A Distributed Admission Control Mechanism for Multi-Criteria QoS

Admission control based on multiple criteria has always been a desirable feature for computer networks. In the past, we presented such a system, but it was based on a centralised decision mechanism, which by itself constitutes a significant limitation. Here, we describe a decentralised version of the initial admission control algorithm, while still keeping the multiple-criteria aspect, with each user being able to specify their Quality of Service (QoS) metrics at the level of the individual. Our scheme decides whether a new call should be allowed to enter the network based on measurements of the QoS metrics on each link of the network before and after the transmission of probe packets. The decision is based on a novel algebra of QoS metrics, inspired by Warshall's algorithm that searches whether there is a feasible path to accommodate the new flow without affecting the existing users. The decision is made at each source node individually, based on either only personal information or also on information exchange among the nodes that are involved. The performance of the algorithm is evaluated in terms of QoS throughout the lifetime of all connections. The experiments presented in this paper were conducted in an actual laboratory test-bed of realistic topology and under highly congested circumstances. The results are particularly encouraging.