estimating, and allocating the available transmission bandwidth to each of the TCP sessions between the transmitting terminal and the receiving terminal, thereby setting an upper limit of the used bandwidth for each TCP session. Limiting the transmission rate of data related to each TCP session according to the upper limit of the used bandwidth.