Study On The Routing Problem For Hybrid Wireless-Optical Broadband Access Network

Wireless Optical Broadband Access Network (WOBAN) is a promising solution for the "Last mile" problem, with huge competitiveness. It combines the advantages of high-capacity and high-speed from Ethernet Passive Optical Network (EPON) with the advantages of flexibility and convenient to construct network from Wireless Mesh Network(WMN). However, WOBAN is a heterogeneous network in its nature. Hence, the routing problem is essential for communication between the wireless domian and the optical domain. In this thesis, the routing problem of WOBAN was discussed by taking the characteristics of the two subnets of the access network into consideration from the view ponit of network convergence. Besides, in order to evaluate of performance for the proposed algorithm, simulations and numerical analysis based on NS-2software platform had been done. The contributions in this thesis can be summarized as follows:Firstly, a routing algorithm for reducing propagation delay in WOBAN was proposed.1) A graph theory model was designed to state the routing problem of WOBAN.2) A divisive graph theory model was proposed to make a statement of the routing problem by the classic graph theory problem.3) A heuristic algorithm named MSTMCF (minimum spanning tree and minimum cost flow) was designed to minimize delay in WOBAN.Secondly, due to the heavy congenstion caused by MSTMCF when the traffic load was high, the congestion problem was in-depth discussed.1) The mechanism of congestion in WOBAN was deeply analyzed.2) According to the congestion mechanism, RQL (relative queue length) and RB (residual bandwidth) were proposed to weigh the congestion of the wireless and optical subnet respectively.3) A routing algorithm named ILCA (Integrated Least Congestion Algorithm) was designed to control the congestion by optimizing the RQL and RB in wireless subnet and optical subnet, respectively.Finally, in order to make a scientific and rational assessment of the new algorithms, a simulation platform based on NS-2was built.1) Optical simulation module was modified to adapt the current NS-2version.2) The routing algorithm was implemented in interpreters and compiler layer.3) The simulation for the devised routing algorithms was accomplished.