Reminiscing our first internet connections (WAS) Re: akamai yesterday - what in the world was that
Bryan Holloway
bryan at shout.net
Mon Jan 27 12:51:42 UTC 2020
On 1/27/20 1:42 PM, Aled Morris via NANOG wrote:
> On Mon, 27 Jan 2020 at 12:13, Rob Pickering <rob at pickering.org
> <mailto:rob at pickering.org>> wrote:
>
> Wasn't the 56/64k thing a result of CAS (bit robbed) signalling
> which was a fudge AT&T did to transport signalling information
> in-band on T1s by stealing the low order bit for OOB signalling (it
> wasnt actually every low order bit, but meant you had to throw away
> every low order bit as CPE didn't know which ones were "corrupted"
> by the carrier).
> Proper ISDN was always 64kbit/s clear path with separate D channels
> carried OOB end to end, away from the B channel data.
>
>
> There was some element of interoperability required with the
> pre-existing data network architecture based on 56k channels and T1
> bearers. This article has the detail:
>
> https://en.wikipedia.org/wiki/T-carrier
>
> /Soon after commercial success of T1 in 1962, the T1 engineering
> team realized the mistake of having only one bit to serve the
> increasing demand for housekeeping functions. They petitioned AT&T
> management to change to 8-bit framing. This was flatly turned down
> because it would make installed systems obsolete./
>
>
> Compared to what was to follow, that all had to suffer the 56k channel
> limitation, there can't have been that many installed systems in 1962!
>
> Aled
I seem to also recall that you couldn't use a 56k modem unless the
far-end was digital.
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