[cisco-voip] Fwd: Cisco ATA Fax Confusion

[Ryan Ratliff]

I am using the terms in the way the SRND talks about them.  The commands are even more confusing as fax pass-through and fax passthrough are two entirely different things.  Modem passthrough and fax pass-through are essentially the same thing.  Fax passthrough is the protocol based one that is compatible with 3rd parties.

This doc talks about the two and their differences.
http://www.cisco.com/en/US/docs/ios/voice/fax/configuration/guide/vf_cfg_fx_passthr_ps6350_TSD_Products_Configuration_Guide_Chapter.html#wp1102637

If you try to fax from an ATA to a VG224 then they must both be using compatible fax protocols for the call to switch over to fax at all.  Since the ATA only supports fax pass-through (modem passthrough) this has to be enabled on the VG224.

-Ryan

On Jan 22, 2010, at 12:26 PM, Rhodium wrote:

I guess when you are using the terms faxpassthrough and modem passthrough, you are referring to IOS commands, and not the actual methods which is what I am using in this context.

To use your terms, if a device supporting modem passthrough (ATA) only sends a fax to a gateway configured with fax-relay and fax pass-through (VG224) , then will the gateway fall back to modem passthrough as there is no way for an ATA to send a fax to this gateway due to protocol incompatibility unless I am missing something?

That is really my question?

--- 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, "Nick" <csvoip at googlemail.com>
> Date: Friday, January 22, 2010, 5:06 PM
> The big difference in modem
> passthrough and fax passthrough is that modem uses NSEs
> (in-band) to signal both ends to switch to fax.  Fax
> passthrough is protocol based, which is what sccp does not
> support.   Because the NSEs are cisco
> proprietary modem passthrough will only work with Cisco
> devices while fax passthrough would be required for a fax
> between cisco and 3rd party IP fax devices.
> 
> -Ryan
> 
> On Jan 22, 2010, at 10:58 AM, Rhodium wrote:
> 
> It is an excellent resource but doesn't go into fax
> passthrough to the level of my question as my concern was
> regarding the interoperability between the two different
> pass through protocols and not fax relay.
> 
> So ATAs support modem passthrough and the difference
> between that and fax passthrough is that modem passthrough
> looks for phase reversals, but it falls back to fax
> passthrough if there are none. Am I correct in the fall back
> assumption?
> 
> Also, trying to work out how a Cisco VG224 configured for
> pass-through (protocols based) can receive faxes from ATAs
> supporting passthrough. Was wondering if there is some kind
> of interoperability going on here a new feature I wasn't
> aware of.
> 
> Guess, debugs will show that....
> 
> 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,
> "Nick" <csvoip at googlemail.com>
>> Date: Friday, January 22, 2010, 3:43 PM
>> The fax section of the CUCM SRND is a
>> very good resource for this.
>> 
>> The ATAs appear to support modem passthrough for fax
> only.
>> 
>> "T.38 fax relay is supported on most of the current
> Cisco
>> voice gateways, especially those running Cisco IOS.
> Notable
>> exceptions are the Cisco Analog Telephone Adaptors
> (ATAs)
>> and legacy products such as the Cisco 6608, 6624, and
>> DT-24/DE-30+.
>> 
>> Most Cisco voice gateways support Cisco fax relay, and
> it
>> is the default fax transport method. Notable
> exceptions with
>> regard to the support of Cisco fax relay are the
> Cisco
>> AS5350 and AS5400 with Nextport DSP cards, the Cisco
> ATA,
>> and the Cisco DT-24/DE-30+. Another exception is that
> the
>> Cisco 2900 and 3900 Series gateways with the PVDM3
> DSPs do
>> not support Cisco fax relay..
>> 
>> Unlike T.38 fax relay, which uses an Unnumbered
> Datagram
>> Protocol Transport Layer (UDPTL) header, Cisco fax
> relay
>> utilizes the standard RTP header, which makes Cisco
> fax
>> relay capable of secure fax transactions using Secure
>> Real-Time Transport Protocol (SRTP).
>> 
>> Modem passthrough is supported by all current Cisco
> voice
>> gateways, including the Cisco ATA as well as most
> legacy
>> voice gateways."
>> 
>> http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/7x/gateways.html#wp1046809
>> 
>> -Ryan
>> 
>> On Jan 22, 2010, at 10:08 AM, Rhodium wrote:
>> 
>> Hi All, Nick and Venkata,
>> 
>> Thanks for the feedback but do you have the issue of
> not
>> being able train the faxes or missed pages?
>> 
>> I am still after an answer to my question about what
> fax
>> protocol is actually supported on the ATAs and on the
> VG in
>> SCCP mode as my theory does not relate to real life?
>> 
>> Regards,
>> 
>> Jason
>> 
>> 
>> 
>> 
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> 
> 
> 
> 
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