[ih] Question re rate of growth of the Arpanet

[Guy Almes]

Steve, Geoff, et al.,
   I actually find this a very interesting thread and a significant gap 
in (at least) my understanding of how the ARPAnet came to be.

   Although I was an ARPAnet user (as a CMU CS grad student), I only 
became aware of how long-distance digital circuits were provided when 
active in the NSFnet regional networks beginning about 1986.  At that 
time, the key technical, regulatory, and business enablers of the needed 
digital services were:
<> technical: the Bell System's DS0, T1, and eventually T3 services. 
The fact that these T1-based services were (more or less) mature by the 
early 1980s was key for us.
<> regulatory: the breakup of the Bell System about 1984 resulted in 
several competing long-distance carriers, each supporting the T1-based 
services and interoperating with the sort-of-regulated monopoly LECs.
<> business: though there's more to it, the essence is the demand for 
more long-distance telephony capacity.  Many of us remember how 
expensive long-distance was and the famous busy signals on Mother's Day.
   This story is pretty well known in our community.
   But we often forget how fortuitous it was that these two 
"prerequisites" were in place by the mid-80s.

   But this thread makes me aware that the corresponding "prerequisites" 
for the ARPAnet are less well understood.
   What I've found so far is this:
<> technical: Western Electric had, by 1966, developed its 303 Type 
Wideband Data Station.  This technology used a "group" of 12 voice 
channels to provide a 50 kb/s service.  (It could also use a 
"supergroup" of 60 voice channels to provide 250 kb/s or a "half-group" 
of 6 voice channels to provide 19.2 kb/s service.)
<> regulatory: Bell System monopoly, but with the government, 
particularly during the Cold War era, as an important special customer.
<> business: here's where I'm weakest.  More in the next paragraph.  Why 
did the Bell System find it "good business" to develop these wideband 
services?
   It occurred to me that I've "always known" that the ARPAnet used 
50-kb/s leased lines based on some kind of "modem".
   If, somehow, those Bell System 50-kb/s digital services had not been 
available, then would the ARPAnet been successful?

   So here are my hunches on the "business" part of the story:
<> I don't think it was used in the SAGE system.  What I've seen so far 
about the technology of SAGE (which was deployed beginning 1959), it 
used 1200-b/s modems.
<> I don't think it was used much by the TV industry.  This had been my 
hunch, and I allow that I might be wrong about this, but my impression 
is that the TV industry had their own technologies for using 
long-distance cables and microwaves.
<> I think it might well have been used for NASA telemetry etc., but I 
don't have any specific evidence.
<> I think it was used by the SABRE airline reservation system.

   But this is pretty sketchy.
   I'd welcome input from others.
   My key objective is to better understand why the long-distance 
telecommunications industry (in this case, the Bell System) had created 
this premium wideband digital service in the pre-T1 era such that, when 
the ARPAnet designers were doing their work, 50-kb/s long-distance 
service was available.

   Thanks in advance to any additions or corrections,
	-- Guy

On 4/21/25 2:08 PM, the keyboard of geoff goodfellow via 
Internet-history 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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