ISDN absolutely was exhilarating “technology from the future” during the 90s and even into ~2000 era just before general cable/DSL proliferation.

It usually just worked consistently and at unbelievably high data rates vs theoretical “56k” even on 64kbit/s single channel. Meaning basically 2x IRL downloads vs 56k at usually tenable full hop bandwidth of constant 8kb/s.

I kept being mesmerized by “just the basics” of ISDN + TCP/IP; it all was working just so flawlessly. For years on end, and each time I went online. Pure wonder and amazement.