rfc89.txt

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   which makes good use of them (in this case a PDP-1 which displays
   them).  (7)  Then the MITDG program either terminates, returns
   control back to the image (as in this case), or waits for more data
   and/or program.  The protocol was implemented in the hosts and used
   to run a Harvard-assembled version of the E&S Aircraft Carrier
   Program (written originally by Harvard's Prof. Cohen) at MITDG and to
   display the resulting dynamic display on Harvard's PDP-1 driven DEC
   scopes.  The Carrier Program was 'flown' from MITDG and the changing
   views thus generated appeared both at MITDG and Harvard.  The picture
   was observed to change (being transmission limited) on the order of
   twice each second (perhaps less often).  But all was not rosey:

   First, it was observed that during the experiment prompting messages
   to the IMP-Teletypes were often garbled.  Most of the garbling can be
   attributed to the ASR-33 itself, some cannot.  There were no errors
   detected during data transmissions not involving the IMP-Teletypes.

   Second, during attempts to fly the Carrier from Harvard, we stumbled
   across a yet undiagnosed intermittent malfunction of (presumably) the
   MITDG hardware and/or software which caused our network connection to
   be totally shut down by the system during bi-directional
   transmission.  This problem is currently under investigation.





Metcalff                                                        [Page 4]

RFC 89            SOME HISTORIC MOMENTS IN NETWORKING    19 January 1971


   Third, the response of the total system was slow compared to that
   required to do real-time dynamic graphics.  One would expect that if
   this limitation is to be overcome, higher bandwidth transmission
   lines, faster host response to network messages, and/or perhaps a
   message priority system will be required.














































Metcalff                                                        [Page 5]

RFC 89            SOME HISTORIC MOMENTS IN NETWORKING    19 January 1971


36-Bit Words Transmitted
From Harvard's PDP-10 to
MITDG's PDP-10
                     +---------------+---------------+ Image control
                     |     -count    |    origin-1   | word.
                     +---------------+---------------|-
        Image:       |    start address of results   | | Filled in by
                     +-------------------------------+  -Harvard's
        Image+1:     |     end address of results    | | program during
                     +-------------------------------+-  its execution.
        Image+2:     |   ---------unused-----------  |  +--        -+
                     +-------------------------------+  |Filled in  |
        Image+3:     |      program stop address     |<-|by MITDG   |
                     +-------------------------------+  |for return |
        Image+4:     |     program start address     |  |of control.|
                     +-------------------------------+  +--       --+
        Image+5:     |                               |
                     +-------------------------------+
Image control word   |                               |
and image arrive in  |                               |
network size buffers |                               |
which are stripped of|                               |
marking and padding  |                               |
and concatenated.    |                               |
                     +-------------------------------+


36-Bit Words Transmitted
From MITDG's PDP-10 to
Harvard's PDP-1
                      +---------------+---------------+
                      |               |    count      |
                      +---------------+---------------+
First word of results |                               |
Specified in Image+0. |                               |
                      |      results                  |
                      |                               |
                      |                               |
                      |                               |
                      |                               |
                      |                               |
                      |                               |
Last word of results  |                               |
specified in Image+1. |                               |
                      +-------------------------------+






Metcalff                                                        [Page 6]

RFC 89            SOME HISTORIC MOMENTS IN NETWORKING    19 January 1971


General Comments

   In producing 'network ASCII messages' we were required to bend over
   backwards to insert marking so that our last data bit could fall on a
   word boundary.  Surely there must be a better way.  The double
   padding scheme and its variants with or without marking should be
   considered.  Given the current hardware, it would seem that double
   padding with marking would be an improvement.  A simple(?) fix to
   host IMP interfaces enabling them to send only good data from a
   partially filled last word would permit a further improvement:
   marking and host-supplied single padding.

   In these initial experiments Harvard used the IMP-Teletype message
   convention or what are call 'IMP ASCII messages' (without marking)
   because it would allow them to use IMP-Teletypes for logging in and
   testing.  Multics, on the other hand, used the standard network
   message format (with marking) to have Host-Host compatibility as per
   accepted protocols.  Both approaches have merit.  The IMP-Teletype
   message format should be changed to conform with the network standard
   - it should have marking.

   Finally, we would like to announce our readiness to participate in
   experiments which will further extend our confidence and competence
   in networking, especially experiments which, like the preceding, will
   have very large returns with relatively small investment.

Roster of those participating

   Ben Barker              Harvard, BBN
   Grenville Bingham       MITDG
   Howard Brodie           MITDG
   Dan Cohen               Harvard
   Tim Knight              MITDG, MIT/AI
   John McQuillan          Harvard
   Bob Metcalfe            MITDG, Harvard
   Ed Meyer                Multics
   Mike Padlipsky          Multics
   Tom Skinner             Multics
   Ed Taft                 Harvard


          [This RFC was put into machine readable form for entry]
          [into the online RFC archives by Lorrie Shiota, 10/01]








Metcalff                                                        [Page 7]