[cisco-voip] Fwd: Cisco ATA Fax Confusion

Nick Matthews matthnick at gmail.com
Sun Jan 24 19:17:13 EST 2010 

He was commenting on the difference of passthrough and normal G.711
operation.  In theory, you should be able to place fax/modem calls
over G.711 since it's not compressed.  This turns out not to be the
case because the way echo cancellers and the jitter buffers used for
voice don't work perfect for modems/faxes.  It can still be done
however, which is why faxes and modems will work sometimes without
doing any configuration.  Passthrough really just disables the ECAN,
disables DTMF, and modifies the jitter buffer, and it's G.711 under
that.

-nick

On Sun, Jan 24, 2010 at 4:00 PM, Rhodium <rhodium_uk at yahoo.co.uk> wrote:
> I appreciate what you are saying and understand the difference between the protocols and how they function.
>
> I do not know of any other protocol apart from the ones you and I mentioned so I was perplexed by an earlier statement made by Ryan as regards low speed fax. Which led to my question on that:
>
> "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"
>
> As far as I am aware, low speed fax is just a term for any fax pass-through, passthrough, relay that uses less than 9600bps, it is not a separate method of fax transmission.
>
> That is my question?
>
>
>
> --- 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, 8:04 PM
>> passthrough and pass-through get you
>> to the same place, just with two
>> different methods.
>>
>> just like protocol based T38 and NSE based T38 get you to
>> the same
>> place, just in two different ways.  The end
>> destination is the same
>> for protocol based or NSE based.  I'm not entirely
>> sure what your
>> question is.  What I'm saying is that there was a new
>> project to make
>> that 'destination' or protocol be able to handle higher
>> speeds.  At
>> the moment I can't remember if it was a 15.0M release or
>> 15.1T
>> release.
>>
>>
>> -nick
>>
>> On Sun, Jan 24, 2010 at 1:06 PM, Rhodium <rhodium_uk at yahoo.co.uk>
>> wrote:
>> > In relation to Ryan's comments, it would be NSE based
>> fax passthrough with the fax negotiating low speed, not
>> something inherently differently to the passthrough
>> protocol. So it is not a different type of FaxoIP method but
>> uses an existing method which is NSE passthrough.
>> >
>> > Am I right?
>> >
>> > --- 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 PM
>> >> 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
>> >> >> >> >
>> >> >> >> >
>> >> >> >> >
>> >> >> >> >
>> >> >> >> >
>> >> >> >> >
>> >> >>
>> _______________________________________________
>> >> >> >> > cisco-voip mailing list
>> >> >> >> > cisco-voip at puck.nether.net
>> >> >> >> > https://puck.nether.net/mailman/listinfo/cisco-voip
>> >> >> >> >
>> >> >> >> >
>> >> >> >>
>> >> >> >>
>> >> >> >>
>> >> >> >>
>> >> >> >>
>> >> >> >>
>> >> >> >
>> >> >> >
>> >> >> >
>> >> >> >
>> >> >> >
>> >> _______________________________________________
>> >> >> > cisco-voip mailing list
>> >> >> > cisco-voip at puck.nether.net
>> >> >> > https://puck..nether.net/mailman/listinfo/cisco-voip
>> >> >> >
>> >> >>
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >>
>> >
>> >
>> >
>> >
>>
>
>
>
>
>

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