Problems with desktop/app sharing/viewing through conference

Question

We have a problem with viewing shared desktop/app with external contacts in a conference. We're able to share/view desktop/app directly with an external users, but not in a conference. We get the error message: "Sharing failed to connect due to network
issues. Try again later."
If we're using the web app on the same computer where we have the problem, we're able to view the content in the conference.
It's working fine internally, it's also working fine when users are outside of our office.
All other functions in Lync are working fine.
We have 1 standard Lync server and 1 Edge, we don't have a reverse proxy but multiple IPs with port forward to corresponding ports on each server.
How does the Lync client connect the shared content?

Answer 1

To Fix your issue, you can follow below steps
A common root cause for this error occurs when required ports are not available. Begin troubleshooting by verifying required ports.
Public --> Edge server:
TCP/443
UDP/3478
TCP/50,000-59,999 (Outbound only)
Determining External A/V Firewall and Port Requirements
Topologies for External User Access
From the Front End pool to the internal Edge:
TCP/5062
TCP/443
UDP/3478
From the internal Edge to the Front End Pool:
TCP/5065
TCP/49152-65335 (Inbound/Outbound)
Ports and Protocols for Internal Servers
From the internal Client to the internal Edge:
TCP - 443
UDP – 3478
Also you can refer below link
http://blogs.technet.com/b/nexthop/archive/2012/11/05/lyncmd-troubleshooting-lync-server-2010-application-sharing-internal-and-remote-scenarios.aspx
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