If you hate long posts as I always suggest go through this video lesson (click here) Now, we already know that in real SIP world, any UA when it wants to communicate with another UA should take the help of “SIP Proxy Server” - which finds the actual location. Because it is not practically possible to remember all other UA’s addresses. All good till now. The next question which comes to mind is How a Proxy Server able to find contact address of an User Agent(Called Party). Here, Proxy Server takes help of “Location Service”. Location Server Location Service helps in providing the exact location of UA. Location server is a server which records and maintain the contact information of each and every UA with in a typical enterprise. Location Server has its own database, which keeps up-to-date info of each UA by another Service called “Registration Service”. The Server which provides this service called as a “Registrar Service”. Registrar Server This Server