Patent ID: 8230109

Claim:
A method of handling a Session Initiation Protocol message in a communications network, the method comprising: at a node in the network, receiving a Session Initiation Protocol message, the Session Initiation Protocol message comprising a Request-URI header; rewriting the Request-URI header in the Session Initiation Protocol message, wherein in the event of the rewriting being caused by a rerouting or translation operation, adding information to the Session Initiation Protocol message, the information identifying a target address prior to the rewriting, and in the event of the rewriting being caused by a retarget operation, determining whether information identifying a target address prior to rewriting from a previous rewriting operation is present in the message and, if so, replacing the information identifying the target address with the target address after the rewriting, adding a tag associated with an entry in a History-Info header of the message, the tag indicating that the entry arose from a re-target operation, removing existing taps associated with a previous target address entered in the History-Info header, and associating a tag with the current target address entered in the History-Info header; and sending the Session Initiation Protocol message to a further node.