Browsing by Author "Dr. Harry G. Perros, Committee Chair"

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Performance Analysis of Congestion Control Schemes in OBS Mesh Networks
(2005-04-07) Jonnadula, Venkata Ratnakar; Dr. Harry G. Perros, Committee Chair; Dr. Rudra Dutta, Committee Member; Dr. Mike Devetsikiotis, Committee Member
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.
Performance Analysis of Optical Burst Switched Networks
(2002-07-29) Xu, Lisong; Dr. Michael Devetsikiotis, Committee Member; Dr. Douglas S. Reeves, Committee Member; Dr. George N. Rouskas, Committee Co-Chair; Dr. Harry G. Perros, Committee Chair
In this dissertation, we studied the performance of Optical Burst Switching (OBS). OBS is a promising new solution for the next-generation optical Internet. In the first part of the dissertation, we studied a novel WDM ring network with OBS. The ring consists of N nodes, and each node owns a home wavelength on which it transmits its bursts. The ring operates under the fixed transmitter tunable receiver (FTTR) scheme. Control information is transmitted on a separate control channel. We proposed five different burst switching access protocols. We also studied the performance of these access protocols in terms of throughput, packet delay, throughput fairness, and delay fairness under different network parameters: average packet arrival rate, maximum burst size, and minimum burst size. Finally, we proposed a new offset calculation method, which can significantly simplify the access protocol design, and reduce the packet delay for all access protocols. In the second part of the dissertation, we analyzed an edge node of a WDM OBS mesh network using a new burst arrival process, which is more realistic than the well-known Poisson process. The edge node is modeled as a closed non-product-form queueing network, consisting of special nodes with orbiting customers. Despite the rich literature in queueing network analysis, this particular queueing network with orbiting customers has not been analyzed before. We developed algorithms for both the single-class and multi-class queueing networks. The single-class queueing network is solved using Marie's method. In the case of no converters, we obtained a closed-form expression of the conditional throughput of the special node with orbiting customers. The multi-class queueing network is analyzed by decomposition. Specifically, a multiple-class queueing network is decomposed into a set of two-class queueing networks, and each of them is then solved by Neuse and Chandy's Heuristic Aggregation Method. We also developed a much faster approximation algorithm for the analysis of an edge OBS node with a large number of wavelengths. Comparisons against simulation data suggest that our algorithms have a good accuracy.