pptp-draft.txt

pptp第二层隧道模块

Hamzeh, et al                                                  [Page 24]

Internet Draft                    PPTP                         July 1997


      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.

      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 2.16.

      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.




Hamzeh, et al                                                  [Page 25]

Internet Draft                    PPTP                         July 1997


      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.

      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 Appendix A
                               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.


























Hamzeh, et al                                                  [Page 26]

Internet Draft                    PPTP                         July 1997


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.

       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.



Hamzeh, et al                                                  [Page 27]

Internet Draft                    PPTP                         July 1997


      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.

      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.



Hamzeh, et al                                                  [Page 28]

Internet Draft                    PPTP                         July 1997


      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                                                  [Page 29]

Internet Draft                    PPTP                         July 1997


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, including the entire PPTP
                               header.

      PPTP Message Type        1 for Control Message.

      Magic Cookie             0x1A2B3C4D.

      Control Message Type     10 for Incoming-Call-Reply.

      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