DACK-XOR: An Opportunistic Network Coding Scheme to Address Intra-flow Contention over Ad Hoc Networks

Abstract

Network coding is a novel technology that exploits the intrinsic broadcast nature of wireless media, to significantly reduce the number of transmissions (hops). Our primary focus is to minimize intra-flow contention by exor-ing TCP-DATA and TCP-ACK packets belonging to the same TCP flow, ensuring that the packets are never delayed in the process. Network coding always comes with the overhead of intermediate nodes having to buffer packets so as to successfully perform decoding. This requires the nodes to maintain large buffers. We also propose a new technique in which we retain only the last delivered packet in the buffer. However, at times when the same node gets access to the medium repeatedly, keeping only the last sent packet in the buffer will not suffice. Hence we introduce a rate based Cross-layer Transport Solution (CLTSP) that inserts a delay interval (called out -of-interference delay) between two consecutive packets transmitted. This reduces intra-flow contentions by leaps and bounds. Our unique combination of using a Network Coding technique along with a suitable TCP variant improves the throughput gains with significant improvement in handling medium contention by reducing the number of transmissions.