The NCS 2015 external connection unit (ECU) is a replaceable module that provides interfaces for passive device inventory and management, multishelf management, and element management. The ECU module available for the NCS 2015 shelf is NCS2015-ECU and is installed in slot 18 of the NCS 2015 shelf.

The ECU contains RJ-45 and SFP interfaces or multishelf and element management. Fourteen USB ports connect to passive devices, two of which are USB 3.0 ports. A backup flash memory is fitted into the ECU to support the database (DB) and image backup in the operation of the NCS 2015.