Prerequisites You must have SIP Trunk license on your AVAYA according to your simultanous call count.
This can be done by editing Endpoint SIP under GoTrunk settings and set port to 5160 You can also set remote SIP port to 5160 under GoTrunk. If you deployed IP Authentication you have one other option.
Verify Registration Check that the PBX has been registered on the SIP server. That is for the sip trunk to send his sip messages back to the public IP address assigned to the IP-PBX.
Here's the critical section where you need to enter a couple of parameters in the PEER Details box to make the trunk work with Lync. On the Add SIP Trunk page, enter a suitable Trunk Name and scroll down till you see Outgoing Settings section.
This article explains how to forcibly disconnect the call so it does not use up one an available port on the switch. For ShoreTel systems version 12.x and lower on rare occasions a call will not fully disconnect and a received call will show as connected and use up one of the available ports even though the original caller has been disconnected. Call queuing is a great way for phone operators to manage high volume of calls.