Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Reexamination Certificate
1999-05-21
2003-12-02
Luther, William A. (Department: 2664)
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
C370S395430
Reexamination Certificate
active
06657964
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a terminal suitable for use in an asynchronous transfer mode network and a variable-length packet network, and particularly to a technique for allocating shaping bandwidths between respective users.
2. Description of the Related Art
An asynchronous transfer mode technique has been widely known as a communication technique which is capable of supporting various types of traffics such as speech, images, data, etc. with efficiency using fixed-length packets called “cells” and suitable for multimedia communications. The asynchronous transfer mode technique has been described in, for example, “The ATM Forum TM4.0” (Prior Art 1).
FIG. 2
show a general network comprised of a plurality of terminals and switches. In the case of an asynchronous transfer mode network, however, cells are transferred through virtual paths called “connections” as described in “2. ATM Service Architecture (p.4)” of the Prior Art 1. When each cell is transferred from one terminal
10
(hereinafter called “source terminal or source end system”) to another terminal
20
(hereinafter called “destination terminal or destination end system”) in
FIG. 2
, virtual paths (connections) are established between the source terminal
10
, switches
30
,
31
,
32
and destination terminal
20
. The cells are transferred over the connections which connect between both the terminals
10
and
20
. As the establishment of the connections, there are two cases: one required by a source terminal and another required by a terminal
15
for network management.
In the multimedia communications, a burst traffic for communicating data and a real-time traffic for communicating signals, such as speech, picture or the like, are simultaneously transferred through different connections lying within the same line. When connections incoming from a plurality of input lines merge with each other at one of output ports of a switch, it is required to carry out cell transmission control (i.e., traffic control) on individual connections. As to the real-time traffic, each bandwidth for use in the transfer of signals, such as speech, picture or the like, can be estimated in advance. In order to reserve a necessary bandwidth (hereinafter called “shaping bandwidth”) within a cell communication path before the commencement of cell transmission and perform low-delay transmission within such a reserved bandwidth, real-time traffic cells are transmitted preferentially to burst traffic cells forwarding to the same output port.
A cell sending apparatus needs to transmit output cells in the secured shaping bandwidth. For this purpose, it is necessary to provide the function of sending cells in a reserved bandwidth for each connection. The cell sending function in this reserved bandwidth will hereinafter be called “shaping”.
A shaping apparatus or a shaper has been disclosed in, for example, Japanese Unexamined Patent Publication No. Hei 6-315034, “Cell Flow Control Device and ATM Communication Network” (Prior Art 2). The “Cell Flow Control Device” in the Prior Art 2 is the same meaning as the shaper. In the Prior Art 2, the shaping apparatus is constructed as shown in FIG.
3
. The shaper
7
comprises a policing part
2
for determining whether an incoming cell interval falls within a prescribed allowable value, a cell sending time arithmetic part
3
for calculating the output time of each cell, a memory
4
for temporarily storing each cell therein, a write control circuit
5
for writing cells into the memory
4
, and a read control circuit
6
for reading out the stored cells from the memory
4
. Even when the incoming cells are received in a bandwidth higher than the sending bandwidth, since these cells are temporarily stored in the memory
4
, these cells can be transmitted maintaining the contracted shaping bandwidth.
The shaping is also required to the burst traffic cells other than the real-time traffic cells. In the case of the burst traffic data communication, the shaping bandwidth cannot be estimated in advance. However, since reducing a transmission delay is not so important in the burst traffic data, the source terminal may start cell sending without ensuring the shaping bandwidth. Even if traffics are concentrated on one of nodes or a network congestion has occurred on one of output lines, high availability of the network may be realized by temporarily storing incoming cells in buffers provided within the network. However, if the amount of cells flow into the network in excess of the ability of the network to process the cells, the cells overflowed from the buffer must be discarded in the course of their transmission.
In the Prior Art 1, two traffic classes are defined for the data communication traffic from the viewpoint of such cell discard.
One of them is an ABR (Available Bit Rate) class for performing dynamic control on the shaping bandwidth in the network. For this class, a congestion notification cell circulated into the network regularly in order to monitor the state of the congestion of the network (hereinafter called “congestion status”) is utilized to decrease the amount of flow of cells into the network upon congestion and increase the amount of flow of cells upon non-congestion, so that cell transfer is smoothly performed without causing cell discard. A model for the ABR class has been described in, for example, “5.10 ABR Flow Control (p.44)” in the Prior Art 1. Another class is a UBR (Unspecified Bit Rate) class. In this class, emphasis is laid on effective use of available bandwidth. Even if a network is placed in a congestion status and brought to a state of causing cell discard, no limitation is imposed on the shaping bandwidth.
In the Prior Art 1, as shown in the model for ABR control in
FIG. 4
(see
FIG. 2-1
in the Prior Art 1), one of switches
30
through
33
or destination terminal
20
having detected the congestion of the network sets a congestion notification bit in a congestion notification cell circulated into each connection to “1”. When the source terminal
10
receives the congestion notification cell whose congestion notification bit is set to “1”, it determines that the network is congested, and thereby decreases the transmission bandwidth to prevent the flow of excessive cells into the network. If a congestion notification cell whose congestion notification bit is not set to “1”, is received, the source terminal
10
determines that the network is not congested, and hence increases the transmission bandwidth to up the availability of the network.
Even when the congestion notification cell whose congestion notification bit is set to “1”, is received at this time, it is unnecessary to reduce the cell transmission bandwidth to a bandwidth which falls below MCR (Minimum Cell Rate) contracted upon connection setting. The dynamic control on the transmission bandwidth can be performed from the network side by executing feedback control using such a congestion notification cell.
FIG. 4
shows only the flow of data cells in one direction from the source terminal
10
to the destination terminal
20
for simplification. Since, however, an actual terminal apparatus performs both operation for the source terminal and operation for the destination terminal, the flow of the data cells from the destination terminal
20
to the source terminal
10
also exists. The above-described one-direction communication model will be explained unless otherwise specified.
In the Prior Art 1, the congestion notification cell is called “RM cell (Resource Management Cell)”. One transferred from the source terminal to the destination terminal is referred to as “forward RM cell”, and one transferred from the destination terminal to the source terminal is called “backward RM cell”. In the following description, the forward RM cell and the backward RM cell are referred to as FRM cell and BRM cell in accordance with the above designations. A distinction between the FRM cell and the BRM cell is made according to a bit (DIR bit) indicative of a transfer d
Aimoto Takeshi
Kohzuki Kiyoshi
Yazaki Takeki
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