The Research Of EPON System

The EPON Project is a part of "The National High Technology Research and Development Program of China"(863 program). In the last composing period of this article, the 802.3ah working group of IEEE Standards Association approved the IEEE Std. 802.3ah in which the technology of EPON is standardized. Nevertheless the practical application of EPON is in the very beginning stage and there is much room for farther developing.Firstly, in this article the structure of EPON system is introduced. Because of the difference between EPON's point to multipoint topology and Ethernet's, new function of Physical layer and MAC layer of actual IEEE 802.3 Std. must be added, including multipoint control protocol to the MAC control sublayer and point to point emulation to the RS sublayer. We also analyse the incompatibility between the point to multipoint topology of EPON and the IEEE 802.1 bridges. By combining several key technologies of EPON, the keystone of this article is raised which is the research and design of LAN emulation function in an EPON system.The LAN emulation function designed here is composed of P2P emulation and shared LAN emulation. The primary function of LAN emulation is achieved mostly in OLT, including the design and control of a MAC address Table in bridge function of emulation layer; the control of data frames in both register stage and normal working mode; the choice of VLAN member's definition which is appropriate for the EPON system designed in this article, and the function achieving of aggregation of ports data among VLAN.At last, with the hardware language VHDL, we give out a practical implementation of this scheme above an EPON system which has achieved simple frame structure.It is recommended in IEEE802.3ah Std. that the EPON system should not connect to an 802.1D bridge port directly without shared LAN emulation function, so it is worth researching the LAN emulation of EPON.