Optical-fibre networks: single-hop and multihop systems

Optical fibre has become the preferred terrestrial transmission medium for telecommunications. The single-mode fibre, which has superior transmission quality due to the absence of modal noise and low loss, offers an enormous bandwidth, in the order of thousands of gigahertz. Various access techniques have been proposed to tap this bandwidth by introducing concurrency among users in the network. Concurrency may be provided in one of three ways: 1) in wavelength of frequency (wavelength-division multiplescing (WDM)); 2) in time (time-division multiple access (TDMA)); 3) in wave shape (spread spectrum or code-division multiple access (CDMA)). Using the available technology to construct optical-fibre networks leads to the definition of two different classes of networks. The first class contains the single-hop networks, which can use either WDM, TDMA, or CDMA. All optical TDMA requires node synchronization to within one time slot; at the same time the modularity of 'tell-and-go' flexibility does not exist, rendering this approach not viable. Consequently, attention has been focused on WDM and CDMA for single-hop networks. The second class consists of the multihop networks, which are specially designed to achieve efficient use of the channel bandwidth.