Performance Analysis of Congestion Control Schemes in OBS Mesh Networks
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Date
2005-04-07
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Abstract
Optical Burst Switching (OBS) is a novel idea offering promising solutions for all-optical WDM networks. It combines the best of optical packet switching and wavelength routing while taking into account the limitations of the current all-optical technology. OBS achieves high traffic throughput and high resource utilization by aggregating multiple packets into a single burst. A control packet sent prior to the burst transmission sets up an optical path between the sender and the receiver. After a pre-determined offset time, the burst itself is transmitted without waiting for an acknowledgment from the receiver. Although OBS networks achieve high resource utilization, burst loss due to contention in the bufferless core can degrade the overall performance of an OBS network significantly. Wavelength conversion (partial and full), optical buffering using fiber delay lines (FDLs) and deflection routing are some approaches for resolving contention. In wavelength conversion, a burst is shifted to a free wavelength on the same link. In buffering, fiber delay lines are used to delay a burst when the outgoing link is busy and in deflection routing, the bursts are deflected to alternate ports in the event of contention. Contention avoidance schemes such as policing the traffic at the source or carefully routing traffic so as to minimize contention can also be used to minimize burst loss in an OBS network.
In this thesis, we analyze and compare the performance of various congestion control schemes in an OBS mesh network using simulations. Partial and full wavelength conversion, deflection routing using FDLs, path restoration using feedback messages and policing at the source node are some of the suggested schemes in the literature for resolving and avoiding contention. These schemes have been studied and evaluated separately in the past. We analyze and compare the performance of some of these congestion control schemes in a single study using simulations, and assuming the following three different traffic classes.
Three traffic classes have been identified for this study. The first class of traffic (Class 1 or Real Time) is a variable bit rate traffic with stringent end-to-end delay constraints, the second class (Class 2) is variable bit rate with no delay constraints, and the third class (Class 3) is non-real-time variable bit rate best effort traffic. The results are compared with respect to the number of real time streams (Class 1) originating at each source node.
The results show that wavelength conversion is a better approach for congestion control in the OBS networks. Specifically, burst loss can be greatly reduced with just a few converters at each node and with restricted converter capability. Moreover, the results show that excessive deflection routing can degrade the network performance significantly. Simple link deflection does not achieve significant benefit and hence one has to use intelligent path restoration techniques (either partial restoration or complete path restoration) for reaping the benefits of deflection routing. Finally, we observed that OBS mesh networks are suitable for real time traffic given a suitable congestion control mechanism.
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Keywords
Deflection Routing, OBS, Wavelength Conversion
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Degree
MS
Discipline
Computer Science
