rfc780.txt

RFC 相关的技术文档

               E: 500, 421
            CONT
               S: depends on previous command
               F: depends on previous command
               E: 500, 501, 502, 504, 421
            ABRT
               S: 201,
               E: 500, 501, 502, 504, 421

































Sluizer & Postel                                               [Page 27]


                                                                        
May 1981                                                         RFC 780
Mail Transfer Protocol                                                  



   5.4.  STATE DIAGRAMS

      Following are state diagrams for a very simple minded MTP
      implementation.  Only the first digit of the reply codes is used.
      There is one state diagram for each group of MTP commands.

      The command groupings were determined by constructing a model for
      each command and then collecting together the commands with
      structurally identical models.

      For each command there are three possible outcomes:  "success"
      (S), "failure" (F), and "error" (E). In the state diagrams below
      we use the symbol B for "begin", and the symbol W for "wait for
      reply".

      First, the diagram that represents most of the MTP commands:

         
                                  1,3    +---+
                             ----------->| E |
                            |            +---+
                            |
         +---+    cmd    +---+    2      +---+
         | B |---------->| W |---------->| S |
         +---+           +---+           +---+
                            |
                            |     4,5    +---+
                             ----------->| F |
                                         +---+
         

         This diagram models the commands:

            HELP, MRCP, MRSQ, NOOP, QUIT, ABRT.















[Page 28]                                               Sluizer & Postel


                                                                        
RFC 780                                                         May 1981
                                                  Mail Transfer Protocol



      A more complex diagram models the MAIL command:

         
                              ABRT       +---+ 1,3
                 CONT ---- ------------->| W |-------
                     |    |              +---+       |
                     |    |1           4,5|  |2      V
         +---+  cmd   -->+---+ 2          |  |     +---+
         | B |---------->| W |-------------------->| E |
         +---+           +---+        ------------>+---+
                         3| |4,5     |    |  |
                          | |        |    |  |
            --------------  ------   |    |  |
           |                      |  |    |   ---->+---+
           |               ----------------------->| S |
           |              |       |  |    |        +---+
           |              |  --------     |
           |              | |     |       |
           V             2| |1,3  |       |
         +---+   text    +---+    |        ------->+---+
         |   |---------->| W |     --------------->| F |
         +---+           +---+-------------------->+---+
                              4,5


         Note that the "text" here is a series of lines sent from the
         sender to the receiver with no response expected until the last
         line is sent.





















Sluizer & Postel                                               [Page 29]


                                                                        
May 1981                                                         RFC 780
Mail Transfer Protocol                                                  



   5.5.  DETAILS

      5.5.1.  MINIMUM IMPLEMENTATION

         In order to make MTP workable, the following minimum
         implementation is required for all receivers:

            COMMANDS -- MAIL
                        QUIT
                        NOOP

      5.5.2.  TRANSPARENCY

         Without some provision for data transparency the character
         sequence "<CRLF>.<CRLF>" ends the the mail text and cannot be
         sent by the user.  In general, users are not aware of such
         "forbidden"  sequences.  To allow all user composed text to be
         transmitted transparently the following procedures are used.

         1. Before sending a line of mail text the sender-MTP checks the
         first character of the line.  If it is a period, one additional
         period is inserted at the beginning of the line.

         2. When a line of mail text is received by the receiver-MTP it
         checks the the line.  If the line is composed of a single
         period it is the end of mail.  If the first character is a
         period and there are other characters on the line, the first
         character is deleted.

      5.5.3.  SIZES

         There are several objects that ought to have defined maximum
         sizes.

            user

               The maximum total length of a user name is 40 characters.

            host

               The maximum total length of a host name or number is 20
               characters.







[Page 30]                                               Sluizer & Postel


                                                                        
RFC 780                                                         May 1981
                                                  Mail Transfer Protocol



            path

               The maximum total length of a sender-path or
               receiver-path is 100 characters.

            command line

               The maximum total length of a command line including the
               command word and the <CRLF> is 200 characters.

            reply line

               The maximum total length of a reply line including the
               reply code and the <CRLF> is 65 characters.

            text line

               The maximum total length of a text line including the the
               <CRLF> is 1000 characters.

         To the maximum extent possible implementation techniques which
         impose no limits at all to the length of these objects should
         be used.


























Sluizer & Postel                                               [Page 31]


                                                                        
May 1981                                                         RFC 780
Mail Transfer Protocol                                                  



APPENDIX A

   TCP Transport service

      The Transmission Control Protocol [1] is used in the ARPA
      Internet, and in any network following the US DoD standards for
      internetwork protocols.

      Connection Establishment

         The MTP transmission channel is a TCP connection established
         between the sender process port U and the receiver process port
         L.  This single full duplex connection is used as the
         transmission channel.  This protocol is assigned the service
         port 57 (71 octal), that is L=57.

      Data Transfer

         The TCP connection supports the transmission of 8-bit bytes.
         The MTP data is 7-bit ASCII characters.  Each character is
         transmitted as a 8-bit byte with the high-order bit cleared to
         zero.



























[Page 32]                                               Sluizer & Postel


                                                                        
RFC 780                                                         May 1981
                                                  Mail Transfer Protocol



APPENDIX B

   NCP Transport service

      The ARPANET Host-to-Host Protocol [2] (implemented by the Network
      Control Program) may be used in the ARPANET.

      Connection Establishment

         The MTP transmission channel is established via NCP between the
         the sender process socket U and receiver process socket L.  The
         Initial Connection Protocol [3] is followed resulting in a pair
         of simplex connections.  This pair of connections is used as
         the transmission channel.  This protocol is assigned the
         contact socket 57 (71 octal), that is L=57.

      Data Transfer

         The NCP data connections are established in 8-bit byte mode.
         The MTP data is 7-bit ASCII characters.  Each character is
         transmitted as a 8-bit byte with the high-order bit cleared to
         zero.



























Sluizer & Postel                                               [Page 33]


                                                                        
May 1981                                                         RFC 780
Mail Transfer Protocol                                                  



APPENDIX C

   NITS