Towards handoff tolerance in TCP: Link layer handoff detection for optimized data transport

With the proliferation of network management tools that adjust link and path characteristics to optimize network performance and health, TCP's are frequently incorporating path characteristic detection mechanisms to quickly adapt to the effects of these changes. Optimal TCP performance, including rapid adaptability, depends on, among other things, an accurate view of the of the bandwidth-delay product (BDP) of the path. Towards the goal of prompt detection of large changes in the BDP, we propose a detection scheme that can be applied as a sender-side only modification. Specifically, we focus on link layer (L2) handoffs at the bottleneck link of the path. Simulation results show that current TCP variants, such as TCP-Reno and TCP-Westwood, are unable to efficiently capitalize on L2 handoffs at bottleneck links that result in substantial changes in the BDP. Such a handoff can occur, for example, during a TCP session over a multi-hop path involving a bottleneck link between two aerial vehicles, wherein a degradation of this link causes a handoff to a backup satellite relay. By making use of BDP and congestion heuristics, our mechanism detects such BDP changes and allows for quick adaptation to the observed change, thereby efficiently addressing this issue. Based on simulated experiments, we observed rapid detection of handoff (up to 7 times faster that TCP Reno), including fairly accurate estimation of the changes in BDP.