Abstract

Abstract
p-Cycle Based Protection in WDM Mesh Networks
Honghui Li, Ph.D.
Concordia University, 2012
WDM techniques enable single fiber to carry huge amount of data. However, optical WDM
networks are prone to failures, and therefore survivability is a very important requirement
in the design of optical networks. In the context of network survivability, p-cycle based
schemes attracted extensive research interests as they well balance the recovery speed and
the capacity efficiency. Towards the design of p-cycle based survivableWDM mesh networks,
some issues still need to be addressed. The conventional p-cycle design models and solution
methods suffers from scalability issues. Besides, most studies on the design of p-cycle
based schemes only cope with single link failures without any concern about single node
failures. Moreover, loop backs may exist in the recovery paths along p-cycles, which lead
to unnecessary stretching of the recovery path lengths.
This thesis investigates the scalable and efficient design of segment p-cycles against single
link failures. The optimization models and their solutions rely on large-scale optimization
techniques, namely, Column Generation (CG) modeling and solution, where segment pcycle
candidates are dynamically generated during the optimization process. To ensure full
node protection in the context of link p-cycles, we propose an efficient protection scheme,
called node p-cycles, and develop a scalable optimization design model. It is shown that,
depending on the network topology, node p-cycles sometimes outperform path p-cycles in
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terms of capacity efficiency. Also, an enhanced segment p-cycle scheme is proposed, entitled
segment Np-cycles, for full link and node protection. Again, the CG-based optimization
models are developed for the design of segment Np-cycles. Two objectives are considered,
minimizing the spare capacity usage and minimizing the CAPEX cost. It is shown that
segment Np-cycles can ensure full node protection with marginal extra cost in comparison
with segment p-cycles for link protection. Segment Np-cycles provide faster recovery speed
than path p-cycles although they are slightly more costly than path p-cycles. Furthermore,
we propose the shortcut p-cycle scheme, i.e., p-cycles free of loop backs for full node and
link protection, in addition to shortcuts in the protection paths. A CG-based optimization
model for the design of shortcut p-cycles is formulated as well. It is shown that, for full node
protection, shortcut p-cycles have advantages over path p-cycles with respect to capacity
efficiency and recovery speed. We have studied a whole sequence of protection schemes
from link p-cycles to path p-cycles, and concluded that the best compromise is the segment
Np-cycle scheme for full node protection with respect to capacity efficiency and recovery
time. Therefore, this thesis offers to network operators several interesting alternatives to
path p-cycles in the design of survivable WDM mesh networks against any single link/node
failures.