EE 284 Lecture 11: sip 4
Document Summary
This number is always incremented when a second request of the same type is made for a given call. Indoingso,theproxycanchangetherequest-uri; and will do so if it knows that the. Request-uri should be mapped to a different address: forexample,ifaproxyisalsoaregistrarandisaware of a contact address for a given address of record, then the proxy will change the request-uri of an invite to the appropriate contact address. If it does not, a problem has occurred and the message is discarded: assumingthatthefirstvia:headerfieldindicatesthe proxy itself, then the proxy removes the header and checks to see if a second via: header exists. If not, then the message is destined for the proxy itself. If there is a second via: header field, then the proxy passes the response to the address in that field. Inthisway,theresponsefindsitswaybacktothe originator of the request along the path that was originally taken by the request. the via: header in the example contains a branch parameter.
