Abstract
Reconfigurable Optical Add/Drop Multiplexers (ROADM) are the optical
switching equipment of transparent optical networks. Directionless ROADMs
permit the network carriers to change the direction of an added and/or dropped
lightpath without the need of a technician on-site intervention in the lightpath
end nodes. Colorless ROADMs provide the same versatility for changing the
lightpath transmission wavelength. Cost-effective directionless ROADM architectures
(colorless or colored) can be built if the maximum number of lightpaths that
can be added/dropped using the same wavelength is limited. We name this limit
as the node add/drop contention factor, and denote it as <i>C</i>. In this paper we investigate the
network lightpath blocking performance as a function of this add/drop contention
factor of the nodes. The scenarios considered are the static planning of a
network (i) with unprotected traffic, (ii) with traffic 1+1 protected for single-link failures,
and (iii) with traffic 1+1 protected for single-link or single-node failures. Since for these
scenarios, the wavelength of an existing lightpath does not have to be dynamically
reconfigured, the work in this paper applies to both colorless and colored
nodes. An ILP model and an effective heuristic are presented to solve the
so-called Add/Drop Contention Aware RWA (ADCA-RWA) planning of the network.
Extensive results are reported. In all the cases, an add/drop factor <i>C</i> = 2 is sufficient
to provide the same performance as contentionless nodes (<i>C</i> = ∞). Furthermore, in all the
tests a factor <i>C</i> = 1 was also sufficient, or produced a minor lightpath blocking performance
degradation (below 0.5% in the unprotected cases, and below 2.5% in the 1 + 1 protected
cases).
© 2011 IEEE
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