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SIP provides a mechanism for forwarding, or redirection of incoming calls. A UAS can redirect an incoming INVITE by responding with a 3xx class message such as 302 (Moved Temporarily). This response contains a contact header field with one or more URIs with new addresses that should be tried. The call flow below demonstrates a call being forwarded.
In this example, UA1 sends an INVITE to UA2. UA2 wants to forward the call to another location, so it responds with a 302 Moved Temporarily message with the URI of UA3 in the contact header field. UA1 then sends an ACK to UA2 to acknowledge receipt of the 302 and ends that transaction. UA1 then sends a new INVITE to UA3 using the URI that it learned from the contact header field of the 302 response.