The Cisco E1/T1 ISDN PRI Network Module's integrated channel service unit (CSU) provides direct connection to the Telecommunications network, thus allowing customers to consolidate customer premises equipment (CPE). This provides multifunction dial access aggregation, routing functionality, VPN and firewall security, and other capabilities right inside the Cisco router in power branch office environments. The Cisco E1/T1 ISDN PRI network modules offer support for balanced and unbalanced E1 connectivity and conform easily to customers' specific applications.The Cisco E1/T1 ISDN PRI network modules also supply connectivity for internal digital modems in the Cisco 3660 and 3700 series routers, with connectivity options for PRI, T1 channel associated signaling (T1-CAS), and E1-CAS R2 signaling. This provides for a high concentration of V.92-compatible modems, while still allowing expandability for other critical services.The Cisco E1/T1 ISDN PRI network modules (NM-xCE1T1-PRI) are software configurable between E1 or T1 operation, balanced or unbalanced E1 termination, and CSU/DSU. Customers no longer need to buy a specific module for T1 support and then another card for E1 connectivity. In addition, the same modules provide for balanced (120-ohm) and unbalanced (75-ohm) E1 termination.