Adaptive Packet Combining for IPv6 soft handover applied to Network Mobility

Seamless vertical handover is one of the major challenges toward seamless inter-networking between heterogeneous access networks. To perform seamless vertical handover even under bad radio conditions in network mobility (NEMO) environments, NEMO-SHO has been proposed as an IPv6 soft handover extension that allows packet bicasting via two different wireless links simultaneously. However, the performance gain for TCP traffic was limited because spurious TCP retransmissions were invoked due to the difference of bandwidth and transmission delay between the two links. This paper proposes adding flow control to the packet combining process in NEMO-SHO, which is called adaptive packet combining. Adaptive packet combining estimates packet arrival time from a slow link and delays packets coming from a fast link based on the estimation, which can hide the difference of bandwidth and transmission delay between two links from TCP without any modification on nodes inside a moving network. Adaptive packet combining is thus able to reduce spurious TCP retransmissions. Using 3G and IEEE802.11b link, our experiments show that adaptive packet combining achieves better TCP goodput than Make-Before-Break handover under lossy radio conditions.