ATA 186 Issue to send faxes

Unanswered Question
Apr 4th, 2010


I have an issue with ATA 186 to send faxes. I have tried many things, but the fax sending  is unsuccessful. I am not a VoIP expert, so it is pretty hard to me to identify the difference between some commands. This is the topology of the network:

Fax Machine --- ATA ---- CCM ---- VoIPGW --- E1(PSTN)

I have the following values in ATA:

AudioMode: 0x00120012

ConnectMode: 0x00008400

This is the dial-peer configured to that Fax:

dial-peer voice 1010 voip
call-block translation-profile incoming 110
call-block disconnect-cause incoming call-reject
preference 1
destination-pattern 1044
voice-class h323 1
session target ipv4:
dtmf-relay cisco-rtp h245-signal h245-alphanumeric
codec g711ulaw
fax rate disable
fax protocol pass-through g711ulaw
no vad

Aditionaly I had the following lines in VoIPGW:

ccm-manager fax protocol cisco
mgcp fax t38 ecm

Recently I changed to:

no ccm-manager fax protocol cisco
mgcp fax t38 inhibit

Not sure if I missing something, in the other hand I would like to know which is the different between  fax protocol pass-through g711ulaw and modem passthrough nse codec g711ulaw

Thanks for your comments....

I have this problem too.
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jrounkles Fri, 04/16/2010 - 09:19

Have you found a solution to this yet? We are having the same problem.

dbarboza27 Sat, 04/17/2010 - 15:56


Actually I dont have a solution to this issue.

I opened a TAC Case last december, and after many tests, Cisco Engineer told me that this is a limitation. The workaround that he gave me is to avoid use ATA to connect faxes. I am absolutely dissapointed about this.

Final message, " Dont buy ATA"

Walter Solano Sun, 04/18/2010 - 12:18


There is one relly important detail on this matter, is the fax machine a super G3 fax machine? this is because as you mention there are some limitation for the ATAs to work with fax machines and modems, this is because the device was not designed for this purpose.}

In the follow link you could find some information about the ATA configuration for faxing:

Another important detail is check if your gateway supports the type of faxing that you are trying to do

Finally this are the configuration steps for you voice gaway:



Walter    Solano

CCNA Voice

UCCX Specialis

Tracy Larson Mon, 04/19/2010 - 10:14

We use ATA's for faxing all over the place. One thing that we noticed is when doing this you can only use the G711 codec on one port and the other port has to be G729. Try setting that up and see if it works for you.


Only one port can be G.729 not both ports if you are faxing across a WAN link, the other will have to be G.711 or another codec.

Walter Solano Mon, 04/19/2010 - 12:49

That is correct if you are doing fax passthrough you should G.711 to avoid any issue during the swich over.


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