On The Multiple-machine Ns Emulation Platform And Fairness Of OBS Network

Up to date,three switching schemes have been proposed, optical circuit switching(OCS), optical packet switching(OPS) and optical burst switching (OBS). Optical burst switching, which combines the advantages of optical circuit switching and optical packet switching and effectively overcomes their shortages, is regarded as a promising solution for realizing IP over WDM.By analyzing the performance of TCP and UDP over OBS networks, it has been found that the OBS network accessed by TCP and UDP will have a serious problem of fairness. TCP congestion mechanism is not suitable for OBS networks. When packets are lost in OBS network, TCP will reduce its sending rate and then the throughput of TCP will be limited at a low level. In order to improve the fairness of OBS, we improve the channel scheduling mechanism as follow, at the edge node, TCP packets and UDP packets are assembled in different bursts, and at the core node, the packet-loss strategy is improved to protect the TCP traffic. This mechanism will improve the fairness of OBS effectively.In order to validate the performance of OBS networks with the fairness mechanism and obtain more accurate experiment results. This paper performs analysis of the Emulation function of NS, expands and improves it, and then sets up a multi-machine Emulation platform OBS-NSE. The OBS network on the platform includes one core node and three edge nodes. The load over the OBS network includes TCP traffic and UDP traffic. We make the physical network load to access the virtual OBS network in Emulation environment and get more realistic experiment results. This paper compares the experiment results between multi-machine Emulation and single-machine Simulation. When the accessing load is relatively small, the results are similar. When the accessing load is relatively heavy, the throughput on the multi-machine Emulation platform is less than the throughput on the single-machine Simulation platform because of the effect of the equipment performance in physical networks.The experiment results show that the OBS-NSE platform will be affected by the equipment performance in physical networks, so the situation of physical networks can be disclosed by the multi-machine Emulation platform. We perform experiments based on the OBS-NSE platform to validate the proposed fairness mechanism. The TCP traffic and the UDP traffic with the same sending rate access to the OBS network, as the sending rate increases, the throughput of UDP increases linearly but the throughput of TCP will be kept at a fixed value after the network load is higher than 0.2. Then we lead the fairness mechanism into the OBS network and the effect of the fairness mechanism on UDP is not obvious, but it is significant improved on TCP traffic, the saturated throughput of TCP increases to 3.8 times (about 5.8dB). The experiment results prove that the fairness mechanism can improve the performance and the fairness of the OBS network effectively.To validate the fairness mechanism more accurately, we should set up physical networks to study. But setting up physical networks means more equipment to invest. As well, there is a long way to improve the performance of the multi-machine Emulation platform, including the fairness mechanism of OBS network, the average delay, QoS, etc. Thus we can make further research on it.