[ih] Arpanet line speed

[Vint Cerf]

no it was really 50 kb/s. Used Bell 303A modems as I recall. A portion of
the BW was for a supervisory voice channel I think (?).  12 voice channels
were bonded producing 36 Khz of analog bandwidth.

Bob Kahn will probably have a more comprehensive answer.

v


On Wed, Jan 18, 2017 at 4:10 AM, Paul Ruizendaal <pnr at planet.nl> wrote:

>
> I'm wondering about (early) Arpanet line speed. Online sources seem to say
> that it was 50kb/s on the long haul connections, provided by AT&T. To me,
> that "50" sounds like a strange number:
>
> - if the modem from the IMP to the Bell System was analog, the best
> technology of the time was perhaps 2.4kb/s (and this speed seems to have
> been considered initially). In this case a speed of 50kb/s is not a
> multiple of 2.4kb/s, and it would have required 21 parallel lines -- more
> logical would have been to use a full T1 connection and have 24 parallel
> lines or 57.6kb/s.
>
> - 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, i.e. a 56kb/s rate. I
> suppose AT&T would have to run special lines from the IMP to the trunk, as
> I don't think digital lines were used for the last mile back then (perhaps
> they were to company/hotel PBX's, I don't know).
>
> Perhaps the "50" is a rounded number, perhaps some capacity is used for
> error correction, perhaps it is plain wrong.
>
> Does anybody have more background information on this?
>
> Thanks,
>
> Paul
>
>
>
>
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