Firstly, upgrade CCA to the latest (3.0(1) as of today) and upgrade the UC540 to software pack to the latest (8.1.0 as of today). Major improvements have been made since version 2.2(2) which is the version that was used to configure your UC540, correct? Also, is this a CCA-only config or was there some CLI involved to get it working? If it's the latter, the issue will be difficult to diagnose. There's a list of 'approved CLI workarounds' but I don't think you need any CLI to get this application working, so it'd best to keep it CCA only.
Based on your call flow example, it sounds like the telco isn't understanding the UC500's connect-signal the first time you pick up, so it just keeps sending the call as if nobody has picked up. I believe this is true because the calling-user hears uninterrupted ring-back tone, correct? Also, since you're not getting caller-id the second time you pick up, that means the telco probably thinks it's the same call because they only send caller-id once per call.
If the above is true, then this is an analog signaling issue. If this is the case, debug voip ccapi wouldn't provide the necessary info because that only outputs info from the VoIP call-control API (see Cisco's Telephony Interface Architecture for more info), which doesn't handle signaling state information of the analog ports. The signaling is handled by the VPM (voice processor module), so you'll need to use 'debug vpm all' (or debug vpm signal) to see what the FXO port is thinking. You may want to run both debugs simultaneously though, to see how the two modules work together.
Lets start with the basics. Here are some questions that may help provide insight into your issue:
-What happens when you connect a simple standard analog phone to that line instead of the UC500? Does the call connect evertime? This will verify the line is OK.
-What would happen if you just set the inbound dial plan to ring one single phone? Running this test will verify it's NOT an analog signaling issue, meaning it's a config issue with the dns/button-assignments.
-What happens on outbound calls? Are outbound calls working perfectly?
-Are you installing this on a new line, or replacing the customer's old PBX over an existing line? If the latter, the telco may have their ports set to connect to a PBX (ground-start) only and not a phone (loop-start --by default, the UC's FXO port appears as a phone to the telco because it's set to loop-start)
-Ask your telco what kind of signaling is running on that line. Is it loop-start or ground-start? Do they want battery-reversal as the connect-signal, etc.? Then check/match those settings in CCA:
-Lastly, hopefully, it'll be fixed after checking the above, but if it still doesn't work, inquire with your telco about the physical condition of the line:
-What is the distance from the telco. Is it really far?
-Is the cabling old or new
-Is the cabling CAT3?
-Do you experience these issues more after it rains?
-Have the telco run a line-test to verify there's no noise on the line.
Good luck!
-Oni
