Routing And Wavelength Assignment In Optical Burst Switching Networks

Optical Burst Switching (OBS). which combines the benefits of wavelength routing and optical packet switching while taking into account the limitations of the current all-optical technology, seems to be a promising solution for all optical networks. Compared with wavelength routing, OBS can transmit bursty traffic efficiently by adopting one-way reservation protocol. On the other hand, OBS can be implemented easily on the basis of the current optical technology compared with optical packet switching.In this thesis, we focus on the Routing and Wavelength Assignment (RWA) of OBS. The main works and innovations are as follows.· RWA algorithm in OBS networks with limited wavelength conversionIn the networks with limited wavelength conversion, wavelength contention is the dominate reason that lead to burst blocking. The two notable features of RWA in OBS networks, the one-way resources reservation and distributed control scheme, make the establishment of the lightpath become rather randomness and uncertainty, especially the networks with limited range wavelength conversions. In this thesis, we present a RWA algorithm called pre-defined lightpath RWA (PL-RWA). In PL-RWA, initial routing of Data Bursts (DBs) is precisely designed to avoid wavelength contentions at intermediate nodes. At the network design stage, for each source-destination pair (s, d), a dedicated set of alternate lightpaths is predefined to guide the routing and wavelength assignment of the DBs of (s, d). The alternate lightpaths subject to the wavelength continuous constraint and are clash free. Source node s will pour the DBs destined for d into the alternate lightpaths predefined for (s,d) as many as possible. For the DBs that cannot be carried by the alternate lightpaths, the shortest path of (s,d) is selected as the route and wavelengths are assigned hop-by-hop in real time. Using alternate lightpaths, the randomness and uncertainty of one-way resources reservation under distributed control are diminished. The selection of alternate lightpaths is formulated as an integer non-linear programming and an integer linear programming respectively. A heuristic algorithm based on tabu search is given.? The routing algorithm in OBS networks with full range wavelength conversionIn the networks with full range wavelength conversion, the routing algorithm becomes the dominate reason that influence the network performance. The current RWA algorithms in OBS networks usually adopt the shortest path between the source-destination pairs as the routes and assign wavelengths hop-by-hop. There are two main problems exist in theses algorithms: (1) If there are common links among the shortest paths of different source-destination pairs, the one-way reservation protocol may cause congestion on these links while other links are underutilized, which may deteriorate the network performance, especially in an unsymmetrical network. (2) Few RWA algorithms take the fault recovery into consideration, which is important for the network to operate smoothly. We propose two routing algorithms called AS-R and PR respectively in this thesis.- An ant system based routing algorithm called AS-R is proposed. The destination nodes send BCP-ACK back for each successfully received Burst Control Packet (BCP). The BCP-ACKs are feed back along the same path as the one through which BCPs are forwarded. BCP-ACKs leave some "pheromone" along the path. The coming DBs will choose the output links with the probability proportioned to their pheromone intensity. The AS-R is robust for the network fault and can decrease burst blocking probability in an unsymmetrical network.- It was found that given the network topology and the traffic matrix, the probabilities that the DBs select different routes is almost unchangeable when the system reach to the stable state. We propose a probability-based routing algorithm in this thesis. Instead of using the shortest paths only, more than one alternate paths are pre-computed for a given source-destination pair (s,d). The DBs of (s,d) select their routes from the alternate paths with different probabilities which can be obtained from a non-linear programming (NLP). The objective of the NLP is to minimize the burst blocking probability of a given network. Numerical results shows that PR can decrease burst blocking probability more efficiently.? The deflection routingDeflection Routing is a important way for contention resolution in the space domain. A DB is sent to a different output link of the node and consequently on a different route toward its destination node. As a result, some part, of the traffic on the congested links are deflected to the underload links. Therefore, the traffic load on various links are balanced. We discuss two different deflection schemes called Forward Deflection Routing and Drop and Backward Deflection Routing and Drop respectively. Meanwhile, a Hop-related Offset Time (HOT) algorithm is proposed to modify the initial offset time of the DBs and weaken the path length priority effect in JET.? Design of the OBS simulation environmentIn view of the complicated behavior of the OBS networks, simulation plays a important role in the process of protocol design, test and evaluation. We develop a simulation platform of OBS network based on NS-2 called OBSns.