[cisco-voip] Fwd: Cisco ATA Fax Confusion

Sun Jan 24 12:50:39 EST 2010

both passthrough, pass-through, and relay can handle up to 14.4.  Some
of the newer 15.0 code is supposed to allow 56k, but I haven't heard
the results of the testing.

-nick

On Sun, Jan 24, 2010 at 9:41 AM, Rhodium <rhodium_uk at yahoo.co.uk> wrote:
> 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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>> >> > https://puck.nether.net/mailman/listinfo/cisco-voip
>> >> >
>> >> >
>> >>
>> >>
>> >>
>> >>
>> >>
>> >>
>> >
>> >
>> >
>> >
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>> >
>>
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