In reply to a post by kitcat:

Recollections that the earliest variant was nicknamed the pizza box as it was that size and had a PON of 64 (feeding 1st and 2nd splitters of 8) with 1 pair of resilient Ge back to the Backhaul via a edge router. It wasn't really scalable.

That's the one I remembered. So the larger ones you could install fabric cards in them but that required more power, cooling and a backplane swap and apparently wasn't done so even on the bigger boxes it was, as mentioned, everything to the supervisors which in turn provided all the backhaul ports.

The gigabit line cards were for cabinets as I vaguely recall. A whole bunch of them scrunched into the backplane and back to a supervisor.

Either way I recalled OLTs with the capacity on the GPON-side badly overbooked between there and backhaul.