19.8 Restoration in the Light Trail Architecture

As stated throughout the book, survivability is a critical issue in the design of light trails for an optical network to survive failures as well due to the fact that a single link failure disrupts all the light trails that use the link. Each light trail carries multiple connections. Therefore the effects would be catastrophic. For instance, if a failed link has W wavelengths, it can carry up to W light trails. Each light trail contains up to ( ) s-d pairs, where denotes the number of nodes in the wth light trail, w =1, 2,..., W. Therefore, in the worst case a link failure may disrupt up to connections. To provide 100% protection in the WDM layer of a light trail architecture implies that a backup light trail needs to be provided at the time of establishment.

Recall that a key difference between the light trail and lightpath architectures is that the intermediate nodes in a light trail can also have access to the medium. Thus the restoration model for a light trail architecture is different from that in a lightpath architecture as all node-pairs on the light trail need to be protected and an assigned alternate path may not be possible. However, as in the case of lightpaths, two possible protection schemes are possible, namely connection-based protection and link-based protection. In the following it is assumed that there is no...