The channelized E1/ISDN Primary Rate Interface (PRI) modules are available with one or two E1 ports with balanced or unbalanced interfaces and are compatible with the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) G.703/G.704 specifications. The channelized E1/ISDN PRI modules receive and transmit data bi-directionally at the E1 rate of 2.048 Mbps and provide up to 30 virtual channels per E1 port.