Re: Can't send Fax but can Receive

On 10/04/2017 01:31 PM, FM wrote:
> I'm using ISSABEL wich is an Elastix Fork. I'm using this with my 
> provider SIP TRUNK and configured as a virtual fax (with IAX 
> Extension). I can receive faxes but it seems I can't send.
>
> Example of Hylafax Logs:

> Oct 04 19:55:08.89: [10375]: DIS/DTC received 3 times; DCS not recognized

> Oct 04 19:59:34.50: [10721]: TRAINING failed

The receiver's repeated FTT (failure to train) or DIS signals mean that 
the signals that you're sending (DCS, FCS) are not getting through 
clearly to the receiver.  The call audio quality is bad, likely due to 
jitter.

You'll have to work with your service provider to remedy that problem.  
Unfortunately, unless the network between you and your service provider 
is controlled by you or them (e.g. not the internet) then there's really 
only so much that you can do about that.

That receiving works but not sending is merely an indication of where 
the jitter is occurring in the audio stream.  (It's happening on your 
uploading more than your downloading.)  It's extremely important for the 
sender to be heard clearly by the receiver because the sender will be 
sending signals to the receiver at much faster bitrates.  The receiver's 
signals back to the sender are only ever V.21 300 bps HDLC, so those are 
likely to get through with a bit of patience.

Unfortunately, if there is only an internet path between you and the 
provider then you're really not going to be able to mitigate jitter 
problems very well or consistently for long.  Ideally you'd get a PSTN 
(POTS, DAHDI) interface with a provider who also uses PSTN rather than 
VoIP ... or you would simply outsource the faxing entirely via an 
on-line fax service provider.

Thanks,

Lee.


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