Licensing is another mysterious area in Unified Communication. Each product has its own licensing model.
CUCM license resides on publisher. The 'host ID' in license file needs to match the MAC address of the publisher.
There are three different types of license for CUCM: node license, feature license and device license (DLU). Node license is for server node. Feature license is required for upgrade or CUCM 7 and above. Device license is required to configure devices (such as phones).
CER (Emergency Responder or e911)
CER license resides on publisher and subscriber (if you have CER subscriber). License file on pub needs to match the MAC address of pub. License file on sub needs to match the MAC address of sub.
If you received a "license expired" message on a two-node CER deployment, 99% of the chance you don't have a license for sub (wrong MAC address).
Like CUCM, CUPS also has node license and device license. Node license resides on CUPS publisher. Device license resides on CUCM (it's just a regular DLU license).
Node license could contain proxy or PE (Presence Engine) or both.