[asterisk-users] dahdi wcb4xxp and fax

[Matthew Fredrickson]

I have a couple of suggestions:

Make sure that your timing configuration is correct in 
/etc/dahdi/system.conf (that it has a valid timing source).

Also, you probably will probably want to use the half_full buffer 
policy, and set the number of buffers used to something reasonable, like 
8, to ensure you don't have any transmit buffer underruns on the B410P. 
  You shouldn't need more than that, since you're not trying to deal 
with clock slips or timing drift in this configuration.

You may also try explicitly disabling the echo canceller.  It seems that 
sometimes the CED tone detection (which disables the EC) takes a really 
long period of time to happen, and if it does, disabling the EC in the 
middle of the fax will usually cause a fax failure.

Matthew Fredrickson
Digium, Inc.

Olivier wrote:
> 
> 
> 2009/2/25 stoffell <stoffell at gmail.com <mailto:stoffell at gmail.com>>
> 
>     Hi all,
> 
>     I wanted to switch from my current setup (mISDN) to the native dahdi
>     with b410p support (wcb4xp). All works fine for normal phone calls
>     but not for faxing. Faxes are distorted, if arriving at all, and
>     hylafax logs the usual bad stuff (HDLC frame not byte-oriented.)
> 
> 
> What about outgoing faxes ?
> 
> 
> 
>     Our setup uses a digium b410p card with asterisk 1.6, latest libpri
>     and dahdi, hylafax with iaxmodem, and all this on 1 machine.
> 
>     chan_dahdi.conf contains:
>     faxdetect=both
> 
>     When receiving a fax call, hylafax (iaxmodem) answers the call after
>     the obligatory wait of 3 seconds (fax detection) but to me it seems
>     that echo cancellation is still being done.
> 
> 
> Theory is that any echo canceller hearing a 2100Hz fax signal would halt 
> itself, so I wouldn't search in that direction first.
> 
> Have you tried native 1.6 sendFax, receiveFax ?
> Maybe it would improve fax performance.
> 
> 
> 
>     Any pointers on this or workarounds? We're back to our old misdn
>     setup for now ;)
> 
>     Here's some output from "dahdi show channel 1" (the one that had the
>     fax connection going), i cut out some non-related stuff :
>     *CLI> dahdi show channel 4
>     Signalling Type: ISDN BRI Point to Point
>     Owner: DAHDI/4-1
>     Real: DAHDI/4-1
>     Callwait: <None>
>     Threeway: <None>
>     Confno: -1
>     DSP: yes
>     Busy Detection: no
>     TDD: no
>     Relax DTMF: no
>     Dialing/CallwaitCAS: 0/0
>     Default law: alaw
>     Fax Handled: yes
>     Pulse phone: no
>     DND: no
>     Echo Cancellation:
>             128 taps
>             (unless TDM bridged) currently ON
>     PRI Flags: Call
>     PRI Logical Span: Implicit
>     Actual Confinfo: Num/0, Mode/0x0000
>     Actual Confmute: No
> 
> 
> 
>     Regards,
>     stoffell
> 
> 
> 
> 
> 
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