Echo cancellation was the next major advance in modem design.Local telephone lines use the same wires to send and receive, which results in a small amount of the outgoing signal being reflected back. This is useful for people talking on the phone, as it provides a signal to the speaker that their voice is making it through the system. However, this reflected signal causes problems for the modem, which is unable to distinguish between a signal from the remote modem and the echo of its own signal. This was why earlier modems split the signal frequencies into "answer" and "originate"; the modem
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