Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Reexamination Certificate
1999-03-04
2003-04-01
Chin, Wellington (Department: 2664)
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
Reexamination Certificate
active
06542467
ABSTRACT:
BACKGROUNDS OF THE INVENTION
1. Field of the Invention
The present invention relates to a bandwidth allocation system of a virtual path for allocating bandwidths for a plurality of virtual paths in a communication network of asynchronous transfer mode, and more particularly to a bandwidth allocation system of a virtual path capable of dynamically controlling a bandwidth allocation ratio depending on a bandwidth ratio adopted in the virtual paths.
2. Description of the Related Art
In an asynchronous transfer mode exchange for use in multi-media communication (hereinafter, referred to as ATM), a virtual path is established between ATM nodes, so to connect a virtual channel. A bandwidth of a virtual path which would be established depending on input traffic is usually fixed, in a large key network. However, when one ATM node accommodates only some hundreds of subscribers like a subscriber access line, a bandwidth used for a virtual path varies extremely, and therefore a bandwidth established for a virtual path would become greater, as contrasted with an average bandwidth generally used. Then, it is necessary to multiplex a plurality of virtual paths, so to make them effectively group, thereby absorbing fluctuation of a bandwidth of each virtual path so as to reduce the whole required bandwidths, in an ATM relay node for exchanging a plurality of virtual paths to transfer data to a physical medium.
In this case, since a bandwidth established for each virtual path is not assured completely, it is necessary to allocate a bandwidth dynamically depending on the necessity. This conventional technique for dynamic bandwidth allocation is disclosed in, for example, Japanese Patent Publication Laid-Open (Kokai) No. Heisei 6-209329, “Bandwidth Allocation Method for Virtual Path in Asynchronous Transfer Mode”.
The structure of an AMT node for realizing the conventional dynamic bandwidth allocation method disclosed in the same publication will be described with reference to FIG.
8
. As illustrated in
FIG. 8
, the ATM node
800
comprises a bandwidth monitor circuit
8000
, a detecting circuit of excess of the upper threshold of Queue length
8010
, a waiting time prediction circuit
8020
, a bandwidth ratio allocation control circuit
8030
, an output bandwidth control circuit
8040
, and cell stored buffers
8050
-
1
to
8050
-
4
respectively established for virtual paths
8200
-
1
to
8200
-
4
.
Cells to be transferred through the virtual paths
8200
-
1
to
8200
-
4
are supplied to the bandwidth monitor circuit
8000
via physical mediums
8060
-
1
to
8060
-
4
. The bandwidth monitor circuit
8000
monitors input cells, calculates a bandwidth adopted to every virtual path
8200
-
1
to
8200
-
4
, and transfers the cells to the corresponding cell stored buffers
8050
-
1
to
8050
-
4
respectively. The cell stored buffers
8050
-
1
to
8050
-
4
respectively holding the upper thresholds TH-
1
to TH-
4
of the Queue length store the input cells and supply the input cells to a physical medium
8070
according to the output bandwidths established by the output bandwidth control circuit
8040
.
The Queue length of a cell stored buffer
8050
-i (i=1, 2, 3, 4) is always monitored by the Queue length upper threshold excess detecting circuit
8010
. When the Queue length becomes equal to the upper threshold TH-i, the Queue length upper threshold excess detecting circuit
8010
sends a control signal
8100
to the bandwidth ratio allocation control circuit
8030
. This processing by the Queue length upper threshold detecting circuit
8010
enables detection of congestion in a cell stored buffer. In the conventional technique disclosed in the same publication, the waiting time prediction circuit
8020
is adopted to detect the congestion of a cell stored buffer by calculating the waiting time of each cell within the cell stored buffers
8050
-
1
to
8050
-
4
, in order to detect the congestion in a cell stored buffer assuredly. The waiting time prediction circuit
8020
calculates the waiting time of each cell within the cell stored buffers
8050
-
1
to
8050
-
4
, according to the bandwidth used for each virtual path
8200
-
1
to
8200
-
4
obtained by reference to the bandwidth monitor circuit
8000
and the output bandwidth of each cell stored buffer
8050
-
1
to
8050
-
4
obtained by reference to the output bandwidth control circuit
8040
. When the calculated waiting time exceeds a predetermined allowance, a control signal
8110
is sent to the bandwidth ratio allocation control circuit
8030
. The bandwidth ratio allocation control circuit
8030
, upon receipt of the both control signals
8100
and
8110
, refers to the current bandwidth information of the virtual paths
8200
-
1
to
8200
-
4
from the bandwidth monitor circuit
8000
, regards the current bandwidth ratio as the bandwidth allocation ratio, and notifies the output bandwidth control circuit
8040
of the bandwidth allocation ratio by use of a control signal
8120
. While, the output bandwidth control circuit
8040
, upon receipt of the control signal
8120
, calculates each output bandwidth of the cell stored buffers
8050
-
1
to
8050
-
4
according to the received bandwidth allocation ratio and modifies the output bandwidth depending on the necessity. A cell stored buffer
8050
-
1
,
2
,
3
, or
4
having the modified output bandwidth supplies the cell within the same buffer to the physical medium
8070
in accordance pith the modified output bandwidth.
The above-mentioned conventional ATM node is defective in requiring too much processing amount of bandwidth allocation control when the Queue length of a cell stored buffer becomes equal to the upper threshold.
More specifically, in allocating an output bandwidth of each cell stored buffer when the Queue length of a cell stored buffer becomes equal to the upper threshold, the conventional ATM node regards the transmission bandwidth of a physical medium on the output side as a bandwidth to be allocated and allocates this bandwidth as the output bandwidth of each cell stored buffer according to a current bandwidth ratio of each virtual path entered into each cell stored buffer. In this case, since the output bandwidth of a cell stored buffer is allocated equally to the bandwidth used for a virtual path entered into the cell stored buffer, the Queue length remains around the upper threshold thereof. Therefore, fluctuation of the bandwidth used for a virtual path entered into a cell stored buffer may increase the opportunity of the Queue length becoming equal to the upper threshold, resulting in an increase of the processing amount of bandwidth allocation control.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide a bandwidth allocation system of a virtual path in a communication network of asynchronous transfer mode, which is able to reduce the processing amount of bandwidth allocation control when the Queue length of a cell stored buffer becomes equal to the upper threshold thereof.
A second object of the present invention is to provide a bandwidth allocation system of a virtual path in a communication network of asynchronous transfer mode capable of making effective use of bandwidth among cell stored buffers, as well as reducing the processing amount of bandwidth allocation control when the Queue length of a cell stored buffer becomes equal to the upper threshold thereof.
According to the first aspect of the invention, a bandwidth allocation system of a virtual path for allocating bandwidths for a plurality of virtual paths in a communication network of asynchronous transfer mode, wherein
a node in the asynchronous transfer mode network comprises
bandwidth monitor means for calculating a bandwidth used for a virtual path by measuring a cell amount entered into each virtual path,
cell storing means for storing the input cell for every virtual path,
bandwidth allocation control means for deciding a bandwidth allocation ratio for output bandwidths in accordance with a used bandwidth ratio obtained by reference to each bandwidt
Chin Wellington
NEC Corporation
Schultz William
Sughrue & Mion, PLLC
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