Multiplex communications – Data flow congestion prevention or control
Reexamination Certificate
1999-10-12
2001-10-09
Hsu, Alpus H. (Department: 2732)
Multiplex communications
Data flow congestion prevention or control
C370S395430, C370S391000
Reexamination Certificate
active
06301226
ABSTRACT:
This invention relates to a system for, and method of, generating different types of cells preferably in an asynchronous transfer mode (ATM) format. The invention is especially concerned with the scheduling of cell transmission so that the cells are transmitted at an optimal, but not excessive, rate.
BACKGROUND OF THE INVENTION
Telephone systems in the United States provide a central office for receiving signals from calling telephones within a particular radius such as one (1) to two (2) miles from the central office and for transmitting telephone signals to such telephones. The telephone signals from a calling telephone are then transmitted through long distances from such central office. The telephone signals then pass to the receiving telephone through a second central office within a radius of one (1) mile to two (2) miles from such central office.
The telephone signals are transmitted long distances between central offices through optical fibers which have replaced other media previously provided for such purposes. The optical fibers have certain distinctive advantages over the lines previously provided. They allow a significantly increased number of signals from different telephones to be transmitted at the same time through the optical fibers. They pass the digitally-encoded signals with a higher accuracy than other media.
Various systems have been adopted to carry digitally-encoded signals for telephone, video and data services. One of such systems now being adopted is designated as asynchronous transfer mode (ATM). This system is advantageous because it recognizes that generally signals travel in only one direction at any one time between a calling subscriber and a receiving subscriber. The system preserves bandwidth in the other direction so that a maximum number of different messages can be transmitted in such other direction.
Various rules have been provided in the prior art to control the regulation of the rates at which the cells are transmitted through the switch(es) between the stations A and B. These rules have involved a significant number of different parameters. These rules have required the performance of calculations involving these different parameters in order to obtain at each instant an indication of the optimal rate, but without any congestion, for the data transmission. The performance of these calculations in the prior art has been relatively slow. A considerable amount of hardware and software has also been required to perform the calculations. Furthermore, the system performing these calculations has been relatively inflexible. For example, when the calculations involve equations, the system is not able to adapt easily if and when changes are made in the equations.
In ATM systems, cells are provided to transmit information between access multiplexes or terminals through central offices or other switching systems. There are different types of cells. For example, when cells are to be transmitted from a station A to a switch B through a switch or a sequence of switches, forward resource management (RM) cells are transmitted from the station A to the station B and backward resource management cells are transmitted from the station B to the station A. Data cells are also transmitted between the station A and the station B.
The switches connected between the stations A and B sometimes provide congestion in the transmission of the cells between the stations A and B. This congestion results in part from loads produced on the switches from different sources which are connected to the switches. The resource management cells provide rate information which is used to control the rates at which the cells are transmitted between the switches A and B so that the cells will be transmitted at an optimal rate, but without any congestion, in the path between the switches A and B.
BRIEF DESCRIPTION OF THE INVENTION
In one embodiment of the invention, an ATM system transmits different types of cells (data, forward resource management (RM) and backward RM) from station A through switch(es) to station B. Different fields in an Available Bit Rate (ABR) table provide controls over the rate of such cell transmissions. First particular field values in such table control the selection of successive ones of cell decision blocks which determine the type of cell to be transmitted. Second particular field values in such table control the selection of one of a plurality of entries in an exponent table which also provides other parameter values controlling the generation of an explicit rate. Third particular field values in the ABR table control the selection of an individual one of a plurality of rate decision blocks each indicating an individual rate of cell transmission from the station A to the station B.
Each of the rate decision blocks includes a plurality of fields which control changes from the individual one of the rate decision blocks to a rate decision block generally providing a reduced rate of cell transmission. These changes are dependent in part upon the relative times for the reception and transmission by the station of the different types of cells. One step in controlling the cell transmission rate is to select the lower one of the explicit rate and the rate indicated in the individual one of the rate decision blocks. By providing the controls specified above, an optimal, but not excessive, rate is selected to transmit the different cells.
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Conexant Systems Inc.
Hale Kelly H.
Hsu Alpus H.
Kind Keith
Nguyen Brian
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