Date of Award
Doctor of Philosophy (PhD)
Electrical and Computer Engineering
Terence D. Todd
Wavelength division multiplexing technologies are proving to be an effective method for bring high bandwidth to data communication networks. Such networks utilize some form of wavelength agility at stations in order to access a set of wavelength channels. Since each channel is represented by a unique wavelength, transmissions on one channel are independent from other channels. Unfortunately, this multi-channel nature acts to complicate system operation and often results in increased optical hardware requirements. Recent advances in photonic amplification have re-motivated the use of ring and bus topologies in single-hop wavelength-division-multiplexed (WDM) networks (Muk92). Most often stations on a ring or bus WDM network utilize multiple transmitters and receivers which are coupled to the fiber via passive devices. Compared to networks based upon passive optical stars, ring and bus networks offer much simplified station synchronization requirements. However, when minimal station hardware is desired, network operation can be complicated. In this thesis, four different WDM bus/ring networks based upon passive coupling technology are considered. All four have user station hardware designs with various reductions in the number of tapping points, number of transmitters and receivers and their tunability requirements. With each reduction in hardware, protocol complexities and performance reductions are introduced. In all cases, dynamic packet-switched operation is achieved. The designs thus give an indication of the cost/performance tradeoffs which are possible as the amount of hardware is reduced at the user stations. Common to each of the designs is the use of a headend controller which attaches to each WDM channel. Media access is achieved through information provided by the controller. In the more hardware intensive designs, media access is achieved through a mini-slot contention mechanism (GT94). The remaining designs rely on a hybrid opto-electronic request/allocation protocol motivated by DCCN (JT93). Analytical models are presented which are validated through discrete-event simulations for each design. Although this passive tap arrangement is very simple, synchronizing to upstream transmissions is much more difficult compared to existing single-channel busses and rings. This affects the types of protocols which are practical in passive designs. In this thesis, we also investigate protocols for multichannel photonic bus/ring LANs which use active wavelength-selective taps rather than passive ones. An example of such an implementation might use couplers based on acousto-optic devices (Che90). There are a number of advantages in such a design. Since stations actively tap the wavelength channel that they are accessing, synchronization is identical to existing single-channel rings. This results in much simpler media access protocols than in the passive case. In addition, spatial re-use is possible in the ring designs. In LANs with active taps, when stations re-tune their couplers at an inappropriate time, transit packets may be destroyed. This action is referred to as a "re-tuning collision". The media access protocols must take special actions in order to prevent this from happening. This places restrictions on the physical parameters over which system performance is efficient. Capacity and delay models are also derived, and comparisons are made with the conventional passive designs developed in this thesis.
Grah, Adrian, "Active and passive coupling in WDM photonic ring and bus networks" (1997). Open Access Dissertations and Theses. Paper 3350.