Quick troubleshooting view
The call is established but one interlocutor does not hear the other. SIP signaling works while, a RTP feed does not return correctly.
- Set missing audio direction
- Internal/external comparison
- Check RTP
- correct NAT andGartan RTP rules
- correct the public address declared
- delete a translation or ALGstat
Contextual technician plan
Note who hears who and in what scenario.
RTP should be visible in both directions with source/destination IP addresses and UDP ports consistent with SDP
Bidirectional RTP is present; investigate codec negotiation, endpoint audio or media processing rather than basic NAT reachability.
Missing RTP in one direction points to NAT/firewall/SDP addressing or an asymmetric media path; keep the capture and correct only the proven path.
Test internal, incoming and outgoing call.
Compare internal, inbound and outbound calls and note for each one whether audio works in both directions.
If all call directions are bidirectional, the failure is not reproduced on this path; compare the endpoint, network and time window of the original incident.
If only one call direction fails, focus on the trunk/SBC/NAT path specific to that direction instead of changing the whole VoIP configuration.
Control UDP flows actually exchanged.
RTP should be visible in both directions with source/destination IP addresses and UDP ports consistent with SDP and the expected NAT path.
Bidirectional RTP is present; investigate codec negotiation, endpoint audio or media processing rather than basic NAT reachability.
Missing RTP in one direction points to NAT/firewall/SDP addressing or an asymmetric media path; keep the capture and correct only the proven path.
Check the rules and disable SIP ALG if the 3CX architecture l requires.
RTP should be visible in both directions with source/destination IP addresses and UDP ports consistent with SDP and the expected NAT path.
Bidirectional RTP is present; investigate codec negotiation, endpoint audio or media processing rather than basic NAT reachability.
Missing RTP in one direction points to NAT/firewall/SDP addressing or an asymmetric media path; keep the capture and correct only the proven path.
Repeat the same validation test after the correction and confirm the original symptom is gone. Validate stability before closing the incident.
Before changing configuration, record the current value and a way back.
Escalader with an example of a horoded call and, if possible, a SIP/RTP capture if the problem is intermittent.
The call is established but one interlocutor does not hear the other. SIP signaling works while, a RTP feed does not return correctly.
Causes probables
- NAT or19th incorrect
- blocked RTP ports
- SIP ALG disrupts the session
- wrong address announced in SDP
Diagnostic étape par étape
- 1
Set missing audio direction
Note who hears who and in what scenario.
- 2
Internal/external comparison
Test internal, incoming and outgoing call.
- 3
Check RTP
Control UDP flows actually exchanged.
- 4
NAT/ALG Control
Check the rules and disable SIP ALG if the 3CX architecture l requires.
Solutions possibles
- correct NAT andGartan RTP rules
- correct the public address declared
- delete a translation or ALGstat
- check the SBC/DECT topology if the problem is located
Escalader with an example of a horoded call and, if possible, a SIP/RTP capture if the problem is intermittent.