I have some problem when I try to send a fax message from a system
with a Fax connected to another system also with a Fax connected.i –
Problem occurred when sending the fax from PSTN FAX to GSM FAX. When
sending fax from PSTN FAX to GSM FAX, if I check the RING incoming to
GSM FAX, the ring comes as "+CRING: VOICE". It should come as "+CRING:
FAX". Shouldn’t it?
Yes of course, here the problem is due to the PSTN that has not
requested a FAX call on the GSM network and therefore the GSM network
reports the call incoming from the PSTN as the default VOICE service.
This occurs especially when the call is issued through a not configured
ISDN PABX. Note that if the PSTN number calling is analog (not ISDN) and
its service is promiscuous (voice/data/fax depending from the device
which issued the call), the GSM network has no means of recognizing the
service you are requiring and therefore it chooses the default voice.
Once the call incomes with a VOICE signature, then there’s no means for
any GSM device to answer it as FAX since it has different network
protocols. Usually to overcome this problem the Network Operator gives
to a Voice/Data/Fax enabled SIM three different numbers, one for
outcoming/incoming VOICE service, one for the incoming DATA calls and
one for the incoming FAX calls. In this case you must call the right
number and the call will be forwarded by the network as the requested
As a general comment, everything is explained in the FAX
class 1 operation specification by ITU-T T.31, other information on Fax
service is contained in the ITU-T T.4 e T.30 specifications. Refer to
these for FAX class 1 operation.
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