On the cable and satellite all channels are transmitted to the subscribers. It is then the decoder to do the sorting. The operation is different by the ADSL
Internet boxADSL is a technology developed to be able to pass computer data through telephone lines. The high frequency bands of ADSL are those not used by the telephone (300 - 3400 Hz), multiplexing and modulation techniques are implemented.
However, using the high frequencies of the telephone line implies the use of a filter on both sides of the line so that there is no disturbance. The streams are asymmetric, which means that
Limited flow on the local loop, the DSLAM transmits only a single string to the Subscriber's home.
Therefore, it is not possible to watch two channels simultaneously, or record one channel on the VCR while you watch another.
When the user wants to change the channel, the set-top-box forwards the request to the DSLAM. It charged to select the good flow.
But the DSLAM either receives all the channels.
It only gets the channels it transmits at this time to these subscribers, and cela to avoid saturating the network.