The IMS B300 TCPlink box is a self-contained unit providing four links and associated system services for connection to target subsystems. The four links are accessed over an Ethernet network by host development computers running SGS THOMSON Toolsets in conjunction with the TCP/ IP protocol suite. The unit supports the development of programs in a network environment. Diagnostic and monitoring facilities are provided via a serial port on the IMS B300. This may be connected to an ANSI compatible video terminal to give interactive information displays on the unit's operation.