Research On Design Protection For WDM Optical Transport Networks

With the development of networking technologies and new services of Internet, there is anexplosive growth trend of Internet traffic, which needs tremendous network bandwidth. Some traditional IP backbone networks are IP/ATM/SONET architecture. Current transport rate of SONET or SDH is mostly 2.5Gb/s and lOGb/s. It is difficult to increase transport rate of SONET further because of the limitation of electronic domain. As we know, a single fiber can support more than SOTHz lower-loss bandwidth in theory. Their bandwidth is still underutilized. Wavelength-division multiplexing (WDM) is a promising approach that can use the enormous bandwidth of the optical fiber. A single fib^r can be employed for multiple data streams simultaneously. All-optical networks employing the concept of WDM and wavelength routing are considered as the transport networks for the future. In this dissertation, we consider following problems: priority-based wavelength assignment algorithm in restorable WDM transport networks, design of resilient WDM mesh networks, design protection for WDM networks without and with considering wavelength continuity constraint, efficient placement of wavelength converters.WDM Network will play important role in future backbone networks. It is necessary that WDM networks have the capability against component failure and support multi-priority. Two priority-based wavelength assignment methods, Wavelength Number Method and Assignment Quota Method, are proposed in Chapter 2. We study network performance when these wavelength assignment methods are used for survivable WDM network in dynamic traffic pattern. Contents include influences on blocking probability from traffic load, total number of available wavelengths per link, and the number of fibers per link.Integer Linear Programming (1LP) method for designing resilient WDM mesh networks is given in Chapter 3. Two types of protection strategies, Shared-Path Protection and Shared-Link Protection, are used. The optimization objective is to minimize the total fiber length needed. CERNET is used as an example. By solving ILP models, the features of different protection strategies are analyzed. The influence of wavelength conversion on the optimization objective is also investigated.In network architecture using overlay mode, internal dependence of lightpaths could lead to the critical status that the failure of a physical fiber leaves the virtual topology unconnected. This may make the restoration of service by the higher level networks using the WDM network (suchas SDH, ATM or IP) impossible. It is necessary to avoid the above cases while embedding virtual topology into physical topology. VTMPD algorithm proposed in Chapter 4 aims at Design Protection, considering load balance and capacity constraint of physical links simultaneously. We also compare the performance of VTMPD with the existent DAP algorithm. The numerical results show that VTMPD algorithm is better than DAP algorithm.DAP algorithm always assumes that all network nodes have full-range wavelength conversion capability. However, full-range converters are still expensive. A new heuristic algorithm, called Virtual Topology Mapping for Design Protection Based on Layered Graph (LG_VTMDP), used in design protection for WDM optical networks is proposed in Chapter 5. The algorithm considers two problems of routing and wavelength assignment simultaneously. Load balancing and capacity constraints of physical links are also considered. The LG_VTMDP algorithm is shown to perform better than the combination of the DAP algorithm and existent wavelength assignment algorithms. Based on the result of the LG_VTMDP algorithm, an efficient Wavelength Converter Placement (WCP) algorithm is presented subsequently.We have used three methods to evaluate all the algorithms mentioned in this dissertation. The main frames of these method and pseudo codes of the algorithms proposed in this dissertation are given in Chapter 6.