Pulsecom DSU-HR NX 56/64 board module

Hubbell / Pulsecom model DSU-HR industrial communication module. This is marked "NX 56/64", "D105389-1G" and also has a bar code stickers marked "DDSUBFP4AB".

This is from the estate of an industrial telecommunications engineer and ham radio enthusiast. We don't know much about it. We have not tested it and the box is worn and dirty from storage.