Performance of Dedicated Path Protection in Transmission-Impaired DWDM Networks

There has been a significant amount of recent research on routing and wavelength assignment for DWDM networks suffering from physical layer transmission impairments. These algorithms attempt to increase the quality of transmission or service and are called QoT (quality of transmission) or QoS aware algorithms. However, protection has not been considered in this context so far, as far as we are aware. In this paper, we investigate the effect of physical layer impairments on dedicated path protection schemes. In dedicated path protection, every connection has resources reserved and dedicated on both a primary and a backup lightpath. While there is no difference in network performance whether the backup path is lit or kept dark in networks that are not transmission-impaired, lighting the backup path has an adverse effect on the network in transmission-impaired networks. By considering two different RWA algorithms - a QoT-aware one and a QoT-unaware one, we study the blocking performance and the vulnerability of the connections to failures for the two cases - dark backup and lit backup. Our results show that there are significant penalties in backup lit case, and that the QoT-aware algorithm considerably outperforms the QoT-unaware algorithm in terms of both blocking and vulnerability to failures.