Calls getting disconnected after one hour in Mediant 1000B

Hi,

We are using Mediant 1000B with Lync server 2013 running at the background.Recently after some users reported and after observing incoming and outgoing calls I found that the calls are getting disconnected after exactly 40 minutes.Iam not able to find the parameter where this timer is set. Please help.

Thank you

Regards

Sriram