Diagnosing the limitations of network coding at transport layer

The recent development on network coding techniques has attracted much attention, with their demonstrated potentials in improving network capacity and reliability, particularly in wireless networks with broadcast capability. While most studies have focused on designing efficient algorithms and protocols to exploit the benefits at lower layers, i.e., the link layer and network layer, we reveal the impacts of network coding on transport layer algorithms. We show that transport layer protocols, such as TCP and UDP, can suffer from the less careful design of network coding algorithms at lower layers. For example, the behavior of TCP flows and its congestion control algorithms is less predictable, when the underlying network is enriched with the network coding capability. We argue that this added capability changes the fundamental assumptions on the networks and the demographics of the packet flows, and thus adversely impacts the end-to-end performance of the applications. We propose approaches to alleviate the impacts of network coding on upper-layer protocols.