Despite your are environmental engineer ;-), I will try to explain what captured data mean. But before it, I downloaded your file, removed irrelevant packets (packets belonging to other device) and attached resulting file here.
Green numbers in paragraphs bellow are reference to packet number in the attached file. In the following text, the term ATA will be used for your SPA112, term phone will mean the analog phone device connected to it.
OK, lets start.
Packets [2] is INVITE packet, announcing the incomming connection to you. Packets [5] and [90] are "100 Trying" and "183 Ringing" responses to the INVITE. The first one mean nothing for us, the second inform the caller your side is ringing (caller should got the ringback tone from it's phone).
So, what happened on your side in real ?
Your ATA has started to send ringing signal to your phone ([41]) 0.1 second before it responded '183 ringing' [90] to caller.
So there has been no noticeable delay between caller's view about your ringing state and ATA ringing signal. Once more - you phone received ringing signal here [41], caller has been informed and should listen ring-back tone here [90].
If you phone remained silent, then it decided not to ring despite ringing signal.
It's not bug but feature.
Caller ID data are transferred ([97] - [106]) between first and second ring. Some phones supress first ring waiting for caller-id data. It's true especially for advanced phones like FSMS capable phones, phones with custom selection of distinct rings, phones with black lists and so on. Such kind of phone need to know the caller info for decision "to ring or not to ring" and for selection of ring type (if decided to ring).
So, the first ring seems to be stolen by phone. The second ring start [107] 5.9s past first ring.
I assume you heared this second ring as your's phone entered [113] off hook state.
Phone becomed off-hook at 9.3 second past first ring = 3.4 second past second ring. The caller has been informed within 0.05 sec [126] about it. Ringback tones had been turned off at caller side, call entered 'established' phase.
Conclusion ? Phone seems to mute first ring, causing 6 second of minimal delay (you are not aware about incoming call untill second ring started). Such delay doesn't hurt in most cases. If you want to avoid it, you need configure your phone not to mute first ring. Most of phones allow such kind of configuration. Problem can't be solved by ATA configuration. Search phone's documentation how disable first ring skip.
Hope it help.
Message was edited by: Dan Lukes - I attached filtered version of capture file and modified accordingly the packet numbers in text.
