IMPAIRMENT AWARE DYNAMIC ROUTING AND WAVELENGTH ASSIGNMENT IN WDM NETWORKS

Optical networks play a major role in supporting the traffic in backbone computer networks. Routing and Wavelength Assignment (RWA) is the technique used to establish a light-path from a source node to a destination node in a Wavelength Division Multiplexed (WDM) optical network. As an optical signal propagates through the network, the quality of the signal degrades due to physical layer impairments. To address this problem, in translucent WDM networks, the signal is regenerated at intervals. The main objective of this research is to propose a fast heuristic for dynamic lightpath allocation in translucent WDM networks and to compare the heuristic with an optimal algorithm that was proposed recently

Survivability algorithms in MPLS and WDM optical networks

In modern ultra-wide bandwidth, high speed and high reliable communication networks, the failure of network components including equipment (such as routers) and transmission media (such as fibers) may cause a huge volume of data loss. Therefore network survivability mechanisms, by which the disrupted traffic upon failures can be restored, are crucial in network design and deserve thorough investigation. In this thesis, we propose some survivability approaches to survive failures in MPLS and WDM optical networks. MPLS is a promising technology that enables much faster failure recovery than conventional IP rerouting in IP networks. While the traditional MPLS path-based protection scheme is capacity efficient, it is relatively slow in restoration; on the other hand, while traditional MPLS link-based scheme has fast restoration speed, its capacity efficiency is low. In this thesis, we propose a new restoration scheme called UNIFR, which can provide fast restoration as link-based scheme while achieving better capacity efficiency than link-based scheme. We present a MPLS resilience framework that supports UNIFR and give two ILP formulations to solve the spare capacity optimization problem for UNIFR-based restoration model. Simulation study shows that the capacity efficiency of UNIFR-based model is much better than that of link-based model and close to that of path-based model. In WDM optical networks, although lots of pervious works have been done in both protection and restoration survivability techniques, to our best knowledge, little study focuses on improving the dynamic restoration success ratio. To address this problem, we first identify two restoration blocking types called primary holding and mutual competition. To address primary holding, we propose a dynamic routing and wavelength assignment algorithm for connection establishment that takes the future possible failures into consideration and choose route and wavelength for the working lightpath that could lead to higher chance of successful restoration for the potential failures. To address mutual competition, we present some heuristics ideas to increase restoration success ratio. Simulation shows that our algorithms can clearly reduce the restoration blocking probability while not affecting primary blocking probability and restoration speed much

Resource allocation and scalability in dynamic wavelength-routed optical networks.

This thesis investigates the potential benefits of dynamic operation of wavelength-routed optical networks (WRONs) compared to the static approach. It is widely believed that dynamic operation of WRONs would overcome the inefficiencies of the static allocation in improving resource use. By rapidly allocating resources only when and where required, dynamic networks could potentially provide the same service that static networks but at decreased cost, very attractive to network operators. This hypothesis, however, has not been verified. It is therefore the focus of this thesis to investigate whether dynamic operation of WRONs can save significant number of wavelengths compared to the static approach whilst maintaining acceptable levels of delay and scalability. Firstly, the wavelength-routed optical-burst-switching (WR-OBS) network architecture is selected as the dynamic architecture to be studied, due to its feasibility of implementation and its improved network performance. Then, the wavelength requirements of dynamic WR-OBS are evaluated by means of novel analysis and simulation and compared to that of static networks for uniform and non-uniform traffic demand. It is shown that dynamic WR-OBS saves wavelengths with respect to the static approach only at low loads and especially for sparsely connected networks and that wavelength conversion is a key capability to significantly increase the benefits of dynamic operation. The mean delay introduced by dynamic operation of WR-OBS is then assessed. The results show that the extra delay is not significant as to violate end-to-end limits of time-sensitive applications. Finally, the limiting scalability of WR-OBS as a function of the lightpath allocation algorithm computational complexity is studied. The trade-off between the request processing time and blocking probability is investigated and a new low-blocking and scalable lightpath allocation algorithm which improves the mentioned trade-off is proposed. The presented algorithms and results can be used in the analysis and design of dynamic WRONs

Improving Routing Efficiency, Fairness, Differentiated Servises And Throughput In Optical Networks

Wavelength division multiplexed (WDM) optical networks are rapidly becoming the technology of choice in next-generation Internet architectures. This dissertation addresses the important issues of improving four aspects of optical networks, namely, routing efficiency, fairness, differentiated quality of service (QoS) and throughput. A new approach for implementing efficient routing and wavelength assignment in WDM networks is proposed and evaluated. In this approach, the state of a multiple-fiber link is represented by a compact bitmap computed as the logical union of the bitmaps of the free wavelengths in the fibers of this link. A modified Dijkstra\u27s shortest path algorithm and a wavelength assignment algorithm are developed using fast logical operations on the bitmap representation. In optical burst switched (OBS) networks, the burst dropping probability increases as the number of hops in the lightpath of the burst increases. Two schemes are proposed and evaluated to alleviate this unfairness. The two schemes have simple logic, and alleviate the beat-down unfairness problem without negatively impacting the overall throughput of the system. Two similar schemes to provide differentiated services in OBS networks are introduced. A new scheme to improve the fairness of OBS networks based on burst preemption is presented. The scheme uses carefully designed constraints to avoid excessive wasted channel reservations, reduce cascaded useless preemptions, and maintain healthy throughput levels. A new scheme to improve the throughput of OBS networks based on burst preemption is presented. An analytical model is developed to compute the throughput of the network for the special case when the network has a ring topology and the preemption weight is based solely on burst size. The analytical model is quite accurate and gives results close to those obtained by simulation. Finally, a preemption-based scheme for the concurrent improvement of throughput and burst fairness in OBS networks is proposed and evaluated. The scheme uses a preemption weight consisting of two terms: the first term is a function of the size of the burst and the second term is the product of the hop count times the length of the lightpath of the burst

Effective fiber bandwidth utilization in TDM WDM optical networks

Ph.DDOCTOR OF PHILOSOPH