Method and apparatus for allocation of available bandwidth

Details Method and apparatus for allocation of available bandwidth Method and apparatus for allocation of available bandwidth

1997-11-24

2003-07-01

Yao, Kwang Bin (Department: 2662)

Multiplex communications

Data flow congestion prevention or control

Flow control of data transmission through a network

C370S400000, C370S395430

Reexamination Certificate

active

06587436

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to data communications networks and more particularly to an Available Bit Rate (ABR) flow control system for regulating the allocation of available bandwidth within an Asynchronous Transfer Mode (ATM) network.
BACKGROUND OF THE INVENTION
Efficient informational flow control has been an important consideration in the research and design of high speed communications networks. The ATM Forum has recently standardized rate-based flow control for best effort traffic in asynchronous transfer mode (ATM) networks. Flow control processing varies a sender's allowable rate of information transfer in response to feedback from the network within which the information is being transferred. In general, there are two standardized types of transfer, viz. explicit forward congestion indication (EFCI) and relative rate (RR) marking. If a network is not congested, the session's source of the information being transferred is allowed to increase the rate at which the information is sent thereby taking greater advantage of available bandwidth. When slight congestion is detected, the rate is maintained at current value (RR). When more congestion is present, the rate is reduced. Typically the sending rate of a session during which information is being transferred will oscillate around a desired operating level.
A session with a short propagation delay receives and reacts to feedback from the network much faster than a session with a long propagation delay. This is the fundamental reason which causes an unfair allocation of available bandwidth within an ATM network, i.e. closer nodes will be granted bandwidth at a disproportionate rate relative to nodes which are located a greater distance away. The sending rate for an information packet is decreased if one of the nodes along its path is congested. That “greater distance” information transfer is therefore at a disadvantage with respect to sessions traversing a single “hop”, or relatively fewer “hops” between source and destination nodes. This results in what is known as a “beat down” problem where long-haul connections are starved.
One solution to this problem has been to use “explicit rate” methods where switches are more intelligent and can compute an estimate of the allowable rate for each session. However, such switches are considerably more complex to implement, especially when the switches are targeted for high speed operation.
Therefore there is a need for an improved methodology for determining and assigning allocations of available bandwidth for data transfers within ATM networks.
SUMMARY OF THE INVENTION
A data transfer flow control system for a packet ATM communications system includes a plurality of nodes interconnected by transmission links. Available bandwidth allocation for data packets or cells is improved by fixing the sampling period and establishing a “Nrm” parameter as the product of an allowable cell rate and the sampling period. The parameter “Nrm” is related to the number of data cells being transmitted between resource management cells in a transmission session, and is set to a number independent of round trip time between source and destination nodes, but varies with the allowable cell rate (ACR).


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