Cisco ATA problem with fax

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Jul 13th, 2009
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Dear cisco team,

We're experienced problem with fax using ATA-186. We've tested either using fax relay or pass-through. When using fax relay, the ATA-186 can't disconnected the call to/from fax machine. And if we using fax pass-through, the fax machine only can receive half of the page with good conditions. Please advice..

For your additional information, we are using UCM 7.0 and router 3845 (using MGCP).

thanks fo your kid help

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f_rojo Tue, 07/14/2009 - 05:01
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In my experience FAX passthrough over G.711 works ok. Check the clock in the E1/T1 interface. You should avoid slips in the E1/T1 clock, if that happens you will have that type of issues.

I have tested it with H323.

Jonathan Schulenberg Tue, 07/14/2009 - 06:38
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    2017 IP Telephony

The ATA does not support fax relay (Cisco or T.38) or fax passthrough. The only option supported is modem passthrough. Note this is a Cisco proprietary NSE-based negotiation.

Also there are settings you must adjust on the ATA if you will be using it for fax.

Cisco ATA 186 and Cisco ATA 188 Analog Telephone Adaptor Administrator's Guide, Configuring and Debugging Fax Services:


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