Research On Congestion Control Methods For OBS Networks

Optical Burst Switching (OBS) emerged in last decades as one kind of switching technologies. Two conditions contribute to the emerge of OBS, one is that the unenlightened optical technology cannot provide optical logic devices needed by superior Optical Packet Switching (OPS), the other is that the wavelength routing strategy and two-way-reservation in Optical Circuit Switching (OCS) mean an inefficient usage of network resources and dissatisfaction with the capacity and real-time requirement of developing internet.As a non-connection-oriented switching technology, the challenges of OBS lie in the network congestion and the large amount of data loss probability due to one-way reservation scheme. Contention resolution and congestion control schemes were proposed with the purpose of reducing burst contention and blocking probability during last several years. For the purpose of reducing the blocking probability of optical burst switched networks, congestion control methods in both traditional telecommunication networks and OBS networks are studied in this thesis and a novel congestion control method is proposed which separates the OBS networks into two parts, the access network-edge node pail and the core network. The edge nodes adjust traffic according to the blocking rate of network and the core nodes adjust routing according to the blocking rate of core nodes. This method derives from traffic control and load balance methods, on one side, traffic streams are reduced by the edge nodes and access networks, on the other side, following the principle of load balancing, distribution of traffic streams on links and wavelengths is improved by routing strategy in which congestion situation of core node is considered.To evaluate the performance of the proposed congestion control method, simulations are carried out with NS network simulation tools, under both regular and irregular network topologies. Simulation results show that the network performance of OBS networks with the proposed congestion control method can be improved.