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 Monday, July 02, 2007

A second standard in a new group of Recommendations from ITU-T's Study Group 15 extends the distance at which multi-vendor DWDM systems can be deployed from 80 to four or five hundred kilometres.

The first standard in the series gave network operators the ability to deploy multi-vendor dense wavelength division multiplexing (DWDM) systems in a metro environment. The new Recommendation extends this to cover regional environments by taking into account the use of optical amplifiers and their potential to create 'optical noise'.

WDM technology is used by the owners of optical fibres to maximise their capacity. The technology achieves this by simultaneously operating an optical fibre pair at more than one wavelength and uses optical amplification to increase transmission distances as well as optical add/drop multiplexers to increase the flexibility of the network. Since operators wish to maximize their cable plant investments and deploy increasingly bandwidth hungry services in a multi-vendor environment, standards development in this field is seen as crucial.

The Recommendation defines values for single-channel optical interface parameters of physical point-to-point and ring DWDM applications on single-mode optical fibres through the use of the "black-link" approach. The black-links covered by this follow-on Recommendation may contain optical amplifiers.

The transport network of most operators is based on the use of equipment from a variety of different vendors. Previously, for those parts of the network involving DWDM optical transmission, this has been achieved via the use of optical transponders which convert the single channel interfaces like those defined in ITU-T Recs G.957 G.691, G.693, G.959.1 into DWDM wavelengths suitable for the particular vendorís proprietary system. With the optical interfaces standardized in new G.698.2 operators can directly connect a wide variety of equipment to the DWDM line system without the need for those additional short reach transmitter and receiver pair per channel (eliminating the transponders) with obvious associated cost savings.