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Inbound one way audio - Cisco to SIP trunk (Lync)

Hello fellow Cisco professionals,

I had a weird issue happening in our environment at the moment. We have a CUCM SIP trunk integration with Lync Mediation servers for outbound/ inbound call in Lync (S4B).

Everything was fine until last week when suddenly there's one way audio for Inbound call issue appeared at this is impacting all Lync Users in the cluster.

Scenario :

> Cisco phone calling Lync using E164

> Mobile phone (PSTN) calling Lync using E164

We did few testing:

1. Check the network reach ability from Voice gateway to Lync client (VG is the MTP) - Okay

2. Check any packet drops on the firewall - All good

3. Check the SIP traces and SDP looks fine as well


1. We disabled Media Bypass on Lync server - call become two way audio

2. When in one way audio call, we press hold and resume the call - call become two way audio

So based on your experience, do share your opinion or suggestion. Thanks in advance



1 Reply 1

Hi Experts out there, would you mind sharing your taught on this?

Really appreciate any input

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