scope:

This European Telecommunication Standard (ETS) specifies a first version of the Integrated Services Digital Network (ISDN) - Global System for Mobile communications (GSM) Public Land Mobile Network (PLMN) signalling interface. This ETS is applicable to the first interconnection of PLMN and ISDN.

NOTE: A future ETS may cover the application of the ISDN User Part (ISUP) version 2 on the signalling interface.

The ISUP interface defined is the trunk signalling interface between the PLMN and the ISDN. It is assumed that the interface between PLMN and ISDN can occur in any point in a national network.

This signalling interface is based on ISUP version 1 (as given in ETS 300 121 [2]) which supports the following services:

Bearer services:

- 64 kbit/s unrestricted;

- Speech;

- 3,1 kHz audio.

Teleservices:

- Telephony;

- Teletex;

- Telefax Group 4;

- Mixed mode;

- Videotex;

- Telefax Group 2/3.

Supplementary services:

- Calling Line Identification Presentation (CLIP)/Calling Line Identification Restriction (CLIR) supplementary services;

- Connected Line Identification Presentation (COLP)/Connected Line Identification Restriction (COLR) supplementary services;

- Closed User Group (CUG) supplementary service;

- User-to-User Signalling service 1 implicit (UUS1i) supplementary service.

The Direct Dialling In (DDI) supplementary service and Multiple Subscriber Number (MSN) supplementary service have no impact on this interface. The Subaddressing (SUB) supplementary service and Terminal Portability (TP) supplementary service are implicitly supported, as part of the basic ETS 300 121 [2] procedures.

An additional parameter is added to prevent looping of forwarded calls across this interface.

The support of the above mentioned services on this interface does not necessarily imply that the services are supported in one or the other of the networks interconnected.

As this interface is used within national networks, ETS 300 121 [2] is modified to be suitable for ISDN/PLMN applications. The application of the echo control procedures is described.