Microsoft Corporation The Session Initiation Protocol (SIP) REFER extension as defined in RFC 3515 automatically establishes a typically short-lived event subscription used to notify the party sending a REFER request about the receiver's status in executing the transaction requested by the REFER. These notifications are not needed in all cases. This specification provides a way to prevent the automatic establishment of an event subscription and subsequent notifications using a new SIP extension header field that may be included in a REFER request. [STANDARDS-TRACK]