[ih] Nit-picking an origin story

[vinton cerf]

Even back in the 1970-1972 period, some of my experiments with Bob Kahn
showed that the ARPANET IMPs were capable of adaptive alternate routing so
that I was able to inject about 80 kb/s of traffic from UCLA destined for
SRI that switched between a direct route and an indirect one through Santa
Barbara even though the direct and indirect paths had at most 50 kb/s each.

v


On Tue, Aug 19, 2025 at 4:50 PM Jack Haverty via Internet-history <
internet-history at elists.isoc.org> wrote:

> On 8/18/25 07:00, John Day via Internet-history wrote:
> > This last one I think doesn’t get enough credit. It is a very small
> thing, but I think was a major contribution to the success of the ARPANET.
> It would have worked at 2.4 or 9.6, but been so glacially slow as to have
> been considered not successful. At 50Kbps, we could do real work that was
> way beyond what people expected. Not to take anything away from the great
> software development that went into the IMPs and the NCPs, etc. I really
> think this gets too little credit for the success.
> Performance was also an issue as the ARPANET grew and traffic
> increased.  One of the limiting factors to performance was the routing
> algorithm.   Packets were always sent on the "shortest" path.   But that
> meant that the aggregate performance was also limited to 56kb/sec, which
> was the maximum line speed of any path. Even after there were multiple
> possible routes across the US, routing would typically only utilize one
> path, whichever was shortest at the time.
>
> There was a lot of analysis, simulation, and testing done over the 80s
> as the IMP's internal algorithms were improved.  One ot the targets was
> "multipath routing", which meant figuring out a way to use more than
> just the shortest path between two IMPs and their attached host
> computers.  That would enable hosts to get more than 56KB/sec throughput
> across the 'net, as well as improve the overall efficiency of use of the
> expensive longhaul circuits.
>
> Such issues were also present in the Internet of course.  A similar
> desire existed to be able to use more than one path through the
> Internet.  The ICCB's "To Do List" contained items such as "Multipath
> Routing" and "Expressway Routing" in the early 1980s. But there couldn't
> be much progress on that since the Internet routing, at that time,
> didn't have any real notion of "shortest path", but used the simple
> metric of "hop counts" as an interim metric for decisions on datagram
> routes.
>
> Most people likely haven't seen much info about the internal algorithms
> used inside the ARPANET, which were captured in reports to the
> government sponsors but not so much in RFCs et al.
>
> There's some large reports on the "ARPANET Routing Improvements" work
> done circa 1980.  One of the reports is online in PDF form at
> https://apps.dtic.mil/sti/html/tr/ADA121350/index.html  Others are
> probably online in DTIC as well, for any historians interested in the
> inner workings of the ARPANET and how it evolved over its lifetime.
>
> Jack Haverty
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