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

[Aled Morris via NANOG <nanog () nanog org>]

On Mon, 27 Jan 2020 at 12:13, Rob Pickering <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