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Figure7 shows a primary path 1-2-3-6-4-5, where node 1 is the source node and node 5 is
the destination node. As depicted in Table 1, the system using partial path protection takes 1-
3-6-4-5 as the protection path against the failure of link (1, 2). Similarly, the network
allocates 1-2-3-4-5 to protect against the failure of (3, 6). Each of these protection paths needs
to be link-disjoint only from the link that it protects.
Figure 7. An example for partial path protection scheme.
Consider the network in Figure8 and let the network have initially no connections. The
network now serves two call requests (1,4) and (4,5) in sequence. Table 2 shows the resource
assignments for primary and protection paths under the path protection and partial path
protection respectively. As Table 2 shows, the two primary paths 1-6-3-4 and 4-5 are
completely link-disjoint from each other. By protection sharing, the system reserves only one
wavelength for protection on link (2, 5), thus improving the utilization of network resources.
In path protection, a wavelength on this link is allocated to protect link (1, 6), (6, 3) and (3,
4), while in partial path protection the wavelength protects only the link (1, 6). Hence, under
the partial path protection, this wavelength can be shared by a future call whose primary path
includes link (6, 3) and (3, 4), but cannot be shared using the path protection [11].
Figure 8. An example network for illustration of the partial path protection and path protection schemes
in protection sharing.
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