<br><font size=2 face="sans-serif">Robert,</font>
<br>
<br><font size=2 face="sans-serif">For larger solutions we have found that
the VG224 or 248 tend to work pretty good.</font>
<br>
<br><font size=2 face="sans-serif">I can honestly say that we do not have
any 224's out there only 248's but as far as I can remember they are similar
hardware.</font>
<br>
<br><font size=2 face="sans-serif">Craig<br>
<br>
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<td width=40%><font size=1 face="sans-serif"><b>Robert Singleton <rsingleton@novateck.com></b>
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<br><font size=1 face="sans-serif">Sent by: cisco-voip-bounces@puck.nether.net</font>
<p><font size=1 face="sans-serif">02/16/2007 04:59 PM</font>
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<div align=right><font size=1 face="sans-serif">To</font></div>
<td><font size=1 face="sans-serif">Voip List <cisco-voip@puck.nether.net></font>
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<div align=right><font size=1 face="sans-serif">cc</font></div>
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<div align=right><font size=1 face="sans-serif">Subject</font></div>
<td><font size=1 face="sans-serif">Re: [cisco-voip] Fax over Voip (was:Color
Cisco Phones)</font></table>
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<br><tt><font size=2>On Fri, 2007-02-16 at 12:26 -0500, Lelio Fulgenzi
wrote:<br>
> A couple of questions....<br>
> <br>
> - can you not reduce the speed of the G3 faxes to a lower speed?<br>
<br>
We are currently down to 9600 on all the machines that allow the<br>
setting, but according to my research, simply lowering the bit rate does<br>
not necessarily change the audio encoding requirements. Without getting<br>
into the deep detail, the bits in a modem audio stream are encoded into<br>
carefully orchestrated phase and level changes in the carrier tones.<br>
Reproducing the analog waveform from end to end is critical to the<br>
transmission of the data. The bit rate presented to the modem and the<br>
audio requirements of the analog path are not theoretically related to<br>
one another. Even if the bit stream was reduced to 2400 bps, the audio<br>
path must still be able to conduct a V.34bis modem carrier with it's<br>
complex bit encoding phase and level changes.<br>
<br>
In practice, it seems that reducing the bit rate on the fax machines to<br>
at most 14.4kbps can increase reliability somewhat. I think this may be<br>
due to the error correction facilities inherent to the V.34bis standard<br>
which, hidden from the user, retransmits data as needed. Reducing the<br>
data feed rate to 14.4kbps probably increases the reliability by<br>
allowing a huge bit error rate to be concealed by error correction<br>
without overrunning any buffers.<br>
<br>
In our case, 9.6kbps doesn't seem much more reliable than 14.4, probably<br>
because the calls tend to be longer and thus more susceptible to other<br>
long haul problems.<br>
<br>
> - how about the vg224 ports? we are looking at expanding our solution<br>
> to a remote site and it's either vg224s or fxs ports in the router.
i<br>
> just want to buy what i know will work.<br>
<br>
Sorry to go so long about modems.<br>
<br>
We have a borrowed IAD-2400 equipped with 12 FXS ports. This old box<br>
does not appear to support VLANs effectively (this from someone who<br>
should know these things; sadly that is not me) so it's hard to ensure<br>
that QoS is in effect. Part of me says, don't worry about QoS because<br>
the IAD-2400 and our router are one the same Catalyst 6509 switch and<br>
may even be on the same module within that switch, we have a clear<br>
channel DS3 from here to the CoLo where the gateways are and the router<br>
and gateways are on the same 3560 over there. I think that if we have<br>
any congestion problems, we would be worrying about the fax machines<br>
later.<br>
<br>
The appeal of the FXS solution is that with no more than a couple of<br>
exceptions, everywhere I have VoIP phones, I have a 2811 and its rare<br>
that I have more than one or two faxes. In those places where I do have<br>
more than a couple, I tend to have andwhere from 8 to 17 of them, so I<br>
will probably need another solution there. The ATAs work wonderfully for<br>
cordless phones and paging systems and they are so easy to deploy, so<br>
the removed units probably wont go to waste.<br>
<br>
Robert<br>
<br>
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