[ih] Arpanet line speed

[Brian E Carpenter]

On 19/01/2017 04:21, Craig Partridge wrote:
> Andy's recollection that stuff was 56 Kbps later on matches my recollection
> when I came on board in '83.
> 
> One thing is I don't remember what the bandwidth was on the satellite links
> to England.  My recollection is it was
> higher than 9.6Kbps but there was some oddity in integrating European and
> US telecom standards such that the bandwidth was different.  But this could
> be entirely wrong -- alas the ARPANET maps don't tell me the data rates.

Google for Peter Kirstein's paper "Early Experiences with the ARPANET and INTERNET in the UK"

It was 9.6 between London and Norway and then 9.6 between Norway and the USA.

9.6 was the lowest common denominator; the US 56k standard was different from
the CCITT 64k standard used in Europe. Just as the US T1 1.5M standard was different
from the CCITT E1 2M standard some years later. This was a pain in the neck for
early transatlantic links above 9.6 (or posibly 19.2). But I suspect that in 1973
the main issue was cost.

   Brian

> 
> Thanks!
> 
> Craig
> 
> On Wed, Jan 18, 2017 at 9:59 AM, Andrew G. Malis <agmalis at gmail.com> wrote:
> 
>> By the time I came on board in '79, almost all of the links were 56 Kbps,
>> with a few 9.6 Kbps links here and there. The 50 Kbps links had been
>> replaced by that point.
>>
>> Cheers,
>> Andy
>>
>>
>> On Wed, Jan 18, 2017 at 9:29 AM, Noel Chiappa <jnc at mercury.lcs.mit.edu>
>> wrote:
>>
>>>     > From: Paul Ruizendaal
>>>
>>>     > - if the modem from the IMP to the Bell System was analog, the best
>>>     > technology of the time was perhaps 2.4kb/s ... a speed of 50kb/s is
>>> not
>>>     > a multiple of 2.4kb/s, and it would have required 21 parallel lines
>>>
>>> If you read the 303 manual, it's clear that i) the signal between a pair
>>> of
>>> 303 modems was analog, not digital, and ii) there was a single line, with
>>> a
>>> wide enough bandpass to carry signals of high enough frequency to carry
>>> that
>>> bit rate - it didn't glue together a bunch of slower lines.
>>>
>>>     > if the modem from the IMP to the Bell System was digital, it would
>>> most
>>>     > likely have used a single channel of a T1 connection
>>>
>>> The whole T hierarchy was just getting started then (initial deployment
>>> in the
>>> early 1960s), and I'm not sure if it was deployed widely enough to have
>>> made
>>> it possible to lease a T1 line from one coast to another.
>>>
>>> Also, many of these lines would have crossed non-AT+T local phone
>>> companies
>>> (the Bell System did not control all of the US phone system, although some
>>> people don't realize that). The "History of the ARPANET: The First Decade"
>>> (which I have previously pointed you at on another list), pg. III-32, says
>>> "In the case of a circuit from UCLA to RAND ... the service would be
>>> procured
>>> from General Telephone" - GT was the largest independent telephone
>>> company in
>>> the US at that point. It's not clear that those local carriers would have
>>> supported T1.
>>>
>>>
>>> Moral of the story: when doing history, it's bad to make assumptions about
>>> what was and wasn't possible, and about what did and did not happen. Find
>>> contemporary documentation.
>>>
>>>         Noel
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>>
>>
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> 
> 
> 
> 
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