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. Both the 1-port and 2-port versions 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.