| With the explosive growth of high bandwidth consuming multimedia applications, such as Internet telephony, network television, video live broadcast, etc., the rate of wireless access network needs to be improved. FiWi network integrated by optical network and wireless access network not only has high bandwidth and high reliability, but also can provide flexible, low cost,movable wireless access capability. It has great application prospect. Since data traffic generated by wireless clients in FiWi networks usually experiences unstable and unpredictable, it is difficult to effectively predict the bandwidth requirement. Meanwhile, the FiWi network may fail to provide enough bandwidth to meet the bandwidth requirements of all wirelesster terminal users. Therefore, efficient and fair dynamic bandwidth allocation(Dynamic Bandwidth Allocation, DBA) mechanism is needed to improve the performance of FiWi networks, such as channel utilization index. On the other hand, the integration of ONU and wireless gateway usually acts as a key part of the back-end fiber network and front-end wireless access network. Its load balancing policy plays an important impact on improving the performance of FiWi network. Gateway load balancing mechanisms in existing FiWi network make each wireless router nodes with high complexity on control. Once the network congested or link disconnected etc,need to re routing process which is time-consuming,result in increased business waiting time, and the QoS of delay sensitive services cannot be guaranted.Based on the above background, the main work of this thesis includes two aspects. On the one hand, a hierarchical DBA mechanism is proposed for FiWi networks composed of EPON and WLAN. To solve the problem that bandwidth allocation for each user over a long period time mismatch its weight, the first level DBA mechanism implemented by OLT jointly takes into account the excess bandwidth proportion factor, different ONU-AP’s priority,actual traffic load and historical actually allocated bandwidth ratio of previous multiple granting cycles for the bandwidth allocation of each ONU-AP. The second level DBA mechanism are mainly from the point of view of guaranteeing the priority of different services and improving the channel utilization, combined with business priorities, the proportion of bandwidth request and network load for bandwidth allocation, solve the problem of QoS guarantee and channel bandwidth waste. Moreover, the proposed FiWi DBA scheme does not refer to a specific bandwidth resource types,thus obtains good generality.The simulation results show that the proposed hierarchical DBA mechanism can obtain proportional fairness, channel utilization and throughput.On the other hand, this thesis introduces software defined network (SDN) architecture in FiWi network, and proposes a load balancing algorithm which takes into account different QoS requirements of different traffic types. In this algorithm, according to the different needs of different types of traffic for the time delay、 load、link delay、available bandwidth and packet loss rate in the network, we choose different paths for different QoS requirements.In the proposed load balancing algorithm, time delay sensitive traffics have the highest priority to select a transmission path with smallest time delay, while other traffics select transmission paths with high available bandwidth, so as to realize the balance of network traffic in the network. The simulation results show that the proposed load balancing mechanism not only guarantees the QoS of high priority traffic, but also improves the QoS of low priority traffic. |
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