one way fax transmission over DID

[999said999]

Hello,
We can send fax through DID (with the service provider) to any PSTN line with no problem. Also, we can receive fax from a GSM modem (in area where there is no land line, a sim card with fax/data feature is used with the GSM modem that gives a fax/telephone port) connected to a fax machine, but we can not send fax to that same GSM modem.
Any ideas? should we change any of our PRI parameters ?
Thanks

 

[hippster2001]

Did this problem just start? We have found that sometimes when the CO changes out to a VoIP switch that it causes havoc on our modems and fax machines. Often they compress too much. In one instance, faxes had problems on a PRI but no problems on copper.