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| Image source : thepcauthority.net |
In landline call, speech and ringing are carried on the same physical "two wire" path called circuit. Ringing is activated by 80v current from exchange sent on the line. Only by giving a loop on the "two wire" circuit, ringing can be stopped (that is by lifting the handset). By replacing the receiver again, the call gets disconnected, as the physical path is broken.In a mobile call, speech and signalling are in separate paths (channels). Speech channel is connected only when the called party answers. Till then, only signalling channel is active and carries ringing information in the form of bits to the mobile phone, which activates ring tone from inside the instrument.By pressing disconnect button, `stop ringing' information is sent to mobile switching centre on the signalling channel. Mobile switching centre immediately recognizes the `stop ring' signal and deactivates.
Source: thehindu.com
