Abstract: A housing (1) serves to receive, for example, primary-access and basic-access plug-in units (2) used as network terminations in ISDN. To be able to connect private branch exchanges of different sizes, it must be possible to add further plug-in units. A housing which can be readily extended and is accessible from all sides contains a chassis module (16, 18, 19) which is attached to a base plate (3). Fasteners (28) can be lengthened with auxiliary fasteners (28) so that additional chassis modules (31) can be added. In the closed condition, all sidewalls (9, 10) of the housing are locked by a lockable cover plate (12).