scope:

The present document defines the general aspects of interworking at the Inter-System Interface (ISI) for Terrestrial Trunked Radio (TETRA) system supporting Voice plus Data (V+D). Those specify the general concepts which are the basis of the ISI operation between TETRA systems. It introduces the Additional Network Features (ANFs) used at the ISI, and specifies:

- the general protocol mechanism, called ISI Generic Functional Protocol (ISI GFP), upon which the definition of each ANF is based; and

- the security requirements for the ISI. The ISI GFP specification applies to any TETRA Switching and Management Infrastructure (SwMI) which supports the ISI.

The security requirements for the ISI only apply to SwMIs which support authentication or encryption over the ISI.

Besides the ISI general design, the present document, interworking at the Inter-System Interface comprises the following other sub-parts:

- Additional Network Feature - ISI Individual Call (ANF-ISIIC);

- Additional Network Feature - ISI Group Call (ANF-ISIGC);

- Additional Network Feature - ISI Short Data service (ANF-ISISDS); and

- Additional Network Feature - ISI Mobility Management (ANF-ISIMM).