Endpoint Admission Control over Assured Forwarding PHBs and Its Performance over RED Implementations

Abstract

The Assured Forwarding Per Hop Behavior (AF PHB) has been devised by the IETF Differentiated Services (DiffServ) working group to provide drop level differentiation. The intent of AF is to support services with different loss requirements, but with no strict delay and jitter guarantees. Another suggested use of AF is to provide differentiated support for traffic conforming to an edge conditioning/policing scheme with respect to nonconforming traffic.

Scope of this paper is twofold. First, we show that, quite surprisingly, a standard AF PHB class is semantically capable of supporting per flow admission control. This is obtained by adopting the AF PHB as core routers forwarding mechanism in conjunction with an End Point Admission Control mechanism running at the network edge nodes. The performance achieved by our proposed approach depend on the specific AF PHB implementation running in the core routers.

In the second part of the paper, we prove that changes in the customary AF PHB implementations are indeed required to achieve strict QoS performance. To prove this point, we have evaluated the performance of our admission control scheme over a simple AF implementation based on RED queues. Our results show that, regardless of the selected RED thresholds configuration, such an implementation is never capable of guaranteeing tight QoS support, but is limited to provide better than best effort performance.