Transferring (Referring) a Session
Session transfer (or refer) is allowed only on existing sessions that are voice, video, or multiparty IM with only two participants. Call transfer can be initiated by either party in the session and each party decides independently whether to maintain the call until the transfer is complete.
The recipient of a transferred call can look at the session cookie and the URI of the party that referred the session to determine whether to accept the call. The party that is being transferred is notified of the transfer and has the option to accept or reject the transfer.