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Getting Caller ID to work with "Unsupported IP Phone" HT-503

Getting Caller ID to work with "Unsupported IP Phone" HT-503
by mcbsys » Fri Oct 10, 2008 6:23 am
This discussion was started some time ago along with other HT-503 issues:


I thought I'd start a new discussion specifically regarding Caller ID.

With some fiddling, I have occasionally gotten the HT-503 to "read" incoming Caller ID and pass it along to 3CX, which then passes it to my phone. But so far it is erratic. Often the HT-503 doesn't detect the Caller ID, it just passes along the virtual extension (10000).

Values I'm testing:

Caller ID Scheme: Bellcore/Telcordia [I'm in San Diego, CA and this is the U.S. standard]
FSK Caller ID Minimum RX Level (dB): -40 [Changing this from -96 to 0 didn't make a difference]
FSK Caller ID Seizure Bits: 240 [at least one standard says to expect 30 bytes x 8 = 240 bits]
FSK Caller ID Mark Bits: 180 [one document says the mark signal is 150ms or 180 bits]

It's the last two values that I've been fiddling with the most. There is lots of info online as to what these mean, for example:


The main message from these documents is that the device receiving the Caller ID signal must be able to accept a wide range of values for Seizure and Mark Bits, since there are multiple standards, and variables within the standards. (This variety is especially evident in that first link.) However it seems that the HT-503 is looking for a very specific values for Seizure and Mark Bits.

Is this a design flaw? I see no way for a normal user to know exactly how many Seizure and Mark bits are being sent by the local telephone company, so how can the user set Seizure and Mark Bits for reliable Caller ID?