Quality of transmission (QoT)-Aware routing in all-optical WDM networks

In this paper, we consider the problem of routing and wavelength assignment (RWA) in all-optical Wavelength Division Multiplexing (WDM) networks, where signals propagate in the optical domain (with no electrical regeneration) from end-to-end. We design and implement a quality of transmission aware routing algorithm for online traffic in all-optical WDM networks. In transparent optical networks the quality of a transmission degrades due to physical layer impairments. In an optical network, a connection is set up to carry a data signal via an all-optical channel (lightpath) from its source to destination node. The optical signal transmitted along the lightpath may need to travel through a number of crossconnect switches (OXCs), optical amplifiers, and fiber segments. While the signal propagates toward its destination, the optical components would continuously degrade the signal quality by inducing impairments. When the signal degradation is so severe that the received bit-error rate (BER) becomes unacceptably high, the lightpath would not be able to provide good service quality to a connection request. Such a lightpath, which has poor signal quality due to transmission impairments in the physical layer, should not be used for connection provisioning in the network layer. To serve a connection, the proposed algorithm finds a path and a free wavelength (a lightpath) that has acceptable signal quality performance by estimating a quality of transmission measure, called the Q factor. We take into account channel utilization in the network, which changes as new connections are established or released, in order to calculate the noise variances that correspond to physical impairments on the links. The quality of transmission routing algorithm finds a set of so called non-dominated Q paths from the given source to the given destination. Various objective functions are then evaluated in order to choose the optimal lightpath to serve the connection.