A Session Initiation Protocol (SIP) session dialog is established between a first user agent and a second user agent. The SIP server receives an in-dialog message for the SIP session dialog. At this point, the SIP server is no longer aware of the SIP session dialog, for example, because the SIP server was rebooted. In response to receiving the in-dialog message, the SIP server sends a request not found message to the first user agent that comprises a server accessible value. The SIP server receives an out-of-dialog SIP REFER message. The out-of-dialog SIP REFER message comprises call state information for the SIP session dialog and is sent based on the server accessible value. The SIP server sends the out-of-dialog SIP REFER message to the second user agent. The SIP session dialog is reestablished. The SIP server can be a SIP proxy server or a Back-to-Back User Agent.