Information Technology Reference
In-Depth Information
•
To form the auxiliary graph (
G
), the reverse link of each directed link belonging to
p
is added to
G
and then the costs of them are set to 0.
•
For each active segment (
S
) of node pair (
s
,
n
i
) where
i
=1,…,
k
, first the links
belonging to
S
as well as other links that are not SRLG-diverse with
S
are removed
from
G
. Then, the SRLG-disjoint backup segment (
BS
) for
S
is attained through the
Dijkstra's algorithm.
•
A directed link is added from
s
to
n
i
. The costs of links of the backup segment
(BS
)
are equal to the link cost.
•
The same procedure is executed for each active segment (
S
) of node pair (
n
i
,
d
)
where
i
=1,…,
k
.
•
Finally, for each node pair (
s
,
d
), the shortest path in
G
is derived through the
shortest path algorithm and corresponding backup segments belonging to the links of
the shortest path are recorded.
3.4. WDM-Shared Non-SRLG Protection [24]
This algorithm determines whether an established backup path can share resources based
on the Shared Risk Link Group (SRLG) or not. Note that the maximum value of the SRLG-
percentage should be considered because it is a unidirectional property, where the constraint
of the SRLG-percentage shows the maximum percentage of the primary links that are shared.
In this algorithm, there are three steps: the link weight scaling; the shortest path
computation; and the wavelength channel reservation. These steps are executed twice: one
time to compute a primary path and another time to calculate a backup path. Computing the
primary path is as follows:
•
The weight of a link is set to infinity, if the link does not have available resources or
has failed. Otherwise, the weight scales based on the percentage of usages.
•
A shortest path algorithm such as Dijkstra is used to calculate the path in the
weighted graph.
•
The entire path is traversed and it is determined which wavelength channel should be
used in each link.
•
In order to establish the backup path, the following process is run:
•
First, the weights of the edges used by the primary path must be set to infinity to
establish the backup path.
•
The shortest path algorithm is run in such a way that the primary links are not
considered as candidates for backup path because the primary and backup paths must
be link-disjoint.
•
The third step is executed similar to the third step of computing the primary path
procedure, only with two tunings. This means that in addition to its regular routines,
it is possible to share a wavelength channel already reserved to another backup path
when backup sharing is used. If the backup sharing is used and in this case a failure
happens, the backup availability test must verify other connections associated with
this backup path.
