At its plenary meeting in Geneva in October 1998, the International Telecommunication Union's (ITU's) Study Group 15 approved Recommendation G.692, "Optical Interfaces for Multichannel Systems with Optical Amplifiers." This document was drafted in the optical experts' group of Q.16, chaired by John Eaves of Lucent Technologies. Issues that delayed the Recommendation's approval at the February 1998 meeting were resolved, resulting in unanimous approval at last October's meeting.
G.692 is the first multichannel optical-interface Recommendation to be approved by the ITU. A standard such as this is urgently needed to provide a common basis for network planning and equipment classification because of the massive new installations and upgrade of high-capacity long-distance wavelength-division multiplexing networks. The technical content was established some time ago (see Lightwave, August 1997, page 22), but modifications were made at the October meeting, which brought the document up to date with respect to current technical developments, as well as some other purely editorial changes.
The first of these technical modifications established rules for higher channel counts. Application codes for 16-channel systems have been developed and included in the document. For higher-channel-count systems (32 and above), the frequencies of a 50-GHz-spaced grid have been added and are based on the original 100-GHz grid, which still applies for all application codes for the systems up to 16 channels defined in this Recommendation.
The frequency grid tables in G.692 presently cover the wavelength range of 1528.77 nm to 1560.61 nm. There was discussion of technical developments that have enabled optical amplifiers whose useful range extends beyond these values. But since the frequency/wavelength limits in the Recommendation were intended to be illustrative only, the text and format of the table illustrating the grid were kept, with some minor editorial amendments.
Other modifications were introduced with respect to possible bidirectional systems. For those systems, the requirements concerning loss, distance, and dispersion are the same as for unidirectional applications. The letter "B" in the application code will indicate bidirectional applications.
The parameter tables and frequency grid contained in this Recommendation have gained some importance since they are taken as the basis for further discussion and specification of transversal- compatible interfaces-despite the fact that G.692 is a standard for long-haul point-to-point systems rather than for optical networking.
In particular, this recognition means that the specified grid and a subset of the parameter tables contained in Chapter 7 of Recommendation G.692 are being used as a basis for the discussion of Draft Recommendation G.959.1, the first step toward achieving transversal compatible multichannel optical-networking interfaces.
Klaus Juergen Rahn works for Lucent Technologies Germany, where he is responsible for technical planning of WDM systems. He is the editor of ITU Recommendation G.692. He can be contacted at tel: +49 911 526 2776; fax: +49 911 526 3795; e-mail: firstname.lastname@example.org.