A communications network has a plurality of nodes interconnected by an optical
transmission medium. The transmission medium is capable of a carrying a plurality
of wavelengths organized into bands. A filter at each node for drops a band associated
therewith and passively forwards other bands through the transmission medium. A
device is provided at each node for adding a band to the transmission medium. Communication
can be established directly between a pair of nodes in the network sharing a common
band without the active intervention of any intervening node. This allows the network
to be protocol independent. Also, the low losses incurred by the passive filters
permit relatively long path lengths without optical amplification.
