8 Signalling aspects

03.463GPPTechnical Realization of Facsimile Group 3 Service - non transparentTS

GSM 07.03 identifies the bearer capability requirements to be supported by the terminal adaptation function in the MT (see GSM 07.01 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 GSM 02.03 and 07.01.

8.1 Handling of tonal signals

Because the CCITT defined service uses modems, there are some signals received from the analogue link at the MSC/IWF and (where used) the fax adaptor which do not have a direct binary representation. These signals cannot therefore be passed across the radio interface in the same way as the CCITT Recommendation T.30 and CCITT Recommendation T.4 information.

These signals are the modem called (CED) and calling (CNG) tones sent at the start of each fax data phase of the call; they are generated locally by the FA/MT and/or FA/IWF, exploiting an end‑to‑end time alignment mechanism, triggered by appropriate messages on the GSM signalling channel. The procedure is detailed in the following.

8.2 Call establishment

8.2.1 Mobile terminated call

The PSTN facsimile group 3 terminal may be manually or automatically calling.

8.2.1.1 Speech then facsimile

Refer to the diagram in figure II.1a/03.46 and II.1b/03.46. In both of the figures the initial call setup is mobile terminated. In figure I.1a/03.46 the DCD is also mobile terminated (MT), while the DCD in figure I.1b/03.46 is mobile originated (MO).

In order to make the transition from the speech phase to the facsimile phase, the MODIFY command must be initiated by MMI at the MS.

In the case where a GSM facsimile machine is used, it will turn on circuit 108/2 when it is connected to the line by manual intervention.

In the case where a fax adaptor at MT is used, it will turn on circuit 108/2, when the mobile fax apparatus is connected to the line by manual intervention.

After determination of the DCD and ICM (see subclause 6.4) and on completion of the synchronization process over the radio interface or the RLP establishment, CT107 shall be turned on by the MT; in case where a FA is used, on receipt of CT107 from MT, the FA will complete the tonal handshaking according to the rules in subclause 6.4.

The analogue link at the FA/IWF side will be established in accordance with the T.30 rec.; provided the synchronization process is completed (CT108.2 ON condition), the appropriate tone according to the rules in subclause 6.4 shall be transmitted. In case of DCD mobile terminated the CED tone shall be transmitted after a silence of 1.8 to 2.5 sec (see T.30, 4.3.3.2) from the call being answered; during transmission of CED tone (2.6 sec minimum duration, followed by a delay period of 75 +/‑ 20 ms) the FA/IWF will process data received from the GSM‑TCH as usual, but relevant information (e.g. preamble of a BCS frame) shall be discarded without any buffering. Note that circuit 109 and circuit 106 (according CCITT Recommendation V.24) at the R interface of the MT must be turned on by the fax adaptor at the IWF before any further procedure can be carried out between the fax adaptors and consequently end‑to‑end. Once the connection is established, both circuit 106 and circuit 109 are clamped to the ON condition by the fax adaptor at the IWF, so fixing a full duplex mode throughout the whole facsimile phase of the call.

8.2.1.2 Auto answer

Refer to diagram in figure II.2/GSM 03.46. A call received from the PSTN will cause the MT to turn on circuit 125 (according to CCITT Recommendation V.24) at the R interface.

In the case where a GSM facsimile machine is used, CCITT Recommendation V.25bis auto answering process is handled directly by turning on circuit 108/2.

In the case where a fax adaptor is used, circuit 125 will cause ring current to be sent to the mobile facsimile terminal. The fax adaptor will turn on circuit 108/2, when the mobile facsimile terminal answers the call.

On receipt of circuit 108/2, the MT will answer the call and initiate the synchronization process and the establishment of the RLP across the radio interface. On completion of the synchronization process or RLP establishment, the modem at IWF will automatically be selected and send CED to PSTN facsimile terminal. Also circuit 107 shall be turned on by the MT.

In the case where a fax adaptor is used, on receipt of circuit 107 from MT, the fax adaptor will initiate the tonal hand‑shake by sending CNG (mandatory).

The analogue links at both the PSTN side and the mobile side (where a fax adaptor is used) will be established in accordance with the appropriate V. series recommendation.

Note that circuit 109 and circuit 106 at the R interface of the MT must be turned on by the fax adaptor at the IWF before any further procedure can be carried out between the fax adaptors and consequently end‑to‑end. Once the connection is established, both circuit 106 and circuit 109 are clamped to the ON condition by the fax adaptor at the IWF, so fixing a full duplex mode throughout the whole facsimile phase of the call.

8.2.2 Mobile originated calls

The PSTN facsimile group 3 terminal may be manually or automatically answered.

8.2.2.1 Speech then facsimile

Refer to the diagram in figure II.3a/03.46 and figure II.3b/03.46. In both of the figures the initial call setup is mobile terminated. In figure II.3a/03.46 the DCD is also MO, while in figure II.3b/03.46 the DCD is MT.

In order to make the transition from the speech phase to the facsimile phase, the MODIFY command must be initiated by MMI at the MS, which will result in an establishment of the RLP across the radio interface and connection to line of the FA/IWF.

In the case where a fax adaptor is used, the mobile facsimile terminal must be connected to line by manual intervention at this stage, and will cause the fax adaptor to turn on circuit 108/2 (according to CCITT Recommendation V.24) towards the MT.

In the case where a GSM facsimile machine is used, circuit 108/2 shall be turned on when the GSM facsimile machine is connected to line by manual intervention.

After determination of the DCD and ICM (see subclause 6.4) and on completion of the synchronization process across the radio interface or the establishment of RLP, the modem at the IWF will be automatically selected and send the appropriate modem tone according to the rules in subclause 6.4 to PSTN facsimile terminal. Also circuit 107 shall be turned on by the MT, whereupon the FA/MT will complete the tonal handshaking according to the rules in subclause 6.4.

In the case where a fax adaptor is used, the receipt of circuit 107 shall cause the fax adaptor to connect to line.

The analogue links at both the PSTN side and the mobile side (where a fax adaptor is used) will be established in accordance with the appropriate CCITT V. series recommendation.

Note that circuit 109 and circuit 106 at the R interface of the MT must be turned on by the fax adaptor at the IWF before any further procedure can be carried out between the fax adaptors and consequently end‑to‑end. Once the connection is established, both circuit 106 and circuit 109 are clamped to the ON condition by the fax adaptor at the IWF, so fixing a full duplex mode throughout the whole facsimile phase of the call.

8.2.2.2 Auto calling

Refer to diagram in figure II.4/GSM 03.46. The auto calling procedure of CCITT Recommendation V.25bis is initiated at the CCITT Recommendation V.24 interface. This is done either directly from the GSM facsimile machine or, in the case where a fax adaptor is used, by loop disconnect or DTMF dialling information between the mobile facsimile terminal and the fax adaptor.

When the call is answered, the synchronization process will be started and the RLP will be established across the radio interface.

On completion of the synchronization process across the radio interface or RLP establishment, the modem at the IWF will be automatically selected and send CNG (mandatory) to PSTN facsimile terminal. Also CT107 shall be turned on by the MT.

In the case where a fax adaptor is used, the receipt of circuit 107 shall cause the fax adaptor to connect to line.

The analogue links at both the PSTN side and the mobile side (where a fax adaptor is used) will be established in accordance with the appropriate V. series recommendation.

Note that circuit 109 and circuit 106 (according to CCITT Recommendation V.24) at the R interface of the MT must be turned on by the fax adaptor at the IWF before any further procedure can be carried out between the fax adaptors and consequently end‑to‑end. Once the connection is established, both circuit 106 and circuit 109 are clamped to the ON condition by the fax adaptor at the IWF, so fixing a full duplex mode throughout the whole facsimile phase of the call.

8.2.2.3 Manual calling

Refer to diagram in figure II.5/GSM 03.46. When the call is answered, the RLP will be established across the radio interface providing circuit 108/2 in ON condition.

In the case where a fax adaptor is used, the mobile facsimile terminal must be connected to line by manual intervention at this stage, and will cause the fax adaptor to turn on circuit 108/2 (according to CCITT Recommendation V.24) towards the MT.

In the case where a GSM facsimile machine is used, circuit 108/2 shall be turned on when the GSM facsimile machine is connected to line by manual intervention.

On completion of the synchronization process across the radio interface or RLP establishment, the modem at the IWF will be automatically selected and send CNG (mandatory) to PSTN facsimile terminal. Also circuit 107 shall be turned on by the MT.

In the case where a fax adaptor is used, the receipt of circuit 107 shall cause the fax adaptor to connect to line.

The analogue links at both the PSTN side and the mobile side (where a fax adaptor is used) will be established in accordance with the appropriate CCITT V. series recommendation.

Note that circuit 109 and circuit 106 at the R interface of the MT must be turned on by the fax adaptor at the IWF before any further procedure can be carried out between the fax adaptors and consequently end‑to‑end. Once the connection is established, both circuit 106 and circuit 109 are clamped to the ON condition by the fax adaptor at the IWF, so fixing a full duplex mode throughout the whole facsimile phase of the call.