Gpon Ranging And Delay Compensation Method

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.