The dial shelf controller card is the main processor card for the dial shelf, and it performs the following functions: links the dial shelf to the router shelf, where data is transferred as Ethernet packets encapsulated in proprietary protocol; interconnects trunk cards and modem cards; a backplane interconnect concentrator on each dial shelf controller card connects to each feature card installed in the dial shelf; boots and reloads software images; provides source clocks used by all dial shelf feature cards and power supplies; extracts an external reference clock from an external E1 or T1 signal through a BNC connector on the front panel; connects to an external alarm source through a DB-15 serial connector also located on the front panel.