A PACKET-SWITCHED MULTIHOP LIGHTWAVE NETWORK USING SUBCARRIER AND WAVELENGTH-DIVISION MULTIPLEXING

We propose a new architecture for a high-speed packet-switched metropo litan-area lightwave network using a combination of wavelength divisio n multiplexing over fiber and subcarrier multiplexing within each wave length. 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 wavelen gth and fixed subcarrier frequency. Rapid tuning between subcarrier fr equencies allows a station to transmit packets to all stations that re ceive on some subcarrier channel on its transmit wavelength. Packets i ntended for stations that do not receive on the wavelength of the tran smitting station must be routed through intermediate stations. By avoi ding rapid tuning between wavelengths, we realize a practical multihop architecture for packet switching with one optical transmitter shared among many stations and one optical receiver per station. This archit ecture imposes a constraint on the multihop connectivity pattern in th e network since all stations using a common transmit wavelength send p ackets directly to the same set of other stations. The same constraint is applicable to shared-channel multihop networks with a single trans mitter and receiver per station. We introduce the notion of ''clustera ble'' directed graphs to represent the connectivity patterns that are possible, and using the properties of these graphs, show that nodes ca n 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 cal culations indicate the feasibility of a 32-wavelength network with fiv e 200 Mb/s FSK subcarrier channels on each wavelength. Our throughput calculations indicate that such a network could support 160 stations w ith a throughput per station of 44 Mb/s.