Comment by nyrikki

An ISDN BRI (basic copper) actually had 2 64kbps b channels, for pots dialup as an ISP you typically had a PRI with 23 b, and 1 d channel.

56k only allowed one ad/da from provider to customer.

When I was troubleshooting clients, the problem was almost always on the customer side of the demarc with old two line or insane star junctions being the primary source.

You didn’t even get 33k on analog switches, but at least US West and GTE had isdn capable switches backed by at least DS# by the time the commercial internet took off. Lata tariffs in the US killed BRIs for the most part.

T1 CAS was still around but in channel CID etc… didn’t really work for their needs.

33.6k still depended on DS# backhaul, but you could be pots on both sides, 56k depended on only one analog conversion.