SPA504G one way voice

[woutervanop]

I have a problem with my spa504g phone. I configured it 2 months ago and it worked perfectly. But since a week ago, if someone calls we can't hear the caller but the caller can hear us. If we call the caller back everything works back perfectly... has anyone a idea what the problem could be?

[George Sotiropoulos]

Hello,

Does the issue occur within the same lan? If not, I would start from checking the traffic between the 2 sides (direction of silence), more specificaly you should check if there are any changes on Routing or blocking access-lists.

George

[woutervanop]

Hello,
Thank you for responding! I'm not a expert in this field so I don't know how to look up these things(maybe you can help?)... but what if there were any changes? What should I do then?

[Dan Lukes]

Audio issues are caused either by firewall or by NAT. In short, RTP (audio) packets are blocked. Capture SIP packets related to SIP call setup and RTP packets related to the call. Identify the network addresses and ports used for RTP (from SDP). Verify the firewall allow such communication.