Re: [hylafax-users] Large number of failures receiving faxes ~38% failure rate

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

Andy H wrote:
> I am trying to attach the respective logs to this as well.  I thought 
> that line quality was the issue and
> had the remote office cordinate with the local telco to check the 
> lines.  Telco said the lines were good.
>  
> I am including two examples each of:
> RSPREC error - got DCN
> Failed to properly detect high speed data carrier
> COMREC received DCN
> T30 T2 timeout, expected signal not received
> No sender protocol - T30 T1 timeout

Aug 10 10:24:32.14: [ 3075]: RECV recv EOP (no more pages or documents)
Aug 10 10:24:32.14: [ 3075]: <-- [9:AT+FRS=7\r]
Aug 10 10:24:32.40: [ 3075]: --> [2:OK]
Aug 10 10:24:32.40: [ 3075]: <-- [9:AT+FTH=3\r]
Aug 10 10:24:32.57: [ 3075]: --> [7:CONNECT]
Aug 10 10:24:32.57: [ 3075]: RECV send RTN (retrain negative)
Aug 10 10:24:32.57: [ 3075]: RECV FAX (000016346): from <UNSPECIFIED>, 
page 1 in 0:55, INF, 3.85 line/mm, 1-D MH, 7200 bit/s
Aug 10 10:24:32.57: [ 3075]: <-- data [3]
Aug 10 10:24:32.57: [ 3075]: <-- data [2]
Aug 10 10:24:33.87: [ 3075]: --> [2:OK]
Aug 10 10:24:33.87: [ 3075]: <-- [9:AT+FRH=3\r]
Aug 10 10:24:34.76: [ 3075]: --> [7:CONNECT]
Aug 10 10:24:35.38: [ 3075]: --> [2:OK]
Aug 10 10:24:35.38: [ 3075]: RECV recv DCN (disconnect)

Here, after receiving the page image data, the sender signals the End Of 
Procedure signal (indicating it's the last page to be sent), but it was 
not of adequate quality, and so HylaFAX signals RTN back (which means 
that the previous page was not received with acceptable quality and that 
a retrain must occur before accepting any more pages).  At this point 
it's really inexact what the sender is supposed to do (it could 
retransmit, but it could also just end the fax there since it already 
transmitted the last page).  The outcome was not unusual, but the real 
problem was that the audio quality on the call was so poor that RTN 
needed to be signaled in the first place.

Aug 13 15:31:43.53: [ 3075]: RECV send PPR (partial page request)
Aug 13 15:31:43.53: [ 3075]: <-- [10:AT+FRM=24\r]
Aug 13 15:31:45.01: [ 3075]: --> [7:CONNECT]
Aug 13 15:31:46.69: [ 3075]: RECV received frame number 133
Aug 13 15:31:47.57: [ 3075]: RECV received frame number 134
Aug 13 15:31:47.57: [ 3075]: RECV received RCP frame
Aug 13 15:31:47.57: [ 3075]: --> [10:NO CARRIER]
Aug 13 15:31:47.57: [ 3075]: <-- [9:AT+FRH=3\r]
Aug 13 15:31:47.96: [ 3075]: --> [7:CONNECT]
Aug 13 15:31:48.60: [ 3075]: --> [5:ERROR]
Aug 13 15:31:48.60: [ 3075]: MODEM Command error
Aug 13 15:31:48.60: [ 3075]: FCS error

Whenever you see PPR being signaled on a fax it means that some audio 
distortion or modulator/demodulator incompatibility caused one or more 
portions of the fax image to not come through correctly, and a 
retransmission is being requested.  The face that you see this happening 
so frequently is a strong indicator that you're looking at line audio 
quality problems.  Furthermore, the ERROR after AT+FRH=3, CONNECT means 
that the audio was so bad that not even V.21 HDLC got through, and that 
really does take very bad audio quality to do that.

Aug 16 14:45:26.11: [ 3074]: <-- [9:AT+FRH=3\r]
Aug 16 14:45:33.11: [ 3074]: --> [0:]
Aug 16 14:45:33.11: [ 3074]: MODEM <Empty line>
Aug 16 14:45:33.11: [ 3074]: MODEM TIMEOUT: waiting for v.21 carrier
Aug 16 14:45:33.11: [ 3074]: <-- data [1]
Aug 16 14:45:33.11: [ 3074]: --> [2:]
Aug 16 14:45:33.11: [ 3074]: --> [2:OK]
Aug 16 14:45:33.11: [ 3074]: RECV FAX: No sender protocol (T.30 T1 timeout)

This means that after answering a call the modem did not detect fax 
signaling on the call.  This is either because it was not a fax call or 
because the audio was so corrupted that the modem could not distinguish 
it as fax.

So to answer your question, yeah, you're almost certainly looking at bad 
line audio quality.  And it's so bad that it begs the question... is 
this a VoIP line?

Thanks,

Lee.



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