Fax / Modem connection wont work reliable

Hi all,

we do have problems with incoming modem connections and outgoing facsimiles…

we do have the following setup (asterisk 1.2.16)

FAX <-> Digium TDM400P (FXS) <-> Asterisk <-> Beronet BN4S0 (mISDN) <-> POTS

MODEM <-> Digium TDM400P (FXS) <-> Asterisk <-> Beronet BN4S0 (mISDN) <-> POTS

Echocancel is deactivated for the the ZAP lines, also echocancelwhenbridged is off for mISDN.

It does not seem to be an interupt problem - vmstat shows me about 1000 interupts per second

When an outgoing fax call is established - then the channels do show me the following codecs:

ZAP Channel:
Native Format: 68 (???)
Write/Read Format: 64 (slin)

mISDN Channel:
Native Format: 8 (alaw)
Write/Read Format: 64 (slin)

so i think it is a problem because asterisk does some fance codec translation on the call. What is the Native Format 68 ?

Normally all formats should be Format 8 (alaw) - this is what also comes from the telco (so the mISDN POTS connection is using format 8 - as it should).

How can i get asterisk to just use format 8 ?

Or is there an other possible problem with this setup ?

What i do also see in the /var/log/messages file is this message “l2 D-channel addr:40000402 frame wrong EA0/EA1” - does anyone know what this does mean ?


Were you able to ever resolve your issue with fax dialing out? If so, can you let me know what you ended up doing? I am running into the same issue.


no - i could not resolve it. Finally the customer switched to a traditional PBX system.


Too bad to head that, but it is not the first time I see that customers go back to a traditional PBX due fax/modem issues…

Would be great if Digium could pay more attention to this issue, working on T.38 issues, or a way to make a more standar solution for the problem related here -> http://www.xorcom.com/documentation/white_papers/fax_modem[/url]