Shaping aggregate LAN flows for transmission over ABR connections

In the current recommendations on Internetworking over Non Broadcasting Med ium Access and Multi-Protocol Over ATM, the issues of ATM bandwidth allocat ion and flow control for best effort external LAN flows, forwarded to ATM c onnections, have not been adequately addressed. In this paper, we integrate the above features in the Access Units (i.e., bridges and routers) to smoo th the bursty aggregate LAN traffic, to minimize losses due to congestion a nd consequently to achieve high end-to-end performance. The proposed flow c ontrol mechanism is based on the knowledge of the bandwidth available in th e backbone network. Bandwidth advertising and explicit congestion notificat ion mechanisms are provided by several network technologies such as Frame R elay and ATM. In the latter case the corresponding transfer capability is t he Available Bit Rate (ABR). The proposed flow control mechanism, counts th e flame delay in the Access Unit, and sends explicit feedback (backpressure ) to neighboring legacy LAN sources. Explicit feedback partially absorbs th e self-similar features of the LAN traffic and can extend the ABR flow cont rol 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, t he mechanism is shown to be efficient and adaptive to changes in the ATM av ailable bandwidth and to a variety of LAN traffic characteristics. It is al so shown that the flow control mechanism can be easily integrated in the pr otocol stacks currently met by today's LANs.