Q-factor-based constraint routing improves performance in optical networks

Abstract

In communication networks, routing involves the identification of a path between the source and destination nodes for each connection request. Traditional routing approaches find a path that minimizes a certain cost parameter, such as the length of the connection. Most of the reported routing and wavelength assignment algorithms (RWAs) assume that once an available path and wavelength have been identified, the connection is feasible. This may not be true in transparent optical networks using wavelength division multiplexing (WDM), where the optical signal experiences and accumulates the effects of physical impairments associated with the transmission line and optical switching nodes. In some cases, this results in unacceptable signal quality. Hence, impairment-constraint-based routing (ICBR) is needed in order to ensure that the connections are feasible. To do this, it is necessary to consider not only the network-level conditions but also the equally important physical performance of the connection. Previously we proposed an RWA that included an ICBR approach. Our technique took into account various physical impairments present in an optical network, and considered different problems independently. Here, a path was assumed to be feasible if a set of criteria reflecting the signal quality (in terms of the different impairments) is satisfied. Here we propose a scheme that integrates routing and wavelength assignment and also considers the physical performance of the network in an ICBR algorithm developed to achieve optimal network performance. This scheme takes into account— through detailed modelling—the various hardware issues and their interplay. This integrated approach produces an estimation of the signal quality (Q) factor and the associated penalties. Figure 1. An impairment-constraint-based routing (ICBR) algorithm optimizes and improves overall network performance with a lower percentage of blocked calls as compared to the performance achieved in a traditional shortest-path (SP) approach.