10 Interworking to fixed networks

23.1463GPPRelease 17Technical realization of facsimile Group 3 non-transparentTS

Only PSTN and ISDN are considered, and may be used as transit networks to complement the PLMN in the end‑to‑end connection between facsimile group 3 terminals (figure 6).

Figure 6: Network interworking

10.1 Interworking to PSTN

As the standard access of facsimile group 3 terminals for this Teleservice is a 2-wire analogue interface, all the technical requirements for network interworking to PSTN are identical in principle to those encountered for the terminal connection to the UE. The key functional block is the FA described in clause 7 of the present document.

As far as network interworking is concerned, the main function to be performed by such a block is the correct managing of a composite modem, in accordance with the requirements of ITU-T Recommendation T.30:

– ITU-T Recommendation V.21 synchronous mode, as standard facility for all BCS phases;

– ITU-T Recommendation V.27ter for message speeds of 4 800 and 2 400 bit/s;

– ITU-T Recommendation V.29 for message speeds of 9 600 and 7 200 bit/s;

– ITU-T Recommendation V.17 for message speeds of 14 400, 12 000, 9 600, 7 200 bit/s.

The mechanism for selecting the correct modem is the following:

– the actual message speed is obtained by detecting the DCS frame (see table 2/ITU-T Recommendation T.30) while in BCS phase;

– on entering the message phase, there is an interchange between the V.21 modem and the actual modem agreed upon between the terminals for message transmission;

– on exiting the message phase (RTC) the ITU-T Recommendation V.21 modem is selected again.

Times for settling the modem shall be in accordance with the requirements of ITU-T Recommendation T.30.

10.2 Interworking to ISDN

The use of 3,1 kHz audio bearer capability of ISDN allows for an interworking of PLMN very similar in practice to the scheme for PSTN (figure 6). The FA function shall comply with the description given in clause 7 of the present document.

Annex A (normative):
Structure and contents of the FA protocol elements