Survivability is a means of introducing redundancy in a network architecture which is
utilized to maintain communication capability under failure conditions. The need for
survivability exists in most communication networks. Fiber optic networks concentrate large
amounts of traffic within a few spans, using their high capacity to achieve a cost advantage. It is crucial to incorporate survivability at minimum cost in the design of such networks. This
problem is conventionally tackled using techniques such as Automatic Protection Switching
(APS), Dual homing and Self-Healing Ring (SHR). These techniques, although relatively
simple to implement, are not efficient in utilizing network capacity. Interconnected ring
topologies use the network capacity more efficiently at the expense of complex fault
detection and routing methodologies. The toroidal grid is shown to be an optimized form of
a generalized survivable interconnected ring topology. It is shown to have significantly lower
capacity requirements than the simple self healing ring networks. The modified toroidal grid
is an improvement on the toroidal grid because it has a planar graph and shorter average link
length. A quantity called link-traffic summation is defined as a metric of total link capacity
requirement in a network. Analytical values for link-traffic summation are obtained for
simple ring, generalized interconnected ring, toroidal grid and modified toroidal grid
networks. Simulations are performed for the modified toroidal grid and their results are
compared with the analytical values obtained.
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