Many LAN designs have been considered using passive star and passively tapped ring and bus architectures. Similar networks can also be designed using active wavelength-selective coupling devices such as those based on acoustooptics. A major advantage of actively coupled designs is that functions such as station slot synchronization are greatly simplified. In this paper, we consider the use of active couplers as station taps in networks 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 wavelength-division multiplexing bus. For this reason, global slot-timing information cannot be derived from any one particular channel. As a result, when conventional protocols are used, the system may suffer from "retuning collision", where a station destroys transit packets on other channels when the coupler is inadvertently retuned. We investigate protocols that can avoid this problem. In the simplest protocol, the overhead drastically restrict the range of physical parameters over which efficient operation can be achieved. The more sophisticated ones significantly extend this range so that metropolitan 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 made with previous systems including passively tapped networks.

Research in photonics is currently aimed at ways to exploit the enormous information-carrying capacity of optical fiber. Many networks based upon wavelength division multiplexing (WDM) have recently been proposed using passive star couplers. However, new advances in travelling-wave and doped-fiber amplifiers have sparked interest in multichannel ring and bus networks. A new network architecture is proposed which is applicable to both multichannel folded busses and rings. The motivation behind the designs is to simplify the user stations as much as possible, thus giving an economical implementation. As proposed by Janoska and Todd (see GLOBECOM'93, vol.1, p.481-487, 1993) this is accomplished through the use of a headend channel controller which assists in the operation of the networks.>