HylaFAX The world's most advanced open source fax server

[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index] [Thread Index]

Re: [hylafax-users] High Error Rates revisited.



On 2004.08.03 02:38 Stephen Carville wrote:
I now have all four incoming lines being handled by USR modems.  The
two
outgoing lines are still attached to a couple of noname modems.  I
know that
this is not ideal but that is what I have :-)

I notice that all the modems default to xon/xoff for flow control when
setup
using faxaddmodem:

ModemFlowControl: xonxoff

Is this ideal? Is there any advantage in switching to rtscts?

Both XON/XOFF and RTS/CTS are simply flow control mechanisms, i.e. their sole design is to keep the software from sending too much data to the device and overrunning its internal buffer and thus losing data. So if one or both of them do that job properly then you can use that one. If one of them doesn't do that job properly then you can't use that one.


You may be surprised at how many modems actually have broken flow control mechanisms. Fortunately, most installations are going to use a 19200 DTE-DCE baud rate (ModemRate in your config file), and most calls are going to be 9600-14400 baud. If you do the math, it would take quite a bit of TIFF data to overrun a moderate buffer with that small of a difference in speeds. However, this issue becomes much more pronounced when involving V.34-Fax-capable modems, as the modem config file is generally using 56K ModemRate.

Furthermore, you may have a hardware design that eliminates the possibility to use hardware flow control. Some serial port cards will interfere with RTS/CTS flow control. Thus you really can't use a modem that doesn't support XON/XOFF with such cards.

XON/XOFF uses signals between HylaFAX and the fax firmware in order to control the DTE-DCE data flow. RTC/CTS uses signals between the serial port hardware and the serial port driver to control the DTE-DCE data flow. I don't particularly see one of those as being better than the other.

Lee.

____________________ HylaFAX(tm) Users Mailing List _______________________
 To subscribe/unsubscribe, click http://lists.hylafax.org/cgi-bin/lsg2.cgi
On UNIX: mail -s unsubscribe hylafax-users-request@xxxxxxxxxxx < /dev/null
 *To learn about commercial HylaFAX(tm) support, mail sales@xxxxxxxxx*




Project hosted by iFAX Solutions