6 Signalling aspects

3GPP43.045Release 17Technical realization of facsimile group 3 transparentTS

3GPP TS 27.003 identifies the BC/LLC/HLC requirements to be supported by the MT.

In case of Teleservice 61 (Alternate Speech/Facsimile), both "Speech" and "Group 3 facsimile" Bearer Capability Information Elements (BC-IE) are necessary to set up the call; the sequence order in which these BC-IEs are transmitted identifies the service to be provided first by the PLMN. For Mobile Originated calls, the MT indicates in the SETUP message the first requirement e.g. speech, by sending this as the first BC-IE; for an "autocalling" facsimile request, the "Group 3 Facsimile" BC-IE is sent as the first one.

For Mobile Terminated calls, the MT may change the order of BC­IEs and send them back in the CALL CONF message.

In case of Teleservice 62, a single BC-IE ("Group 3 Facsimile") is used.

Interworking between Teleservice 61 and 62 is specified in 3GPP TS 22.003 and 3GPP TS 27.001.

6.1 Handling of Tonal Signals

Because the ITU-T defined service uses modems, there are some signals received from the analogue link at the 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 T.30 and 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 FA/IWF, exploiting an end‑to‑end time alignment mechanism, triggered by appropriate messages on the PLMN signalling channel. The procedure is detailed in the following.

6.2 Call establishment

The PSTN Facsimile apparatus may be manually or automatically calling.

6.2.1 Mobile Terminated Call – Speech then Fax

Refer to diagrams in figure II‑5a/43.045 and II‑5b/43.045. In both of the figures the initial call setup is mobile terminated. In figure II‑5a/43.045 the data call direction is also mobile terminated, in figure II‑5b/43.045 it is mobile originated.

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 PLMN facsimile machine is used, it will turn on CT108.2 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 CT108.2 when the mobile Fax Apparatus is connected to the line by manual intervention.

After determination of the data call direction and ICM (see subclause 4.3.1) and on completion of the synchronization process over the radio interface, CT107 shall be turned on by the MT; in the case where a Fax Adaptor is used, on receipt of CT107 from MT, the Fax Adaptor will complete the tonal handshaking according to the rules in subclause 4.3.1. The analogue link at FA/IWF side will be established in accordance with the T.30 Recommendation; provided the synchronization process is completed (CT108.2 ON condition), the appropriate tone according to the rules in subclause 4.3.1 shall be transmitted. In case of data call direction "mobile terminated" the CED tone shall be transmitted after a silence time 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 m/sec) the IWF/FA will process data received from GSM‑TCH as usual, but the relevant information (e.g. preamble of a BCS frame) shall be discarded without any buffering.

Note that CT109 and CT106 at the R interface of the MT must be in the ON condition before any further procedure can be carried out end-to-end between the Fax Adaptors; therefore, as soon as the synchronization process over the radio interface is completed, both CT109 and CT106 (MT side) are clamped to the ON condition by the FA/IWF (by setting the appropriate status bits in the V.110 frame), so fixing a full-duplex mode throughout the whole data phase of the call.

6.2.2 Mobile Terminated Call – Auto answer

Refer to the diagram in figure II‑6/43.045.

A call received from the PSTN will cause the MT to turn on CT125 at the R interface.

In the case where a PLMN facsimile machine is used, V.25bis auto answer process is handled directly by turning on CT108.2. In the case where a Fax Adaptor is used, CT125 will cause ring current to be sent to the mobile Fax apparatus. The Fax Adaptor will turn on CT108.2 when the mobile Fax Apparatus answers the call.

On receipt of CT108.2, the MT will answer the call and initiate the synchronization process over the radio interface.

On completion of the synchronization process over the radio interface, CT107 shall be turned on by the MT; in the case where a Fax Adaptor is used, on receipt of CT107 from MT, the Fax Adaptor will initiate the tonal handshaking by sending CNG (mandatory).

The analogue link at IWF side shall be established in accordance with the T.30 Recommendation; the same considerations apply as detailed in the previous subclause 6.2.1 for CED transmission.

Note that CT109 and CT106 at the R interface of the MT must be in the ON condition before any further procedure can be carried out end-to-end between the Fax Adaptors; therefore, as soon as the synchronization process over the radio interface is completed, both CT109 and CT106 (MT side) are clamped to the ON condition by the FA/IWF.

6.2.3 Mobile Originated Call – Speech then Fax

Refer to diagrams in figure II‑7a/43.045 and II‑7b/43.045. In both of the figures the initial call setup is mobile originated. In figure II‑7a/43.045 the data call direction is also mobile originated, in figure II‑7b/43.045 it is mobile terminated.

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 a synchronization phase over the radio interface and connection to line of FA/IWF.

In the case where a Fax Adaptor is used, the mobile Fax apparatus must be connected to line by manual intervention at this stage, and will cause the Fax Adaptor to turn on CT108.2 towards the MT. In the case where a PLMN facsimile machine is used, CT108.2 shall be turned on when the PLMN facsimile apparatus is connected to line by manual intervention.

After determination of the data call direction and ICM (see subclause 4.3.1) and on completion of the synchronization process over the radio interface, the modem at IWF will be automatically selected and send the appropriate modem tone according to the rules in subclause 4.3.1 to the PSTN Fax apparatus. Also CT107 shall be turned on by MT, whereupon the FA/MT will complete the tonal handshaking according to the rules in subclause 4.3.1.

Note that CT109 and CT106 at the R interface of the MT must be in the ON condition before any further procedure can be carried out end-to-end between the Fax Adaptors; therefore, as soon as the synchronization process over the radio interface is completed, both CT109 and CT106 (MT side) are clamped to the ON condition by the FA/IWF.

6.2.4 Mobile Originated Call – Auto calling

Refer to the diagram in figure II‑8/43.045.

Over the V.24 interface the autocalling procedure of V.25bis is initiated, using the relevant HDLC format commands. This is done either directly from the PLMN facsimile machine or, in the case where a Fax Adaptor is used, by loop disconnect or DTMF dialling information between the mobile Fax apparatus and the Fax Adaptor.

When the call is answered, a synchronization phase will take place over the radio interface.

On completion of the synchronization process over the radio interface, the modem at IWF will be automatically selected and send CNG (mandatory) to PSTN Fax apparatus. Also CT107 shall be turned on by MT. In the case where a Fax Adaptor is used, the receipt of CT107 shall cause the Fax Adaptor to connect to line.

Note that CT109 and CT106 at the R interface of the MT must be in the ON condition before any further procedure can be carried out end‑to‑end between the Fax Adaptors; therefore, as soon as the synchronization process over the radio interface is completed, both CT109 and CT106 (MT side) are clamped to the ON condition by the FA/IWF.

6.2.5 Mobile Originated Call – Manual calling

Refer to the diagram in figure II‑9/43.045.

When the call is answered a synchronization phase will take place over the radio interface, provided CT108.2 is in ON condition.

In the case where a Fax Adaptor is used, the mobile Fax apparatus must be connected to line by manual intervention at this stage, and will cause the Fax Adaptor to turn on CT108.2 towards the MT.
In the case where a PLMN facsimile machine is used, CT108.2 shall be turned on when the PLMN facsimile apparatus is connected to line by manual intervention.

On completion of the synchronization process over the radio interface, the modem at IWF will be automatically selected and send CNG (mandatory) to PSTN Fax apparatus. Also CT107 shall be turned on by MT. In the case where a Fax Adaptor is used, the receipt of CT107 shall cause the Fax Adaptor to connect to line.

Note that CT109 and CT106 at the R interface of the MT must be in the ON condition before any further procedure can be carried out end-to-end between the Fax Adaptors; therefore, as soon as the synchronization process over the radio interface is completed, both CT109 and CT106 (MT side) are clamped to the ON condition by the FA/IWF.

6.3 Call release

The normal call release procedure will be initiated at the MS, either by the PLMN Facsimile Machine or by the FA/MT, forcing CT108.2 in OFF condition; this will follow DCN frame (disconnect, see subclause 5.2.5 of the present document) occurrence, either sent over the GSM‑TCH towards the remote Fax terminal or received via GSM‑TCH from the remote Fax terminal.

In the former case CT109 will be actually turned OFF after a time delay of 200 m/sec from DCN being sent. In the latter case no delay is necessary before turning CT108.2 in OFF condition; when the received DCN is corrupted and hence undetected in the MS by the FA, the Call Control entity in the MSC/IWF will release the call over the PLMN connection element, following the disconnection over the PSTN.