[cisco-voip] Fwd: Cisco ATA Fax Confusion

[Ryan Ratliff]

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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