Re: Reminiscing our first internet connections (WAS) Re: akamai yesterday - what in the world was that

[Bryan Holloway <bryan () shout net>]

On 1/27/20 1:42 PM, Aled Morris via NANOG wrote:
> On Mon, 27 Jan 2020 at 12:13, Rob Pickering <rob () pickering org 
> <mailto:rob () 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.