Difference between restoration and protection
Sometimes protection and restoration confuse us much. Both of them are related to network survivability. Protection in general is a type of pre-planning process. That is, we plan for sufficient protection capacity to prepare for a network failure such that certain restorability (for example, 100%) can be ensured. In contrast, restoration is normally a post-operation process, which searches for spare capacity within the network to maximally recover a network failure. Depending on the amount of remaining spare capacity within a network, the restorability of restoration process cannot be guaranteed with 100% recovery.
In addition, due to preplanned capacity of the protection scheme, it can often react to a network failure fast and make a failure recovery fast. In contrast, because the restoration process needs to search for spare capacity in the network, it may take a longer time for failure recovery. However, because restoration can use any unused protection capacity within a network, it can often achieve better spare capacity utilization.
To jointly exploit the benefits of protection and restoration processes, we often implement these two techniques together. A concept called “first failure protection and second failure restoration” is just a good example of such a type of collaboration. Normally people plan protection capacity for a single network failure (e.g., for link failure), when there is a second failure occurred to the network, the preplanned spare capacity for the single failure is not sufficient to recover the second failure. In this case, we need to refer to the second failure restoration process to search for unused spare capacity within the network to maximally recover the second failure.
