A REQUEST routed using only IP addresses will reach only one end point—only one device. Since communication is typically user-to-user INSTEAD of device-to-device, a more useful addressing scheme would allow a particular user to call another particular user, which would result in the request REACHING the target user regardless of which he is currently using, or if he has multiple devices.SIP URI is a name that is resolved to an IP ADDRESS by using SIP proxy server and DNS lookups at the time of the call.

A request routed using only IP addresses will reach only one end point—only one device. Since communication is typically user-to-user instead of device-to-device, a more useful addressing scheme would allow a particular user to call another particular user, which would result in the request reaching the target user regardless of which he is currently using, or if he has multiple devices.SIP URI is a name that is resolved to an IP address by using SIP proxy server and DNS lookups at the time of the call.