Routing and Grooming in Two-Tier Survivable Optical Mesh Networks

Abstract

While deploying the next generation of optical networks with a mesh topology, telecommunications carriers are being confronted with a choice between wavelength switches that can switch traffic at SONET STS-48 (2.5 Gbps) granularity and sub-wavelength grooming capable switches that can switch at STS-1 (51 Mbps) granularity. The former cannot switch circuits of capacity lower than STS-48 without the help of external grooming devices, and consumes high fragmented/unused capacity to support low capacity end to end circuits using high capacity STS-48 channels. The latter almost eliminates such capacity wastage by supporting STS-1 level switching, but involves larger switching delays leading to slower restoration and requires more complicated hardware design that decreases switch scalability with increasing port count.This paper proposes an intelligent packing and routing algorithm in a network architecture which contains both kinds of switches configured in two tiers, and compares it with the other two network architectures - one with only wavelength switches with STS-48 granularity, and another with only grooming switches with STS-1 switching granularity. It is shown that the two-tier architecture with our routing scheme is comparable in capacity efficiency to the STS-1 only network, while its scalability and restoration delays are at par with the STS-48 only network.Furthermore, we propose a partial two-tier network architecture where the functionality of STS-1 grooming is deployed at a subset of the network nodes. Our simulations show that the capacity efficiency of this architecture does not decrease significantly with reduction in the number of STS-1 switch equipped nodes.