[Sip-implementors] Need of location server

[Ashwani Kumar Kesharwani]

Why is location server needed in the SIP. When all the registration information is in Registrar itself,  then why it is needed that registrar will first tell this information to location server and then location server will tell this information to proxy or redirect servers. Why not these informations could directly be fetched by registrar itself.     One more thing, is there any information exchange between registrars of two domains. If not then how does one registrar will know the information about a user of other domain. if yes then how is this information exchanged.   Please clarify Thanks in Advance Ashwani