The Study Of Contention Resolution Methods In Optical Burst Switching Network

Optical burst switching (OBS) network has been proposed as the developing trend for next generation optical network. In the core nodes of OBS network, the contention will occurs when several bursts are contending for the limited data (wavelength) resources at the same time. Excogitating the effective contention resolution methods which based on differential network statuses will has the great significance for the OBS network's resource utilization, throughput, etc.The theory of burst segmentation method has been illustrated in this paper firstly. Against to the limitation for current study of burst segmentation method, which only referring to the single channel contention, the several channel contention issue for bursts has been presented in this paper. Then, the several channel contention resolution methods which could decrease the data losing in furthest degree and could effectively support the quality of service (QoS) of network also has been proposed in this paper.The performance of burst segmentation method with the optical buffering method has been compared in this paper. We can observe from the results that burst segmentation method has the more steadily resolution performance than that of optical buffering method. And under certain network configurations, when the traffic load is relatively high, burst segmentation method could gets the lower packet loss probability than that is get by optical buffering method.The three priority based contention resolution methods all has a disadvantage that there is exists the probability that dropping the entire burst in contention. Against to the disadvantage, an improved burst segmentation method named priority base double-direction burst segmentation (DBS) method has been proposed in this paper. In order to adapt to DBS, a novel burst assembly technique named middle high-class composite burst assembly technique also has been proposed. Through the simulations we can observe that when the traffic load is relatively low, the bursts loss probability is get by DBS will lower than that is get by the burst tail-segmentation method almost one quantity level. The result indicates that DBS could effectively protect the relatively high-class IP packets in low priority burst.Another issue named unfairness of burst segmentation or dropping issue which caused by the optical composite burst switching (OCBS) technology in OBS multi-hop network also has been discussed in this paper. Referring to the disadvantage of the conventional resolution method that may cause the lager data losing, an improved resolution method has been proposed in this paper. In the improved method, the length ratio between contending burst and original burst has been considered. The improved method could decrease the data losing through reducing the dropping probability of long length burst.Simulations prove that the improved method not only could maintain the advantage of the conventional method which could make the bursts loss probability coherence in OBS multi-hop network but also could decrease the data losing for 19 %, and also could increase the throughput for 10 % when comparing with the conventional method. The output process for bursts could be considered as"on-off"model. In existing on-off model based OBS system studies, when consider the choosing probability for bursts to choose the output ports, they all only suppose that all the bursts to use the probability 1 N( N is the number of output port for a core node) to choose the output ports for transmission. But in fact, the output port choosing probability will be changing when the bursts choose differential routing for transmission. Hence, the unequal outputting probability issue is been proposed and discussed in this paper at the first time. From the analytical results we could see that if the outputting probability changing from 0.6 to 0.9, when the probability increases 0.1, the blocking probability of bursts will reduces 6 .4%,6 .9% and 7 .5%, respectively. If the core node is equipped with 1 to 4 FDLs, when adds one FDL, the blocking probability of bursts will reduces 35 .1%, 26 .0%and 20 .6%, respectively.