Msg: 6814 *Conference*

10-04-96 18:59:48

From: RON WIESEN

To : RICHARD HANSON

Subj: REPLY TO MSG #6793 (CALLER ID PROJECT)

Sorry it took so long to get this info for the "Caller ID" project.  Been on
the road much lately so I've been "unplugged" from my telephony clients for a
while.  Maybe it's too late but it's the best I could do.  So here's the dope.
 
Message consists of the caller's phone number or name, along with the date and
time of the call.  While the subscriber's instrument is in the on-hook state,
message transmission takes place during the "silent" interval of the ringing
cycle.  Transmission occurs during the first long silent interval (three
seconds or more) of the ringing cycle.
 
Transmission is by audio tone carrier using Frequency Shift Keying (FSK).  The
FSK transmission takes approximately 742 milliseconds (average) for a message
consisting of 18 characters plus overhead.  Message transmission conforms to
the following specifications:
 
* Simplex via two-wire analog telephone line
* Application of data - serial, binary, character-asynchronous
* Modulation - phase-coherent FSK
.   Logical 1 (mark) - 1200 +/-12 Hz
.   Logical 0 (space) - 2200 +/-22 Hz
* Phase continuity - maintained to end of message
* Transmission level - 13.5 +/-30 (???) dBm into a resistive load of 900 ohm
* Transmission rate - 1.2 kbit/s
* Bit duration - 833 +/-50 microseconds
.   start and stop bits have the same duration as a standard bit
* Bit-serial character framing:
.   one start bit (space)
.   8 character bits, in the bit-order of LSB (bit "0") first
.   one stop bit (mark)
* Bit error rate - less than 1 out of every 100,000 bits
* Character-serial aspects:
.   Character-order - text temporal
.   Maximum message length - 18 characters
.   Asynchronous delay of successive characters - from 0 to 16.7 milliseconds
 
Note the question marks I put in the transmission level.  I think +/- 30 dBm is
a typo.  Way too wide a tolerence.  Likely +/- 3 dBm is correct, that
translates to double/half power tolerance.  The nominal level of 13.5 dBm
translates to about 20 milliwatt which sounds right to me.  So figure the range
is 10 to 40 milliwatt.