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Table 9. Blocking probability vs. session size when W=32, load is 80 Erlangs and
required reliability is 0.96
Session size
Algorithm
3
6
9
12
15
18
21
ADT
0.1
0.12
0.14
0.29
0.345
0.355
0.37
ADT_DiR
0.035
0.05
0.15
0.26
0.33
0.34
0.355
CSP
0.01
0.04
0.11
0.17
0.18
0.2
0.21
PTP
0.35
0.05
0.13
0.18
0.235
0.24
0.26
Table 10. Blocking probability vs. multicast group size when W=64, and load
is 10 Erlangs
Multicast group size
Algorithm
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
TP-SPT
0
0.04
0.14
0.019
0.25
0.275
0.29
0.335
0.345
0.35
TP-OSPT
0
0.02
0.035
0.04
0.045 0.045 0.048 0.05 0.05 0.05
C
ONCLUSION
Network survivability is an important concern for WDM optical networks. In this
chapter, we have reviewed the protection schemes that are used to survive link failures in
optical networks supporting the unicast and multicast traffic. According to our study, we have
found out that the best schemes for unicast traffic could be the techniques that are based on
the dedicated protection, if the capacity is not of our main concern because these schemes
have low recovery time and network complexity. Otherwise, when either the network
complexity is not important, or the network is not sensitive to the recovery time, the schemes
that are based on the shared protection and the schemes that divide networks into several
areas and
p
-cycle are better choices. Note that the path-based shared protection needs more
capacity compared to other schemes based on the shared protection. Among the schemes that
are based on the shared protection or sub protection, the schemes that protect a whole primary
path have longer recovery time compared to the schemes that protect either a link or a
segment in a primary path.
In unicast protection algorithm, we saw that for the same number of wavelengths, TS has
a lower blocking probability than RSSP in higher load, but blocking probability of RSSP is
lower at light loads. However, TS has lower complexity than RSSP. Moreover, for the same
number of wavelengths, LSA has the lower blocking capability than FT-ABR and HCSPP.
The basic protection schemes have some challenges in tree networks. For example, 1+1
and 1:1 schemes include excessive use of resources and are unable to discover link disjoint
trees in a mesh network, which may lead to the blocking of a large number of multicast
sessions while trying to establish them. In addition, in path protection, a backup link disjoint
path in the multicast tree from the source to a given destination node is derived.
Consequently, this scheme does not consider spare capacity sharing among different multicast
trees. Moreover, any change in cycle network topology or demand will need every node in the
network to re-compute the protection/restoration cycle path, even though the change or failure
