ABE: Providing a Low Delay Service Within Best-Effort

We propose Alternative Best-Effort (ABE), a novel service for IP networks, which retains the simplicity of the original Internet single class, best effort service, while providing low delay to interactive, adaptive applications. With ABE, applications choose between either a lower end-to-end delay or more overall throughput. Every best effort packet is marked as either green or blue. Green packets are guaranteed a low bounded delay in every router. In exchange, green packets are more likely to be dropped (or marked using congestion notification) during periods of congestion than blue packets. For every packet, the choice of one or other colour is done by the application, based on the nature of its traffic and on global traffic conditions. Typically, an interactive application with real-time deadlines, such as audio, will mark most of its packets as green, as long as the network conditions offer a large enough throughput. In contrast, an applications that is transferring binary data, such as bulk data transfer, will seek to minimise overall transfer time and send blue traffic. There is benefit for all traffic in that green traffic achieves a low delay and blue traffic receives at least as much throughput as it would in a flat, that is existing, best-effort network. The key feature of ABE is that neither packet colour can be said to receive better treatment, thus flat rate pricing may be maintained, and there is no need for reservations or profiles. ABE is thus different from differentiated or integrated services: it offers no priorities, reservations or guarantees, but it offers a new dimension to best-effort services. In this paper, we define the ABE service, its requirements, properties and usage. We discuss the implications of replacing the existing IP best effort service by the ABE service, and analyse in particular the relationship with TCP friendliness. We identify the ABE router requirements. We propose and implement a method for supporting the ABE service at the output port of a router. We discuss its algorithmic aspects and compliance to the ABE router requirements, and present initial simulation results.