The Alternative Best-Effort Service

Alternative Best-Effort (ABE) is a novel service for IP networks which offers applications the choice between receiving a lower end-to-end delay and receiving more overall throughput. Every best effort packet is marked as either green or blue. Green packets receive a low, bounded queueing delay. To ensure blue packets do not suffer as a result, green flows receive less throughput during bouts of congestion. The unique combination of lower delay with reduced throughput for green makes it different from recent differentiated service proposals such as expedited forwarding and assured forwarding. The incentive to choose one or other is based on the nature of one's traffic and on traffic conditions. Typically, green flows have real-time deadlines (e.g. interactive audio), while blue traffic (e.g. bulk data transfer) seeks to minimise overall transfer time. There is benefit for all traffic in that green traffic achieves a low delay and blue traffic will receive at least as much throughput as it would in a flat best-effort network and usually more. Neither traffic type can be said to be better, thus flat rate pricing may be maintained, and there is no need for reservations or profiles. We first describe the ABE service. We then describe and simulate a first generation router implementation. It combines packet drop differentiation with differential scheduling for blue and green packets. Green packets have a fixed bounded delay. Differential dropping is done by ensuring blue flows 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 the definition of the ABE service.