Performance Analysis of Dynamically-Reconfigurable Wavelength-Division Multiplexed Networks

Wavelength-Division Multiplexing (WDM) has emerged as a promising technique for opening up the Terahertz transmission bandwidth of single-mode optical bre. In simple WDM networks, a connection between two nodes along a particular route must use a single wavelength on all links within the route. However, this restriction may be removed by the introduction of wavelength converters into network cross-connects. A wavelength converter is a device which takes as its input a data channel modulated onto an optical carrier with a xed wavelength and produces at its output the same data channel modulated onto an optical carrier with a di erent wavelength. An ideal wavelength converter is able to transfer the data from any input wavelength to any output wavelength, so that a connection can be established along a route if there exists at least one wavelength which is available on each link of the route. This leads to improved network performance. However, the introduction of wavelength converters into WDM cross-connects increases the hardware cost and complexity. It is therefore important to establish precisely what advantages wavelength converters o er to network performance. Accurate predictions about the tra c performance available from various hardware and network architecture choices are important in designing a WDM network. E cient and accurate models of performance are also required in dimensioning networks so that adequate resources are available to satisfy grade-of-service requirements, and in determining route choices during network operation as the load and state of the network varies over time. Network simulations are often relatively time consuming, or provide inaccurate estimates of the point-to-point blocking probabilities. E cient and accurate analytical models are thus required. In this thesis we model and investigate the performance of dynamically-recon gurable WDM networks, with and without wavelength converters. Networks which have a full set of ideal wavelength converters in every cross-connect are equivalent to traditional circuit-switched networks, and thus existing analytical techniques may be used to model their performance. However, new analytical techniques are required to model networks which do not use wavelength converters, or which use non-ideal wavelength converters. We develop analytical techniques for modelling WDM networks which do not use wavelength converters. We then use analytical models and network simulations to examine the e ectiveness of wavelength converters in improving network performance. Discussions within the literature have shown that the performance improvements o ered by wavelength converters depend on a number of factors, such as network topology and size, the routing and wavelength assignment schemes used and the number of bres on each link. We extend the discussions presented within the literature to examine the bene ts of wavelength converters in dynamically-recon gurable WDM networks with di erent numbers of wavelengths on di erent links and with non-Poisson input tra c. i ii Realistic wavelength converters are often limited in the conversions which can be performed. Also, due to the increased hardware complexity and cost, it may be preferable to have wavelength converters in only selected cross-connects, or to have limited numbers of wavelengths converters in each cross-connect. Networks with limited numbers of wavelength converters or with realistic, nonideal, wavelength converters are described as having limited wavelength conversion. In networks with limited wavelength conversion, the set of allowable conversions along a route is restricted. Analytical models and network simulations are developed and used in this thesis to examine the performance of networks with limited wavelength conversion. Particular focus is placed on networks which use wavelength converters based on four-wave mixing in semiconductor optical ampli ers. Finally, multiwavelength Time-Division Multiplexed (TDM) networks are examined. Two different implementations of multiwavelength TDM networks are considered, with network simulations and analytical results used to examine the performance improvements o ered by wavelength converters and time-slot interchangers. Declaration To the best of my knowledge, this thesis contains no material previously published by any other person, except where due reference or acknowledgment has been made in the text of the thesis. Furthermore, I declare that none of the work presented in this thesis has been submitted for any other degree or diploma at any University and that this thesis is less than 100,000 words in length, excluding gures, tables, footnotes and appendices. Jennifer Yates iii