RFC 1661                Point-to-Point Protocol                July 1994


      unacceptable, and triggers the transmission of a corresponding
      Configure-Nak or Configure-Reject.

      Implementation Note:

         These events may occur on a connection which is already in the
         Opened state.  The implementation MUST be prepared to
         immediately renegotiate the Configuration Options.

   Receive-Configure-Ack (RCA)

      This event occurs when a valid Configure-Ack packet is received
      from the peer.  The Configure-Ack packet is a positive response to
      a Configure-Request packet.  An out of sequence or otherwise
      invalid packet is silently discarded.

      Implementation Note:

         Since the correct packet has already been received before
         reaching the Ack-Rcvd or Opened states, it is extremely
         unlikely that another such packet will arrive.  As specified,
         all invalid Ack/Nak/Rej packets are silently discarded, and do
         not affect the transitions of the automaton.

         However, it is not impossible that a correctly formed packet
         will arrive through a coincidentally-timed cross-connection.
         It is more likely to be the result of an implementation error.
         At the very least, this occurance SHOULD be logged.

   Receive-Configure-Nak/Rej (RCN)

      This event occurs when a valid Configure-Nak or Configure-Reject
      packet is received from the peer.  The Configure-Nak and
      Configure-Reject packets are negative responses to a Configure-
      Request packet.  An out of sequence or otherwise invalid packet is
      silently discarded.

      Implementation Note:

         Although the Configure-Nak and Configure-Reject cause the same
         state transition in the automaton, these packets have
         significantly different effects on the Configuration Options
         sent in the resulting Configure-Request packet.

   Receive-Terminate-Request (RTR)

      This event occurs when a Terminate-Request packet is received.
      The Terminate-Request packet indicates the desire of the peer to




 RFC 1661                Point-to-Point Protocol                July 1994


      close the connection.

      Implementation Note:

         This event is not identical to the Close event (see above), and
         does not override the Open commands of the local network
         administrator.  The implementation MUST be prepared to receive
         a new Configure-Request without network administrator
         intervention.

   Receive-Terminate-Ack (RTA)

      This event occurs when a Terminate-Ack packet is received from the
      peer.  The Terminate-Ack packet is usually a response to a
      Terminate-Request packet.  The Terminate-Ack packet may also
      indicate that the peer is in Closed or Stopped states, and serves
      to re-synchronize the link configuration.

   Receive-Unknown-Code (RUC)

      This event occurs when an un-interpretable packet is received from
      the peer.  A Code-Reject packet is sent in response.

   Receive-Code-Reject, Receive-Protocol-Reject (RXJ+,RXJ-)

      This event occurs when a Code-Reject or a Protocol-Reject packet
      is received from the peer.

      The RXJ+ event arises when the rejected value is acceptable, such
      as a Code-Reject of an extended code, or a Protocol-Reject of a
      NCP.  These are within the scope of normal operation.  The
      implementation MUST stop sending the offending packet type.

      The RXJ- event arises when the rejected value is catastrophic,
      such as a Code-Reject of Configure-Request, or a Protocol-Reject
      of LCP!  This event communicates an unrecoverable error that
      terminates the connection.