This section describes the operation of various PPTP control connection functions and the Control Connection messages which are used to support them. The protocol operation of the control connection is simplified because TCP is used to provide a reliable transport mechanism. Ordering and retransmission of messages is not a concern at this level. The TCP connection itself, however, can close at any time and an appropriate error recovery mechanism must be provided to handle this case.
Some error recovery procedures are common to all states of the control connection. If an expected reply does not arrive within 60 seconds, the control connection is closed, unless otherwise specified. Appropriate logging should be implemented for easy determination of the problems and the reasons for closing the control connection.
Receipt of an invalid or malformed Control Connection message should be logged appropriately, and the control connection should be closed and restarted to ensure recovery into a known state.