INTERNATIONAL TELECOMMUNICATION UNION ITU-T RECOMMENDATION SUMMARY Rec. No. : G.957 Title : Optical interfaces for equipments and systems relating to the synchronous digital hierarchy Study Group : XV - Transmission Systems and Equipment Version : New Date of adoption : 1990 Notes : Recommendation G.957 covers optical interface parameter specifications for equipments and systems supporting the Synchronous Digital Hierarchy (SDH) defined in Recommendations G.707, G.708 and G.709 and operating on single-mode optical fibres conforming to Recommendations G.652, G.653 and G.654. The purpose of Recommendation G.957 is to provide specifications for the optical interfaces of SDH equipment, described in Recommendations G.782 and G.783, and line systems described in Recommendation G.958, to achieve the possibility of transverse (multivendor) compatibility on elementary cable sections, i.e. the possibility of mixing various manufacturers' equipments within a single optical section. However, the specifications in Recommendation G.957 are also intended to be in accordance with Recommendations G.955 and G.956 which provide the possibility to achieve longitudinal compatibility for equipment of comparable hierarchical level and application. Recommendation G.957 is based on the use of one fibre per direction. Any other optical arrangements may require different specifications and are for further study. To order the complete text of this Recommendation, please use the Order Form for ITU-T Recommendations. An electronic version of this form is available on ITUDOC (Winword: UPI=ITU-5265; ASCII: UPI=ITU-2488).