Hello Fedex/pharden,
What pharden said is correct, to be more accurate it is documented here:
ATA 186 3.2 Admin guide
http://www.cisco.com/en/US/docs/voice_ip_comm/cata/186_188/3_0/english/administration/guide/sccp/sccpaape.html#wp1061348
The problem:
So basically when the ATA186 is configured on CCM to use G729 it can only support one g729 call, and the other port will use G711 always no matter what we do (that is due to the ATA DSP capabilities), what we can tweak is which port will be affected by this behavior by changing the LBRcodec parameter, clearly this will not solve the problem - only change which port will be affected - but at least it will help you out to understand the situation better.
Now why the ATA is using G729? which is basically what is causing this due to the ATA limitation explained above. There might be a diferent number of reasons, maybe because the ATA is on a remote site where the bandwidth savings of the G729 codec are benign but in the other hand causes this problem.
The Solution:
There are 2 possible:
1- Make sure that the ATA devices have a hardware XCODER available on the Media Resource Group List (as of now MRGL), the fact that you get a fast busy is due to a codec issue (the second port supports only G711 and the gateway probably only supports G729 or the Region configuration says that between the ATA and the GW only G729 should be used).
So if a transcoder is available it will be use to XCODE and the second port will work as well, make sure to do update/reset on the second port once you assign the proper MRGL.
2- The solution is to use G711ulaw on the second port always (once again there might be a reason to use G729 on both ports of the ATA and if you are not willing to use G711 on the second port then don't bother reading the rest of the post), how do we change this?
As you probably know each port shows up on CCM as different devices (different MAC addresses) when you do a search for devices.
Look at the Device Pool assigned to both ports, most likely they are under the same Device Pool (as of now referred as DP), this DP has a region assigned (on the DP config on CCM), the region pretty much says wich codec will be used, between devices on this region and devices on another region.
Look for the Voice Gateway on CCM where the calls are being sent out to the PSTN, then look for the DP, take note of that DP, look for the config of that DP and check the region assigned to that DP.
Now its time to compare, the region of the DP where the second port is assigned and the region of the DP where the Gateway is assigned.
You will need to make sure that the regions talk one to the other G711, if they don't - which I bet is the current situation - change it so that both talk G711 one to another.
Keep in mind that this will affect all the devices on that DP (because the same region is assigned to this DP) and probably some other IP phones are on this same DP, so if you do not want to affect the other devices, create a new DP with a new region and ensure that the new region and the region of the GW talk G711.
If the Voice gateway is MGCP you should be done by now and calls from the second port will work just fine.
If the Gateway is H323 or SIP you will need to define the inbound voip dial peer, and add a voice-class so that it supports G711 besides G729
Both ATA ports on CCM should be assigned to
device is assigned on CCM to a Device Pool
Hope that this helps!
