rfc2637.txt

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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Length             |      PPTP Message Type        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Magic Cookie                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Control Message Type      |           Reserved0           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Call ID            |       Peer's Call ID          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Result Code  |  Error Code   |          Cause Code           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Connect Speed                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Packet Recv. Window Size    |    Packet Processing Delay    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Physical Channel ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Length                   Total length in octets of this PPTP message,
                            including the entire PPTP header.

   PPTP Message Type        1 for Control Message.

   Magic Cookie             0x1A2B3C4D.

   Control Message Type     8 for Outgoing-Call-Reply.

   Reserved0                This field MUST be 0.

   Call ID                  A unique identifier for the tunnel, assigned
                            by the PAC to this session.  It is used to
                            multiplex and demultiplex data sent over the
                            tunnel between the PNS and PAC involved in
                            this session.

   Peer's Call ID           This field is set to the value received in
                            the Call ID field of the corresponding
                            Outgoing-Call-Request message.  It is used
                            by the PNS to match the Outgoing-Call-Reply
                            with the Outgoing-Call-Request it issued. It
                            also is used as the value sent in the GRE
                            header for mux/demuxing.







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RFC 2637        Point-to-Point Tunneling Protocol (PPTP)       July 1999


   Result Code              This value indicates the result of the
                            Outgoing-Call-Request attempt.  Currently
                            valid values are:

                                  1 (Connected) - Call established with
                                    no errors

                                  2 (General Error) - Outgoing Call not
                                    established for the reason indicated
                                    in Error Code

                                  3 (No Carrier) - Outgoing Call failed
                                    due to no carrier detected

                                  4 (Busy) - Outgoing Call failed due to
                                    detection of a busy signal

                                  5 (No Dial Tone) - Outgoing Call
                                    failed due to lack of a dial tone

                                  6 (Time-out) - Outgoing Call was not
                                    established within time allotted by
                                    PAC

                                  7 (Do Not Accept) - Outgoing Call
                                    administratively prohibited

   Error Code               This field is set to 0 unless a "General
                            Error" condition exists, in which case
                            Result Code is set to 2 and this field is
                            set to the value corresponding to the
                            general error condition as specified in
                            section 2.2.

   Cause Code               This field gives additional failure
                            information.  Its value can vary depending
                            upon the type of call attempted.  For ISDN
                            call attempts it is the Q.931 cause code.

   Connect Speed            The actual connection speed used, in
                            bits/second.

   Packet Recv. Window Size The number of received data packets the PAC
                            will buffer for this session.







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RFC 2637        Point-to-Point Tunneling Protocol (PPTP)       July 1999


   Packet Processing Delay  A measure of the packet processing delay
                            that might be imposed on data sent to the
                            PAC from the PNS.  This value is specified
                            in units of 1/10 seconds.  For the PAC, this
                            number is related to the size of the buffer
                            used to hold packets to be sent to the
                            client and to the speed of the link to the
                            client.  This value should be set to the
                            maximum delay that can normally occur
                            between the time a packet arrives at the PAC
                            and is delivered to the client.  See section
                            4.4 for an example of how this value is
                            determined and used.

   Physical Channel ID      This field is set by the PAC in a vendor-
                            specific manner to the physical channel
                            number used to place this call.  It is used
                            for logging purposes only.

2.9.  Incoming-Call-Request

   The Incoming-Call-Request is a PPTP control message sent by the PAC
   to the PNS to indicate that an inbound call is to be established from
   the PAC.  This request provides the PNS with parameter information
   for the incoming call.

   This message is the first in the "three-way handshake" used by PPTP
   for establishing incoming calls.  The PAC may defer answering the
   call until it has received an Incoming-Call-Reply from the PNS
   indicating that the call should be established. This mechanism allows
   the PNS to obtain sufficient information about the call before it is
   answered to determine whether the call should be answered or not.



















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RFC 2637        Point-to-Point Tunneling Protocol (PPTP)       July 1999


       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Length             |       PPTP Message Type       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Magic Cookie                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Control Message Type      |           Reserved0           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Call ID            |      Call Serial Number       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                       Call Bearer Type                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Physical Channel ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Dialed Number Length      |     Dialing Number Length     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                   Dialed Number (64 octets)                   +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                  Dialing Number (64 octets)                   +
      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      +                    Subaddress (64 octets)                     +
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Length                   Total length in octets of this PPTP message,
                            including the entire PPTP header.

   PPTP Message Type        1 for Control Message.

   Magic Cookie             0x1A2B3C4D.

   Control Message Type     9 for Incoming-Call-Request.

   Reserved0                This field MUST be 0.

   Call ID                  A unique identifier for this tunnel,
                            assigned by the PAC to this session.  It is
                            used to multiplex and demultiplex data sent
                            over the tunnel between the PNS and PAC
                            involved in this session.





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RFC 2637        Point-to-Point Tunneling Protocol (PPTP)       July 1999


   Call Serial Number       An identifier assigned by the PAC to this
                            session for the purpose of identifying this
                            particular session in logged session
                            information.  Unlike the Call ID, both the
                            PNS and PAC associate the same Call Serial
                            Number to a given session. The combination
                            of IP address and call serial number should
                            be unique.

   Bearer Type              A value indicating the bearer capability
                            used for this incoming call.  Currently
                            defined values are:

                                  1 - Call is on an analog channel

                                  2 - Call is on a digital channel

   Physical Channel ID      This field is set by the PAC in a vendor-
                            specific manner to the number of the
                            physical channel this call arrived on.

   Dialed Number Length     The actual number of valid digits in the
                            Dialed Number field.

   Dialing Number Length    The actual number of valid digits in the
                            Dialing Number field.

   Dialed Number            The number that was dialed by the caller.
                            For ISDN and analog calls this field is an
                            ASCII string.  If the Dialed Number is less
                            than 64 octets in length, the remainder of
                            this field is filled with octets of value 0.

   Dialing Number           The number from which the call was placed.
                            For ISDN and analog calls this field is an
                            ASCII string.  If the Dialing Number is less
                            than 64 octets in length, the remainder of
                            this field is filled with octets of value 0.

   Subaddress               A 64 octet field used to specify additional
                            dialing information.  If the subaddress is
                            less than 64 octets long, the remainder of
                            this field is filled with octets of value 0.








Hamzeh, et al.               Informational                     [Page 27]

RFC 2637        Point-to-Point Tunneling Protocol (PPTP)       July 1999


2.10.  Incoming-Call-Reply

   The Incoming-Call-Reply is a PPTP control message sent by the PNS to
   the PAC in response to a received Incoming-Call-Request message.  The
   reply indicates the result of the incoming call attempt.  It also
   provides information to allow the PAC to regulate the transmission of
   data to the PNS for this session.

   This message is the second in the three-way handshake used by PPTP
   for establishing incoming calls.  It indicates to the PAC whether the
   call should be answered or not.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Length             |       PPTP Message Type       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Magic Cookie                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Control Message Type      |           Reserved0           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Call ID            |       Peer's Call ID          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Result Code  |  Error Code   |   Packet Recv. Window Size    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Packet Transmit Delay     |           Reserved1           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Length                   Total length in octets of this PPTP message,