[cisco-voip] Fwd: Cisco ATA Fax Confusion

[Nick Matthews]

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
>> >
>> >
>> >
>> >
>> >
>> > _______________________________________________
>> > cisco-voip mailing list
>> > cisco-voip at puck.nether.net
>> > https://puck.nether.net/mailman/listinfo/cisco-voip
>> >
>> >
>>
>>
>>
>>
>>
>>
>
>
>
>
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