Reduction of restoration capacity requirements in advanced optical networks

This paper investigates the required excess capacity and the required number of optical transceivers for restoration against single link or node failures in future metropolitan area networks (MANs) and wide area networks (WANs). The following aspects of optical networking technology are taken into account: (i) electronic switching and optical transmission with one wavelength per fiber, (ii) wavelength division multiplexing (WDM), (iii) tunable transmitters and receivers, (iv) optical bypass technology, and (v) wavelength conversion. An example network is studied. It is concluded that all of the gain in fiber miles is obtained by wavelength division multiplexing, which provides a gain of about M, the number of wavelengths. The number of transmitters and receivers (equivalently, the electronic switch size) is reduced slightly by tunable transmitter and receivers; to reduce these numbers to their minimum (a reduction by a factor of two) requires optical bypass technology. These results lead to the conclusion that with an electrical cross-connect, and in particular, due to its flexible granularity, with an asynchronous transfer mode (ATM)-based cross-connect, and with WDM-based point-to-point optical transport, very efficient failure recovery techniques can be constructed. More advanced optical technology for switching reduces the number of transceivers and electronic switch sizes by a factor of two for restoration purposes. The absolute gain in fiber miles, number of transceivers, and electronic switch sizes increases when the network demand increases. However, the prohibitive cost of laying new fiber cable makes the gain achieved by WDM alone the most important factor in advanced optical network restoration.