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Fax outdial retries consume all voice channels on SIP 484 error (Cisco 2911)

I've been seeing a nasty fax/VoIP problem on a 2911, running  IOS 15.0(1r)M12.  Any suggestions would be welcome.

 

I have a 2911 which is set up to do T.37 offramp fax delivery (SMTP message is sent to 2911, which places a VoIP call over SIP/RTP/T.38 to deliver the fax).  The mainline case is set up, and working correctly - faxes are delivered without issue.  If a destination address is selected such that the VoIP switch returns a SIP 484 error, then everything fails in a spectacular fashion:

  • The outdial is immediately retried, placing another SIP INVITE to the switch, with the same destination address, which obviously also gets the same 484 response.
  • Each time the outdial takes place, it consumes voice channels on the DSP, which are not released on receipt of the 484.
  • When there are no free voice channels, a no circuit (0x22) error is returned, and all the voice channels are finally released.
  • The MTA that submitted the SMTP message retries every minute (it doesn't get a permanent failure report when the 2911 fails to place the call)

 

This leads to a situation where no fax calls can be placed, as all the voice channels are being used up by retrying this call that can never succeed.

 

Some other relevant information:

  • The VoIP switch does not return a 484 immediately.  First it sends a SIP 183, and plays early media (an announcement about how the call isn't allowed).
  • It takes 8 seconds before the 484 is returned.  The 2911 sends a new SIP INVITE every 8 seconds (as soon as it gets a 484 for the previous attempt).
  • The "sip-ua" statistics show that the INVITE retry counter is not  being incremented (i.e. this is not a retry at the scope of the SIP stack).
  • The T1 cable is looped-back to the 2911, so that the complete path for fax delivery looks like this:

    MTA ---SMTP---> 2911 ---T1---> 2911 ---SIP---> VoIP switch

  • If I set "mta receive generate permanent-error", then I still see this retry behaviour, with all the voice channels being consumed.  Once that has happened (after about 3 minutes) the MTA does get the error response, and no longer retries every minute after that (although this setting has other negative effects that I'd like to avoid).

 

Does anyone have any idea how I can get the 2911 to return a permanent failure to the MTA after just a single outdial has failed with a SIP 484?

 

Here is the dial-peer config:

!
dial-peer voice 1 voip
 translation-profile incoming IncomingVoip
 incoming called-number .
 voice-class codec 1
 dtmf-relay rtp-nte
 fax protocol t38 version 0 ls-redundancy 3 hs-redundancy 0 fallback pass-through g711ulaw
 no vad
!
dial-peer voice 2 pots
 destination-pattern ^0005
 port 1/1:23
 forward-digits all
!
dial-peer voice 3 pots
 translation-profile incoming IncomingPRI_1_0
 service onramp-app
 incoming called-number ^0005
 direct-inward-dial
 port 1/0:23
!
dial-peer voice 4 mmoip
 service fax_on_vfc_onramp_app out-bound
 destination-pattern .
 information-type fax
 session target mailto:$m$@<DOMAIN NAME>
 image encoding MH
!
dial-peer voice 101 mmoip
 translation-profile incoming IncomingMMoIP
 service offramp-app
 information-type fax
 incoming called-number .
!
dial-peer voice 102 pots
 destination-pattern .
 port 1/0:23
 forward-digits all
!
dial-peer voice 103 pots
 translation-profile incoming IncomingPRI_1_1
 incoming called-number ^0007
 direct-inward-dial
 port 1/1:23
!
dial-peer voice 104 voip
 translation-profile outgoing OutgoingVoip
 destination-pattern ^0008
 session protocol sipv2
 session target ipv4:<VoIP SWITCH IP ADDRESS>
 voice-class codec 1
 dtmf-relay rtp-nte
 fax protocol t38 version 0 ls-redundancy 3 hs-redundancy 0 fallback pass-through g711ulaw
 no vad
!

 

 

  • IP Telephony
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