Let me see if I get this straight... If I configure the CUP PUBLISH Trunk service parameter to the name of a SIP trunk, then CUCM will send all presence notification for all DN's and users through that trunk, presumably to an CUPS Server. This will also include all user information and license capabilities for each user.
If, however, I leave the CUP PUBLISH Trunk field blank, then the Presence server will have to send a SIP SUBSCRIBE packet to the CUCM for each DN that it is monitoring. And the Presence server will have to send a SUBSCRIBE packet for each device at least every 20 minutes. In return, the CUCM will send a SIP NOTIFY packet to the Presence server whenever a subscribed DN's status changes. Are you will me so far?
So, what we lose by using the SUBSCRIBE/NOTIFY rather than the PUBLISH method is the automatic transfer of user information and capability assignment. Does this mean that if I am not using the SIP PUBLISH trunk, I do not need to update the License Capabilities page on CUCM for CUP and CUPC? Also, can I pull the users from AD (so long as the usernames match, case-sensitive, with the CUCM usernames) and assign the lines and license capabilities within CUPS?
SIP trunk between CUCM and CUPS is for phone presence only.
User information/license does not goes through SIP trunk. They are handled by SyncAgent service on CUPS.
The difference PUBLISH model and SUBSCRIBE/NOTIFY model is:
1) PUBLISH model is supposed to be less chatty (ie. less traffic on the network).
2) PUBLISH model is on line apperance while SUBSCRIBE is on device.
3) You don't have to worry about SUBSCRIBE CSS on PUBLISH model.