"Brian K. White" <brian@aljex.com> wrote in message
news:029701c8ab4b$77248c80$6b00000a@venti...

----- Original Message -----
From: "Enrique Arredondo" <atk@sbcglobal.net>
Newsgroups: comp.unix.sco.misc
To: <distro@jpr.com>
Sent: Tuesday, April 29, 2008 5:25 PM
Subject: Re: OSR 507 using an external modem with an USB serial to Ethernet
adapter


>
> "Brian K. White" <brian@aljex.com> wrote in message
> news:036901c8a979$f60c7e50$3a8d53d0@venti...
>
> ----- Original Message -----
> From: "Enrique Arredondo" <atk@sbcglobal.net>
> Newsgroups: comp.unix.sco.misc
> To: <distro@jpr.com>
> Sent: Monday, April 28, 2008 3:52 PM
> Subject: OSR 507 using an external modem with an USB serial to Ethernet
> adapter
>
>
>>I have a device called the UDS1100 made by lantronix that let's me convert
>> any serial device into a TCP IP device, I tried this on printers and dumb
>> terminals and it works really good. My final task is to move my fax
>> modems
>> that I run with VSIFAX on unix from tty1A13 or tty3E13 into this new
>> device.
>>
>> Has anyone played out with this configuration and figure out a way of
>> making
>> the scripts or dialers that communicate with the modem to hit the
>> assigned
>> IP address and port so the modem works ?
>>
>> In the case of the printer my "model" file starts with :
>>
>> #!/bin/sh
>> YOUR_PRINTER_OR_IP="192.168.2.19"
>> PORT=9100
>>
>>
>> and then I just assign the printer to that model and use /dev/null and
>> that
>> works out great.
>>
>>
>> Can I do the same trick for the external modem thru the "Serial-Ethernet"
>> device that wants to be called on port 10001 ?
>> IP address= "192.168.6.182"
>> Port="10001"
>>
>> Thanks
>
> I have used a few different serial device servers (digi, equinox, perle)
> with fax modems and both hylafax and vsifax.
>
> However:
>
> * In all cases the device had a driver and/or daemon that provided tty
> device nodes that work just like ordinary hardware serial ports. vsifax
> didn't need any special config, just tell it the tty device name and
> perhaps
> doctor the permissions on those tty's for vsifax.
>
> * You are really not supposed to use fax modems over tcp like that because
> the fax protocol is very timing dependant, and the tcp/ip layer makes few
> promises about timing, so you may or may not see a lot of failed faxes
> even
> though everything is configured absolutely perfectly. This is not my
> opinion
> but the word right from ifax (hylafax) and VSI.
>
> I had a lightly loaded gigabit network and only about 8 modems on a 32
> port
> digi (or a 16 port equinox for a while). Nics, switch, and digi were all
> pretty over specced for the dribble of traffic 8 14.4kb modems can
> deliver.
> It _mostly_ worked ok. I don't do that any more though.
>
> --
> Brian K. White brian@aljex.com http://www.myspace.com/KEYofR
> +++++[>+++[>+++++>+++++++<<-]<-]>>+.>.+++++.+++++++.-.[>+<---]>++.
> filePro BBx Linux SCO FreeBSD #callahans Satriani Filk!
>
>
> How about if I create a "VIRTUAL Serial Port" and then use that one
> instead
> ? Is there such thing on SCO Unix ?

What did I just say?
Thats exactly what I just said the drivers for most such devices provide.

I looks and smells just like a serial port, so, from the software's point of
view it thinks it's fine.

But that doesn't mean it will actually _work_ well, even though the virtual
port driver is perfectly robust.

The problem has to do with timing. The fax protocol requires things to
happen within specific windows of time, and tcp/ip does not garantee that
any given packet will get delivered within any specific window of time.

Confusingly, on most reasonable lan's it'll actually work ok mostly, but
even on an over-spec'd lan, tcp/ip just plain doesn't make promises about
how long a given packet will take to get delivered. That means sometimes the
fax protocol will break no matter what. Even on a lightly loaded lan there
are spikes and bursts of other traffic, and those will cause your virtual
port traffic to incur little pauses, a packet may take 300 ms to get
delivered instead of .01 ms, and the fax that was in progress fails because
the handshaking protocol broke because the server needed to acknowledge the
next phase within 50ms and it took 10 ms to actually do the work and then
the virtual port took another 300 ms to react to a command because the
tcp/ip packet that delivered the command took that long to get to the serial
device server.

If you had a switch that allows you to set QoS levels then you could give
traffic on the tcp port that the virtual serial driver uses higher priority,
like what you do for voip. That would probably reduce the occurance of
delayed commands significantly.

And if you use only fax class 2 modems then since they do most of the fax
protocol in the modem hardware, that will probably also help to ensure it
works even more often since it would reduce the number of timing-critical
commands between the server and the modem.

But it still can never be 100% that way because tcp/ip just plain does not
promise that anything ever will happen either instantly nor even within any
specific time, whereas the fax protocol does require and promise that
various things happen within various times.

--
Brian K. White brian@aljex.com http://www.myspace.com/KEYofR
+++++[>+++[>+++++>+++++++<<-]<-]>>+.>.+++++.+++++++.-.[>+<---]>++.
filePro BBx Linux SCO FreeBSD #callahans Satriani Filk!

I did it!!

I compiled this code :
ftp://ftp.lantronix.com/priv/svr_tty/svr_tty-README.txt

created a config file,

runned the daemon

and fax is working!!!!!

the only thing is that now ssh can't create ptyp ports or some strange thing
that I thing is related to this program that locks a device.