Empirical study of buffer management scheme for Diffserv assured forwarding PHB

The IETF Differentiated Services Working Group has recently standardized the assured forwarding (AF) per hop behavior (PHB). RFC 2597 recommends that an active queue management (AQM) technique be used to realize the multiple levels of drop precedence required in the AF PHB. The most widely used AQM scheme is RED (random early detection). There are several ways to extend RED to a multi-level RED (MRED) algorithm suitable for the AF PHB. This work compares two possible MRED implementations and their ability to protect lower drop precedence traffic: WRED (weighted RED) and RIO (RED with in/out). Based on an empirical study, this paper makes the following key contributions: firstly, the results show that for ON-OFF traffic, RIO is better than WRED in protecting packets marked for treatment with lower drop precedence. Secondly, for short-lived flows, RIO achieves higher transactional rates than WRED. Thirdly, for bulk transfer, RIO and WRED achieve comparable long-term throughput. Finally, this paper also reports the results of experiments with 3 different models for setting of WRED and RIO parameters. We recommend the "staggered" model as best suited to achieve the requirements of the AF PHB.