Analysis of subwavelength traffic grooming efficiency in optical mesh networks

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 subwavelength grooming capable switches that can switch at STS-1 (51 Mbps) granularity. The former consumes high fragmented/unused capacity to support low capacity end-to-end circuits using high capacity STS-48 channels (given current subwavelength traffic levels) while the latter may require relatively complicated hardware design that decreases switch scalability. Two-tier network architectures combine the benefits of STS-1 and STS-48 switches by using an upper tier of STS-48 switches for routing and restoration and a lower tier of STS-1 switches for grooming efficiency. A partial two-tier architecture, where STS-1 switches are restricted to a subset of the network nodes, has been shown in to closely match the grooming benefits of a full lower STS-1 tier. We furnish a detailed upper hound analysis of how the fragmented/unused capacity in STS-48 channels (fragmentation loss) varies with the grooming capability of a network for arbitrary traffic scenarios. We show that the upper bounds derived in this paper are in agreement with results obtained using efficient routing and grooming algorithms discussed. Because the bounds obtained do not make any assumptions about traffic and are easy to compute, they are suited for incorporation into a network engineering tool for deciding strategic placement of STS-1 switches in partial two-tier networks. Our work is not biased towards any particular network architecture but aims to analyze the grooming efficiency of two-tier networks.