The FCD-24 integrating multiplexer supports E1 and Fractional E1 services. The FCD-24 integrating E1 multiplexer has two or four synchronous data channels and one E1 sub-link which can be connected over the public E1 network, while paying only for the bandwidth required. The E1 sub-link enables PABX connection to the E1 interface. Alternatively the unit can be used as a multi-channel short range modem.