[cisco-voip] T.38 Fax Issue

Mon Jan 17 14:53:42 EST 2011

Sometimes faxing works without any configuration, which can be misleading.
The difference between passthrough and straight g.711 is a longer jitter
buffer, disabling dtmf, and disabling the echo canceller.

That is odd that a zte device would send proprietary cisco nse packets.
Maybe that is what changed, the gateway?

I don't think they are using pt 96 for dtmf because the event numbers
generally match the dtmf digit pressed.

Instead of seeing nse packets you should be seeing a sip reinvite with a
t.38 sdp since it should ve a protocol based negotiation.
On Jan 17, 2011 12:22 PM, "Antonio Soares" <amsoares at netcabo.pt> wrote:
> It’ s a SIP trunk between a Cisco GW (the one I have control) and a ZTE
> device… It was working with the config I have shown. Something was changed
> on the other side. I was trying to make it work using the options
available
> at our side. Unfortunately I don’t have the debugs captured when this was
> configured so I still have a doubt. What PT should be used in this T.38
> negotiation ? PT=100 or PT=101 ?
>
>
>
> PT=100: Designates an NSE (Named Signaling Event packet). NSE packets can
> signal a variety of different messages so it is helpful to know the NSE
> Event ID.
>
>
>
> PT=101: Designates an NTE (Named Telephony Event) as defined in RFC 2833.
>
>
>
> Check this table:
>
>
>
> https://supportforums.cisco.com/docs/DOC-1387
>
>
>
> I was convinced that it was PT=100 (NSE) but as you said, they are Cisco
> proprietary. So maybe it should be PT=101 (NTE) ?
>
>
>
>
>
> Thanks.
>
>
>
> Regards,
>
>
>
> Antonio Soares, CCIE #18473 (R&S/SP)
> <mailto:amsoares at netcabo.pt> amsoares at netcabo.pt
>
>
>
> From: matthn at gmail.com [mailto:matthn at gmail.com] On Behalf Of Nick
Matthews
> Sent: segunda-feira, 17 de Janeiro de 2011 17:56
> To: Antonio Soares
> Cc: Peter Slow; cisco-voip at puck.nether.net
> Subject: Re: [cisco-voip] T.38 Fax Issue
>
>
>
> When you say SIP trunk, are you implying that this is going to a SIP
> provider? Or is this just a SIP gateway and the fax is going out a TDM
> interface?
>
> If it's a SIP trunk you're sending the fax over, forget about anything
using
> NSEs - like Pete said they're Cisco proprietary.
>
> You'll need to configure the other device for protocol based T.38
switchover
> like you've got it configured on your end.
>
> -nick
>
> On Mon, Jan 17, 2011 at 10:21 AM, Antonio Soares <amsoares at netcabo.pt>
> wrote:
>
> We tried the "fax protocol t38 nse force" but it didn't work.
>
> Now with "fallback cisco" we have something different:
>
> --------------------------------------
> s=VoIP d=DSP payload 0x60 ssrc 0xFFD5D4C sequence 0x291 timestamp
> 0x19A50
>
> <<<Rcv> Pt:96 Evt:136 Pkt:01 40 50
> --------------------------------------
>
> s=DSP d=VoIP payload 0x61 ssrc 0xFFE2 sequence 0x0 timestamp 0x0
> Pt:97 Evt:0 Pkt:00 04 00 <Snd>>>
> --------------------------------------
> s=DSP d=VoIP payload 0x60 ssrc 0x0 sequence 0x0 timestamp 0x0
> Pt:96 Evt:0 Pkt:00 00 00 <Snd>>>
> --------------------------------------
> s=VoIP d=DSP payload 0x60 ssrc 0xFFD5D4C sequence 0x292 timestamp
> 0x19AA0
>
> <<<Rcv> Pt:96 Evt:136 Pkt:01 40 50
> --------------------------------------
>
> s=DSP d=VoIP payload 0x61 ssrc 0x60014 sequence 0x1 timestamp 0x1
> Pt:97 Evt:0 Pkt:01 00 00 <Snd>>>
> --------------------------------------
> s=VoIP d=DSP payload 0x60 ssrc 0xFFD5D4C sequence 0x293 timestamp
> 0x19AF0
>
> <<<Rcv> Pt:96 Evt:136 Pkt:01 40 50
> --------------------------------------
>
> s=DSP d=VoIP payload 0x61 ssrc 0x0 sequence 0x2 timestamp 0x2
> Pt:97 Evt:0 Pkt:01 00 00 <Snd>>>
> --------------------------------------
> s=VoIP d=DSP payload 0x60 ssrc 0xFFD5D4C sequence 0x294 timestamp
> 0x19B40
>
> <<<Rcv> Pt:96 Evt:136 Pkt:01 40 50
> --------------------------------------
>
> s=DSP d=VoIP payload 0x61 ssrc 0x0 sequence 0x3 timestamp 0x3
> Pt:97 Evt:0 Pkt:01 00 00 <Snd>>>
> --------------------------------------
> s=DSP d=VoIP payload 0x7A ssrc 0xFFFFFFFF sequence 0x9EBF
> timestamp 0x2FE4CED0
> Pt:122 Evt:0 Pkt:52 3A 00 <Snd>>>
> --------------------------------------
>
> Now we see:
>
> Pt:96 Evt:136 (Sent by a voice gateway to signal a switchover to Cisco
> fax relay)
> Pt:97 Evt:0 (Sent by a voice gateway to confirm a successful switchover
> to Cisco fax relay)
> Pt:122 Evt:0 (Indicates Cisco fax relay data)
>
> So I was expecting this would mean it was working but apparently it still
> doesn't work.
>
> I'm using this document as reference:
>
> Cisco RTP Payload Types
>
> https://supportforums.cisco.com/docs/DOC-1387
>
> Any other ideas ?
>
>
>
> Thanks.
>
> Regards,
>
> Antonio Soares, CCIE #18473 (R&S/SP)
> amsoares at netcabo.pt
>
>
> -----Original Message-----
> From: Peter Slow [mailto:peter.slow at gmail.com]
>
> Sent: segunda-feira, 17 de Janeiro de 2011 12:16
> To: Antonio Soares
> Cc: cisco-voip at puck.nether.net
> Subject: Re: [cisco-voip] T.38 Fax Issue
>
> No, "fallback cisco" is different. You need to try the "fax protocol
> t38 nse force" command.
>
> -pete
>
>
> On Mon, Jan 17, 2011 at 6:58 AM, Antonio Soares <amsoares at netcabo.pt>
wrote:
>> It was working before so I assume the other end's configuration was
> changed.
>> This is a SIP trunk and we have this configuration for the T.38 fax:
>>
>> voice service voip
>> fax protocol t38 ls-redundancy 0 hs-redundancy 0 fallback pass-through
>> g711alaw
>>
>> We are now trying the following:
>>
>> voice service voip
>> fax protocol t38 ls-redundancy 0 hs-redundancy 0 fallback cisco
>>
>> This should match their PT=96 request, right ?
>>
>>
>> Thanks.
>>
>> Regards,
>>
>> Antonio Soares, CCIE #18473 (R&S/SP)
>> amsoares at netcabo.pt
>>
>>
>> -----Original Message-----
>> From: Peter Slow [mailto:peter.slow at gmail.com]
>> Sent: segunda-feira, 17 de Janeiro de 2011 11:50
>> To: Antonio Soares
>> Cc: cisco-voip at puck.nether.net
>> Subject: Re: [cisco-voip] T.38 Fax Issue
>>
>> Usually t.38 Fax relay operates by switching to t.38 based on an MGCP
>> MDCX, a new h245 TCS/OLC etc, or a SIP re-invite. this is referred to
>> as protocol based switchover, and is generally how people's gateways
>> are configured for t.38 when it is being used. it would appear that
>> the other GW you are talking to is set up for NSE based switchover,
>> which AFAIK is a cisco proprietary method. You may be configured for
>> protocol based switchover still, while it sounds like perhaps the
>> other side went and changed something and is now trying to do NSE
>> based switchover...
>>
>> Check out this link:
>>
>
http://www.cisco.com/en/US/docs/ios/12_3/vvf_c/cisco_ios_fax_services_over_i
>> p_application_guide/t38.html#wp1156699
>>
>> It is tough to help you out beyond what I've said without knowing what
>> protocol (h.323, MGCP..) you are using for call control. More insight
>> there, plus perhaps some asn1 or mgcp packet debugs would help, but
>> try setting your side to use nse based switchover if it isnt set that
>> way already.
>>
>> -Peter
>>
>>
>>
>> On Mon, Jan 17, 2011 at 5:48 AM, Antonio Soares <amsoares at netcabo.pt>
> wrote:
>>> Hello group,
>>>
>>> A few days ago, fax stopped working on one gateway. The "debug voip rtp
>>> session nse" gives me this:
>>>
>>>
>>
>
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>> ++++++++++++++
>>> s=VoIP d=DSP payload 0x60 ssrc 0x509B391F sequence 0x18E
>> timestamp
>>> 0xF8C0
>>> <<<Rcv> Pt:96 Evt:136 Pkt:02 80 50
>>> s=VoIP d=DSP payload 0x60 ssrc 0x509B391F sequence 0x18F
>> timestamp
>>> 0xF910
>>> <<<Rcv> Pt:96 Evt:136 Pkt:01 40 50
>>> s=VoIP d=DSP payload 0x60 ssrc 0x509B391F sequence 0x190
>> timestamp
>>> 0xF960
>>> <<<Rcv> Pt:96 Evt:136 Pkt:01 40 50
>>> s=VoIP d=DSP payload 0x60 ssrc 0x509B391F sequence 0x191
>> timestamp
>>> 0xF9B0
>>> <<<Rcv> Pt:96 Evt:136 Pkt:01 40 50
>>> s=VoIP d=DSP payload 0x60 ssrc 0x509B391F sequence 0x192
>> timestamp
>>> 0xFA00
>>> (...)
>>>
>>
>
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>> ++++++++++++++
>>>
>>> Most likely, the problem is on the other end, a gateway that I do not
>>> control.
>>>
>>> I believe for this to work I need to receive PT=100 and EVT=200:
>>>
>>> Payload Type 100: Designates an NSE (Named Signaling Event packet). NSE
>>> packets can signal a variety of different messages so it is helpful to
>> know
>>> the NSE Event ID.
>>>
>>> Event 200: Triggered by the detection of a V.21 fax preamble when T.38
is
>>> configured. This message initiates the switchover of the call from voice
>> to
>>> T.38. This message is sent by the terminating fax gateway to notify the
>>> originating fax gateway of the switch to T.38.
>>>
>>> And I'm receiving PT=96 and EVT=136. PT=96 means " Sent by a voice
> gateway
>>> to signal a switchover to Cisco fax relay". I wasn't able to find the
>>> meaning of EVT=136.
>>>
>>> With this information, can I assume that the problem is on the other end
> ?
>>> Can I do anything on my side to force the desired PT/EVT combination ?
>>>
>>>
>>> Thanks.
>>>
>>> Regards,
>>>
>>> Antonio Soares, CCIE #18473 (R&S/SP)
>>> amsoares at netcabo.pt
>>>
>>>
>>> _______________________________________________
>>> cisco-voip mailing list
>>> cisco-voip at puck.nether.net
>>> https://puck.nether.net/mailman/listinfo/cisco-voip
>>>
>>
>>
>
>
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