A Study On MAC Protocol And Bandwidth Allocation In EPON System

Since the rapid development of the network technology, the access network has become the bottle-neck of the whole network. Ethernet Passive Optical Network (EPON) integrates the simplicity of Ethernet, the high bandwidth of the optical transfer, and technology of Passive Optical Network (PON). EPON emerges to be a promising candidate for the next-generation broadband access networks. In the downstream direction, Optical Link Terminal (OLT) broadcasts packets to all Optical Network Unit (ONU). In the upstream direction, multiple ONUs share the same transmission channel under the control of a multi-point access scheme and dynamic bandwidth allocation (DBA). Recently, upstream access and DBA, which have important meaning in improving the quality of service (QoS) and reducing packet delay, have become a hot topic for local area.The research is mainly focused on the dynamic bandwidth allocation schemes of EPON upstream channel. Firstly, this thesis discussed the development of the access network, some kinds of comparison of PON. Then from definition of EPON system, we illuminate structure of EPON system and operation principle, up and down frame, analyzes the characteristics and key techniques of EPON. Secondly, for the static bandwidth allocation and basic DBA algorithm (IPACT algorithm), we analyze some strategy problems in the process of bandwidth allocation, such as priority queuing scheduling and interleaved polling scheme should be taken in account to guarantee the QoS. After analyzing the disadvantages of the current DBA algorithms, this thesis presents a novel QoS-guaranteed Predicted DBA algorithm (AMDBA) in EPON. To avoid the "T+2" queuing delay of high priority services, the algorithm predicts bandwidth requirements for different services in a supercycle which is made up of multi-sub cycles, and in a subcycle we allocate the guaranteed bandwidth by referring to the predicted one. Besides, we add access management (AM) modules which help to obtain steady QoS. And appropriate control will prevent the hacker from sending data more than their service level. Simulation results show that AMDBA algorithm can not only improve the utilization of bandwidth effectively and meet the delay demands of various services, but also provide steady QoS level.