Passive star (tree and branch)

Written on 2:31 PM by ooe

Passive star architectures can be implemented with either passive power dividers or with wavelength division multiplexing (WDM) components. Both offer a one-to-many optical concentration function. The passive optical network (PON) approach, shown in, makes use of passive power dividers in the network and promises lower cost and more flexibility for early deployment. It may use any available multiplexing schemes in the equipment at either end of the network. WDM on the other hand promises a lower power budget and is therefore capable of giving more bandwidth per user on a dedicated basis, rather like a point-to-point fibre. The PON or tree architecture allows many signals to be combined onto a common bearer into the central node by suitable choice of multiplexing rather like conventional cable TV over coaxial cable. Traffic may be concentrated at any point in the network. In general, costs are minimised if the concentration point is near the customers. In the downstream direction, the multiplex is broadcast to all users. In the upstream direction broadcasting does not occur but a multiplex may be formed optically ‘on-the-fly’ using multiplexing such as WDM or TDM in the terminal equipment. The multiplex must be designed to avoid mutual interference, which would arise if channels are chosen at random.