The Alternative Best-Effort Service

Alternative Best-E ort (ABE) is a novel service for IP networks which o ers applications the choice between receiving a lower end-to-end delay and receiving more overall throughput. Every best e ort packet is marked as either green or blue. Green packets receive a low, bounded queueing delay. To ensure blue packets do not su er as a result, green ows receive less throughput during bouts of congestion. The unique combination of lower delay with reduced throughput for green makes it di erent from recent di erentiated service proposals such as expedited forwarding [19] and assured forwarding [21]. The incentive to choose one or other is based on the nature of one's tra c and on tra c conditions. Typically, green ows have real-time deadlines (e.g. interactive audio), while blue tra c (e.g. bulk data transfer) seeks to minimise overall transfer time. There is bene t for all tra c in that green tra c achieves a low delay and blue tra c will receive at least as much throughput as it would in a at best-e ort network and usually more. Neither tra c type can be said to be better, thus at rate pricing may be maintained, and there is no need for reservations or pro les. We rst describe the ABE service. We then describe and simulate a rst generation router implementation. It combines packet drop di erentiation with di erential scheduling for blue and green packets. Green packets have a xed bounded delay. Di erential dropping is done by ensuring blue ows are compensated for the increased delay by higher throughput. Given these constraints, the parameters of the system are regulated to minimise green losses. Simulations show that our implementation is able to implement our de nition of the ABE service. Contact author: paul.hurley@ep .ch, Ph. +41-21-693-6626, Fax +41-21-693-6610