[ih] NCP and TCP implementations

Tony Finch dot at dotat.at
Wed Jul 22 08:40:57 PDT 2020

the keyboard of geoff goodfellow via Internet-history <internet-history at eli...:

> can anyone recall WHO and/or WHERE it was that had their NCP (don't think
> it was TCP) implementation apparently running in "user space" as a job or
> process (as opposed to as part of the OS/Kernel) and "complained" how much
> it was co$ting them/their departments budget to be connected to the ARPANET?

Sounds like MULTICS. I read Mike Padlipsky's Elements of Networking Style
a few months ago, and I'm fairly sure he had some choice words about
Multics and ARPANET billing, probably the exact incident mentioned in
RFC425? Despite the lack of index I found it at the end of chapter 4:

> Again, the Multics NCP, in its reluctance to "waste interrupt time",
> employed a specific process wake-up to handle the [ECO] command. When
> the network bills tripled one week, the cause soon became apparent - all
> those ECOs. Now even though it is not germane to detail just how much
> trouble this one caused before it was finally resolved, the point for
> present purposes should be clear: Even after protocols are properly
> designed, documented, and implemented, problems can be engendered by
> their use in ways not concieved of by the designers.

Well that advice has aged well :-)

Also, https://multicians.org/mx-net.html - section 2.2.1 NCP

> The Network Control Program daemon originally ran in Ring 1 on the 645,
> resulting in incredible amounts of overhead and $ charges to the ARPANET
> group for running the NCP. This stemmed from the fact that the ARPANET
> was considered a research project at the time and not part of the
> System. Later, as the ARPANET became more accepted, execution of the NCP
> daemon functions was moved into Ring 0, and the greatest consumer of
> daemon resources in the NCP, the handling of ALLOC (data space
> allocation) messages, was done at interrupt time in the IMP DIM (in a
> violation of what would later be understood as strict protocol layering,
> but, heck, it saved $$ AND improved performance).

f.anthony.n.finch  <dot at dotat.at>  http://dotat.at/
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