Congestion control of AAL3/4 and AAL5 traffic over ATM networks

This paper presents a new congestion control scheme for data traffic over an ATM network. The aim of the Early Burst Discard Algorithm (EBDA) is to increase the network throughput by concentrating the cell loss to as few packets as possible. Simple cell discard causes a lot of packets to be corrupted and hence to be retransmitted by higher layer protocols. This increased retransmission rate and the continued transmission of cells from a corrupted packet reduce the network throughput. Several similar schemes have been proposed e.g. a CLP tagging mechanism and SUN Microsystem's Partial Packet Discard (PPD) and Early Packet Discard (EPD) algorithms. The CLP tagging mechanism operates on both AAL3/4 and AAL5 traffic, but only at a per inlet level, whereas the SUN Microsystem algorithm operate exclusively on AAL5 traffic at a per VC level. EBDA will be able too operate down to per VC level on both AAL3/4 and AAL5 traffic. EBDA performance has been simulated for both TCP and UDP traffic models across a single 16X16 output buffered switch. A set of simulations were run that produced the aggregate TCP and UDP effective throughout against a range of output port buffer sizes and various UDP/TCP traffic mix ratios. As a benchmark to compare performance, Sun's PPD and EPD were also simulated. Results show that EBDA has an improved performance when compared with the PPD algorithm. Although, in some cases, EBDA shows a slight degradation of performance when compared to EPD algorithms, EBDA is much fairer and has the ability to operate under a wider range of conditions.