Call Transfer Issue

[ntnetzeband]

We have two SIP trunks that we use. Telnyx for primary which we just ported our numbers to and Flowroute as secondary. We are having an issue where incoming external calls that are answered and then transferred to another external number causes the call to fail through Telnyx but go through fine through Flowroute.

The error coming back is below:

Q.850;cause=96;text="MANDATORY_IE_MISSING"

Telnyx says that the invite message is missing the Contact and SDP fields.

We have no issues for regular calls through Telnyx and the call connects fine through Flowroute so my question is, is there different outbound parameters for transfers versus regular calls or does anyone know why these invite messages would be missing these fields?

 

[eddv123]

Hi ntnetzeband,

This cause indicates that the equipment sending this has received a message which is missing an information element which must be present in the message before that message can be processed.

So they are probably right, Telnyx are a supported provider as far as I can see so should be able to assist more than what they have done so far. Have you performed this yet ?
https://www.3cx.com/blog/docs/ironton-telnyx-sip-trunks/

 

[ntnetzeband]

I tried adding that but we still get the same issue.

They determined what fields were missing but didn't know how it was handled through 3CX when a call is transferred.

Regular calls work just fine but it's only when we transfer to an external number.

Are SIP invites handled differently on transfers versus normal outbound calls?

 

[leejor]

I'm wondering if it has anything to do with the caller ID (validity, as determined by the provider) "attached" to the transferred number.

 

[YiannisH_3CX]

Hello @ntnetzeband

Can you tell me the exact version PBX you are running and the scenario the calls fail so i can try and replicate? For example: The incoming call comes into a queue and is answered by an agent. Then it is transferred using blind transfer to an external number. Is the number also a US number?