Users configure their devices (IP phones, AV conferencing tools, Instant Messaging tools) to connect to a selected Server when they go on-line.
Each user has a unique "XMPP identifier" or "SIP identifier", also called AOR (Address of Record).
For session-less protocols such as SIP, the Server registers the users by remembering their "SIP identifier" and the network (IP) addresses they use.
Each user may have several registrations active if that user has several communication devices in the on-line mode (an office IP Phone, a desktop computer, an instant messaging program on a laptop, etc.)
Registrations allow SIP users to communicate with each other without the knowledge of the network addresses being used, using just the "SIP identifiers" (AORs).
AORs have the same form as E-mail addresses: username@domainName. The CommuniGate Pro user AOR is the full name of the user Account, so the user SIP AOR name is exactly the same as the user E-mail address.