From: Kurt Bergsbaken (kbergsbaken@yahoo.com)
Date: Mon Dec 08 2003 - 15:19:22 GMT-3
Giralt's book on Troubleshooting IP Telephony has an
excellent chapter on all the subtleties of fax-relay
and pass-trough. VAD, codecs and the fact that fax
operates in full-duplex, (differently than a voip
conversation would) are all considerations, p. 446
nails these questions.
--- Scott Morris <swm@emanon.com> wrote:
> You can use any fax rate unless you limit it
> someplace else (like on the
> command line for relay). Otherwise, an uncompressed
> 64k channel is
> capable of faxing at any speed.
>
> As for your errors, that would depend on the fax
> machines being ECM
> capable or not. Routers will do nothing about the
> packet loss, it's a
> UDP thing.
>
> As for the FXS port diffferentiating, the cards have
> the ability of
> detecting a T.30 fax tone. At that point there are
> some differences in
> the way the the codec will handle things and kicking
> it into a
> passthrough mode.
>
> Scott
>
>
>
> -----Original Message-----
> From: John Tafasi [mailto:johntafasi@yahoo.com]
> Sent: Monday, December 08, 2003 12:52 PM
> To: swm@emanon.com; 'ccielab'
> Subject: Re: Simple FAX over IP question
>
>
> Scott,
>
> Thank you for the link. I actually reviewed that
> document before. The
> configuration is pretty simple but I still have some
> questions in my
> mind, assuming no modems are used:
>
> If the fax machines are not connected to modems and
> are connected
> directly to voice ports, can I use any fax rate in
> the dial peer
> configuration? How will the fax machines or the
> routers react to packet
> loss? (in other words i tend to think that error
> correction will be
> handled by the fax machines and not the routers) The
> FXS port is able to
> differentiate between a voice call and fax call. Is
> that true? The same
> FXS port can handle both voice and fax calls from
> the connected machine
> that is acting as both a fax and a telephone
> device. Is that true?
>
> Thanks
> John Tafasi
>
> ----- Original Message -----
> From: "Scott Morris" <swm@emanon.com>
> To: "'John Tafasi'" <johntafasi@yahoo.com>;
> "'ccielab'"
> <ccielab@groupstudy.com>
> Sent: Monday, December 08, 2003 5:32 AM
> Subject: RE: Simple FAX over IP question
>
>
> > The answer is "it depends". Whether you are doing
> simple passthrough,
>
> > or setting up a relay, there are different
> commands involved. At a
> > mininum, you'll want to be sure you are able to
> relay DTMF tones
> > correctly, but there are many other varieties as
> well.
> >
> > On the doc CD, check out:
> >
> >
>
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122new
> > ft
> > /122t/122t11/faxapp/
> >
> > HTH,
> >
> >
> > Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service
> Provider) #4713,
> > CISSP, JNCIS, et al. IPExpert CCIE Program Manager
> > IPExpert Sr. Technical Instructor
> > swm@emanon.com/smorris@ipexpert.net
> > http://www.ipexpert.net
> >
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com
> [mailto:nobody@groupstudy.com] On Behalf
> > Of John Tafasi
> > Sent: Monday, December 08, 2003 3:59 AM
> > To: ccielab
> > Subject: Simple FAX over IP question
> >
> >
> > I have two remote fax machines each is connected
> to an FXS voice port
> > on a router. The two routers are connected with an
> IP network.
> >
> > Is there any SPECIAL VoIP configuration needed to
> make the two fax
> > machines to sommunicate with each other?
> >
> > Thanks
> >
> > John Tafasi
> >
> >
>
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