A packet-switched multihop lightwave network using subcarrier and wavelength division multiplexing

We propose a new architecture for a high-speed packet-switched metropolitan-area lightwave network using a combination of wavelength division multiplexing over fiber and subcarrier multiplexing within each wavelength. Each station transmits on a fixed-wavelength (that may also be used by some other stations) at any one of many available subcarrier frequencies within that wavelength, and receives on some fixed wavelength and fixed subcarrier frequency. Rapid tuning between subcarrier frequencies allows a station to transmit packets to all stations that receive on some subcarrier channel on its transmit wavelength. Packets intended for stations that do not receive on the wavelength of the transmitting station must be routed through intermediate stations. By avoiding rapid tuning between wavelengths, we realise a practical multihop architecture for packet switching with one optical transmitter shared among many stations and one optical receiver per station. This architecture imposes a constraint on the multihop connectivity pattern in the network since all stations using a common transmit wavelength send packets directly to the same set of other stations. The same constraint is applicable to shared-channel multihop networks with a single transmitter and receiver per station. We introduce the notion of “clusterable” directed graphs to represent the connectivity patterns that are possible, and using the properties of these graphs, show that nodes can be added to and removed from the network with minimal disruption to the other nodes. We show that some well-known multihop topologies such as shufflenets and de Bruijn graphs are clusterable. Power budget calculations indicate the feasibility of a 32-wavelength network with five 200 Mb/s FSK subcarrier channels on each wavelength. Our throughput calculations indicate that such a network could support 160 stations with a throughput per station of 44 Mb/s