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Figure11. Architecture of a wavelength-routed network.
Every t time, in the forward ant step, the ant with a given probability ρ starts moving
from each node to the randomly selected destination. An ant stochastically determines its next
hop according to its selecting probabilities in the pheromone table. Each ant is considered to
be a mobile agent. Then, the forward ant collects information on its travel and updates routing
tables on visited nodes. Moreover, forward ant updates the pheromone table with collected
information. The moving nature of agents and the update of the pheromone table makes ant-
based mobile agents tend to follow paths with shorter length and larger number of free
wavelengths. After the ant reaches the destination, it moves back to the source node based on
the same forward rules. Note that backward ant should check its path not to move on the
visited links so that all the visited nodes will formulate a cycle. If the ant cannot find a node
to move, it will be killed. After that the ant arrives at the source node, it reports the cycle to
the routing table and then is killed. In order to select a minimum cost link, the cost of primary
path and the cost of backup path are first computed for each wavelength. Then, a set of cycles
with the minimum cost of primary path are selected among the cycles with at least one
wavelength on which cost of the backup path is not infinity. Finally, the cycle with minimum
cost of link is selected.
3.8. Recursive Shared Segment Protection (RSSP) [28]
In order to achieve better recovery time and resource utilization, [28] has proposed a
recursive shared segment protection (RSSP) that calculates the backup segments through a
recursive method and selects the optimized of them to partition the working path. In RSSP,
there are several restricts: each link and node belonging to a working path can only be a part
of one working segment or at most two working segments. Moreover, any working segment
should not be a subset of any other working segment. Finally, the hop count parameter of
each backup segment should be limited by a threshold value, where the threshold is a positive
integer represented by H c . The RSSP is executed as follows:
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