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 application_number US 37257799 A description referring now to fig1 a wdm wavelength division multiplexed ring network generally referenced 1 consists of two counter rotating rings 2 3 containing a plurality of nodes 4 5 6 7 8 providing interfaces to the rings 2 3 it will be understood that fig1 shows the physical layout of the network the rings 2 3 physically consist of optical fibers which are capable of carrying multiple wavelengths generated by lasers in the nodes the interconnectivity between the nodes is provided by wdm connections in a manner to be described each ring may carry for example 16 or 32 wavelengths divided into eight bands which provide the interconnectivity between the nodes typically there are either two.