More IIUC notes. As always, feel free to correct as needed.
To match inbound calls to a dial peer, CME (and CUCM?) uses the following steps.
- Match DNIS (the dialed number) with the incoming called-address config in the dial peer
- Match the ANI (the calling number or caller ID) with the answer-address config in the dial peer
- Match the ANI with the destination-pattern config in the dial peer
- Match an incoming POTS call to the port config in the dial peer
- Match dial peer 0
Matching dial peer 0 is bad, and it took me an inquiry on Twitter and a buddy to realize why. Here are a few highlights as to why. I believe the full scope of the badness of dial peer 0 is really beyond the IIUC exam.
- It takes whatever codec is sent to it and can't be hard-coded.
- DTMF is sent in the audio stream, so, if you wind up with a G.729 or other highly-compressed codec, you may have problems getting DTMF across successfully.
- IP precedence values are stripped out of the packets, so it's just plain data now.
- RSVP is disabled.
- No application support, so you can't do IVR. [Will AA work?]
- No DID support. This means the wife can't dial your desk with your published number.