Breakout Box is a troubleshooting tool used to determine the wiring of an RS-232 interface on a networking device or computer.
What is Breakout Box (in computer networking)?
A troubleshooting tool used to determine the wiring of an RS-232 interface on a networking device or computer. A breakout box can be inserted between two RS-232 devices to determine which wires are active.

Breakout boxes are useful in troubleshooting RS-232 connection problems resulting from a manufacturer’s device not using standard pinning.
Breakout boxes are specific examples of a more general category of network testing equipment called «status monitors». Status monitors are available for testing a variety of serial interfaces, including RS-232, RS-449, V.35, and X.21. They generally come with a variety of connectors and are quick and easy to use for isolating problems with serial transmission connections in networking, telecommunications, and industrial settings.