Design and Analysis of Flow Control Protocols for Metropolitan Area Networks

Abstract

In this paper we study the problem of flow control for LAN’s interconnected through a high speed MAN. We consider several input bridges feeding data through the MAN to an output bridge and specifically concern ourselves with the avoidance or minimization of buffer overflow at these bridges. We study the behavior of four flow control policies that differ from each other according to the type of information passed aroundamong the bridges. The most complex protocols use queue length information whereas the simpler protocols use either no information or packet age information. We show that the protocols using queue length information are optimal in the sense that they minimmize buffer overflow for a broad class of systems. In addition we compare the performance of these policies through a combination of analysis and simulation. We observe that using age information, which is relatively inexpensive to acquire, yields half of the benefit of queue length information. Furthermore, if most of the buffers are allocated to the output bridge, then there is little difference between the behavior of these policies. This suggests that simple protocols may work well under such allocations. Last, we study the issue of fairness when input bridges are not identical. We observe that the policies based on queue length information provide fairer treatment when the performance metric is probability of loss and the simple policies provide fairer treatment in the case of mean packet delay.