scope:

Scope of the Document

This specification covers the definition of the TacISDN interface from the physical level to the signalling used across the interface.

This document does not seek to provide an introduction to ISDN signalling. Readers requiring such an introduction are referred to the many textbooks on the subject, see Annex A, references [36], [37] and [38]. Other introductory texts do exist.

The specification concentrates on the military features that have been added to the civil ISDN signalling standards. These features are defined as being supported through the use of Codeset 6 Information Elements to extend the civil signalling.

To cover the variety of options that are possible with ISDN signalling some aspects are defined as "optional". Individual projects intending to use this specification are expected to define their own profile of these options, with the expectation that some may be deleted, with others becoming mandatory. However, items marked as mandatory may not be removed, or changed to "optional", if compliance with this specification is to be claimed.

Pro-formas for Protocol Implementation Conformance Statements (PICS) are provided for the lower and higher level issues.

When complete, these define which of the optional elements of the specification have been implemented in a particular case.

This specification is concerned with information transport across the interface. Some management issues are addressed within this specification, however the wider questions of the management of individual interfaces and the management of the interfaces within a network of networks are matters for consideration elsewhere.

It is recognised that different communications systems are likely to use different representations of equivalent traffic (speech, data etc). This specification defines how these the signalling of these representations is to be used to control the transcoding of the information to permit end-to-end services to be supported through different networks. This control of transcoding is such as to allow the number of transcodes to be minimised for speech; an important consideration if intelligibility is to be maintained.