SPA8800 not detecting FXO ringing

[enrico.lorenzoni1]

Hi all, I have a SPA8800 connected to a "telecom nt1 plus" ISDN adapter in Italy.

Another SPA8800 on another nt1 plus works fine without any customization, but this one can't detect the line ringing.

Voltage is negative, about -50V, and I can call with this line.

I have tried editing almost every international parameter but still no luck.

how can I scientifically diagnose the problem and fix it?

thanks.

Enrico

[Dan Lukes]

I'm unsure about your topology. SPA8800 have no ISDN terminal inside, as far as I know, so you can't plug a ISDN line into it. I assume the "telecom/another nt1 plus" you mentioned convert ISDN into POTS line first.

Well. So you are asking about scientific method of diagnose.

The ring on POTS is claimed by AC voltage superposed on DC voltage. It's frequency vary in the range of 20-50Hz, voltage is about 30-80V, the waveform is either sinusoid or trapezoidal. The ring/idle pattern and timing vary so much. All those parameters are local phone network dependent. Some countries use country-standards to lower the entropy.

I don't know what kind of RING signal the ring signal generator inside of telecom nt1 plus should generate.

But you have two of them, one working, one not, so you can measure both then compare the results.

The best is to use oscilloscope but even voltmeter may give you some data.

If you are not equipped for such kind of scientific diagnose, you can just switch both SPA8800 between places. If the issue will move as well, it's rather SPA8800 related (either hardware fault or misconfiguration), if it will not move it's rather NT1 plus related. You can switch NT1 plus then to verify the conclusion. Even NT1 may be either faulty or misconfigured.

[enrico.lorenzoni1]

hi, thanks for the quick answer.

right now I can't go there and hook my oscilloscope, but I guess I'll do it soon if I can't find a solution.

this morning I'm checking the second SPA8800 (that is of course hooked to POTS lines of NT1 plus). It detects ringing but sees each ring as another call. I mean, when the line is not ringing it reaches a timeout too quickly or something like that.

any hints about this? maybe "ring timeout" is the parameter to check?

also I have got "line voltage" of -41V on the working SPA8800 and -54V on the other. maybe this can help?

thanks

Enrico

[Dan Lukes]

It detects ringing but sees each ring as another call.

Unless there's VERY long pause between rings, there must be a DC event on line between rings. Like short removal of DC power. It may be considered CPC signal, thus hangup. Try turn off CPC in configuration. Note the SPA8800 may become unable to recognize end of incoming call because of it.

There's no configurable ring timeout as far as I know, but if the issue is caused by explicit signal the timeout configuration will not solve it.

also I have got "line voltage" of -41V on the working SPA8800 and -54V on the other. maybe this can help?

DC line voltage is switch specific and vary in wide range. Also, different length of local loop and the wire used affect the voltage on client's side (voltage drop on loop wire). I assume the NT1 just follow ISDN line voltage on POTS side.

Despite both -41V as well as -54V fit most common voltage range, it reveal something.

I assume the -54V is end voltage of 60V (nominal) switch (on operator side). The -41V on other line is caused either by very different equipment on operators side (48V switch) or there is also 60V switch , but so large voltage drop on ISDN loop. May be because it's very long and/or wires are so thin and/or wires are in poor shape (sometime it happen if someone use long UTP cable to wire phone to different place in the building).

If different equipment, then even RING signal may be different (in the terms of AC voltage, wave form, pattern ...). Edit: no, the POTS RING is generated by NT1, so it will be the same as long as NT1 is the same (note name printed on black box doesn't prove the identity of equipment inside).

If line with so large voltage drop on ISDN side, then then NT1 may be underpowered and may be unable to generate proper RING. If voltage drop happened on POTS loop then RING signal may be attenuated so much as well.