XCel Systems are designed so that functionality is included on the individual XCel System CTU card, including power supply, signal processing and status display and processing.

XCel common card needs are therefore minimal. In most systems only one common card is required, an ACU MOD H AD card. An Alarm Control Unit card is required per shelf hosting XCel Systems to collect and report alarms and to support a timing reference for V.90 XCel POTS operation.

Alarm Control Unit (ACU) Processes a timing reference and distributes it to POTS CTUs in support of V.90 signal processing. Collects and processes alarms from the CTUs. Displays Major and Minor Alarms and supports contact alarm connections on the backplane. Diagnostics and software download.