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Figure 1. Link protection scheme.
2.1.1. Link-Based Dedicated Protection [13]
The trade of this protection is that the protection capacity is saved for each link and
protection resources are not shared among different links. In theory, finding another route for
each physical link in a mesh optical network is possible, however in practice, it is hard to find
such paths for all the links of an optical network. Moreover, stored capacity in a mesh
topology has to be at least twice the working traffic capacity; therefore, it is not so common in
an optical network to use this approach (i.e., using two parallel fibers for each physical link).
2.1.2. Link-Based Shared Protection [13]
In this scheme, various links, which may not fail simultaneously, are able to share the
same resources for protection. Thus, shared protection can reduce the total amount of
resource required for protection. But in this scheme, extra time is necessary for signaling and
configuration processes.
2.1.3. Virtual-Link Protection [13]
This scheme can be used in optical networks that permit end-to-end traffic to move on a
sequence of multiple working paths. The protection path is computed for each virtual link,
which can be reserved in advance, so a very high efficient protection assurance with the
minimum amount of resource for protection is anticipated. Virtual protection needs complex
computations because of the failure spreading issues. When a failure occurs, the end nodes of
the failed virtual links begin the restoration process. Two virtual link-based protections can be
implemented as:
virtual link-based shared protection : signaling and configuration processes must be
completed before the source node of the failed virtual link is permitted to switch the
traffic to the protection path.
virtual link-based dedicated protection : the waiting time that should be spent for
completion of the configuration process can be omitted by performing pre-
configuration. Then, traffic can be switched to the protection virtual link
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