ATM Forum Contribution, March 1994

Postscript Version

This contribution describes an adaptive credit allocation algorithm for credit-based flow control over ATM networks. At each node the allocation of credit buffers between flow-controlled VCs sharing the same switch memory can adapt dynamically to reflect their actual bandwidth usages.

There are two advantages of this adaptation capability. First, since the credit buffer size can be derived automatically, there is no need for the user or the system to specify it. This significantly eases the use and implementation of ABR services. Second, since inactive VCs can automatically yield their unused buffer space to other active ones, the total buffer size required by the flow-controlled VCs at the node can be minimized. In particular, for those VCs charing a link their total buffer need not be larger than a small multiple of the product of the link bandwidth and round-trip link propagation delay. The total buffer can be kept the same size for a large number of flow-controlled VCs, while guaranteeing no cell loss due to congestion and ensuring high link utilization.

Simulation results demonstrating the effectiveness of this adaptive credit scheme are given.