Question : PSTN Signaling

I have doing some self studding on PSTN network , but can't find the answer to the below question. I tried searching online, but did not get anywhere.
Here it, thanks,

. Identify three types of signaling used on PSTN networks
A.      Information
B.      Address
C.      Fallback
D.      Supervisory
.


Answer : PSTN Signaling

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