Loco Net adaptor, Big Boy.

Fast Clock with large digital display.
more info here

Digitrax LocoNet Repeater Improves LocoNet Operation.
• LED Diagnostic display for systems
• Automatic isolation of bad network segment
• Hardware buffering & isolation on large layouts lets you add “tons” of LocoNet devices
• Protects against RJ11 or wiring faults
• Plug N’ Play LocoNet device

Three RJ12's.