ITU-T X.80 PDF

General

Principles

This Recommendation provides a set of interworking specifications for CCITT circuit-switched data signalling systems. Interworking is defined as the controlled transfer of signalling information across an interface between different signalling systems where the significance of the transferred information is identical, or where significance is translated in a defined manner, and includes the performance of the appropriate interworking procedures in association with the transfer. These interworking procedures will be performed by an interworking function at a boundary between the two interworking signalling systems.

Interworking commences at call set-up when a link is established between two circuits using different signalling systems and continues throughout the call until release of the connection occurs. Interworking ceases with the release of the connection, whether the release is initiated by the reception of a clear condition from either of the signalling systems involved or by the interworking function itself in response to some abnormal condition.

Presentation

The specifications are basically represented by flow charts consistent with the CCITT Specifications and Descriptions Language (SDL), described in Recommendations Z.101 to Z.103; and are used to describe the logical requirements of the interworking function. In addition, two tables are included to show the signalling sequences required for a typical interworking situation. Narrative description has been reduced to a minimum.

SDL provides a method of presentation which is both comprehensive and independent of implementation, ensuring that all interworking conditions can be covered in a systematic manner. The logic of each signalling system is covered in the relevant signalling Recommendations X.60, X.70 or X.71.