Research Of DBA Algorithm Based On Multi-service In EPON Uplink Access

Ethernet Passive Optical Network (EPON) combines the advantages of Ethernet technology and Passive Optical Network (PON) technology, with the accessing speed up to 1Gbps at lower price and the accessing scope of 20 km. So EPON is considered as the very prospect solution of the "first mile" problem. The uplink of EPON system is a multipoint-to-point structure, that is, a number of Optical Network Unit (ONU) occupies a common standard channel. It is necessary to adopt a certain dynamic bandwidth allocation (DBA) algorithm to control channel allocation, in order to avoid the collision of Ethernet data frames when many ONUs transmit dates simultaneously. And DBA algorithm is related directly to the bandwidth utilization and data delay of uplink channel, as well as QoS (Quality of Service) requirements. Therefore the DBA is the key of EPON technology.This thesis introduces the development of EPON technique firstly, then from definition of EPON system, illuminates the tructore and working principle, and analyzes the key techniques and relational protocols of EPON system. After analyzing the advantages and disadvantages of existing algorithms, a novel fixed polling cycle DBA algorithm is proposed, which supports multi-service and guarantees QoS. The improved algorithm uses two-tier scheduling mechanisms: Intra-ONU and Inter-ONU. In the Intra-ONU, the Optical Line Terminal (OLT) allocates a transmission window to every ONU. In the Inter-ONU, services are classified different priority levels and different services are granted different transmission windows. The high priority bandwidth is granted regularly fixed allocation to satisfy the periodical charaeteristic of EF service, and reduce the idle time. While the middle priority bandwidth and the low priority bandwidth are granted owing to the allocation sehemes of the improved algorithm. And in light load, the AF traffic of the waiting time is simply estimated.In the end, the simulation model of the EPON system is set up using the advanced network simulation tool OPNET. By analyzing the results of the simulation, it showed that the improved DBA algorithm guarantees the efficient utilization of uplink bandwidth, and the throughput and the average delay have shown a good performance.