Forum Discussion
One-way-audio in some incoming calls from PSTN to MS Teams Client
Hi all,
We have a direct routing setup in place and it is working fine for the most of the times.
(2 x Cisco 4300 Series SBC with the supported SW version, SBC has a public IP assigned directly - no NAT and the required ports on Firewall are open)
For some of the incoming calls (PSTN --> SBC --> Microsoft Cloud --> Teams Client) the caller does not hear the MS Teams user. It happens randomly.
In the SBC logs i see that the same caller had other succesful calls with the same MS Teams without any issues. So it should not be a configuration issue.
Comparing these two calls (one with two-way audio and one with one-way-audio), the only difference I see is, that Microsoft is not sending a RE-INVITE during call setup. (In every succesful call Microsoft is answering the initial INVITE with an 200 OK with SDP and then sends a RE-INVITE to the SBC where the IP address for RTP in SDP is modified)
Can someone help me with this issue? I could provide SIP logs for good and bad calls.
Thanks & Regards,
Levent
IT turned out to be a NAT issue, needed to modify firewall config. Now it is working properly.
- Hi Levent,
Can you please check for the calls with One Way Audio what are the IP Address being used by the in the SDP Calls. Are those IP whitelisted on your firewall? Microsoft have made some changes to the IP Address and ports on the official documentations. Can you please refer to the same?
From my experience the issue only happens when there is a Port or IP Address block on the firewall. If you could share the logs I can look at the same.
With Regards,
Satish UHi Satish, the IP range is up-to-date and allowed on the Firewall. Attached SIP messages for a good and a bad call. The only difference seems to be the RE-INVITE coming from MS.
IT turned out to be a NAT issue, needed to modify firewall config. Now it is working properly.
I agree with Satish (@RealTime_M365) on this. One way audio is usually always a firewall issue resulting from media legs not being allowed. The most common case I've found is defining a media range in your SBC to be from ports X to Y, but only allowing some portion of that range through.
I've seen this on AudioCodes SBCs when doing the configuration because you define the starting port, and the number of media legs, for example 50000, and 100, which one might think would be from ports 50000-50100, but they space out the ports, and it's more likely to be 50000-51000 because of the spacing.
