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Digitizing Voice Signals
Analog Telephone Cores
The early telephone networks had analog cores. Frequency division multiplexing (FDM) was used to transmit a number of voice signals over the single line. Twelve calls were multiplexed into a group. Five groups were multiplexed into a supergroup.
Digital Telephone Cores
The present telephone networks have digital cores. This requires that the analog signals in the local loops are converted to digital signals that are transmitted via the trunks. This is done by codec (coder decoder). Time division multiplexing (TDM) is used to multiplex digital signals in the trunks, since it can be entirely handled by digital circuitry.
Codecs in Telephone Networks
Codec is an electronic device that encodes a signal for transmission and storage, and then decodes it for usage. In telephone networks, it is used for coding analog signals to digital form using pulse code modulation (PCM) techniques.
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