TUCoPS :: AOH Caller ID :: cnd_spec.txt

Calling Number Delivery (aka Caller-ID) - A basic specification

This is a copy of the data sheet picked up at the Rockwell
booth at the COMDEX show.

Calling Number Delivery (CND), better known as Caller ID, is a
telephone service intended for residential and small business
customers.  It allows the called Customer Premises Equipment
(CPE) to receive a calling party's directory number and the date
and time of the call during the first 4 second silent interval in
the ringing cycle.  The customer must contact a Bellcore Client
Company to initiate CND service.

According to Pacific Bell representatives, the following states
and district currently support CND service:  Delaware, District
of Columbia, Florida, Georgia, Idaho, Kentucky, Louisiana, Maine,
Maryland, Nebraska, Nevada, New Jersey, Oklahoma, Tennessee,
Vermont, Virginia, and West Virginia.

The following states are scheduled to support CND service by
April, 1992:  Alaska, Arizona, California, Colorado, Illinois,
Indiana, Iowa, Massachusetts, Mississippi, New Hampshire, New
York, North Carolina, North Dakota, Ohio, Oregon, Rhode Island,
and South Carolina.

The data signalling interface has the following characteristics:
	Link Type:				2-wire, simplex
	Transmission Scheme:		Analog, phase-coherent FSK
	Logical 1 (mark)			1200 +/- 12 Hz
	Logical 0 (space)			2200 +/- 22 Hz
	Transmission Rate:			1200 bps
	Transmission Level:			13.5 +/- dBm into 900 ohm load

(I have copied this data as presented.  I believe the
transmission level is meant to be -13.5 dBm.)

The protocol uses 8-bit data words (bytes), each bounded by a
start bit and a stop bit.  The CND message uses the Single Data
Message format shown below.

Channel	Carrier	Message	Message	Data		Checksum
Seizure	Signal	 Type	 Length	Word(s)	  Word
Signal			 Word	  Word

The channel seizure is 30 continuous bytes of 55h (01010101)
providing a detectable alternating function to the CPE (i.e. the
modem data pump).

The carrier signal consists of 130 +/- 25 mS of mark (1200 Hz) to
condition the receiver for data.

The message type word indicates the service and capability
associated with the data message.  The message type word for CND
is 04h (00000100).

The message length word specifies the total number of data words
to follow.

The data words are encoded in ASCII and represent the following

o  The first two words represent the month
o  The next two words represent the day of the month
o  The next two words represent the hour in local military time
o  The next two words represent the minute after the hour
o  The calling party's directory number is represented by the
   remaining  words in the data word field

If the calling party's directory number is not available to the
terminating central office, the data word field contains an ASCII
"O".  If the calling party invokes the privacy capability, the
data word field contains an ASCII "P".

The Checksum Word contains the twos complement of the modulo 256
sum of the other words in the data message (i.e., message type,
message length, and data words).  The receiving equipment may
calculate the modulo 256 sum of the received words and add this
sum to the reveived checksum word.  A result of zero generally
indicates that the message was correctly received.  Message
retransmission is not supported.

An example of a received CND message, beginning with the message
type word, follows:

04 12 30 39 33 30 31 32 32 34 36 30 39 35 35 35 31 32 31 32 51

04h=	Calling number delivery information code (message type word)
12h= 18 decimal; Number of data words (date,time, and directory
	number words)
ASCII 30,39= 09; September
ASCII 33,30= 30; 30th day
ASCII 31,32= 12; 12:00 PM
ASCII 32,34= 24; 24 minutes (i.e., 12:24 PM)
ASCII 36,30,39,35,35,35,31,32,31,32= (609) 555-1212; calling
			  party's directory number
51h=	Checksum Word

To receive CND information, the modem monitors the phone line
between the first and second ring bursts without causing the DAA
to go off hook in the conventional sense, which would inhibit the
transmission of CND by the local central office.  A simple
modification to an existing DAA circuit easily accomplishes the

(I will mail the Rockwell data sheet, which includes the
suggested schematic diagram.)

Although the data signalling interface parameters match those of
a Bell 202 modem, the receiving CPE need not be a Bell 202
modem.  A V.23 1200 bps modem receiver may be used to demodulate
the Bell 202 signal.  The ring indicate bit (RI) may be used on a
modem to indicate when to monitor the phone line for CND
information.  After the RI bit sets, indicating the first ring
burst, the host waits for the RI bit to reset.  The host then
configures the modem to monitor the phone line for CND

(I'm skipping some Rockwell-specific information here.)

According to Bellcore specifications, CND signalling starts as
early as 300 mS after the first ring burst and ends at least 475
mS before the second ring burst

Modem manufacturers will soon be implementing new modem features
based on CND information as this service becomes widely

Once CND information is received the user may process the
information in a number of ways.

1.	The date, time, and calling party's directory number can be

2.	Using a look-up table, the calling party's directory number
	can be correlated with his or her name and the name

3.	CND information can also be used in additional ways such as

	a.  Bulletin board applications
	b.  Black-listing applications
	c.  Keeping logs of system user calls, or
	d.  Implementing a telemarketing data base

For more information on Calling Number Delivery (CND), refer to
Bellcore publications TR-TSY-000030 and TR-TSY-000031.

To obtain Bellcore documents contact:

	Bellcore Customer Service
	60 New England Avenue, Room 1B252
	Piscataway, NJ   08834-4196
	(908) 699-5800

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