its a digital loop carrier

the digital carrier loop system

Highly variable. For example, DSL (Digital Subscriber Loop) uses open telephone twisted pairs to transmit a symbol modulated 2 MHz carrier.

yes

for transmission of the signal to take place smoothly,digital tranmission needs to be modulated over a carrier

In digital circuits modem is used to multiplex and demultiplex the digital data.multiplexing means the digital signals amplitude or frequency or phase is varied with a carrier signal.at the receiver end the carrier signal is separated out and original digital signal is received