The Study Of Dynamic Bandwidth Allocation Algorithm In Ethernet Passive Optical Network (EPON)

Ethernet passive optical network (EPON) with its simple maintenance, low cost and good compatibility with the existing Ethernet, etc., has become the best candidate for solutions of fiber access network. As a key technology in EPON, Dynamic Bandwidth Allocation (DBA) is essential for improving the performance and efficiency of EPON system. A good dynamic bandwidth allocation algorithm should be able to guarantee all users'fairly sharing of upstream bandwidth, and also to ensure the EPON system has high throughput in both the uplink and the downlink channels. Besides, the dynamic bandwidth allocation algorithm should also support the classification of service (CoS) and quality of service (QoS) guarantees.The existing dynamic bandwidth algorithm, few can meet all these requirements. This paper analyzed and summarized the advantages and disadvantages of a large number of the existing DBA algorithms, and then proposes a new DBA algorithm, which uses ordinates and the corresponding slopes to represent the service envelope function, in this manner it can use the standard REPORT message defined in IEEE802.3ah standards to report the the service envelope function to the OLT. This is conducive to achieving interoperability of different EPON systems and ensuring the global fairness among all users. On the other hand it uses dual-subcycles with fixed-polling-cycle-time polling mechanism, which can completely eliminate the bandwidth loss caused by the idle time of uplink channel in centralized-grant DBA schemes, then ensure the upstream channel has a higher throughput.What's more, less bandwidth of downlink channel occupied by GATE messages in the new DBA algorithm, contributes to improve the downlink channel throughput. The simulation results show that the performance of the new algorithm in the average packet delay and seriously delayed EF packets ratio is not as good as IPACT algorithm,but in fairness, uplink or downlink throughput and delay jitter of EF service, the new algorithm is significantly better than the existing IPACT algorithm.