On 26/10/2018 21.32, James Knott wrote:
On 10/26/2018 02:56 PM, Carlos E. R. wrote:
Two pairs? Ah, two T1 lines. Coaxial lines. But they carried 1 Mbit on each. 1.544 Mb/s, or 2 Mb/s on E1, on each direction.
The North American T1 was over 2 twisted pairs. Living in Canada, I have no experience with E1. The international carriers, that transported telecom between countries & continenents, would have to deal with conversion between T1 & E1.
They were split into channels which were sent their different ways inside the switch (exchange). The problem were the channels, because they had different capacities: 64 Kbps on the E1 and 56 kbps on the T1, IIRC. I think there was a software conversion done, but I never saw it. A further consideration was the µ-law algorithm, different each side of the Atlantic (A-law my side). I did not need to know ;-) That 56 Kbps was the reason why modems had that top speed at that side of the Atlantic. And ISDN too. Linux had to know that (lame excuse, I know). -- Cheers / Saludos, Carlos E. R. (from 42.3 x86_64 "Malachite" (Minas Tirith))