[Asterisk-Users] Re: SpanDSP TXFax and multipage faxes problems (aditional info)

[Lee Howard]

Nenad Radosavljevic wrote:

> OK I see the ponit (although I never said that second page is 
> interrupted - I said that in some combinations of resolutions and TIFF 
> options receiving fax "spits" another blank sheet of paper beside the 
> clearly received first page).


Oh.  Well, then that's another matter.

>
> I have read someware (some faxing tutuorial) that there is some kind 
> of control code (6 EOLs I belive) that should be in TIFFs between 
> pages and that is called RTC (return to control).


This is correct.  In traditional (non-V.34) fax the high-speed data 
carrier (V.17, V.29, or V.27ter) is raised by the sender and listened 
for by the receiver, and the page image data is transmitted on that 
carrier.  The receiver (in non-ECM mode) decodes the data and counts 
lines using EOLs as a reference.  When the receiver encounters six 
consecutive EOLs (RTC) it knows that it has reached the end-of-page and 
can expect the sender to drop the high-speed carrier.  The receiver will 
then wait for the sender to raise a V.21 carrier to transmit what you've 
called "handshaking".

In practice, though, the receiver pretty much just needs to wait for the 
carrier drop.  The RTC signal may or may not be used by the sender, and 
it may or may not be corrupt.  The carrier drop is the end-of-page 
signal for the fax protocol.  RTC is the end-of-page signal for the 
image data.  So if we're talking T.4 then the end-of-page signal is 
RTC.  If we're talking T.30 then the end-of-page signal is a carrier drop.

> Whole thing wasn't explained completly, and since I have no access to 
> adequate specifications, I have thought that problem is there (I mean 
> I thought that there is some negotiation before every page sent).


Well, it could be a txfax problem, but Steve would need to look into 
it.  I can't help there.  I use HylaFAX attached to ttys, so I don't use 
txfax/rxfax.

> Anyhow, as a workaround, I will modify faxing program I have made for 
> secretary, to sent one page at the time (so multi page faxes are sent 
> in multiply calls to a receiving fax).


If you do much faxing that could get more costly than just buying a fax 
modem and faxing with something like HylaFAX.  For best results you'll 
need a PSTN line not coming directly from Asterisk (as Asterisk seems to 
have some kind of problem on the TDM FXS cards that bothers only faxing).

Lee.