Multiplex communications – Data flow congestion prevention or control – Control of data admission to the network
Reexamination Certificate
1999-08-25
2001-12-11
Marcelo, Melvin (Department: 2663)
Multiplex communications
Data flow congestion prevention or control
Control of data admission to the network
C370S412000, C370S468000
Reexamination Certificate
active
06330227
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cell output control apparatus and method in communication systems using asynchronous transfer mode, and particularly to a cell output control circuit apparatus and method suitable for use in communication systems which provide available bit rate services.
The U.S. Pat. No. 5,313,454 has disclosed a conversion system having an available bit rate (herein-after, abbreviated ABR) traffic class incorporated in order to make feed-back control for preventing the congestion in a communications network in which cells of asynchronous transfer mode (hereinafter, abbreviated ATM) are processed. Here, the ABR traffic class is for transmitting and receiving ATM cells from a source (transmitting terminal, or a transmitting node) at an allowed cell rate (hereinafter, abbreviated ACR) in an ATM communications network. This system sets up such an ACR that when a resource management cell (hereinafter, abbreviated RM cell) including the congestion information of the network is inserted in the cell flow that is transmitted and received within the network, and transferred back to the source from the destination (receiving terminal, or receiving node), the source changes the ACR in accordance with the information of the received RM cell so that the congestion within the network can be decreased as much as possible and that the cells can be transmitted at a large transfer rate.
When the cells are transmitted from the source at the ACR, the ATM-communication system decides whether a cell is allowed to transmit at each ATM cell time slot or not in order to transmit at the ACR. In general, after a cell is transmitted on a certain cell time slot, the next cell time slot to be produced is calculated, and the cell is timely transmitted on that slot. More specifically, when the line cell rate (hereinafter, abbreviated LCR) and the ACR are 150 Mb/s and 50 Mb/s, respectively, a cell can be transmitted at each three time slots. Therefore, after a cell is transmitted on a certain time slot, the next time slot is produced three cell time slots later. In other words, when a cell is transmitted on a certain cell time slot, the next cell time slot is produced LCR/ACR cell time slots later.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a cell output control method and apparatus capable of absorbing quantization error produced when the ratio LCR/ACR is quantized into an integral value in order that cells are allotted to cell time slots and transmitted on the slots.
It is another object of the invention to provide a cell output control method and apparatus capable of transmitting cells with the quantization error surely absorbed by a simple construction and of easily adapting to even fast transfer rates in order that the communication systems can provide ABR services with ease.
According to the invention, the output control apparatus used in the communication systems includes a cell time slot allotment circuit for allotting cells to cell time slots with the cell transmission intervals changed by the feedback of the quantization error so that the cells can be transmitted at a rate near ACR.
This cell time slot allotment circuit includes a first holder circuit for holding the ACR calculated in the communication systems according to the traffic state of the network, a first calculator circuit for calculating a rate at which cells are transmitted, on the basis of the ACR and LCR, a quantizer circuit for quantizing the calculated results and controlling the cell time slot allotment on the basis of the quantization error produced by the quantization, a counter for counting the number of the cell time slots, or the cell time slot value, a second calculator circuit for calculating the rate at which cells are transmitted on the cell time slots on the basis of the quantized value and the count, and a second holder circuit for holding the calculated results.
The first calculator circuit has a table and a bit shift circuit. The table has rates previously set up at which cells are transmitted, in order that the cell output rates can be obtained by only bit-shifting the output produced from the table when the ACR value is inputted to the table, or that there is no need to use complicated arithmetic circuits.
The quantizer circuit includes a decision circuit for deciding the intervals of the cell time slots on which cells are transmitted, on the basis of the quantized value and the quantization error, and a calculator circuit and quantization error holder circuit for producing the remainder of the quantization error and feeding it back to the decision circuit after the cell output intervals are decided.
Therefore, the cell output control method and apparatus including these circuits controls the allotment of cells to cell time slots so that each time a cell is allotted to a cell time slot and transmitted on the slot, the ACR calculation, cell time slot interval decision and quantization error calculation are repeated to reduce the quantization error to zero, or that cells are allotted to cell time slots with the cell transmission interval changed and are transmitted at a rate near ACR.
The above construction makes it possible to allot cells so that the cells can be transmitted at a rate near ACR, by holding the difference between the calculated value and the cell time slots per unit time and using it for the next calculation when the quantization computation is made for cell time slots on the basis of the rate (ACR) allotted to the ABR traffic class. Then, the cell time slots for cell transmission can be calculated from the ACR. In addition, when the ratio of ACR to LCR is quantized for cell time slots, the produced quantization error can be absorbed. Particularly when ACR is near LCR, the quantization error is absorbed by allotting cells to any ones of a plurality of cell time slots with the cell transmission interval changed, thus making it possible to transmit cells at a rate near ACR.
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Abe Hajime
Kozaki Takahiko
Miyoshi Kota
Takase Akihiko
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Marcelo Melvin
Nguyen Phuongchau Ba
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