SPA3102 + FAX

Unanswered Question
Mar 11th, 2010


   I have one SPA3102 with its FXS connected to a PBX and FXO to POTS. If I send one fax from PBX side the call seems connect with remote side but after some secons the operation fails. Outgoing fax are sent from FXS to FXO directly via dialplan. All works ok without connect SPA. Must I change any param from standard params? It has CED and CNG detection on. I am from Spain.


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Alberto Montilla Thu, 03/11/2010 - 05:46

Dear Sir;

This is not normal at all, as this is a normal loop. Please try the following: increase the gain on the FXS side (both input and output) and try again. Typically PBXs derives less signal or are less sensitive than PSTN or short loops.


mrlooper82 Fri, 03/12/2010 - 14:05

I think it is not a gain problem because I have echo. I've spent a lot of time trying make it dissapear but it was impossible. I have a lot of doubs about how SPA3102 treats one call:

- How can I know if a echo problem in a call from FXS to FXO (or FXO to FXS) refers to FXS gain or FXO gain config value?
- How exactly FXS input gain affects one of those calls?
- How exactly FXS output gain affects one of those calls?
- How exactly SPA to PSTN gain affects one of those calls?
- How exactly PSTN to SPA gain affects one of those calls?
- Could FXO and/or FXS impedance have any influence on echo?
- Which would be good values of impedance for Spanish telcos? Is there any way to know which is the best value to use?

- Regarding SPA echo cancel capabilities, What is the differente between Echo Canc Enable, Echo Canc Adapt Enable and Echo Supp Enable? How the affect to echo cancel of SPA? If I set to yes those three values I cannot send faxes correctly.

Is there any guidelines to follow when echo appears? Is there any tech document explaining all these config values fully explained?

Sorry for asking so many questions but I've trying to make work SPA for hours without success.


Tested also with a SIP to PSTN call having the same echo problem. Configuring SPA with another PSTN line from another telco I get the same result. Always I hear my voice echoed...

mrlooper82 Thu, 03/18/2010 - 00:12

I tested all possible impedances without success. I read usual impedances for Spain are 600r and 900r. May be a 5.1.10 firmware bug?


Alberto Montilla Wed, 03/24/2010 - 03:27

Dear Sir;

Please try 5.1.7. My suggestion (if possible) is that you downgrade, perform a factory reset and reconfigure. Let me know the results.


mrlooper82 Wed, 03/31/2010 - 00:23

Same echo problems once donwgraded to v5.1.7 Any other idea?



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