Mobility aware TCP congestion control

Abstract

We examine the performance of TCP over wireless networks. In wireless environments, packets may be lost until a mobile terminal completes registration with an access router. The technique of post registration handover is expected to reduce this loss since the mobile terminal sends a binding update to the previous care-of address after handover and packets are forwarded to the mobile terminal. However, if several packets have been lost, TCP throughput may become worse than not forwarding packets. Upon receiving the forwarded packets, the mobile terminal returns duplicate ACKs, and these ACKs force the sender into the congestion control phase. In New-Reno TCP, the sender's transmission rate is extremely limited during the period. As a result, the throughput is reduced significantly. We solve the problem by using either TCP flow control or congestion control functions according to the number of packets lost. Results from simulations show that our proposal keeps the throughput high even if many packets are lost. Our study makes clear the need for a reliable transport protocol that is handover-aware and suggests how to adapt the protocol to yield better performance in wireless environments.