The Total Access 850 is a modular device, with two common slots and eight access slots. Common cards required for operation are a power supply unit (PSU) and a router control unit (RCU).ADTRAN offer the RCU 850 unit. The RCU is a card that currently supports TDM-based applications, but can be easily upgraded to an ATM-based controller as requirements migrate. The RCU includes a T1 network interface, Nx56/64 V.35 interface and built-in IP/IPX router.