TCP Explicit Congestion Notification over ATM-UBR: A Simulation Study

Abstract

The enhancement of Transmission Control Protocol’s (TCP’s) congestion control mechanisms using Explicit Congestion Notification (ECN) over Asynchronous Transfer Mode (ATM) networks is overviewed. TCP’s congestion control is enhanced so that congestion is indicated by not only packet losses as is currently the case but an agent implemented at the ATM network’s edge as well. The novel idea uses EFCI (Explicit Forward Congestion Indication) bits (available in every ATM cell header) to generalize the ECN response to the UBR (Unspecified Bit Rate) service, notify congestion, and adjust the credit-based window size of the TCP. The authors’ simulation experiments show that TCP ECN achieves significantly lower cell loss, packet retransmissions, and buffer utilization, and exhibits better throughput than (non-ECN) TCP Reno.