See the Level 1 basic diagnostic/testing/support workflow.


#1-Is Skype for Business (Lync) client running?  Run it.

#2- Are calls being cut off after 30 seconds? Get a valid registration key.

#3-Can you replicate the problem running ONLY the Skype for Business (Lync) client? It is a Skype for Business issue.
#4-Are you using a USB Headset? Try with just USB Headset and NOT an IP Phone/BTOE device.

See enclosed diagram/workflow file: