Yes these modems were almost-ISDN (minus the razor fast call setup). And required a full digital backend to work. They could only do 56k6 in one direction, to the user too. But they were made for internet access so that didn't really matter.
ISDN had much, much better latency than even 56k modems. Modems were around 150ms minimum. ISDN was often in the sub 20 ms range. This made a big difference for chatty protocols like HTTP, telnet, etc.
True, though in those days that didn't really matter except for gaming. The bandwidth was so low and the web going in content so fast that the local uplink bandwidth was usually congested causing delays due to queueing and pending acknowledgements. Switches and routers weren't quite as optimised for low latency either. A lot of local networks were still 10base2 (or 10baseT with hubs, not switches) so collissions added further latency.
What I loved the most about ISDN was the quick call setup. Took like 1 second max and you had a 64kbit channel. 56k modems went through a dialling phase, a connection phase, endless handshaking...
Or gaming. I never got good at quake because of it. IIRC they added hardware compression to the later versions (I think starting at 33.6?) that added latency, too.
I remember my brothers friend in rural Portugal having one way satellite Internet back in the 90s to very early 00s - you used a standard dial up for the upstream, but with a satellite dish got much much faster downloads. Blew my mind that you could go out one way and receive another and still get a functioning (and fast) connection.
Hey, in early 00 I briefly worked for an ISP trying to do rural Portugal/Spain satellite internet (to exploit rather large subsidies offered at the time)! Afair it was 1-2 Mbit downstream for all subscribers in one area from geo stationary sat with 500-1000ms pings. Almost unusable for normal browsing. Company was from defense background and from my limited understanding at the time they were piggybacking on some military leftovers tech. Idea was to use commercial Wifi to link local customers to central location with some magic proxy server trying to hide all that latency.
The first cable Internet service I had was telephone return. Downstream was over the cable modem at ~512Kbps (IIRC) but upstream was over a dial-up modem.
It was cool having a fast downstream but the slow upstream over finicky dial-up was a pain in the ass. If the dial-up dropped the in progress downloads all died because no ACKs could be sent. Gaming was no better than plain dial-up since your upstream had the same shitty latency as plain dial-up.
