rfc983.txt

RFC 相关的技术文档

Cass & Rose                                                    [Page 14]



RFC 983                                                       April 1986
ISO Transport Services on Top of the TCP


                          P E E R   S T A T E S

   state        event                   action                      goto
   -----        -----                   ------                      ----
   P0           TCP: data ready         TCP: read TPKT
                                        parse, on error
                                          TCP: send DR, close
                                          SS: T-DISCONNECT          end
                                                .INDICATION
                                        code is DT
                                          SS: T-DATA.INDICATION      P0
                                        code is ED
                                          SS: T-EXPEDITED DATA       P0
                                                .INDICATION
                                        code is DR
                                          TCP: close
                                          SS: T-DISCONNECT          end
                                                .INDICATION
                                        otherwise
                                          TCP: send DR, close
                                          SS: T-DISCONNECT          end
                                                .INDICATION

   P0           TCP: other              TCP: close
                                        SS: T-DISCONNECT            end
                                                  .INDICATION

   P0           SS: T-DATA.REQUEST      TCP: send DT                 P0

   P0           SS: T-EXPEDITED DATA    TCP: send ED                 P0
                        .REQUEST

   P0           SS: T-DISCONNECT        TCP: send DR, close         end
                        .REQUEST

   P0           SS: other               TCP: send DR, close
                                        SS: T-DISCONNECT            end
                                                .INDICATION











Cass & Rose                                                    [Page 15]



RFC 983                                                       April 1986
ISO Transport Services on Top of the TCP


6.  Packet Format

   Two TS-peers exchange information over a TCP connection by
   encapsulating information in well-defined packets.  A packet, denoted
   as "TPKT" in the previous sections, is viewed as an object composed
   of an integral number of octets, of variable length.

      NOTE:  For the purposes of presentation, these objects are shown
      as being 4 octets (32 bits wide).  This representation is an
      artifact of the style of this memo and should not be interpreted
      as requiring that a TPDU be a multiple of 4 octets in length.

   A packet consists of two parts: a packet-header and a pseudo-TPDU.
   The format of the header is constant regardless of the type of
   packet.  The format of the pseudo-TPDU follows the [ISO-8073]
   recommendation very closely with the exceptions listed below.  As per
   [ISO-8073], each TPDU consists of two parts: header and data.

   It is EXTREMELY important to observe that TPKTs represent
   "indivisible" units of data to the TS-user.  That is, a
   T-DATA.REQUEST initiated by the TS-user at the sending end of a
   connection should result in exactly one T-DATA.INDICATION being
   generated (with exactly that data) for the TS-user at the receiving
   end.  To ensure this behavior, it is critical that any INDICATION
   event resulting from a TPKT be initiated ONLY after the entire TPKT
   is fully received.  Furthermore, exactly one such INDICATION event
   should be generated by the TS-peer.  The packet length field, as
   described below, can accommodate on the order of 65K octets of user
   data.  This should be well above the requirements of the size of any
   SPDU (Session Protocol Data Unit) for any real implementation.  As a
   result, version 1 of this protocol has no need to either fragment or
   re-assemble TS-user data.  If an application arises which requires an
   SPDU of size greater than 65K octets, this memo will be revised.

   The format of the packet-header is as follows:

       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 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      vrsn     |    reserved   |          packet length        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

      1.  vrsn                  8 bits

         This field is always 1 for this memo.


Cass & Rose                                                    [Page 16]



RFC 983                                                       April 1986
ISO Transport Services on Top of the TCP


      2.  packet length         16 bits (min=8, max=65535)

         The length of entire packet in octets, including packet-header.

   The format of the TPDU (to re-phrase from [ISO-8073]) depends on the
   type of a TPDU.  All TPDUs start with a fixed-part header length and
   the code.  The information following after the code varies, depending
   on the value of the code.  In the context of this memo, the following
   codes are valid:

      CR: connect request
      CC: connect confirm
      DR: disconnect request
      DT: data
      ED: expedited data

   The format of a CR or CC TPDU is:

       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 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | header length | code  | credit|     destination reference     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       source reference        | class |options| variable data |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    ...        |      ...      |      ...      |      ...      |
      |    ...        |      ...      |      ...      |      ...      |
      |    ...        |   user data   |      ...      |      ...      |
      |    ...        |      ...      |      ...      |      ...      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

      3.  header length          8 bits (min=6, max=min(254,packet
      length-6))

         The TPDU-header length in octets including parameters but
         excluding the header length field and user data (if any).











Cass & Rose                                                    [Page 17]



RFC 983                                                       April 1986
ISO Transport Services on Top of the TCP


      4.  code                   4 bits

         The type of TPDU.  Values, in the context of this memo, are:

            value       meaning
            -----       -------
             14         CR: connection request  (binary 1110)
             13         CC: connection confirm  (binary 1101)
              8         DR: disconnect request  (binary 1000)
             15         DT: data                (binary 1111)
              1         ED: expedited data      (binary 0001)
            all other   reserved                             

      5.  credit                 4 bits

         This field is always ZERO on output and ignored on input.

      6.  destination reference 16 bits

         This field is always ZERO on output and ignored on input.

      7.  source reference      16 bits

         This field is always ZERO on output and ignored on input.

      8.  class                  4 bits

         This field is always 4 (binary 0100) on output and ignored on
         input. It is anticipated that future versions of this protocol
         will make use of this field.

      9.  options                4 bits

         This field is always ZERO on output and ignored on input.

      10.  variable data        (header length - 6) octets

         This portion of the TPDU is of variable length.  For most
         TPDUs, this portion is empty (the header length field of the
         TPDU is exactly 6).  The contents of the variable data consist
         of zero or more "parameters".  Each parameter has the following
         format:

            parameter code        1 octet in size
            parameter length      1 octet in size, value is the number
                                    of octets in parameter value
            parameter value       parameter data


Cass & Rose                                                    [Page 18]



RFC 983                                                       April 1986
ISO Transport Services on Top of the TCP


         Normally, the parameter length is 1 octet.  Any implementation
         conforming to this version of the protocol must recognize all
         parameter types listed in [ISO-8073].  With the exception of
         the parameters listed below, these parameters are simply
         ignored.

         o   Parameter name:       Transport service access point
                                   identifier (TSAP-ID) of the client
         TSAP

            Parameter code:        193 (binary 1100 0001)
            Parameter length:      variable
            Parameter value:       TSAP-ID attributes

            Each TSAP-ID consists of 1 or more attributes.  Each
            attribute has this format:

               Attribute code      1 octet in size
               Attribute length    1 octet in size, value is the number
                                     of octets in attribute value
               Attribute value     attribute data

            In version 1 of this protocol, only two attributes are
            defined. All others are reserved.

               Attribute name:     Internet Address

               Attribute code:     1
               Attribute length:   6
               Attribute value:    IP address (4 octets)
                                   session port (2 octets, unsigned
                                   integer)

                  This attribute is ALWAYS required.  Values for session
                  port can be found in Appendix A of this memo.

               Attribute name:     Internet Address for Expedited Data

               Attribute code:     2
               Attribute length:   6
               Attribute value:    IP address (4 octets)
                                   TCP port (2 octets, unsigned integer)

                  This attribute is required ONLY if expedited data is
                  to be exchanged.  The attribute value is an <IP
                  address, TCP port> pair designated by the TS-peer for
                  use with expedited data.


Cass & Rose                                                    [Page 19]



RFC 983                                                       April 1986
ISO Transport Services on Top of the TCP


         o   Parameter name:       TSAP-ID of the server TSAP

            Parameter code:        194 (binary 1100 0010)
            Parameter length:      variable
            Parameter value:       TSAP-ID attributes

         o   Parameter name:       Additional option selection

            Parameter code:        198 (binary 1100 0110)
            Parameter length:      1
            Parameter value:       additional flags

            The additional flags octet consists of 8-bits of optional
            flags.  Only one bit is of interest to this memo, the
            remaining bits should be ZERO on output and ignored on
            input.  This bit indicates if the transport expedited data
            service is to be used.  If this bit is set (bit mask 0000
            0001) or this parameter does not appear in the TPDU, then
            the expedited data service is requested.  If this parameter
            appears in the TPDU and the bit is not set then the service
            is disabled.  If the service is requested, then the TSAP-ID
            of the sender of the TPDU must include an attribute
            indicating the internet address to use for expedited data.

         o   Parameter name:       Alternative protocol classes

            Parameter code:        199 (binary 1100 0111)

            Parameter length:      variable
            Parameter value:       64 (binary 0100 0000) in each octet

               This is used as a NOOP in the variable data.  Its use is
               HIGHLY discouraged, but for those implementors who wish
               to align the user data portion of the TPDU on word (or
               page) boundaries, use of this parameter for filling is
               recommended.

      11.  user data            (packet length - header length - 5)
                                   octets

         This portion of the TPDU is actual user data, most probably one
         or more SPDUs (session protocol data units).







Cass & Rose                                                    [Page 20]



RFC 983                                                       April 1986
ISO Transport Services on Top of the TCP


   The format of a DR TPDU is:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | header length | code  | credit|     destination reference     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       source reference        |     reason    | variable data |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+