An End-to-End Transport Protocol for Extreme Wireless Network Environments

As the Joint forces move towards the vision of network-centric warfare (NCW), it is extremely important that the network services be reliable and dependable, even under degraded network conditions. Tactical wireless and satellite based networks are prone to disruptions over multiple time-scales: bursty bit errors and packet loss (small time-scale), interference, jamming and capture effects (medium time-scale) and long-term path disruptions due to persistent channel impairments and mobility (large time-scale). TCP does not work well over such channels because it misinterprets erasure for congestion. TCP's throughput suffers significantly, particularly when there are disruptions. Large round-trip-times (RTT) as in satellite networks, and uncoordinated optimizations at multiple layers (PHY, MAC and transport) lead to poor performance. In this paper we describe LT-TCP, an enhancement to TCP which makes it robust and applicable for extreme wireless environments including a mix of ad-hoc meshed networks (MANETs), airborne networks and satellite networks. LT-TCP uses an adaptive, end-to-end hybrid ARQ/FEC reliability strategy and exploits ECN for incipient congestion detection. The novelty lies in our adaptive methods that respond to learning about the underlying random packet loss and disruption process. The overhead of FEC or smaller segments is imposed just-in-time and targeted to maximize the performance benefit even when the path characteristics are uncertain. We show that LT-TCP substantially improves performance over regular TCP even for packet loss rates of up to 40%-50%, thus substantially extending the dynamic performance range of TCP over lossy wireless networks