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Dear Community,

I have a one way audio scenario on hard phones but soft phones on the same location dont have an issue. Where could I start tshooting this? Inbound calls dont have an issue just outbound.

I have a third party gateway not the cisco router.

Much appreciated as always,



6 Replies 6

One way audio issues is mostly due to routing issue. 
Media flow from phone to phone. So check the network rechability  from the subnet which you don’t hear to the other phone subnet. 

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Hi Nithin,

I appreciate the feedback.

The routing I have confirmed to be ok. There is end to end reachability. The issue is when calls are made outbound. How can I begin, tshooting this?





any firewall involved ? asymetric routing ?

what protocols used ?

use dna and protocl logs on gateway to find what endpoints are involved in the rtp connectoins.

allow end point connectivity to the gateway voip sourcing ip for testing.

access the webpage of the softphone/hardphone and observer the streams there to find source desintaiton.

make a call flow to find the source destination for rtp streams then ensure routing and rtp ports access .. allow b/w 15000 to 33000  ports between them as these are what rtp uses

Is it a generic issues or only for the branch phones ?

I mean it happens only when calling numbers through branch gateway ?

what pstn connection you have, sip or PRI ?

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Sadav Ansari
VIP Alumni
VIP Alumni

Make a call from both CIPC and Hard phone and check the media steam via the phone web access by accessing the phone ip.

it could be disabled so enable the web access for those phone which you will on testing.

On the phone web access under steam section you can see the remote and local party address along with RTP port.

Here you can identified what port are using for both of the case and those RTP port should be open at firewall end if firewall coming in the picture also you can check the packets from which side you are not receiving so based on that you can identify the problem.

Also check the Vlan config for both working and non working case.


Pls rate if its “Helpful”. If this answered your question pls click “Accept as Solution”.



Sadav Ansari


it's possible that there is an issue with the way the hard phones are configured to communicate with the third-party gateway.

Here are some steps you could take to troubleshoot the issue:

  1. Check the network configuration: Make sure that the hard phones are properly configured to communicate with the third-party gateway. Check the network settings on the phones, including IP addresses, subnet masks, and default gateways.

  2. Check the codec settings: Make sure that the hard phones are using the same codec as the third-party gateway. If the codec settings are not compatible, it could cause one-way audio.

  3. Check the firewall settings: Make sure that the firewall settings on the network are not blocking the communication between the hard phones and the third-party gateway.

  4. Check the NAT settings: If the third-party gateway is behind a NAT device, make sure that the NAT settings are configured correctly.

  5. Check the SIP settings: If the hard phones are using SIP to communicate with the third-party gateway, make sure that the SIP settings are configured correctly. Check the SIP server settings, authentication settings, and any other relevant settings.

If none of these steps solve the issue, you may need to consult with a network or telephony specialist to help diagnose the problem.

I hope this helps!

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