Re: [hylafax-users] LOG EXPLAIN (RTN meaning)

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

Jonny Berthiaume wrote:

> I understand why the fax machine cannot resend the page, I didn't 
> thought about it that way. But, you must admit that a sheet-fed fax 
> machine where it does not have sufficient memory to store the entire 
> page image is nowadays somewhat a rare bird in the jungle.


Yes, I suspect that any modern fax machine will have enough memory to 
store just about any legal-sized page that it may need to fax.  That 
said, I strongly suspect that most fax products out there - including 
both fax machines and fax modems - run on maintained legacy code that 
originates from the early 1990's... or earlier.  So certain behaviors 
may have been created in response to hardware particulars from long ago, 
and those behaviors may have never changed since then because the legacy 
fax code being used is merely maintained and not redesigned or revised.  
So just because they could be able to do something does not necessarily 
mean that they will.

> I was refering to an impressive number of Ricoh multi-function 
> products which treat the RTN as "Over and out -- hang  up ...".


I'm not sure what you mean here.  Do you mean to say that the Ricoh 
machines, when acting as a fax sender and receiving an RTN signal, will 
not continue to the next page and will not signal an error to the user?  
I don't expect them to retransmit the same page again - and I've already 
expressed why I can anticipate that - but the fax machine *should* 
proceed to the next page, according to spec.  If it does not, then 
indeed it does treat RTN as "Over and out -- hang up...".

If you mean that the Ricoh machines, when acting as a receiver, send the 
RTN signal in an effort to get the sender to hang up, and will not 
accept any more pages, then that is something that I have not seen 
before, and yes it would indicate the "Over and out -- hang up..." 
interpretation.

I don't have any Ricoh machines on-hand to test this with.  I'm curious 
to know how you've come to these conclusions about the Ricoh's 
interpretations of the RTN signal.

> I don't know if all their product use that code that way, but there is 
> a large selection of models who does. I didn't come across any other 
> fax machine that respond that way, but I believe that if a world wide 
> company like Ricoh is doing it, I guess others do it as well.


Dmitry was specifically working with Canon fax machines when he was 
developing the RTNHandlingMethod feature.

> And with this fact in hand, I might not be so prompt to delete the 
> specified statement in the man pages.


I didn't say that I wanted to delete the statement, but that I wanted to 
rewrite it.  And, in fact, I already did rewrite it (at least in 
HylaFAX+ sources).  It reads this way now (let me know if you disagree):

*RTNHandlingMethod*
   Specifies how to react to an RTN signal received from the remote:
   one of ``Retransmit'', ``Giveup'',``Ignore'', or ``Retransmit-Ignore''.

   ``Retransmit'' assumes that the page is not received successfully.
   HylaFAX will make up to two additional attempts to send the page,
   decreasing signalling rate and retraining. If RTN continues, up to 2
   additional calls will be placed. The downside is that if the remote
   always responds with RTN, the page will be sent 9 times and no
   following pages will be sent. Many fax machines will not behave this
   way, although T.30 specification seems clear that this is the intent
   of the RTN signal.

   Many fax machines will interpret RTN as meaning to not send the same
   data again. That is because RTN may indicate problems with flow
   control, incorrectly encoded T.4 data, or some incompatibility other
   than line noise. Fax machines that interpret RTN this way will
   disconnect and require a manual retransmission. This ``over and
   out'' behaviour can be activated by the ``Giveup'' value. The
   advantage to this behavior is that the same page of image data will
   not be sent multiple times, but the downside is that the following
   pages will not be sent.

   ``Ignore'' is similar to ``Giveup'' in that it makes the assumption
   the data cannot be automatically accepted by the receiver. However,
   rather than disconnecting the page of image data is abandoned and
   processing moves on to the next. The remote is left to decide what
   to do with the unacceptable page of image data. The downside to this
   behavior, is that the remote may or may not have kept the page,
   depending on its interpretation of the RTN signal - but it does
   allow us to continue on to the next page.

   ``Retransmit-Ignore'' is a combination of ``Retransmit'' and
   ``Ignore''. The page of image data is retransmitted up to two
   additional times, but rather than disconnecting after a third RTN
   signal for the same page, processing then continues on to the next
   page. This approach is an effort to satisfy both interpretations of
   an RTN signal. It allows the receiver to hopefully receive a better
   copy of the image data while not failing to send subsequent pages.
   If the receiver saves or prints a copy of pages for which it
   transmits RTN, then it could save or print up to three copies of
   every page.


Thanks,

Lee.


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