7.1 Interworking to PSTN

3GPP43.045Release 16Technical realization of facsimile group 3 transparentTS

As the standard access of Group 3 facsimile 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 MT.

The key functional block is the Fax Adaptor described in clauses 4 to 6 of the present document. As far as network interworking is concerned, the main function to be performed by such block is the correct managing of a composite modem, in accordance with the requirements of ITU-T Rec. T.30.

– V.21 synchronous mode, as standard facility for all BCS phases;

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

– V.29 for 9 600 and 7 200 bit/s message speed.

– V.17 for 7200, 9600, 12000 and 14400 bit/s message speed.

The mechanism for selecting the right modem is the following:

– the actual message speed is obtained by detecting the DCS frame (see table 2/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 the V.21 modem is selected again.

Times for settling the modems will be in accordance with the requirements of Recommendation T.30.

Figure 8/43.045: Network interworking