Based Mac Protocol For Ethernet Passive Optical Networks Research

While in recent years backbone bandwidth has experienced substantial growth, little has changed in the access network, The rapid growth Internet traffic has aggravated the lag of access network capacity. "Last mile" still remains the bottleneck between a high capacity LAN and the backbone. The most widely deployed "broadband" solutions today are Digital Subscriber Line (DSL) and Cable Modem (CM) technologies. Although they are an improvement compared to 56Kbps dial-up line ,but still do not provide enough bandwidth for emerging services such as Video-On-Demand (VoD), interactive games or two-way video conferencing. A technology for access networks is required that is inexpensive, simple, scalable, and capable of delivering integrated voice, data, and video services to an end-user subscriber over a single network.Just in this background, IEEE EFM group present EPON technology in 2001 and print the standard IEEE802. 3ah in July 2004. EPON technology represents the convergence of low-cost broadband Ethernet equipment with low-cost fiber network, and is regarded as the best candidate technology for next generation access technology because of its broad bandwidth, excellent performance-to-cost ratio, simple configuration, and certain "quality of service" promise.EPON can be deployed in tree topology .Since EPON is a multipoint-to-point system in upstream direction, upstream traffics from different ONUs will collide in the trunk optical .So a particular media access control (MAC) mechanism is needed for upstream traffic to avoid traffic collision. The MAC protocol has to support different service classes, and has to allocate bandwidth fairly and efficiently and treat users fairly. In this paper, we introduce four representative MAC protocols in EPON firstly, and based on analyzing the fourprotocols' advantages and disadvantages, we present an improved MAC protocol. The improved MAC protocol adopts "Apply-Grant-Deliver" polling scheme, liked the IPACT protocol. OLT, as the muster controller, distributes bandwidth among ONUs dynamically according to instantaneous network load. Differently, the improved scheme classify services into three priority categories: Expedited Forwording (EF),Assured Forwording(AF) and Best Effort(BE). In this article, we propose a bandwidth scheme that implements weight-based priority for this need. First, satisfy the request of high-priority; Second, medium-priority and low-priority based on it' s weigh. In the program, all ONU proportionally share the bandwidth based on their instantaneous demands. The weight set for two class prevent high-priority traffic from monopolizing the bandwidth under heavy load. In the other, the ONUs are divided into equal two group. The OLT polling the two group ONU in circulation. Then the idle time are avoided.In the last part of this paper simulation is given to show the performance of the propose scheme. We also provide the performance of the ONU in two-queue for comparison with the same traffic access, and prove the superiority of the MAC protocol.