Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1998-10-01
2002-08-20
Vincent, David (Department: 2661)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S395100, C370S232000, C370S428000
Reexamination Certificate
active
06438138
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an asynchronous transfer mode network and, more particularly, to a buffer controller for an available bit rate service in the asynchronous transfer mode network and a method for controlling thereof.
DESCRIPTION OF THE RELATED ART
An available bit rate service is proposed for an asynchronous transfer mode in ATM (Asynchronous Transfer Mode) Forum Traffic Management Specification version 4.0, 1996. An Allowable cell rate means the transmission cell rate at a terminal, and is dynamically changed depending upon the status of the network. The cell transmission rate is managed through a feedback control in the available bit rate service, and the feedback control reduces the cells to be disposed. Thus, the available bit rate service aims at provision of equal right to occupy each part of the network between users.
The available bit rate service is detailed hereinbelow. In the following description, term “terminal” is applied to not only actual terminals for the users but also virtual transmission terminals and virtual receiving terminals such as a virtual source and a virtual destination defined in the ATM Forum Traffic Management Specification version 4.0.
FIG. 1
illustrates the prior art asynchronous transfer mode network
1
. A switching unit
2
is incorporated in the prior art asynchronous transfer mode network
1
, and terminals
3
/
4
are connected to the asynchronous transfer mode network
1
. The terminal
3
and the terminal
4
are assumed to be a data source and a data destination, respectively. When the terminal
3
transmits data to the terminal
5
, the terminal
3
firstly transmits a forward resource management cell, which is abbreviated as “FRM” in
FIG. 1
, to the switching unit
2
, and the switching unit
2
transfers the forward resource management cell FRM to the terminal
4
. When the terminal
4
receives the forward resource management cell FRM, the terminal
4
returns a backward resource management cell, which is abbreviated as “BRM” in
FIG. 1
, through the switching unit
2
to the terminal
3
. The switching unit
2
has pieces of status data information representative of the congestion of the network
1
, and writes control bits ER, a congestion indication bit CI and a no increase bit NI in the forward resource management cell FRM or the backward resource management cell BRM. The control bits ER are representative of an explicit rate, and the explicit rate is determined on the basis of the current status of the network
1
. The congestion indication bit CI indicates whether the network is in congestion status or not, and the no increase bit NI indicates whether the terminal
3
/
4
is allowed to increase the transmission rate or not. The congestion indication bit CI is changed between “1” indicative of congestion status and “0” indicative of non-congestion status. The no increase bit NI is also changed between “1” indicative of prohibition from increase of transmission rate and “0” indicative of permission to increase the transmission rate. The terminal
3
maintains or changes the transmission rate of data cells on the basis of the control bits, the congestion indication bit and the no increase bit NI written in the backward resource management cell BRM, and transmits data cells through the switching unit
2
to the terminal
4
at the data transmission rate. Thus, the terminals
3
/
4
carry out the data transmission under the control of the switching unit.
As described hereinbefore, a virtual source and a virtual destination are defined for the available bit rate service. The virtual source and the virtual destination are located in the asynchronous transfer mode network, and virtually behave as the terminals. In other words, the virtual source and the virtual destination virtually process the forward resource management cell FRM and the backward resource management cell BRM, and divide the transmission control loop for the forward/backward resource management cells into segments. The division into the segments is desirable, because the segments accelerate the transmission of the control data information. The acceleration of the transmission results in improvement of the rate controlling characteristics in the terminal
3
.
FIG. 2
illustrates another prior art asynchronous transfer mode network for the available bit rate service, and the prior art asynchronous transfer mode network
10
provides a data transmission control loop between terminals
11
/
12
. In the following description, a combination of the virtual source VS and the virtual destination VD is referred to as “virtual terminal module”, and a position closer to a transmission terminal and another position closer to a receiving terminal are called as “upstream side” and “downstream side”, respectively.
Two virtual terminal modules
13
/
14
are inserted into the transmission control loop, and divide the data transmission control loop into segments
15
a
/
15
b
/
15
c
. The terminal
11
communicates with the virtual terminal module
14
, and a forward resource management cell FRM
1
and a backward resource management cell BRMI are used for the transmission control therebetween. The virtual terminal modules
13
and
14
communicate with each other by using a forward resource management cell FRM
2
and a backward resource management cell BRM
2
. The virtual terminal module
14
communicates with the terminal
12
, and a forward resource management cell FRM
3
and a backward resource management cell BRM
3
are used for the transmission control therebetween. The data transmission is carried out from the terminal
11
through the virtual terminal modules
13
/
14
to the terminal
12
, and the data transmission rate is varied between the segments
15
a
/
15
b
/
15
c.
In the prior art asynchronous transfer mode networks
1
/
10
, burst traffic from multiple terminals, variation of area available for the data transmission and variation of transmission rate due to congestion at a terminal cause the switching unit
2
and the virtual terminal module
13
/
14
to pile up a large amount of data cells to be transferred. Cell buffers are provided in the switching unit
2
and the virtual terminal module
13
/
14
so as to temporarily store the data cells. When the data cells are piled up in the cell buffer, the switching unit and the virtual terminal module enter into congestion status. Therefore, the prior art asynchronous transfer mode networks
1
/
10
require a buffer controller for prohibiting the cell buffer from the congestion status.
Japanese Patent Publication of Unexamined Application No. 8-223174 teaches a controller for the cell buffers. According to the Japanese Patent Publication of Unexamined Application, the congestion detector monitors the buffer memory to see how many asynchronous transfer mode cells enter into a queue. When the queue reaches a predetermined length or an asynchronous transfer mode cell overflows the buffer memory, the controller determines that the asynchronous transfer mode network has entered into congestion status, and notifies plural paths selected from a connection table. Thus, the criterion is the queue length or the number of asynchronous transfer mode cells stored in the buffer memory
Another method for controlling congestion status is disclosed in Japanese Patent Publication of Unexamined Application No. 7-183886. According to the Japanese Patent Publication of Unexamined Application, two pairs of thresholds, i.e., four thresholds, are given to the buffer in each node, and the buffer is monitored to see whether or not the queue reaches any one of the thresholds. The first pair of thresholds offer a boundary for notification of the congestion status to a receiving terminal and a boundary for the recovery therefrom. The second pair of thresholds offer a boundary for an interruption of cell transfer from a transmitting terminal and a boundary for a recovery therefrom. Thus, the queue length or the number of asynchronous transfer mode cells is the criteria of the congestion status.
Yet another congestion con
Foley & Lardner
NEC Corporation
Phunkulh Bob A.
Vincent David
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