Flow Control in Local-Area Networks of Interconnected Token Rings

We investigate flow-control issues in local-area networks consisting of multiple token rings interconnected through bridges. To achieve high throughput, bridges perform only a very simple routing and store-and-forward function, but are not involved in error- or flowcontrol. In case of congestion, bridges discard arriving frames, which will be recovered through an appropriate end-to-end protocol between the communicating stations. The end-to-end protocol considered is the IEEE 802.2 type-2 logical-link-control (LLC) protocol. Extensive simulations show that performance can be severely degraded if, in such a network, the LLC protocol is employed as defined today. Therefore, we suggest an enhancement to this protocol in the form of a dynamic flow-control algorithm. As our results demonstrate, this enhancement guarantees close-to-optimal network performance under both normal traffic load and overload conditions.