[cisco-voip] Fwd: Cisco ATA Fax Confusion

[Rhodium]

Hi Nick,

Thanks for replying.

So low speed fax as mentioned by Ryan is just fax "passthrough" (NSE based) with the fax negotiating a speed of <=9600 bps.

Regards,

Jason

--- On Sun, 1/24/10, Nick Matthews <matthnick at gmail.com> wrote:

> From: Nick Matthews <matthnick at gmail.com>
> Subject: Re: [cisco-voip] Fwd: Cisco ATA Fax Confusion
> To: "Rhodium" <rhodium_uk at yahoo.co.uk>
> Cc: "Ryan Ratliff" <rratliff at cisco.com>, "cisco-voip at puck.nether.net Group" <cisco-voip at puck.nether.net>
> Date: Sunday, January 24, 2010, 5:50 AM
> To clarify:
> 
> fax pass-through:  protocol based pass through. 
> Supported in SIP/H323.
> fax passthrough: nse based passthrough.  Same thing as
> modem passthrough
> fax relay:  a method of turning g711 packets into
> specific fax
> packets.  Options are T38 and Cisco.
> Cisco fax relay:  The default method in IOS versions
> before 15.0, and
> uses Cisco NSEs for transport and negotiation.  This
> is not the
> suggested option, as it is legacy.
> T38 NSE switchover:  this is cisco proprietary, and is
> supported with
> SCCP, SIP, MGCP, and H323
> T38 protocol switchover:  This is standards based and
> what you will
> use with 3rd party devices.  Supported in SIP, H323,
> and MGCP.
> NSE:  A cisco proprietary packet value for RTP
> (normally 101) that is
> used between Cisco devices to signal certain fax events.
> 
> modem passthrough: used for both fax and modem passthrough
> using G711.
>  Available in the 4 protocols.  Only thing that ATAs
> officially
> support.  It turns off the echo canceller, and changes
> the playout
> buffer (for jitter).  Cisco proprietary since it uses
> NSEs.
> 
> Faxes can work on G711, but that is if the echo canceller
> and playout
> buffer work for that particular stream and associated fax
> machines.
> It's very likely that high speed faxes (speed > 14.4)
> will not work on
> normal G711.
> 
> 
> Faxing is confusing :)
> 
> -nick
> 
> On Fri, Jan 22, 2010 at 4:52 PM, Rhodium <rhodium_uk at yahoo.co.uk>
> wrote:
> > Can't find anything about that particular fax oIP
> method from googling or on CCO??
> >
> > All I can find are the relay types, and the
> pass-through/passthrough types.
> >
> > Regards,
> >
> > Jason
> >
> > --- On Fri, 1/22/10, Ryan Ratliff <rratliff at cisco.com>
> wrote:
> >
> >> From: Ryan Ratliff <rratliff at cisco.com>
> >> Subject: Re: [cisco-voip] Fwd:  Cisco ATA Fax
> Confusion
> >> To: "Rhodium" <rhodium_uk at yahoo.co.uk>
> >> Cc: "cisco-voip at puck.nether.net
> Group" <cisco-voip at puck..nether.net>
> >> Date: Friday, January 22, 2010, 9:40 PM
> >> It's basically the same as the
> >> straight g.711 fax pass-through.  I think the
> only
> >> difference with this and modem passthrough is that
> when we
> >> detect the fax tones we'll turn off some of the
> DSP features
> >> (ecan, etc) that are useful for voice but not for
> fax.
> >>
> >> -Ryan
> >>
> >> On Jan 22, 2010, at 4:34 PM, Rhodium wrote:
> >>
> >> Thanks for following it up internally. :)
> >>
> >> What is this by the way in terms of fax
> protocols:
> >>
> >> > The other option is that it has fallen back
> to g.711
> >> low
> >> > speed fax and you are getting lucky.
> >>
> >>
> >> --- On Fri, 1/22/10, Ryan Ratliff <rratliff at cisco.com>
> >> wrote:
> >>
> >> > From: Ryan Ratliff <rratliff at cisco.com>
> >> > Subject: Re: [cisco-voip] Fwd:  Cisco ATA
> Fax
> >> Confusion
> >> > To: "Rhodium" <rhodium_uk at yahoo.co.uk>
> >> > Cc: "cisco-voip at puck.nether.net
> >> Group" <cisco-voip at puck.nether.net>
> >> > Date: Friday, January 22, 2010, 9:26 PM
> >> > I ran this by somebody that actually
> >> > works fax issues every day and there are two
> ways your
> >> call
> >> > can be working.
> >> >
> >> > The first is that modem passthrough is
> actually being
> >> > used.  This can be confirmed by waiting 10
> >> seconds
> >> > after the call is answered and looking at the
> output
> >> of
> >> > 'show call active voice brief'.  If you see
> >> modem-pass
> >> > here then it's switched to modem
> passthrough.
> >> >
> >> > The other option is that it has fallen back
> to g.711
> >> low
> >> > speed fax and you are getting lucky.
> >> >
> >> > -Ryan
> >> >
> >> > On Jan 22, 2010, at 4:15 PM, Ryan Ratliff
> wrote:
> >> >
> >> > Are your calls working in one direction only
> or both
> >> > ways?  We are all in agreement that the ATA
> only
> >> > supports NSE based passthrough and I do know
> that the
> >> > default fax protocol on cisco routers is
> modem
> >> passthrough
> >> > so maybe there's another bit of your config
> that's
> >> allowing
> >> > the call to proceed.
> >> >
> >> > In the doc you referenced it mentions that
> no
> >> fall-back
> >> > will still allow for the fax to proceed if
> modem
> >> passthrough
> >> > is configured..  Maybe this also applies if
> fax
> >> > pass-through fallback isn't successful.
> >> >
> >> > -Ryan
> >> >
> >> > On Jan 22, 2010, at 3:50 PM, Rhodium wrote:
> >> >
> >> > Yep, I am aware of the hyphenations. Been
> trying to
> >> use
> >> > them in the right context if you look at my
> emails.
> >> ;o)
> >> >
> >> > I don't think the fall back command applies
> to NSE
> >> > passthrough but protocol based pass-through:
> >> >
> >> > http://www.cisco..biz/en/US/docs/ios/12_3/vvf_c/cisco_ios_fax_services_over_ip_application_guide/t38.html#wp1156682
> >> >
> >> > Also, the written documentation I have shows
> it under
> >> > protocol based pass-through.
> >> >
> >> > Which led me to ask the question, why is it
> working?
> >> Are
> >> > you sure that it refers to protocol based
> pass-through
> >> and
> >> > not NSE?
> >> >
> >> > Regards,
> >> >
> >> > Jason
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >
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> >> >
> >> >
> >>
> >>
> >>
> >>
> >>
> >>
> >
> >
> >
> >
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