GPON的测距与时延补偿方法的研究

【作者】 孙文燕；

【导师】 张春业； 宋玉炎；

【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,社会信息化进程加快,数据业务激烈增长,电信业务种类也在不断扩大,已由单一的电话电报业务扩展到多种业务。通信网的主干部分已经发生了巨大的变化,而在接入部分却变化很少。Internet数据流的激增加剧了接入部分的容量限制。“最后一公里”的接入部分仍然是高速局域网和主干网之间的瓶颈。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。 采用光纤接入网(OAN)可以减少传统铜缆网维护运行费用,降低故障率;支持开发新业务,特别是多媒体和宽带业务,满足用户希望较快提供业务,改进业务质量和可用性的要求;也可以节约城市拥挤不堪的地下管道空间,延长传输覆盖距离。而其中基于无源光网络(PON)的接入技术以其低成本、可靠稳定的性能和提供透明宽带的传送能力成为接入网有效的解决方案。 PON自从在20世纪80年代被采用至今已经历经了APON、EPON、GPON几个发展阶段,电信运营商和设备制造商开发了多种协议和技术以便使PON解决方案能更好地满足接入网市场要求。GPON是由FSAN组织于2002年9月推出的具有吉比特高速率、高效率,支持多业务透明传输,同时提供明确的服务质量保证和服务级别以及电信级网络监测和业务管理的吉比特解决方案,支持的最高速率可达2.488Gb/s。2003年1月,ITU-T批准确立了GPON标准G.984.1和G.984.2。GPON被认为是最后一个也是最优的PON技术。 GPON系统在上行方向上是多点到点网络结构,不同ONU采用TDMA的多址接入。由于ONU到OLT的距离不同,每个ONU的数据流经过不同长度的光纤传输后,会产生不同的时延;而且,由于环境温度的变化和器件的老化,传输延时也在不断地变化。因此,不同ONU的数据流进入光分配器的共用光纤,如果不加控制,就有可能发生碰撞和重叠。所以,GPON系统需要对每一个ONU与OLT的距离进行测定,控制每个ONU发送上行数据的时刻,避免数据冲突。本文首先介绍了G.983.1标准中定义的测距和均衡延时补偿方法。由于上行信号在传输过程中会出现一定的相位漂移和抖动,从而使更多还原

【Abstract】 In recent years, with the rapidly developing information and technology, data services are rising. The kind of telecom has been extended from simplex telephone telegram to several services. The narrowband ISDN generally supplies at 128kb/s speed. Access network has been the bottleneck of network to broadband. A technology for access networks that is inexpensive, simple, scalable, and capable of delivering integrated voice, data, and video services to an end-user subscriber over a single network is required.Optical Access Network is an effective technology. Firstly, it can reduce the maintenance, circulation expense and malfunction rate of traditional copper network, and support new services, especially multimedia and broadband. Secondly, OAN can satisfy the request of offering service more quickly and improving quality and usability of service. Thirdly, using optical can economize underground ductwork of city, and can prolong transmission overcast distance. Thereinto, PON technology of low cost, stabilization and transparent transmission becomes the effective way.PON technology has come through APON, EPON and GPON several phases since eighty years twentieth century. Telecom managers and equipment manufacturers have been managing to exploit protocol and technology for PON. GPON is put forward by FSAN in September 2002, with gigabit speed, high efficiency, bearing multi-service transparent transmission, supplying specific quality of service, service level, network inspect and operation management. It can work at maximal speed of 2.488Gb/s. Its criterions G.984.1 and G.984.2 have been established by ITU-T in January 2003. It is regarded as the last and optimum PON.GPON is of multi-point to point network topology structure in upstream direction. Different ONU adopts TDMA access technology. The data stream from every ONU appears different delay through fibers of different length because of different distance between ONUs and OLT. In addition, the delay is varing with thetemperature of circumstances and aging of equipments. Then, after data streams’entering the common optical fiber, collision and superposition among data of ONUs may come forth if without control. So ranging between OLT and ONU is needed to control the beginning time of upstream data of ONU to avoid collision. In this paper, we introduce the ranging method and delay compensation of standard G.983.1 firstly. In this way, the precision of ranging is limited because upstream data appears somewhat offset and twitter. Additionally, OLT considers the furthest ONU as delay benchmark, which adds the packet delay a certain extent. Then we can measure the round-trip time between OLT and ONU based on Multi-Point Control Protocol in EPON.Then OLT can calculate the time when it transmits grant to ONU according to scheduling arithmetic in IPACT MAC protocol. After receiving the grant from OLT, ONU can send its data frame immediately without delay. So the average packet delay of waiting and transmission is decreased, and the link utilization between OLT and splitter is improved. And ONU is made simple and economic, while the synchronization and delay equalization of system are both accomplished all the same.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 delay compensation in G.983.1 for comparison with the same traffic access, and prove the superiority of the ranging method.更多还原