TCP and UDP performance for Internet over optical packet-switched networks

A strong candidate for the future Internet core is optical packet-switched (OPS) network. In this paper, we study the impact of mechanisms as employed in OPS networks on the performance of upper layer Internet protocols represented by TCP and UDP. The mechanisms we investigate are packet aggregation, deflection routing, and ingress buffering. We show that packet aggregation in general improves TCP throughput, and the improvement increases with the aggregation interval (or optical packet size). With the packets destined to the same egress optical switch, aggregation may be done at different granularities: aggregating all the packets (full aggregation), aggregating packets from the same traffic class (per-class aggregation), and aggregating packets from the same flow (per-flow aggregation). We show that with per-class aggregation and per-flow aggregation some flows may be severely penalized in throughput at large aggregation intervals, resulting in significant degradation in TCP fairness, because of the synchronization problem with shared queueing. By using weighted fair queueing (WFQ) at the ingress buffer, in contrast, we show that differentiated QoS (in terms of throughput) can be provisioned for both TCP and UDP traffic even with deflection routing. Deflection routing avoids packet losses, but results in out-of-order packet delivery and increased packet delay jitter. We show that TCP throughput can be significantly improved by deflection routing in spite of the packet reordering, and the UDP packet delay jitter introduced by deflection routing can be alleviated by packet aggregation and ingress buffering. We also show that ingress buffering significantly improves TCP throughput and the ingress buffer only needs a small size (in terms of the number of optical packets). (C) 2004 Elsevier B.V. All rights reserved.