SIP registrar accepts SIP user registrations allows one or more IP addresses to be associated with a particular SIP URI ■SIP redirect server redirect a SIP client session to a new SIP URI Location server maintains the location database for registered SIP user agents ◼ SIP registrar accepts SIP user registrations allows one or more IP addresses to be associated with a particular SIP URI ◼ SIP redirect server redirect a SIP client session to a new SIP URI ◼ Location server maintains the location database for registered SIP user agents