| Ethernet Passive Optical Network (EPON) combines boths the advantages of Ethernet (e.g. mature technology, low cost, good compatibility, etc.) and Passive Optical Networks (high reliability and good OAM capability) which makes it one of the best choices in customer access networks. EPON adopts point-to-multiple-ponints topology which makes all the Optical Network Units (ONU) placed in same conflict area. The bandwidth allocation algorithm is intrudced to avoid the conflict. Dynamic Bandwidth Allocation (DBA) algorithm can assign bandwidth according to the network load while also improving the bandwidth utilization efficicency in upsteam link and the Quality of Sevrvice (QoS). This thesis presents a comprehensive and indepth study on DBA algorithm in EPON.Firstly, this thesis presents the current situation of access network and major tecgnologies, EPON technical features and development trends, respectively. Follwed are the introduction of EPON system architecture, working principles and key techniques. Then two classic DBA algorithsms (IPACT and cyclic-polling) are studied in detail and compared. A novel transmission scheme which can eliminate the idle time is proposed on base of the analysis of the existing schemes. Various allocation schemes and numerical calculation of link utilizations improvements are presented for different load conditions. Finanly, this thesis gives a performance analysis of modified algorithm with OPNET tools. Simulation results show that the modified algorithm improves upstream bandwidth efficiency, ensures QoS for different services and has good delay characteristics. |
PDF Full Text Request