302 The handbook of optical communication networks
between nodes 24 (S) and 18 (D), if the primary path is established along
the unique shortest path between them, it is easy to see that there cannot
exist an end-to-end protection path but there will be a segmented protection
path as presented in the figure.
We illustrate yet another advantage of segmented protection paths in
Figure 16.3
. A dependable connection will be established between N19 (S2)
and N11 (D2). The primary path, end-to-end protection path, and seg-
mented protection path are routed as shown. We can see that while the
end-to-end protection path requires eight hops, all the protection segments
together require only seven hops, hence lesser resource reservation.
Because the end-to-end protection path is a special case of segmented
protection path, we can safely say that the shortest segmented protection path,
which is defined as the segmented protection path for which the sum of
the hop counts of all its protection segments is minimum, results in better
spare resource reservation than the end-to-end protection path. Saradhi
and Murthy
28,29
presented an algorithm to select this shortest segmented
protection path and showed that its complexity is the same as that of any
shortest-path-finding algorithm.
We now demonstrate how the segmented protection paths offer more
flexibility in providing D-connections through
Figure 16.5
. Assume that each
link on the mesh is having only one wavelength. Two D-connections will be
established: N19 (S1) to N10 (D1) and N21 (S2) to N12 (D2). The primary
Figure 16.4
No end-to-end protection path but segmented protection path exists.
Primary path
Segmented protection path
S
27
26
22
23
19
18
15
13
7
11
14
20
21
25
24
10
6
0
1
2
3
12
5
8
9
D
16
17
4
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