G.711 Rightfax faxes failing at 15 minutes

[Tanner Jackson]

A change was recently made on one of our Rightfax Servers to use G.711 instead of T.38 and outbound faxes now drop at 15 minutes (change was made to avoid ongoing T.38 issues with transmission errors)

We see the initial outbound invite where the fax establishes as G.711 and we see another T.38 re-Invite 4 seconds later from the far end as that is their preferred method in which the Rightfax Server responds with a 488 Media Not Acceptable and the fax begins transmitting in G.711.

Call Manager sends another Invite at the 15 minute mark at which point the Rightfax Server responds with another 488 Media Not Acceptable and the fax drops. Cause code Q.850 reason 96

2 failed call flows are below. I believe the issue to be with the CUCM or Rightfax Servers responses to CUCM SIP keep alive methods at 15 minutes.

Fails at 15 minutes in BOTH scenarios:

G.711 Rightfax Server --> CUCM 12.5 --> T.38 Rightfax Server

G.711 Rightfax Server --> CUCM 12.5 --> CUBE --> Lumen Voice Complete (SIP) --> Far Endpoint

We see CUCM is indeed initiating the re-Invite at 15 minutes and believe that is behaving correctly but believe CUCM does not like the Rightfax Servers response.

Attached is packet capture screenshot between G.711 Rightfax Server and CUCM. RTP traffic omitted 

[Elliot Dierksen]

This is my mostly standard voice service voip block for a CUBE. What does yours look like?

voice service voip
 mode border-element
 media statistics
 media bulk-stats
 allow-connections sip to sip
 fax protocol t38 version 0 ls-redundancy 0 hs-redundancy 0 fallback pass-through g711ulaw
 no fax-relay sg3-to-g3
 fax-relay ans-disable
 sip
  session refresh
  midcall-signaling passthru media-change

[Tanner Jackson]

Below is our CUBE configuration. We felt that if we could sort out the simpler flow first T.38 Rightfax --> CUCM --> G.711 Rightfax were there was no CUBE involved, we'd potentially solve for the more complex issue to external parties.

voice service voip
ip address trusted list
mode border-element
allow-connections sip to sip
redundancy-group 1
no supplementary-service sip refer
signaling forward none
fax protocol t38 version 0 ls-redundancy 0 hs-redundancy 0 fallback pass-through g711ulaw
trace

[Elliot Dierksen]

15 minutes is where the default session refresh occurs. Try adding this.

voice service voip
sip
  session refresh

[Tanner Jackson]

We don't have a CUBE in this flow T.38 Rightfax --> CUCM --> G.711 Rightfax. So the Session Expires Timeout on the CUCM is what would be causing the timeout. In the RTMT SIP Messages diagram we see the CUCM initiating the INVITE at the 15 minute mark.

[Elliot Dierksen]

What device is your PSTN connection? In the situation I referenced, it is ITSP -> CUBE -> CUCM -> Rightfax.

[elvinmorales]

Hi Tanner, I am seeing similar behavior from Rightfax in my environment. Did you find a solution ?

[Tanner Jackson]

Hi Elvin, we ended up having to cut out the CUCM in the outbound call flow which resolved the issue. Inbound call flow remained the same:

Inbound - PSTN -> CUBE -> CUCM 12.5 -> G711 Rightfax server

Outbound - G711 Rightfax server -> CUBE -> PSTN

[Alex Schuette]

Something you can try if you are still having this issue...

I ran into a similar issue when we started using G711 renegotiation for specific callers. The solution ended up being on the RightFax server. As Tanner notes above, the Sip Session Expires Timer, by default on call manager is 1800 seconds, at half that value 900 seconds (15 minutes) Call manager sends out a reINVITE to verify the call is still active. The Rightfax server was not responding to this reINVITE so Call manager would tear down the call. After making the following change, the RightFax server responds to the reINVITE message and keeps the call up. 

1. Launch Enterprise Fax Manager and select Services.
2. Configure RightFax DocTransport Module.
3. Expand Brooktrout, Select RightFax OEM
4. Select Configure Brooktrout
5. Click OK when prompted to login
6. Select Advance Mode
7. Select SIP
8. Select T.38 Parameters tab
9. Select Show Advanced
10. Make sure that the option "Support G.711 fallback SIP RTP reINVITE" is set to True."

I will mention the previous responses in this post are also helpful with making sure g.711 is supported as a failback on the server and on CUBE dial peers. I had settings set as they have noted. This particular change was the one that fixed the 15 minute issue.