Dynamics of an Explicit Rate Allocation Algorithm for Available Bit-Rate (ABR) Service in ATM Networks

this paper we study the performance of an explicit rate allocation algorithm for ATM Networks using the available bit-rate (ABR) class of service. We examine the behavior of ABR traffic with simple cell sources, and demonstrate that the allocation algorithm is fair and maintains network efficiency in a variety of network configurations. We also study the behavior of TCP/IP sources using ABR service in a network of switches employing the rate allocation algorithm; the results show substantial improvements in fairness and efficiency in comparison with the performance of TCP on an underlying datagram-based network. Even in a dynamic network configuration with frequent opening and closing of ABR connections, TCP connections were able to make sustained progress with a switch buffer size as small as 1 Kbyte, providing an average link utilization of approximately 60% of the attainable maximum. We also study the performance of ABR traffic in the presence of higher-priority variable bit-rate (VBR) video traffic and show that the overall system achieves high utilization with modest queue sizes in the switches, and the ABR flows adapt to the available rate in a fairly short interval. Scalability of the ABR service is an important criterion. We demonstrate the scalability of the rate allocation algorithm with respect to the number of connections by increasing the number of active connections with very long round-trip times by a factor of 13; this caused only a three times increase in the switch queue size, while still maintaining maximal link utilization. Keywords: Explicit rate allocation, congestion control, TCP over ATM This research is supported by the Advanced Research Projects Agency (ARPA) under Contract No. F19628-93C -0175 and by the NSF Young Investigator Award No. MIP-92..