Fujitsu LTU35A is a 64kb/s kilostream Line Terminating Unit.
Three LJU style connectors are provided, the left hand side is the private circuit, the two right hand side ones are for dial on demand backups using analogue phone lines.
This LTU came from Baskerville House in Birmingham and the other end of the circuit was at Cedar House, also in Birmingham. It was used for mainframe connectivity.
Although this unit is made by Fujitsu I think the circuit drawing here (by Telspec) will be the same.