Packet-switched local area networks using wavelength-selective station couplers

In recent years, many LAN designs have been considered using passive star a nd passively tapped ring and bus architectures [16], Similar networks can a lso be designed using active wavelength-selective coupling devices such as those based on acoustooptics [5], [6]. A major advantage of actively couple d designs is that functions such as station slot synchronization are greatl y simplified. In recent work, these types of devices have been considered f or use in add/drop multiplexers where device reconfiguration occurs very in frequently [21], [17], [13], In this paper, we consider the use of active couplers as station taps in ne tworks that support packet-switched modes of operation. When used for this purpose, a major source of complexity results from the fact that at a given time, an unknown number of stations may be inserted into a particular wave length-division multiplexing bus. For this reason, global slot-timing infor mation cannot be derived from any one particular channel. As a result, when conventional protocols are used, the system may suffer from "retuning coll ision," where a station destroys transit packets on other channels when the coupler is inadvertently retuned [20], We investigate protocols that can a void this problem. In the simplest protocol, overhead drastically restrict the range of physical parameters over which efficient operation can be achi eved. The more sophisticated ones significantly extend this range so that m etropolitan coverage is possible at reasonable data rates. In addition, we consider the use of active station taps in multichannel dual-bus networks. Capacity, delay, and power models are also derived, and comparisons are mad e with previous systems including passively tapped networks.