| Summary: | 碩士 === 國立高雄應用科技大學 === 電機工程系 === 99 === Ethernet passive optical network (EPON) has been considered as one of solutions for broadband access network due to simple architecture, extensive area and easy maintenance. The data is transmitted from OLT to all ONUs with broadcast in the downstream channel, but all ONUs only share a common channel when them are sending data to the OLT in the upstream channel. Therefore, to prevent data collision and ensure efficient transmission, EPON must employ a media access control (MAC) protocol to allocate the shared resource of a common upstream transmission medium. So how to design an effective DBA algorithm is an important issue for many specialist and scholar.
This thesis combines the advantages of offline-based and sort-based DBA algorithms to propose an adaptive DBA algorithm based on dual-polling scheme. The first polling scheme was optical line terminal(OLT) allocated bandwidth and calculated remaining bandwidth according to REPORT message of optical network unit(ONU); due to the packet fragmentation is prohibited according to IEEE 802.3.ah the remaining bandwidth will be wasted when OLT allocates it to all heavy loaded of ONUs. To address the issue, in second polling scheme, the demand of heavy loaded ONU will obtain the total or most remaining bandwidth in turn. Finally, the sort-based DBA algorithm that sorts all grant bandwidth at the next transmission cycle and fully utilize the idle time between cycles as long as at least one ONU requests a long enough transmission window is used in DP-DBA algorithm.
Moreover, this article also analyzes the affect of performance under asymmetrical traffic load of ONUs and super EPON. Finally, event-driven simulations show that DP-DBA can significantly improve the network performance in terms of transmission delay, average queue length, and throughput, as compared with the well-known IPACT, DBA2, and sort-based DBA algorithms. Moreover, DP-DBA is slight the influence of system performance under extend distance and asymmetric traffic loaded of ONUs than the others DBA algorithms. Therefore, above results indicate that of the DP-DBA algorithm is an excellence DBA algorithm for EPON system.
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