When two modems want to connect to each other, at first they send some hand shake signals such as unscrambled binary 1 , scrambled binary 1, etc. When they are connected to each other with specified speed, they are ready to send and receive user data. The question is that when we do not put data on any of the connected modems, what is it that they put on the line?!
Here is a pdf of V.32 ITU signaling standards...As far as I understand one of the modem has to initiate- first, take control of the channel and then to establish the communication. Signaling and handshaking takes some time and only then data is sent across. Even in general telephone (POTS) the handset goes off-hook => the exchange closes the loop and then a dial tone (line is alive) is sent for you to dial numbers !
Thank you for your answer. I read the document, but I did not get the answer of my question.
When I record the line signal in idle mode, the voltage of the line change like when there are some data sending over the line. I think the modems must send an specified data (for example binary 1) in idle mode. But I dont exactly what they send!
As far as POTS are considered it used to be -48 (i think not very sure) , like a DTMF tone,a modem should as send a pattern . I guess handshake signals(signaling protocols) are critical... Again check for ADSL protocols. They are all standardized Ghashem. If u have a fair idea of what tour are Reading then i guess patterns make sensé...
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