Cisco – Configure SIP Trunk from Lync 2013 to Cisco Call Manager v6

ciscolyncsipunified-communicationsvoice

I'm implementing Enterprise Voice for Lync, and I have to get Lync to work with a antiquated Cisco Call Manager version 6. The SIP trunk has been created but I get this error on my Lync servers:

A PBX gateway has been marked as down.

Gateway name: 192.168.1.14.
Cause: A gateway failed to respond to a request within allotted time or was unable to route the request due to some error.
Resolution:
Verify that the gateway is up and can respond to calls.

192.168.1.14 is the IP address of the call manager. I can ping the call manager. Port configuration on both Lync and Call manager look correct (TCP 5060). Performing telnet from Lync FE to 192.168.1.14:5060 is successful.

I have no idea what could be wrong. The version of call manager is so old that I can't find any information on making it work with Lync 2013.

So I'm hoping that someone on these forums has done something similar and can point me in the right direction.

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