Mac Protocol For Epon System Research And Design

While in recent years backbone bandwidth has experienced substantial growth, little has changed in the access network."Last mile"still remains the bottleneck between a high capacity LAN and the backbone.Digital Subscriber Line (DSL) and Cable Modem (CM) technologies, compared with 56Kbps dial-up line ,offer a great improvement, but still do not provide enough bandwidth for emerging services such as Video-On-Demand (VoD),interactive games or two-way video conferencing. The rapid growth of user demand and Internet traffic has aggravated the lag of access network capacity. 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 at the LAN/MAN Standard Committee in 2001. EPON technology represents the convergence of low-cost Ethernet equipment with PON. 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.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 two representative MAC protocols in EPON firstly, and based on analyzing the two protocols'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. The polling message is interleaved with frame transmission so that the bandwidth is fully used. Differently, the improved scheme explicitly incorporates the SLAs into MAC protocol design, distributes different bandwidth to ONUs according to their SLA. The unused portion of guaranteed bandwidth is distributed to each of the highly loaded ONUs. further more, considering the IPCAT scheme is not suitable for delay and jitter sensitive services,the improved MAC protocol adopts fixed bound on cycle length.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 IPACT for comparison with the same traffic access, and prove the superiority of the MAC protocol.