[ih] Question re rate of growth of the Arpanet

[John Day]

theRoberts had originally planned to use 2.4Kbps lines. Roger Scantlebury (and others) at the Gatlinburg Operating System Conference in the Fall of 67 (it appears to have been one of *those* bar discussions) ;-) convinced him that given NPL’s experience with their packet-switched network they had found that that was way too slow and he should use 50Kbps.

Both Baran and Davies independently had come to the conclusion that 1.5Mbps would be best but it wasn’t available yet.

There are two things I find amusing about this:
1) The ARPANET would have worked at 2.4 or 9.6, etc. But would have been deemed so slow to prove that the effort wasn’t really successful. At 50K, we could really get work done. Not many systems could sustain that and there weren’t many applications needing all of that. Using 50K was a much larger part of the ARPANET’s success than we often give it credit for.

2) Roger’s experience was for the NPL campus network. I am not sure Roger had any idea what 50K (which were expensive!) would do to Roberts budget for a nation-wide network in the US.  ;-) At the time, most Europeans and many East Coast Americans had no sense of distances in the US. (I remember a tale of 3 IBMers sent from Poughkeepsie to Detroit to work on some customer's system, who thought as long as they were that far West, they could drive to Las Vegas for the weekend.) (!!) ;-) (31 hours now with Interstates which were not complete then.)  Good thing ARPA’s pockets were deep. ;-)

O, and at that conference, Roger convinced Roberts to use packet switching, which he had not heard of. (He did find Baran’s papers in a stack he hadn’t read when he got back to DC.)

Both are great serendipity, that had a profound effect and for the most part lost in history. I always find these kinds of things delightful.

Take care,
John 

> On Apr 21, 2025, at 14:08, the keyboard of geoff goodfellow via Internet-history <internet-history at elists.isoc.org> wrote:
> 
> steve, can you elucidate any history with respect to how/why the speed of
> 50 kb/s was chosen for the ARPANET lines?  were there great speeds
> available then?
> 
> yours truly kinda (perhaps mistakenly) recalls these 50 kb/s "wideband
> circuits of the day" were primarily used for linking tv broadcast affiliate
> stations to/with their motherships (cbs, nbc, abc, ...)?
> 
> geoff
> 
> On Mon, Apr 21, 2025 at 7:26 AM Steve Crocker via Internet-history <
> internet-history at elists.isoc.org> wrote:
> 
>> Thanks for the pointer to RFC 597.
>> 
>> As I looked at it, an aspect I hadn't considered before came to mind.
>> 
>> Installation of an IMP required provisioning 50 kb/s lines to two or three
>> other points.  In the early days, we installed roughly a new IMP once a
>> month.  (The lead time for ordering 50 kb/s lines from AT&T was NINE
>> months.)
>> 
>> Once an IMP was installed, new hosts could be added to the IMP as quickly
>> as the site could build or obtain the host-IMP interface and write or
>> obtain the software for their operating system.
>> 
>> If anyone has the dates for each of the hosts, it would be interesting to
>> compare the growth of IMPs vs growth of hosts.
>> 
>> Steve
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> 
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> Geoff.Goodfellow at iconia.com
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