On the trade-offs between ODU and OCh preplanned shared restoration in transport networks

Failure survivability mechanisms are indispensable in transport networks but their support can demand a significant overprovisioning of network resources. Shared restoration is seen as a mechanism that can help in reducing the amount of extra resources needed, while still providing a reasonable capability to withstand failures. By having all restoration resources defined in advanced, Preplanned Shared Restoration (PSR) can reduce the down time between a failure occurrence and the conclusion of all steps of the restoration process. Noteworthy, PSR schemes can be employed either with fine granularity via electrical cross connects or with coarse granularity via optical cross connects or even using both, depending on the target Service Level Agreement (SLA). This paper overviews both flavors of PSR, looking at the requirements they impose to the transport network, comparing them qualitatively, and presenting a case study to compare their overprovisioning requirements, thereby hinting at which network and traffic scenarios are best fitted to using one or the other.