Almost 30 years ago, I worked on a corporate campus with several different buildings spread out over about 5 miles. There was a SONET ring linking them. I remember a coworker showing me this add-drop multiplexer thing so he could provision a fractional T1 of bandwidth out of the ring. CSU/DSUs, thick serial cables, cisco 2501 routers... We'd laugh at these speeds today.
I've seen some very old cubicle setups that had two strands of 62.5/125 multimode (OM1) pulled to each desk for a FDDI connection. Very costly in its era.
what a man does in his own homelab, even if it does involve ATM, is none of our business.