Showing results for 
Search instead for 
Did you mean: 

Cisco ATA 187 inbound Fax not working



We used to have cisco ATA 186 for Fax machines with Pass through mode which worked fine with both inbound and outbound mode. Wherein we had configured audio mode parameters on ATA 186.

But now using ATA 187 for the same place and same config. Only out bound Fax to PSTN is happening while inbound call gets established but drops after about 5-10 seconds.

We are having  H.323/225 trunks with service provider using codec g.729 for Voice calls but g.711ulaw pass through for fax calls. There is no problem with Cisco ATA 186 on same platform but 187 is not working fro inbound calls.

We are using CUCM v8.0.3.

Since 186 is no more avilabale we have to use 187

I would really like to know how we can solve this.



11 Replies 11

Marcel Ammann


The ATA 187-I1 provides multiple impedance, such as 600 ohm for American SKU, 900 ohm for European SKU, 220 ohm (820 ohm || 120nF) for Australian SKU, and so on.

In a customer environment in germany we set it to 220 ohm (820 ohm || 120nF).

Kind regards,

Marcel Ammann

Hi Marcel Ammann

Thanks for the response. Do you know any idea for impedence for UK. I have tried all available otions in the setting for impedance..


i have set the impendance in my home office to 270 Ohm + (750 Ohm || 150 nF). Also i have set Fax-Mode to Fax-Pass-through.

Please post you gateway configuration.

Kind regards,

Marcel Ammann


As I mentioned in my post we have H.225 trunk from service provider. We do not have any gateway in our DC. All PSTN voice reaches to us over MPLS from Service provider gateways.

We do not have access to any gateway config. how ever I have log files received from Servcie provider. I can post them if you want..


could you post your Trunk-Configuration (Screenshots)? Also you can send it via PM.

I have the same problem this weekend with a back2back sip trunk. We disabled the MTP on the Trunk and then inbound fax works.

Also if you use a CUBE (i know you use H225) with greater version 15 you must add the IPs of the endpoints to the CUBE trustlist.

Kind regards,



we do not have any CUBE either as it was not required as per design. following are screen shots.


Did you ever find a solution for this? We are having the same problem.

No not really. Infact C&W came back with statement that they will

not support it as they have not tested it yet.

They said they were not aware of the fact that 186 is EOL. So now we are going to use VG202 and 204's for the same function.

hi all,

i've remarked a particular behaviour on the ATA 187. when it has already established a logical media channel negotiated with g.711alaw the ATA sends a SIP/SDP invite to change the media for g.711ulaw, which make the channel to breakdown as we don't do media renegotiation. so i guess it's a ATA 187 bug, it was not supposed to send a SIP/SDP invite when RTP is already opened.

even this happens it's supposed to work with g.711ulaw with your network was designed for g.711u.

hope it helps something



Did anybody find a solution for the incoming dropped calls after 5 seconds? I am facing the same issue: Outgoing calls ok, incoming are being drop by the ATA.

We are using passthrough because some devices involved do not support T.38.

we fixed it with new ata firmware release...

Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community:

Recognize Your Peers