Admission control over assured forwarding PHBs: a way to provide service accuracy in a DiffServ framework

The assured forwarding per hop behavior (AF PHB) has been devised by the IETF differentiated services (DiffServ) working group to provide drop level differentiation. This paper shows, quite surprisingly, that a standard AF PHB class is semantically capable of supporting per flow admission control. This is obtained by adopting the AF PHB as the core router forwarding mechanism in conjunction with an end point admission control mechanism running at the network edges. Our work appears to prove that the extent of the AF PHB can be larger than was originally expected, since it can support an admission control mechanism, which is deemed necessary in recent RFCs to offer QoS aware services. An interesting related issue is whether the expedited forwarding PHB, devised to support flows with strict delay requirements, and based on a single DSCP tag, should be redesigned as a PHB class to comply with end point admission control. Preliminary performance results show that, under suitable assumptions, our scheme can provide as much as hard QOS guarantees (see Bianchi, G. et al., IEEE Globecom, 2001; http://drake.diei.unipg.it/netweb/GRIP_-tech_- rep.pdf)