The multichannel E1 and T1 Integrated Services Digital Network (ISDN) Primary Rate Interface (PRI) port adapters are single-wide modules that integrate channel service unit (CSU) functionality, data service unit (DSU) functionality, and E1 or T1 channel support into the Cisco router.These port adapters provide four or eight independent T1 (100-ohm) or E1 (120-ohm) connections via RJ-48C connectors. Each T1 or E1 port adapter can provide up to 128 separate full-duplex HDLC fractional or full T1 or E1 channels. Individual T1 connections of the DSX-1 version of the port adapters can connect to external CSUs, to digital cross connects (DACS), or to any other equipment that uses a DSX-1 interface.