scope:

This 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. In the future, a new ETS wilt cover application of the 1SDN User Part (ISUP) version 2 [1] on the signalling interface.

The ISUP interface being 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 (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/Restriction (CLIP/CLIR);

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

- Closed User Group (CUG);

- User-to-User Signalling Service 1 Implicit (UUS1 Implicit).

Direct Dialling In (DDI) and Multiple Subscriber Number (MSN) are without significance to this interface. Subaddressing (SUB) and Terminal Portability (TP) 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 services mentioned on this interface does not necessarily mean 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.

The Message Transfer Part (MTP) protocol shall conform to the requirements in ETS 300 008 [3] with the appropriate value for the Network Indicator (NI).

It is preferred that NI value 10 (national network) is used within GSM networks as in the fixed national network. Based on national agreement, any NI value may be applied on the interface between GSM networks and the fixed networks.