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In- depth explanation about the technical aspects o
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From [email protected] Sun Dec 1 14:20:22 1991
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Date: Sun, 1 Dec 1991 13:20:11 -0600
From: TELECOM Moderator <[email protected]>
Message-Id: <[email protected]>
To: [email protected]
Subject: Caller-ID Specifications
Status: RO
From: Jeff Sicherman <[email protected]>
Message-Id: <[email protected]>
Newsgroups: comp.dcom.telecom
Subject: Caller-ID Specifications
Organization: Cal State Long Beach
This is a copy of the data sheet picked up at the Rockwell
booth at the COMDEX show.
INTRODUCTION
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.
PARAMETERS
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.)
PROTOCOL
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
CHANNEL SEIZURE SIGNAL
The channel seizure is 30 continuous bytes of 55h (01010101)
providing a detectable alternating function to the CPE (i.e. the
modem data pump).
CARRIER SIGNAL
The carrier signal consists of 130 +/- 25 mS of mark (1200 Hz) to
condition the receiver for data.
MESSAGE TYPE WORD
The message type word indicates the service and capability
associated with the data message. The message type word for CND
is 04h (00000100).
MESSAGE LENGTH WORD
The message length word specifies the total number of data words
to follow.
DATA WORDS
The data words are encoded in ASCII and represent the following
information:
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".
CHECKSUM WORD
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.
EXAMPLE CND SINGLE DATA MESSAGE
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
DATA ACCESS ARRANGEMENT (DAA) REQUIREMENTS
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
task.
(I will mail the Rockwell data sheet, which includes the
suggested schematic diagram.)
MODEM REQUIREMENTS
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
information.
(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
APPLICATIONS
Modem manufacturers will soon be implementing new modem features
based on CND information as this service becomes widely
available.
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
displayed.
2. Using a look-up table, the calling party's directory number
can be correlated with his or her name and the name
displayed.
3. CND information can also be used in additional ways such as
for:
a. Bulletin board applications
b. Black-listing applications
c. Keeping logs of system user calls, or
d. Implementing a telemarketing data base
REFERENCES
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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