A Load-Adaptive ACK Pacer for TCP Traffic Control

Introduction Delivering reliable per-flow Quality of Service in a broadband access network entails a comprehensive congestion control solution at the edge router. The edge router has no direct control over the downstream traffic sources and its egress channel (access link) usually has a smaller bandwidth than its ingress channel. Therefore, to minimize QoS-damaging congestions while maximizing the access link utilization, we leverage on TCP’s congestion control mechanism to pace downstream traffic flows at their sources. Some well-known approaches in the area of traffic shaping and/or packet buffering mechanisms include token bucket rate-limiting and random early detection (RED)[1]. This paper presents the idea of using a TCP acknowledgement (ACK) pacer at the edge router to regulate downstream TCP traffic in accordance with the downstream buffer occupancy at the edge router. Although the general idea of holding ACKs has been studied in [2] and [3], our ACK rate allocation scheme is devised by viewing the problem as an adaptive control system with the control target being to guide the buffer occupancy on a desired queue-length trajectory. Some preliminary simulation results are included.