rfc2.txt

RFC 的详细文档！


RFC 2


            3b1a2 Several fields may be added and folded in parallel, if
            they are folded appropiately after the addition.

              +---------+---------+---------+---------+
              | FIELD 4 | FIELD 3 | FIELD 2 | FIELD 1 |
              +---------+---------+---------+---------+

              +---------+---------+---------+---------+
              | FIELD 8 | FIELD 7 | FIELD 6 | FIELD 5 |
              +---------+---------+---------+---------+
            ADD
            +-+---------+---------+---------+---------+
            | |         |         |         |         |
            +-+---------+---------+---------+---------+
             |      |        |         |         |
             |      |        |         |         v
             |      |        |         |    +---------+
             |      |        |         |    |         |
             |      |        |         |    +---------+
             |      |        |         |
             |      |        |         \    +---------+
             |      |        |          `-> |         |
             |      |        |              +---------+
             |      |        |
             |      |        \              +---------+
             |      |         `-----------> |         |
             |      |                       +---------+
             |      |
             |      \                       +---------+
             |       `--------------------->|         |
             |                              +---------+
             |
             \                                    +---+
              `-----CARRY------------------------>|   |
                                                  +---+
                                  ADD
                                  +---------+---------+
                                  |         |         |
                                  +--CARRY--+---------+
                                       |
                                       \        +-----+
                                    ADD `-----> |     |
                                                +-----+

                                            +---------+
                                            |         |
                                            +-RESULT--+




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                  3b1a2a Using this scheme, it is assumed that, if there
                  are n fields, the carries from the first n-1 fields
                  are automatically added into the low order position of
                  the next higher field, so that in folding, one need
                  only add the [n] result fields to the carry from the
                  nth field, and then add in an appropiately sized carry
                  from that addition (and repeat the desired number of
                  times to achieve the result.

            3b1a3 A checksum computed in this manner has the advantage
            that the word lengths of different machines may each be used
            optimally:

               3b1a3a If a string of suitable length is chosen for
               computing the checksum, and a suitable checksum field
               length is selected, the checksum technique for each of
               the machines will be relatively optimal.

                  3b1a3a1 Field length: 288 bits (lowest common
                  denomenator of (24,32,36)

                  3b1a3a2 Checksum length: 8 bits (convenient field size
                  for all machines)

         3b1b If a message is divided into groups of fields, and each
         group is checksummed in this manner, an order dependent
         checksum may be got by shifting the checksum for each group,
         and adding it in (successively) to the checksum of the next
         group

   3c A facility will be provided where two HOSTs may enter a mode which
   requires positive verification of all messages. This verification is
   sent over the control link.

4 MONITOR FUNCTIONS

   4a Network I/O drivers

      4a1 Input

         4a1a Input message from IMP.

         4a1b Do error checking on message.

            4a1b1 Verify checksum,

            4a1b2 Send "message recieved" aknowledgement over control
            link if aknowledge mode is in effect.



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RFC 2


         4a1c (trans)character translation

            4a1c1 There is a strong possibility that the character
            translation may be done in the IMP.

            4a1c2 This needs to be explored further with BBN.

            4a1c3 There are two main considerations

               4a1c3a Should the translation be done by table or
               algorithm?

                  4a1c3a1 Initially it seems as though the best way to
                  go is table.

               4a1c3b How should we decide which messages should be
               translated, i.e. is it desirable to not translate
               everything (YES!!) and by what means can we use to
               differentiate?

         4a1d Decode header, and pass message to correct recipient as
         identified by source, and link.

      4a2 Output

         4a2a Build header

         4a2b Character translation

            4a2b1 See remarks under the section on output translation
            (trans).

         4a2c Create checksum

         4a2d Check status of link

            4a2d1 If there has not been a RFNM since the last message
            transmitted out the link, wait for it.

         4a2e Transmit message to IMP

         4a2f If aknowledge mode is in effect,wait for

            4a2f1 RFNM from destination IMP.

            4a2f2 Response from destination HOST over control line 0.





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   4b Network status

      4b1 Maintain status of other HOSTs on network

         4b1a If an IMP is down, then his HOST is considered to be down.

      4b2 Maintain status of control lines.

      4b3 Answer status queries from other HOSTs.

      4b4 Inform other HOSTs as to status of primary and auxilliary
      links on an interrupt basis.

      4b5 Inform other HOSTs as to status of programs using primary and
      secondary links

5 EXECUTIVE PRIMITIVES

   5a Primary Links

      5a1 These require the HOST number as a parameter.

         5a1a Establish primary link

         5a1b Connect controlling teletype to primary link

         5a1c INPUT/OUTPUT over primary link

         5a1d Interrogate status of primary link

            5a1d1 Don't know what, exactly, this should do, but it seems
            as though it might be useful.

         5a1e Disconnect controlling teletype from primary link

         5a1f Kill primary link

   5b Auxilliary Links.

      5b1 Establish auxilliary link.

         5b1a requires the HOST number as a parameter

         5b1b It returns a logical link number which is similar to a
         file index. It is this number which is passed to all of the
         other Auxilliary routines as a parameter.

      5b2 INPUT/OUTPUT over auxilliary link



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RFC 2


      5b3 Interrogate status auxilliary link.

         5b3a Don't know what, exactly, this should do, but it seems as
         though it might be useful.

      5b4 Kill auxilliary link.

   5c Special executive functions

      5c1 Transparent. INPUT/OUTPUT over link

         5c1a This may be used to do block I/O transfers over a link

         5c1b The function of the monitor in this instance is to
         transfer a buffer directly to its IMP

         5c1c At does not modify it in any way

            5c1c1 This means that the header and other control
            information must be in the buffer.

         5c1d The indended use of this is for network debugging.

6 INITIAL CHECKOUT

   6a The network will be initially checked out using the links in a
   simulated data-phone mode.

      6a1 All messages will be one character in length.

      6a2 Links will be transparent to the monitor, and controlled by
      user program via a special executive primitive.

         6a2a The initial test will be run from two user programs in
         different HOSTs, e.g. DDT to DDT.

         6a2b It will be paralleled by a telephone link or similar.


           [  This RFC was put into machine readable form for entry  ]
           [  into the online RFC archives by Robbie Bennet 10/1998  ]
           [  This RFC was nroffed by Kelly Tardif, Viagenie 10/1999 ]









Duvall                                                         [Page 10]