[COFF] Fwd: [ih] NCP and TCP implementations

[Warner Losh]

>>>  In addition to the Berkeley BSD work, I remember Gurwitz, Wingfield,
Nemeth, and others working on TCP implementation for the PDP-11/70 and Vax.

This is new. I'd like more info The name Nemeth is interesting. Is that
Evi? And does that body of code still exist?

>>> I think I speak authoritatively here, since I wrote and debugged that
first Unix TCP code.   I still have an old, yellowing listing of that first
Unix TCP.

I wonder if you could write him and see if this listing can be scanned /
preserved...

Warner

On Tue, Mar 10, 2020 at 11:52 AM Clem Cole <clemc at ccc.com> wrote:

>
> Given the recent discussion of pipes and networking ...  I'm passing this
> along for those that might not have seen it.
>
> ---------- Forwarded message ---------
> From: Jack Haverty via Internet-history
> Date: Tue, Mar 10, 2020 at 1:30 PM
> Subject: Re: [ih] NCP and TCP implementations
> To: *Internet-History*
>
>
> The first TCP implementation for Unix was done in PDP-11 assembly
> language, running on a PDP-11/40 (with way too little memory or address
> space).   It was built using code fragments excerpted from the LSI-11
> TCP implementation provided by Jim Mathis, which ran under SRI's
> home-built OS.  Jim's TCP was all written in PDP-11 assembler.  The code
> was cross-compiled (assembled) on a PDP-10 Tenex system, and downloaded
> over a TTY line to the PDP-11/40.  That was much easier and faster than
> doing all the implementation work on the PDP-11.
>
> The code architecture involved putting TCP itself at the user level,
> communicating with its "customers" using Unix InterProcess
> Communications facilities (Rand "Ports").   It would have been
> preferable to implement TCP within the Unix kernel, but there was simply
> not enough room due to the limited address space available on the 11/40
> model.  Later implementations of TCP, on larger machines with twice the
> address space, were done in the kernel.  In addition to the Berkeley BSD
> work, I remember Gurwitz, Wingfield, Nemeth, and others working on TCP
> implementation for the PDP-11/70 and Vax.
>
> The initial Unix TCP implementation was for TCP version 2 (2.5 IIRC), as
> was Jim's LSI-11 code.  This 2.5 implementation was one of the players
> in the first "TCP Bakeoff" organized by Jon Postel and carried out on a
> weekend at ISI before the quarterly Internet meeting.  The PDP-11/40 TCP
> was modified extensively over the next year or so as TCP advanced
> through 2.5, 2.5+, 3, and eventually stabilized at TCP4 (which it seems
> we still have today, 40+ years later!)
>
> The Unix TCP implementation required a small addition to the Unix kernel
> code, to add the "await" and "capac" system calls.  Those calls were
> necessary to enable the implementation of user-level code where the
> traditional Unix "pipeline" model of programming
> (input->process->process...->output) was inadequate for use in
> multi-computer programming (such as FTP, Telnet, etc., - anywhere where
> more than one computer was involved).
>
> The code to add those new system calls was written in C, as was almost
> all of the Unix OS itself.  The new system calls added the functionality
> of "non-blocking I/O" which did not previously exist.  It involved very
> few lines of code, since there wasn't room for very many more
> instructions, and even so it required finding more space by shortening
> many of the kernel error messages to save a few bytes here and there.
>
> Randy Rettberg and I did that work, struggling to understand how Unix
> kernel  internals worked, since neither of us had ever worked with Unix
> before even as a user.   We did not try to "get it right" by making
> significant changes to the basic Unix architecture.  That came later
> with the Berkeley and Gurwitz efforts.  The PDP-11/40 was simply too
> constrained to support such changes, and our mission was to get TCP
> support on the machine, rather than develop the OS.
>
> I think I speak authoritatively here, since I wrote and debugged that
> first Unix TCP code.   I still have an old, yellowing listing of that
> first Unix TCP.
>
> FWIW, if there's interest in why certain languages were chosen, there's
> a very simple explanation of why the Unix implementation was done in
> assembler rather than C, the native language of Unix.  First, Jim
> Mathis' code was in assembler, so it was easy to extract large chunks
> and paste them into the Unix assembler implementation.  Second, and
> probably most important, was that I was very accustomed to writing
> assembler code and working at the processor instruction level.  But I
> barely knew C existed, and was certainly not proficient in it, and we
> needed the TCP working fast for use in other projects.  The choice was
> very pragmatic, not based at all on technical issues of languages or
> superiority of any architecture.
>
> /Jack Haverty
>
>
> On 3/9/20 11:14 PM, vinton cerf via Internet-history wrote:
> > Steve Kirsch asks in what languages NCP and TCP were written.
> >
> > The Stanford first TCP implementation was done in BCPL by Richard Karp.
> > Another version was written for PDP-11/23 by Jim Mathis but not clear in
> > what language. Tenex was probably done in C at BBN. Was 360 done in
> PL/1??
> > Dave Clark did one for IBM PC (assembly language/??)
> >
> > Other recollections much appreciated.
> >
> > vint
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