Ovislink OV804WV User Manual page 190

SIP Registrar: maintains mappings from names (user ID) to
addresses. How can an invite call identify you from so many
users who use SIP to communication? The secrete is your user
ID, which you have registered on the SIP registrar. SIP proxy
uses user ID routes the coming call to your POTS.
NOTE: SIP server usually has SIP proxy and SIP registrar's
function.
Figure 153 SIP application
4.6.1.2 SIP Call Flows
Registration
SIP user agent sends a register message to registrar server,
containing its SIP URL and location. Registrar server stores the
binding of the two in its database, named location database.
When other request provides a SIP URL and queries this
database for the corresponding location, location database
server responds with the IP address.
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