TCP-Derwood: A TCP variant to address link switches

Switching between line of sight (LOS) links and satellite links in an airborne network (AN) environment causes many challenging problems for the transport protocol. The typical bandwidth of a satellite link may be in the order of 1 Mbps and the round trip time (RTT) may be around 500 ms. The bandwidth of a LOS link is in the order of 300 Kbps and the RTT is just a few milliseconds. Therefore, switching between these links can cause significant changes in both the capacity and the RTT. Most current TCP variants perform poorly under such network dynamics. In this work, we propose a new TCP variant, called TCP-Derwood, to address this issue. TCP-Derwood is a sender-only modification and addresses the link switch challenges by using information readily available at the sender side. TCP-Derwood detects link switch events using the timing characteristics of returned ACKs and adjusts its congestion control parameters accordingly. Simulation and experimental results show that TCP-Derwood can effectively detect and respond to switches between LOS and satellite links. Moreover, TCP-Derwood connections can fairly share the available bandwidth in scenarios with or without a link switch.