[cisco-voip] T.38 Fax Issue

[Peter Slow]

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
>>
>>
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>>
>
>