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.