TCP Performance Enhancement Incorporating Handoff Analysis in Mobile IPv6 Networks

摘要

Mobile IP, the most popular host mobility solution for the Internet, is experiencing transient packet sequence disruption as well as packet loss during the handoff. It is well known that this transient impacts can severely hurt the performance of conventional TCPs, which were designed without considering mobility. To address this issue, mobile TCP solutions have been introduced focusing on freezing the transfer during the handoff. However, recently, fast handoff ideas are introduced, especially for Mobile IPv6, to reduce handoff latency as well as packet loss. In this paper, we first show that out-of-sequence packets can be generated during the fast handoff of the Mobile IPv6. By applying timing analysis to the TCP behavior in the fast handoff mobile networks, the timing relationship related with the out-of-sequence packets are analyzed. We then propose a new TCP, Delayed-duplicated ACK (DDA) TCP, to overcome the out-of-order delivery problem. The proposed TCP estimates an unstable time period (UTP) while the packets can be out-of-order. It then suppresses sending duplicated ACK during the UTP so that it can prevent un-desired retransmissions. Simulation result shows that the proposed scheme can yield improved performance than the conventional TCP and freeze-focused TCP.