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Faxing using ATA's and/or VG's

Running into a situation with fax machines.  I am in the process of pulling all of our fax machines into the VOIP environment versus individual POTS lines for each fax.  I am able to fax between two ATA attached fax machines or an ATA attached and a VG attached within my local site using 4 digit dialing with no problem, but when I try to do the same to another location I receive a status sheet indicating a hang up or line failure.  All sites are part of the same VOIP infrastructure, with a publisher and subscriber at our main site and a subscriber at a secondary site.  There is a gateway (3900) at each location. The senior UC engineer and myself believe it is something on the gateways between sites, but we have not figured out what we are missing.  Any thoughts or ideas will be appreciated.  Thanks.


It is very important that the

It is very important that the faxing method, such as T38, fax pass-through, etc., match between the ATAs, VG analog devices, and the PSTN voice gateways.  If it doesn't match, you could have issues with faxing.  The specific settings will depend on the exact equipment, protocols, and PSTN connection.



If you're using a digital

If you're using a digital trunk to the PSTN (e.g. ISDN) check where you are clocking from.


Faxes, etc. are *very* sensitive to clocking errors. You often don't notice it on voice calls.



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