Shaping Aggregate LAN Flows for Transmission over ABR Connections

Abstract

AbstractIn the current recommendations on Internetworking over Non Broadcasting Medium Access and Multi‐Protocol Over ATM, the issues of ATM bandwidth allocation and flow control for best effort external LAN flows, forwarded to ATM connections, have not been adequately addressed. In this paper, we integrate the above features in the Access Units (i.e., bridges and routers) to smooth the bursty aggregate LAN traffic, to minimize losses due to congestion and consequently to achieve high end‐to‐end performance. The proposed flow control mechanism is based on the knowledge of the bandwidth available in the backbone network. Bandwidth advertising and explicit congestion notification mechanisms are provided by several network technologies such as Frame Relay and ATM. In the latter case the corresponding transfer capability is the Available Bit Rate (ABR). The proposed flow control mechanism, counts the frame delay in the Access Unit, and sends explicit feedback (backpressure) to neighboring legacy LAN sources. Explicit feedback partially absorbs the self‐similar features of the LAN traffic and can extend the ABR flow control to the non‐ATM legacy LAN stations. The shaping performed by the AU can be considered independent to the specific bandwidth advertising mechanism of the backbone network; in our case the ABR. In the performance results, the mechanism is shown to be efficient and adaptive to changes in the ATM available bandwidth and to a variety of LAN traffic characteristics. It is also shown that the flow control mechanism can be easily integrated in the protocol stacks currently met by today's LANs.