The PA-MC-E3 provides one multi-channel E3, medium-speed serial interface. The physical E3 link on the PA-MC-E3 port adapter consists of two female BNC connectors, one for receive (RX) and one for transmit (TX). You must use 75-ohm coaxial interface cables with male BNC connectors to connect the PA-MC-E3 interface with external E3 equipment. The PA-MC-E3 divides the E3 signal stream into four multi-channel E2 data channels and then into 16 E1 lines. The E3 is designed to comply with the CCITT/ITU G.703 physical layer standard.