View Full Version : Japanese Caller ID

10-30-09, 08:59 AM
The Japanese Caller ID works this way:

The Telco sends a few (4-6) fast rings on the line.
The phone of the called party does not ring when these fast rings are sent.

After any of these fast rings, the phone goes off-hook, the Telco detects this
and sends the Caller ID information, then the phone goes back on-hook and then it starts
ringing. So basically, the CID info is sent before the phone actually starts ringing.

The CID information is sent as an FSK signal.

From the tests and recordings that have been done here with the Japanese TLS,
when the line is taken OFF-HOOK, there is a certain silent period (120-140ms)
before the CID information is sent. So on the recordings, there is the OFF-HOOK glitch,
then a silence and then the FSK signal.

From the recordings we have seen from NTT (Nippon Telephony and Telegraph
Network -> aka Bell Canada here), as soon as the line goes OFF-HOOK, the noise from the
trunk going off hook is superimposed over the FSK signal.