Architectural Comparisons

Abstract

We have seen in the previous chapter that metro WDM networks typically have either a ring or star topology. The benefits of a star configuration are numerous [BR99b]. Star configurations are easy to install, configure, manage, and troubleshoot. This has advantages in terms of installation, troubleshooting, and reconfiguration, reducing the cost of installation and ownership for the entire network. In addition, a star network based on a PSC or an AWG is reliable due to its passive nature. As opposed to ring (and bus) topologies it does not suffer from tapping loss which grows linearly with the number of nodes (in dB). However, PSC based star networks suffer from splitting loss (as opposed to the AWG which does not introduce splitting loss). But the splitting loss grows only logarithmically with the number of attached nodes (in dB). Note that star networks exhibit a single point of failure, i.e., when the central hub goes down the entire network connectivity is lost. Therefore, for survivability reasons the central hub has to be protected. This issue is addressed in Chapter 9.