Unified communication is one of those terms that are used widely throughout the industry, without anybody exactly knowing what it stands for. It somehow means that the good old PBX is integrated with other IT systems in the company. For example users don't have to enter phone number again, instead they can just click on the number and magically the phone starts to dial that number.
While UC might be fuzzy, the standard that does most of the heavy lifting around it, is everything else than fuzzy: CSTA. It defines a large range of commands that can control the phone system, from such simple commands like starting a call to more esoteric ones like increasing the volume the phone.
We have recently revised our interoperability with the UC plus server from Mondago, which was working already surprisingly well, was missing one call to accept the call while the phone was ringing. Of course there is a CSTA command for this, and the PBX was supposed to make it happen; it just did not work.
The SIP standard did not have that in any RFC, but many phones offer a way to make it happen anyway. We were using snom phones; in the old time they did this right out of the box; but it seems that security concerns were raised: If you are using the phone with a classical SIP proxy, the caller could actually send the talk event through the proxy, and this way easily implement a intercom solution without explicit agreement of the called party. This could turn your phone into a spy microphone. Anyway, the new settings essentially tells the phone that the server that handles the phone makes sure that such proxy messages are not passed through to the phone, which is clearly the case with the Vodia PBX.
After amending the provisioning templates for the snom phones, the phones would now honor the talk notifications and voila! the phones could accept calls now even through the click on the UC plus client. These are the moments when we really appreciate the CSTA protocol and the tools that use them. Next release will ship the new provisioning templates, so that those using snom phones can use the CSTA answer call feature right out of the box.