asterisk users - Jun 2005 - TxFax: can't get a fax to destination (log inside)

Can someone explain me what's going on and why the receiver of this fax 
guives up saying communication error?


Slow carrier up
Slow carrier down
Slow carrier up
<<< CSI: 40 20 20 20 20 20 20 20 34 39 34 35 36 34 39 35 30 20 39 33 2b
CSI without final frame tag
Remote fax gave CSI as: "+39 059465494       "
<<< DIS: 80 00 ee f8 c4 00
DIS with final frame tag
In state 10
DIS:
   Prefer 256 octet blocks
   Can receive fax
   Supported data signalling rates: V.27ter, V.29 and V.17
   R8x7.7lines/mm and/or 200x200pels/25.4mm
   2D coding
   Scan line length: 215mm
   Recording length: A4 (297mm) and B4 (364mm)
   Receiver's minimum scan line time: 0ms at 3.85 l/mm: T7.7 = T3.85
   Error correction mode
   T.6 coding
DCS:
   Can receive fax
   Selected data signalling rate: V.29, 9600bps
   2D coding
   Scan line length: 215mm
   Recording length: A4 (297mm)
   Minimum scan line time: 20ms
   Minimum scan line time for higher resolutions: T15.4 = T7.7
Start sending document
Start tx document
Changed from phase 2 to 4
 >>> DCS: 83 00 86 80 80 80 00
HDLC underflow in state 3
Changed from phase 4 to 6
Changed from phase 6 to 3
Slow carrier up
<<< CFR: 84
CFR with final frame tag
In state 4
Trainability test succeeded
Start tx page 0
Slow carrier down
Changed from phase 3 to 6
Changed from phase 6 to 4
Start tx page 1
 >>> EOP: 2f
HDLC underflow in state 14
Changed from phase 4 to 3
Slow carrier up
<<< RTN: 4c
RTN with final frame tag
In state 14
Changed from phase 3 to 4
 >>> DCN: fb
HDLC underflow in state 2
Disconnecting
Changed from phase 4 to 7
Changed from phase 7 to 8

Marco Parmeggiani wrote:
> Can someone explain me what's going on and why the receiver of this 
> fax guives up saying communication error?
>
> Start tx page 1
> >>> EOP: 2f
> <<< RTN: 4c
> >>> DCN: fb
> Disconnecting

The receiver says communication error because txfax's response to the 
receiver's RTN signal was a DCN (disconnect) signal instead of a usual 
Phase B signal (i.e. DCS), also known as "retraining".

In non-ECM mode a receiver analyzes the "quality" of the incoming
image
data and determines whether or not it is of an "acceptable quality".  
Then, after the sender transmits the post-page signal (EOP in this case, 
meaning "last page"), the receiver transmits either MCF (confirmation,
meaning the received page quality was acceptable) or RTN (meaning the 
page quality was unacceptable and that retraining is required before the 
next page is received).

My understanding of T.30 (and I'm not alone in this thought) was that 
RTN is meant to be the antithesis of MCF.  So not only does it mean that 
retraining is required for the next page, but it also means that the 
previous page was *not* received properly (i.e. not printed).  So, 
basically the page will need to get resent for the page to get through.  
However, many fax senders (especially old fax machines) were incapable 
of retransmitting a page because they didn't have the memory to store a 
full page of image data and so they sent data as they scanned it.  So of 
necessity these senders had to treat RTN as a confirmation and they left 
it up to the receiver to call back and request a retransmission of 
whatever pages came through uncleanly.  Some senders may have even 
produced a transmission report indicating to the sender which pages 
should be retransmitted in a new call.  Ultimately what this did for the 
fax community, though, was that it gave us a very confused understanding 
of an RTN signal.  And so various things were programmed with this 
confusing understanding programmed-in, and this programming often 
persists in "modern" fax machines because manufacturers don't
rewrite
their fax code very often if ever.

So txfax is behaving as many fax senders out there behave, although my 
opinion is that it is behaving incorrectly... and apparently this 
receiver that you are working with shares that opinion.

Lee.