Guarantee of service expectation level and fairness by precise queue weight allocation in AF PHB

Assured Forwarding Per-Hop Behavior (AF PHB) is a forwarding scheme for providing QoS in DiffServ networks. It defines four classes and three drop precedence, where buffer space and bandwidth are defined as forwarding resources for each AF class [1]. RIO [2] could be used as drop policy in a DiffServ router. AF PHB could be implemented by WRR, WFQ, CBQ, etc. When network managers provide AF PHB using the scheduling mechanisms, they want to guarantee accurate achievement of service expectation level, which results from precise queue weight allocation to each AF class with respect to forwarding resources, i.e., buffer space and bandwidth. In order to provide a guideline for the precise queue weight allocation, this paper proposes a simple analytical model for AF PHB designed on RIO and M/M/1 queue, and uses this model to obtain queue weight equation (QWE), which performs fine calculation of queue weight for AF classes. Average buffer space and bandwidth allocated for each AF class are used in derivation of QWE. The model verification is performed by simulation in which we use WRR for simplicity. Simulation results show that the QWE supports an accurate allocation of the forwarding resources, and, as a result, makes four AF classes achieve fairness as well as service expectation levels.