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.