Design Considerations for the Virtual Source / Virtual Destination ( VS / VD ) Feature in the ABR Service of ATM Networks 1

The Available Bit Rate (ABR) service in ATM networks uses end-to-end rate-based ow control to allow fair and eecient support of data applications over ATM networks. One of the architectural features in the ABR speciication 1] is the Virtual Source/Virtual Destination (VS/VD) option. This option allows a switch to divide an end-to-end ABR connection into separately controlled ABR segments by acting like a (virtual) destination on one segment, and like a (virtual) source on the other. The translation and propagation of feedback in the VS/VD switch between the two ABR control segments (called \coupling") is implementation speciic. In this paper, we model a VS/VD ATM switch and study the issues in designing the coupling between ABR segments. We identify a number of implementation options for the coupling and show that the choice of the implementation option signiicantly aaects the system performance in terms of a) the system stability in the steady state, b) the time to respond to transient changes and converge to the steady state, and c) the buuer requirements at the switches.