Overview#Calling Number Delivery (CND), commonly referred to as Caller ID, is a Telecommunications service that provides the calling party's Phone Number to the Customer Premises Equipment (CPE).
On Land Line (a standard Loop Start line), then Calling Number Delivery is provided by the Service Provider's Local Exchange. Since the network does not connect the caller to the callee until the phone is answered, generally the Calling Number Delivery signal cannot be altered by the caller. Most service providers however, allow the caller to block caller ID presentation through the Vertical Service Code *67.bit data words (bytes) using ASCII Encoding and represent the following information:
- The first two words represent the month
- The next two words represent the day of the month
- The next two words represent the hour in local military time
- The next two words represent the minute after the hour
- The calling party's Phone Number is represented by the remaining words in the data word field