Study On The Key Technologies Of Passive Optical Networks Based On ATM

The demand for accessing Internet with high speed and supporting multi-media applications has greatly accelerated the development of broadband access networks. As one of the major researching areas of broadband access networks, the passive optical networks based on ATM (APON) combine the ATM's statistic multiplexing function with PON's broadband transparent transmission, so as to support different Quality of Service (QoS) as well as broadband access. APON have a lot of virtues, such as big capacity, reasonable ratio of performance and price, and easy to upgrade. However, since APON has a tree-based topology and the rates in both way are high, there are some technical or theoretical problems, such as ranging, burst mode optical receipt, burst synchronization and dynamic bandwidth allocation. The dissertation will mainly concentrate on the study of dynamic bandwidth allocation, upstream burst synchronization and the key functions in OLT抯 TC layer. Firstly, in the introduction of this dissertation (chapter 1 ),we briefly present the researching and developing status of modem telecom networks and broadband access networks, and indicate the importance of developing APON. In chapter 2, we introduce the configuration and requirement of APON systems at first, then we expatiate on the three functional blocks in detail. Finally, we describe what the key technologies are for APON. In chapter 3, based on the "moving ceiling" allocating scheme and "transfer belt" allocating scheme proposed by John D. Angelopoulos et al, a MAC protocol suitable for APON is proposed. The services are classed as two priorities according to different delay requirement in the protocol. The real-time services have a higher priority, and can be permitted first. Non real-time services are not sensitive to delay, but sensitive to cell loss ratio (CLR). "moving ceiling" allocating scheme gives the ONU, in which there are more cells waiting, more chance to send, so this protocol can debase the CLR of non real-time services when the buffers are definite in the ONU. For the first time, the APON's upstream access process is analyzed in this thesis, and some primary results are met. In the chapter's end, the performances of the proposed MAC protocol are simulated. The simulations?results show that the protocol has good access performances. In chapter 4, based on correlating synchronization scheme proposed by Stephen Topliss et al, a synchronization scheme suitable for APON's upstream burst synchronization is proposed according to the high-speed and burst-mode characteristics of APON's upstream information. Delay line technique is used to get eight clocks in the receiver. The phase difference among the eight clvcks is 45 degrees. The eight clocks sample the receiving signal, and get eight inputting data. a The eight inputting data are sent to eight 8-bits registers respectively. The registers? values are compared with a known key word, which has a good self-correlation. When the key word in the burst packet arrive, there must be one ,or even several results are maximal. According to correlation principle, the inputting data with maximal result is the best sampling data, and the corresponding clock is the best sampling clock. Using correlation synchronization scheme, we carry out a burst- mode synchronization with a rate of 155.52OMbit]s. This fruit sweep away a key obstacle in APON's exploitation. In chapter 5, the functions of TC layer in OLT are analyzed in...