Caller ID
Format
The following 2 formats are used in the United States to send the CID information:
- SDMF - Single Data Message Format
- MDMF - Multiple Data Message Format
SDMF supports a single data type and is used to send the phone number
for number only service.
MDMF supports multiple data types and is used to send name and number
information. It is structured so that new types of data can be added
easily (address?, city?, state?, etc).
Both formats include a value to determine the type of data to follow
(data type word), a value to indicate the length of the data (data length
word), and a checksum. See below for an example of each format.
SDMF Example
Here is an example of a SDMF message. Each byte is in HEX.
04 12 30 39 33 30 31 32 32 34 36 30 39 35 35 35 31 32 31 32 51
04 - message type word - 4 indicates SDMF 12 - 18 decimal, number of
bytes in date, time and phone number 30,39 - 09, September (ASCII) 33,30 -
30, 30th day (ASCII) 31,32 - 12, 12 hour (ASCII) 32,34 - 24, 24 minutes
(12:24 PM) (ASCII) 36,30,39 - 609, Area code (ASCII) 35,35,35 - 555,
prefix (ASCII) 31,32,31,32 - 1212, sufix (ASCII) 51h = Checksum Word
Thus, the CID string can be summarized as follows:
The message is in SDMF format, consisting of 18 bytes of information,
not including the checksum. The call was made on September 30 at
12:24pm. The calling party's phone number was (609)555-1212.
If the calling party's directory number is not available to the
terminating central office, the phone number field contains an ASCII 'O'.
If the calling party invokes the privacy capability (blocking), the phone
number field contains an ASCII 'P'.
The following SDMF string is an example of a call that was blocked. The
50 just before the checksum is the ASCII code for a 'P'.
04 09 30 39 33 30 31 32 32 34 50 12
MDMF Example
Here is an example of a MDMF message. Each byte is in HEX.
80 20 01 08 30 33 32 34 30 39 30 32 07 08 4A 4F 48 4E 20 44 4F 45 02 0A
38 30 30 35 35 35 31 32 31 32 7D
- 80 - Message type word, 80 indicates MDMF
- 20 - Length of data, 32 bytes in date,time,name and number
- 01 - data type, 1 = date & time
- 08 - length of date and time, 8 bytes
- 30,33 - 03, March
- 32,34 - 24, 24th day
- 30,39 - 09, hour
- 30,32 - 02, minutes (9:02am)
- 07 - data type, 7 = name
- 08 - length of name, 8 bytes
- 4A - 'J'
- 4F - 'O'
- 48 - 'H'
- 4E - 'N'
- 20 - ' ' (space)
- 44 - 'D'
- 4F - 'O'
- 45 - 'E'
- 02 - data type, 2 = phone number
- 0A - length of phone number, 10 bytes
- 38 - 8
- 30 - 0
- 30 - 0
- 35 - 5
- 35 - 5
- 35 - 5
- 31 - 1
- 32 - 2
- 31 - 1
- 32 - 2
- 7D - Checksum
The following is a list of possible data types:
- 1 - date & time
- 2 - phone number
- 4 - number not present
- 7 - name
- 8 - name not present
If the calling party's directory number is not available to the
terminating central office, the phone number and name fields contain
an ASCII 'O'. If the calling party invokes the privacy capability
(blocking), the phone number and name fields contain an ASCII 'P'.
From what I have seen, the types 4 and 8 are always followed by a
length value of 1 and then either a 'P' or an 'O' to indicate
unavailable or blocked, respectively.
Checksum
The checksum value 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 received
checksum word. A result of zero generally indicates that the message
was correctly received. Message retransmission is not supported.
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