SOLUTION: Peer to Peer audio video Works but does not work in a Lync meeting from Internet

Solution: Peer to Peer voice video works but does not work in a Lync meeting from Internet

Applies to: Lync 2013 & Lync 2010 Server


If a Lync client user connects from internet starts voice or video (Lync Call) to another user it works. But if the user creates a meeting (by meet now option in Lync client and Use Lync full audio and video option) after few seconds the user gets “you have left the call” error and rejoin button. Even before the user invites the second user. Off course rejoin does not work, as a result audio and video does not work in the meeting.

Same problem in web meeting. If user joins a Lync meeting from Internet using web browser then audio video does not work.

So audio/video works in peer-to-peer Lync call from Internet but not in a meeting. Even there is only 1 user (meeting organizer) in the meeting.


If a meeting is created then Lync Front End Server acts as a MCU for the meeting with Lync Server Audio/Video Conferencing service. (C:\Program Files\Microsoft Lync Server 2013\OCSMCU\AV Conferencing\AVMCUSvc.exe ) . All voice/video traffic must be delivered by Lync 2013 Front End server (unlike peer-to-peer call)

And TCP 443 and UDP 3478 ports are closed from Lync 2013 Front End to Lync 2013 Edge server


Open the following ports on Firewall:


Lync 2013 Front End server with MCU role. IP (Lync Server Audio/Video Conferencing Service)


Lync 2013 Edge server Internal interface IP


TCP 443 and UDP 3478

Make sure that Front End server resolves FQDN of the internal interface of Edge server and Edge server can resolve Lync pool FQDN and all Enterprise Front End servers in the pool.

More Info:

If you get a network trace during the problem with Wireshark you see ICMP packets with the description ICMP Destination unreachable (port unreachable). Which reminds me to check ports mentioned above.

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