Link layer-based TCP optimisation for disconnecting networks

This paper discusses a link layer approach to improving TCP performance in the face of periodic network disconnections. Network disconnections are encountered in many scenarios, including being out-of-range in a wireless network, during network handoff, and also in the case of Networked Surfaces, a novel LAN technology which provides the motivation for this work. A "smart link layer" employing repetition of selected packets at reconnection time is shown to improve TCP's utilisation of a disconnecting network to nearly 100%. This solution is also demonstrated in the context of a Networked Surface prototype, improving TCP performance for both bulk transfers and interactive traffic. The smart link layer solution is lightweight, requiring little processing and buffering only one packet per TCP connection. It is therefore easily retro-fitted to existing TCP-capable devices, without modifying the internal operation of those devices.