Research And Design Of GPON System ONU MAC Layer's Downstream Chain

The access network is the bridge of connecting user network and MAN(Metropolitan Area Network). As the process of social informationization was speeding up, the access network has become the bottle-neck of the development of wideband. In order to appease the requirement of users, new technologies of access network was continuous welled up. At present, the technologies of access network mostly include xDSL, hybrid access technology, fiber access technology and wireless access technology. In the field of wired solutions, fiber access technology becomes the mainstream technology of access network step by step due to their bandwidth capacity and litter attenuation. Passive optical network (PON) is the fiber access technology that attracts the most attention. PON has experienced three periods as APON, EPON and GPON. GPON provides gigabit-capable bandwidth for users, high efficiency of loading IP and TDM, it will be the most perfect solvent in the FTTP/FTTH field. Along with the technology of GPON becames more and more ripe and progressive, it is believed that GPON will be the developing direction of wide band optical access network.The technology character of GPON mainly shows on medium access control (MAC) layer. Many key technologies are achieved on MAC layer such as channl multiple technology, dynamic bandwidth assignment, encrypt/decrypt and ranging. It is significant to research and design of GPON system ONU MAC layer's downstream chain for the research of GPON.At first the dissertation introduces the technology of optical access network, including three main kinds of passive optical networks such as APON, EPON and GPON, and the actuality and development of GPON; secondly, from the definitions of GPON, we illuminate GPON's standards, system structure, delamination structure,and key technologies; then stressly introduces the Transmission Convergence(TC) Layer, including the protocol model, key functions,functions of the sub-layers, and frame structure; according to the analysis of TC layer, we design the whoie structural drawing of ONU medium access control layer, introduce the function of every module; based on the analyzing in detail every module of downstream chain, we design and simulate the modules using Verilog HDL language on the development environment of Quartus II; at last, it summed up the research work what had been done and pointed out what needed to proceed with, and expected the development of GPON in future.