[ih] Nit-picking an origin story

[Jack Haverty]

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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