[ih] More topology

[Vint Cerf]

Barbara,
I had not realized you were involved in the partitioned network solution.
Wasn't Radia Perlman also engaged on that?

So ELF was the OS for the BCPL gateway. I had forgotten that. Dick Karp at
Stanford did his first TCP in BCPL for our PDP-11/40

v


On Mon, Aug 30, 2021 at 5:07 PM Barbara Denny via Internet-history <
internet-history at elists.isoc.org> wrote:

>  Just a Guess. The Packet Radio station software probably made use of the
> router code base you mention.  The station software was written in BCPL and
> ELF was the operating system.  I don't know the timelines of the router
> development and the Packet Radio station development.  Ginny Strazisar
> (Travers)  probably can clarify this or perhaps Mike Beeler or Jil Westcott.
> barbara
>     On Monday, August 30, 2021, 12:59:28 PM PDT, Noel Chiappa via
> Internet-history <internet-history at elists.isoc.org> wrote:
>
>      > From: Jack Haverty
>
>     > I never did learn how the PE handled RFNMs, in particular how it
>     > interacted with its associated NCP host that it was "stealing" RFNMs
>     > from.
>
> I know a bit about the Port Expander; we were planning on using it at MIT
> at
> one point, since MIT had no spare IMP ports for an IP gateway (router). (We
> didn't get an IMP port for the MIT gateway until MIT got its third IMP, one
> of the first C/30's.) That didn't work out, as I'll explain later.
>
> The PE didn't share the NCP 'host' among connected hosts; all NCP traffic
> coming in from the IMP is sent to the 'main' subsidiary host's port:
>
>   ; WHEN A TYPE 0 OR TYPE 3 MESSAGE IS RECEIVED, FIRST CHECK THE MESSAGE'S
>   ; LINK NUMBER.  IF THE MSG IS NOT ON AN INTERNET LINK, THEN SEND THE MSG
> TO
>   ; THE PORT THAT RECEIVES ALL NON-INET TRAFFIC (PORT INDEX IS IN NCPPRT)
>
> For IP traffic, the PE acts as a gateway (i.e. router), and there's a table
> which says which downstream port various IP hosts are on.
>
> The way it handles RFNM's is that it has a database of "CONNECTION BLOCK"s
> which record messages sent out to the IMP; when a RFNM arrives, it uses the
> CB database to work out the downstream host which originated the message
> the
> RFNM is for; the RFNM is then handed to it.
>
>
> As the above excerpt probably made clear, I still have the PE code (it had
> been squirreled away on the MIT-CSR Unix - I made a full dump of that
> machine
> before it croaked, so we now have access to all that history; I guess I was
> concerned about history even back then).
>
> I don't think I have the _original_, unmodified PE code; what I have is a
> bodged version that I hacked to act as a gateway to the MIT 1 Mbit/sec ring
> LAN. I.e. it did't have any subsidiary hosts attached to 1822 ports; just
> the
> main 1822 port (connected to the IMP) and the LAN. I'm too lazy to
> see exactly what I did with RFNM's there; probably just pitched them
> (no RFNM's on a LAN :-).
>
> While I was looking for that, I ran across some other old code that
> might be interesing:
>
> - the TIU (kind of a predecessor to the TAC, a _very_ early implementation
> of
>   TCP in Macro-11 for the PDP-11, written by Jim Mathis, which I believe
>   was the basis for Jack's first UNIX TCP at BBN);
> - a couple of modules from the BCPL gateway code from BBN (the one that
>   ran under ELF); historically interesting, as it was the very first
>   IP router code _ever_.
>
> If anyone is interested in any of this stuff, let me know and I'll look
> into getting it uploaded and made available.
>
>
> The reason we couldn't get the PE to work was that the SRI 1822 interface
> (which is what were planning to use on our PE) didn't _exactly_
> electrically
> duplicate the IMP 1822 interface; the latter used optp-isolators on the DH
> interface, and the SRI interface didn't have them.
>
> The plan was to put the PE in from of the DM ITS machine, but when
> we tried it, it didn't work. Ken Pogran looked into the issue, and
> discovered that the person who did DM's IMP interface (I wonder who
> that was :-) had done some 'trick' (the exact details of which now
> escape me - it was something to do with the ground he used for the
> DH interface signals),and without the opto-isolators the SRI
> 1822 interface wouldn't talk to it.
>
>
>     Noel
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