EPON系统MAC协议的研究与设计

【作者】 张欣；

【导师】 宋玉炎； 姜威；

【作者基本信息】 山东大学 ， 通信与信息系统， 2005， 硕士

【摘要】 近年来,电信骨干网持续发展,而接入网却进展不大,“最后一公里”成为大容量局域网和骨干网的发展瓶颈。DSL和Cable Modem技术相对56Kbps的拨号线有了很大的提高,但是还不能综合支持视频点播(VoD)、交互游戏或双向的视频会议等。用户需求和网络通信的迅猛发展更加恶化了接入网容量的滞后发展。人们迫切需要一种经济、简单、易升级、能够综合传输语音、数字和视频业务的新的接入网络技术。EPON就是在这种背景下由国际标准化组织IEEE EFM(Ethernet for the FirstMile)工作组于2001年底在LAN/MAN标准委员会(LMSC)会议上提出的。它将目前最为简单和广泛应用的以太网技术与PON系统想结合,具有大带宽、高性价比、结构简单和一定服务质量保证等特点,被业界普遍看好,成为能够满足上述要求的下一代接入网的最佳候选技术。由于在上行方向上EPON是多点到点网络,来自不同ONU的上行数据流可能会发生碰撞,因此需要采用媒质接入控制(MAC)协议来避免不同ONU发送数据之间的冲突,并且该MAC协议应该具有透明性、高效性和公平性等特点。本文首先介绍了EPON系统中现有的有代表性的MAC协议(重点分析了IPACT协议),在分析其优缺点的基础上提出一种改进的MAC协议。改进MAC协议仍采用IPACT协议中“申请-授权-发送”的轮询方式,OLT作为集中控制器,根据网络的实时负载情况动态分配带宽;协议中将控制信息嵌入上、下行数据流中,充分利用了系统带宽。不同的是,在分配带宽时改进MAC协议将用户服务水平协议(SLA)考虑到MAC协议的设计中,对于SLA要求不同的ONU分配大小不等的可用带宽。且对保证带宽的未利用部分依SLA进行重新分配。另外,考虑到部分实时业务对时延及抖动的敏感性,改进的MAC协议采用固定的轮询周期。在文章最后,对本文所设计的MAC协议的进行了仿真和性能分析,并在相同的业务接入条件下,将它与IPACT协议进行比较,证明了改进MAC协议所具有的优越性能。更多还原

【Abstract】 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.更多还原