The Audio/Video Conferencing Server could not establish a network connection for the SIP channel Audio/Video Conferencing ...

The Audio/Video Conferencing Server could not establish a network connection for the SIP channel

Audio/Video Conferencing Server Pool: %2; Microsoft Lync Server 2010 Front End Pool: %1 Exception: %3
Cause: This issue may occur due to network connectivity, DNS lookup failure, TCP failure or TLS issues.
Resolution:
Resolve network connectivity issues between the Audio/Video Conferencing Server and the Microsoft Lync Server 2010 Front End.