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Content for  TS 23.146  Word version:  17.0.0

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8  Use of terminal adaptation functionsWord‑p. 21

The protocol stack of the connection type is shown in Figure 4.
The TAFs described in TS 27.002 for asynchronous bearer capabilities in the non transparent mode. The interchange signalling mapping is in accordance with TS 27.002.

8.1  Principles of terminal adaptation functionsWord‑p. 21

The TAF, located at both PLMN ends, is in charge of:
  • call set-up, in particular the BC negotiation;
  • establishment and maintenance of a Layer2 protocol link between the FA and the TAF according to TS 27.002, where applicable;
  • establishment and maintenance of an L2RCOP link between the TAFs according to TS 27.002;
  • initiation of the In-Call Modification (ICM) procedure.
The basic approach of the present document for facsimile group 3 is:
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8.2  Specific TAFs for facsimile serviceWord‑p. 22

In order to perform the procedures described in the present document, the UE and the IWF environment shall be designed to transmit and receive facsimile data continuously with flow control. This specifically applies between RLP entities, L2RCOP (within TAF) entities, and between the FA and the TAF entities within the UE or the IWF.
Furthermore, the RLP entity shall be able to make error recovery by using the SREJ command/response.

9  Signalling aspectsWord‑p. 22

3GPP TS 27.002 identifies the bearer capability requirements to be supported by the terminal adaptation function in the MT (see TS 27.001 for BC and HLC coding). The specific signalling requirements are those for "speech" and "facsimile group 3" or "facsimile group 3" only, respectively. The MT indicates in the call set up request the requirements, e.g. first speech, second facsimile by sending the bearer capability information element(s) in the appropriate order. For an "auto calling" facsimile request, the facsimile group 3 bearer capability is sent as the first or the only bearer capability for Teleservice 61 or 62, respectively.
For interworking between Teleservice 61 and Teleservice 62, refer to TS 22.003 and TS 27.001.
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9.1  Handling of tonal signalsWord‑p. 22

Because the ITU-T defined service uses modems, there are some signals received from the analogue link at the MSC/IWF and (where used) the FA which do not have a direct binary representation.
These signals are the modem called (CED) and calling (CNG) tones sent at the start of each fax data phase of the call. These tonal signals shall be used for the selection of ATD or ATA. No later than 3 sec after connecting the fax apparatus to the line the FA/UE is able to determine the AT command. If a CNG tone or nothing is detected by the FA/UE the mobile fax station is the calling station, if a CED tone or a BCS signal frame is detected by the FA/UE the mobile fax station is the called station. If the associate fax is the calling station, the FA shall transmit ATD toward the TAF. If the associate fax is the called station, the FA shall transmit ATA toward the TAF.
After the link of the FA_protocol is established, these tonal signals shall be sent to the opposite FA as the IFP_packet(CNG,CED). The FA receiving the FA_packet(CNG,CED) shall generate the tonal signal and transmit the signal toward the associated facsimile terminal.(see figure D.3)
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9.2  Call establishmentWord‑p. 22

9.2.1  Mobile terminated callWord‑p. 22

The call may be set-up manually or automatically by the PSTN facsimile group 3.

9.2.1.1  Speech then facsimileWord‑p. 23

Refer to the diagrams in figures C.1a and C.1b. In both of the figures, the initial call setup is mobile terminated. In figure C.1a, the DCD is also mobile terminated (MT), while the DCD in figure C.1b is mobile originated (MO).
The connection of the FA to the TAF causes the initialization between the FA and the TAF. At this time, the setting of speech/facsimile call should be done in the FA. The operation of the FA for the speech/facsimile call setting is implementation dependent.
At first, the FA at the UE shall turn on circuit 108/2 and circuit 105. After that, the TAF at the UE shall turn on circuit 106 and circuit 107 toward the FA. The FA which detected ON condition of circuit 106 and circuit 107 requires facsimile call of the TAF by appropriate AT command (e.g. AT+CMOD=1, AT+FCLASS=1, 2). If the AT command is recognized, the TAF shall transmit "OK" to the FA as a result code.
In order to make the transition from the speech phase to the facsimile phase, the MODIFY message shall be initiated by the MMI at the facsimile terminal, which shall result in the establishment of RLP across the radio interface and connection to the line of the FA/IWF.
When the facsimile machine is connected to the line by manual intervention, the facsimile machine should transmit tonal signal (CNG or CED) toward the FA. The FA shall select ATD or ATA according to the rules in subclause 9.1 and transmit ATD or ATA toward the TAF.
On detecting ATD or ATA, the TAF shall transmit the MODIFY message that has G3FAX ability as a bearer capability. After that, RLP and L2RCOP shall be established across the radio interface.Once the connection is established, circuit 109 shall be clamped to the ON condition by the TAF at the IWF. Then, the FA protocol shall be started between the FAs.
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9.2.1.2  Auto answerWord‑p. 23

Refer to the diagram in figure C.2. The connection of the FA to the TAF causes the initialization between the FA and the TAF. At first, the FA at the UE shall turn on circuit 108/2 and circuit 105. After that, the TAF at the UE shall turn on circuit 106 and circuit 107 toward the FA. The FA which detected ON condition of circuit 106 and circuit 107 shall require facsimile call of the TAF by appropriate AT command (e.g. AT+FCLASS=1, 2). If the AT command is recognized, the TAF shall transmit "OK" to the FA as a result code.
When the MT receives a call in the condition finished the above initialization, the TAF shall transmit the result code "RING" toward the FA. "RING" shall cause a ring current to be sent to the facsimile terminal. The FA shall transmit ATA toward the TAF when the FAX terminal connects to the line and begins behaviour of receiving. On receiving ATA, the FA shall transmit a signal that notifies the calling side that called facsimile terminal connected to the line.
Once the connection is established, circuit 109 shall be clamped to the ON condition by the TAF at the IWF. Then, the FA protocol shall be started between the FAs.
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9.2.2  Mobile originated callsWord‑p. 23

The PSTN facsimile group 3 terminal may manually or automatically answer the call originated by the mobile station.

9.2.2.1  Speech then facsimileWord‑p. 23

Refer to the diagrams in figure C.3a and figure C.3b. In both of the figures, the initial call setup is mobile originated. In figure C.3a the DCD is also MO, while in figure C.3b the DCD is MT.
The connection of the FA to the TAF causes the initialization between the FA and the TAF. At this time, the setting of speech/facsimile call should be done in the FA. The operation of the FA for the speech/facsimile call setting is implementation dependent.
At first, the FA at the UE shall turn on circuit 108/2 and circuit 105. After that, the TAF at the UE shall turn on circuit 106 and circuit 107 toward the FA. The FA which detected ON condition of circuit 106 and circuit 107 requires facsimile call of the TAF by appropriate AT command (e.g. AT+CMOD=1, AT+FCLASS=1, 2). If the AT command is recognized, the TAF shall transmit "OK" to the FA as a result code.
In order to make the transition from the speech phase to the facsimile phase, the MODIFY message shall be initiated by the MMI at the facsimile terminal, which shall result in the establishment of RLP across the radio interface and connection to line of the FA/IWF.
When the facsimile machine is connected to the line by manual intervention, the facsimile machine should transmit tonal signal (CNG or CED) toward the FA. The FA shall select ATD or ATA according to the rules in clause 9.1 and transmit ATD or ATA toward the TAF. On detecting ATD or ATA, the TAF shall transmit the MODIFY message that has G3FAX ability as a bearer capability. After that, RLP and L2RCOP shall be established across the radio interface. Once the connection is established, circuit 109 shall be clamped to the ON condition by the TAF at the IWF. Then, the FA protocol shall be started between the FAs.
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9.2.2.2  Auto callingWord‑p. 24

Refer to the diagram in figure C.4. The FA at the UE shall turn on circuit 108/2 and circuit 105 when the fax apparatus is connected to the line by manual intervention. After that, the TAF at the UE shall turn on circuit 106 and circuit 107 toward the FA. The FA which detected ON condition of circuit 106 and circuit 107 shall require facsimile call of the TAF by appropriate AT command (e.g. AT+FCLASS=1, 2). If the AT command is recognized, the TAF shall transmit "OK" to the FA as a result code.
The FA shall make ATD [Dial signal] from DTMF dialling information and transmit ATD[Dial signal] toward the TAF. On detecting ATD [Dial signal], the TAF shall transmit the call set-up signal that has G3FAX ability as a bearer capability. When the call is answered, the synchronization process shall be started and the RLP shall be established across the radio interface.
After that, RLP and L2RCOP are established across the radio interface. Once the connection is established, circuit 109 shall be clamped to the ON condition by the TAF at the IWF. Then, the FA protocol is started between the FAs.
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9.2.2.3  Manual callingWord‑p. 24

Refer to the diagram in figure C.5. The connection of the FA to the TAF causes the initialization between the FA and the TAF. At first, the FA shall turn on circuit 108/2 and circuit 105. After that, the TAF at the UE shall turn on circuit 106 and circuit 107 toward the FA. The FA which detected ON condition of circuit 106 and circuit 107 shall require facsimile call of the TAF by appropriate AT command (e.g. AT+FCLASS=1, 2). If the AT command is recognized, the TAF shall transmit "OK" to the FA as a result code.
After the initialization of the FA and the TAF, the dialling operation shall be done at the MT. Then, the MT shall transmit the call set-up signal that has G3FAX ability as a bearer capability.
After that, RLP and L2RCOP shall be established across the radio interface. Once the connection is established, circuit 109 shall be clamped to the ON condition by the TAF at the IWF. Then, the FA protocol shall be started between the FAs. And the fax apparatus is connected to the line by manual intervention.
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10  Interworking to fixed networksWord‑p. 25

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).
Copy of original 3GPP image for 3GPP TS 23.146, Fig. 6: Network interworking
Figure 6: Network interworking
(⇒ copy of original 3GPP image)
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10.1  Interworking to PSTNWord‑p. 25

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.
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10.2  Interworking to ISDNWord‑p. 25

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.

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