Analysis of sub-wavelength traffic grooming efficiency in 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 consumes high fragmented/unused capacity to support low capacity end-to-end circuits using high capacity STS-48 channels (given current sub-wavelength 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 [3] to closely match the grooming benefits of a full lower STS-1 tier. We furnish a detailed upper bound 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 in [3]. 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.