Multi-rate and multi-hop optical carriers in WDM ring

Transparency of the optical layer offers the possibility to design a network that operates at varying transmission bit rates. While variable bit rate interfaces are being tested and will soon provide the possibility to optimally select the transmission rate for each lightpath, the potential advantages of relying upon multiple transmission rates in the optical network are ready yet to be fully explored. In this paper we define the concept of Multi-hop and Multi-rate (M&M) network in which the tributary signal is transmitted over a sequence of lightpaths, with each lightpath operating at its own transmission rate, which is determined by a number of factors including the end node's interface, amount of multiplexed traffic and cost of the network components. The potential advantages provided by the M&M network when compared to first generation optical networks (i.e., SONET/SDH), single- and multi-hop (constant bit rate) optical networks, are discussed in general and demonstrated numerically in a WDM ring. Presented results show that the network cost reduction achieved by the M&M design is a function of the cost ratio between the optical bandwidth (wavelengths) and the optical terminals.