Study On The Key Technologies Of Broadband Passive Optical Network

Nowadays, it is information technology society. Access networks, which is "in the last mile" of telecommunication, develop slowly because its complexity and massed of access technologies. Broadband passive optical network based on the ATM (BPON) is one of the most attractive access network solution currently.Based on the introduction of structure, researching status and developing tendency of BPON, some key technologies in BPON are discussed and studied, including registering process, ranging procedure, MAC protocol and Dynamic bandwidth allocation, designing of ONT. By combination of the theory analysis and software simulation experimentation, some significative ideas, methods and technologies are proposed and also some conclusions are gotten. Furthermore, the experimental data are discussed.First, in chapter 1, telecommunication network development and some problems faced to access network are introduced, the current broadband access technologies and researching status are expatiated on, main resesarching work of this paper are presented.In chapter 2, after the introduction of BPON system framework, the key technologies of BPON, researching status and some existing problems, studying focus of this paper are presented.In chapter 3, ranging process of BPON is analysized, the registering method of ONU device are researched. After the discussion of traditional binary tree algorithm, one registering algorithm based on the binary exponential back-off (BEB) is proposed. Compared with the binary tree, BEB algorithm can eliminate the collision to perform the registering process by backing off with random, it is one method of remote terminal adapting, not the local terminal controlling. Through the computer simulation, the results show that BEB algorithm has lower registration time delay than binary tree, can be implemented easily and efficiently.Then, the ranging procedure is researched. On the basis of enhancing the ranging efficiency and simplifying the ranging procedure, on the condition of cold PON, cold ONU, a one-by-one ranging procedure is proposed. This procedure is compatible of SN searching process and performes ONU ranging procedure in turn.By using the network simulation software, BPON is modeled and ranging procedure is emulated. The experimental results show that the presented ranging procedure can get equalizationdelay (Td) precisely, ranging time delay is shortened, ranging procedure is simplifed, and with good compatibility. The designing of ranging procedure provide the software research a kind of reliable pre-verifying method.In chapter 4, after discussing the media access control (MAC) protocol, we analyze the upstream access process using queuing theory, get the cell queue length, staying time, waiting time and their probability density distribution, provide the theory secundum for application designing.Then, according to the two DBA ways of ITU-T G983.4, that is status reporting (SR) and non status reporting (NSR, also called idle cell monitoring), researchingmethods and work of DBA based on SR at home and abroad is analyzed, one DBA algorithm based on NSR is proposed, called predictive dynamic bandwidth allocation.The predictive dynamic bandwidth allocation algorithm, which predicate the bandwidth needed according to the utilization, divide the service into high priority (realtime service) and low priority (non-realtime) service based on the time delay, realtime service is transmitted first. The grant allocation scheme of realtime service is first in first out and is spaced, the cells in different queue of same priority are permitted with random for fairness, so the cell transfer delay (CD) can be lowered. The non-realtime service is protected by preserving bandwidth. In the grant allocation scheme the step-wise increasing and step-wise decreasing of bandwitdh are taken, which assure that the ONUs with longer cell length can get more grant, so the cell loss ratio is decreased and Quality of service (QoS) of different class service is ensured.Through the computer simulation of predictive DBA algorithm, CD distribution, cell delay variation distribution, queue length distribution and their relationship with load are obtained, experimental results show that the bandwidth allocation algorithm is severely impact on the character of system and quality of service.In chapter 5, as the key device of BPON system, optical network terminal (ONT) designing is researched. Structure of ONT, processing upstream and downstream data flow, handling and function of transmission convergence (TC) layer are discussed, the hardware designing of ONT is outlined.The key models of ONT TC layer is studied, software requirements and high level designing are implemented. Software designing is marked out 5 function modules, the flow charts are designed. So the system supports the ranging function, providing downstream service churning key, backlogging cell reporting function, message handling function, and can provide at least one channel of voice service and one channel of fast Ethernet service, is conform to ITU-T G983 recommendation, can meet with the practical system requirements of ONT and the performance.