When you say it is not connecting what exactly do you mean by that? Does the extension ring, but you cannot answer the call as it is immediately dropped or does the extension not ring at all? Those are two very different things and would have different reasons for why it happens. The first one would indicate an issue with codecs and the second an issue with visibility in the calling device assigned CSSs, device and/or line.
If you do a DNA for the calling device what does that say?
To me this sounds like you have an issue with routing of IP traffic to the device at the branch office as it seems like the signaling is not reaching the device at the location where it is situated as it doesn't rings when you call it and that you have one way audio for the other call flow you outlined.
This part however, highlighted makes me somewhat confused on the call path.
Where is the number you are trying to call to located, is it at the branch or at HQ, or at location A and B as you initially referenced them by? For us that does not know your specific system landscape it is somewhat confusing when you switch nomenclature, so please keep it to one style of naming your sites and please be more specific with the description of your call flows. I'd like to say explain it as if the recipient is a five year old, so be as specific as you can as that will help us help you more efficient.
Lets say that the extension you are wanting to call to is located at your location named B. What happens if you assign that directory number to another device on a second line, does that make the call work to the other device? If it does it's not related to call routing configuration, but IP routing of your traffic as that other device would have a different IP than the original device.
Thanks, then it was two different call flows, one from A to B and another from B to A. This is an important distinction. As I wrote earlier this is very likely not a a problem with call routing, but an issue with IP routing for traffic from site A, where I’d assume that your Call manager is located, to site B. This would lead to signaling traffic from CM to not reach the phone in site B, explaining your first error description and also leading to media traffic not working in both directions, resulting in one way audio, and thus explaining your second described issue.
If you want to verify this please setup the same extension on another, working, device and test both call flows again.
