When you make a telephone call, the signalling is the bit that contains all the call information - A number, B number, type of call etc. There are many types of signalling, eg tone and pulse dial for the last mile or local loop, the the ISDN types such as euroISDN/ ISDN30, DASS2 and CAS, then the C7 types which handle signalling between exchanges or switches.

Otherwise you'd be saying 'can I have Delhi 34253' to an operator, like in the movies.

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