Access Control in Shared Access Networks Supporting Internet DiffServ

Shared access networks such as hybrid fiber/coaxial and passive optical networks have emerged as promising ways to reduce the cost of the transition to a broadband access infrastructure and provide a graceful upgrade path towards the photonization of the local loop. The TDMA multiplexing of traffic entering such a system is governed by the MAC (Medium Access Control) protocol, which arbitrates the allocation of bandwidth to the shared feeder. At the same time the need to integrate telecom services presenting demanding quality requirements with plain Internet best-effort services over the same infrastructure, brings new issues to the design of such an access mechanism. The MAC protocol as the only arbiter of the upstream bandwidth directly affects the Quality of Service (QoS) provided to each upstream traffic flow and must meet several constraints. Such constraints include the adequate speed of operation exploiting in the highest degree the speed of H/W implementation, flexibility to support efficiently the largest number of services and applications offering an adequate number of QoS classes like the differentiated services (DiffServ)and independence of higher layers, protocols and future extensions to traffic management specifications. The implementation of a mechanism targeting these goals and its evaluation using computer simulation are presented in this paper.