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there is a shortest path between the pair of nodes, then an edge is added between them. Cost
of the new edge is equal to the cost of the shortest path. Then, the backup path for each leaf
node in X is found. For example, consider leaf node L of X . Primary path of source s to L is
determined and then the cost of every link that is not in the primary path is set to infinity. The
shortest backup path between s and L is found and these links are marked in G and P . The
algorithm checks whether a marked link is located in both G and P . If a marked link exists in
both G and P, then the cost of every link is set to zero and L is removed from the nodes of X .
Finally, X is removed from the primary tree set. The algorithm is repeated for all trees, and
backup paths are computed for all source and leaf nodes. In [35], SLPP has been compared
with disjoint-segment (DS) and source-destination path pairs (SDPP). Simulation results
show that the blocking probability of SLPP is lower than the blocking probability of both DS
and SDPP.
4.4. Adaptive Shared Segment Protection (ASSP) [36]
The ASSP algorithm is a segment protection technique which does not require to identify
the segments for a multicast tree in advance . ASSP is executed at two stages. A multicast tree
is created firstly and then in order to protect paths of the multicast tree against link failures,
backup paths are constructed. In this algorithm, s is the source node, D is the set of
destination nodes, and N t represents the set of nodes that are on the current multicast tree.
Firstly, N t is set to s .
To create multicast tree T , the first shortest path for every pair of nodes in N t and D ( u , v )
is found. Every link in the shortest path is added to T . Every MC node on the shortest path is
added to N t if MC node is different from both u and v . Each MI node is removed from N t if
MI node = u and MI node ≠ s . Finally, v is deleted from D and is added to the MI node.
After constructing the multicast tree, backup paths should be determined. Firstly, the
connection degree of all nodes located on the tree are calculated. Moreover, the set of end
nodes N E on T is determined. The shortest path for any pair nodes in N E on T is computed.
Then, the backup path for every segment is calculated so that the calculated backup path
should be the most efficient backup path among other backup paths. Note that each backup
path should be link-disjointed from the corresponding segment. Backup paths are added to
protecting paths set and the cost of each link on segments and backup paths is set to zero for
resource sharing. It has been shown in [36] that the blocking probability of ASSP is lower
than the link-disjoint algorithm and the shared disjoint path algorithm.
4.5. Shared Segment Protection with Re-Provisioning
(SSPR) [37]
The SSPR is another proposed multicast protection scheme based on the shared segment
protection. In this algorithm, a primary light tree is created and then a corresponding link-
disjoint backup segment is requested for each multicast connection. Network nodes are
equipped with MC-OXC, which have the full splitting capability. Moreover, each node has
the full wavelength conversion capability. In this algorithm, it is assumed that only one
connection request arrives at a time. In establishing dependable route stage, the multicast
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