Recently a client running Lync Server 2013 had a poor experience with anonymous external dial-in users getting kicked out of meetings at a certain point in time- usually around the 30minute mark. The odd thing is that we didn't see this happen on a consistent basis. However after some Q and A with a small survey group, we could narrow for certain that it was anyone calling into the dial in access number associated with NSW (Sydney, Australia) users.
Searching through some Microsoft articles on TechNet, there are ways to adjust certain fields via PowerShell to ensure a better user experience.
The main cmdlet is:
Lync Server relies on the User Services service to help maintain presence information for users and to manage meetings and conferences. In turn, the CsUserServicesConfiguration cmdlets are used to administer User Services configuration settings at the global, site, and service scope.
The Set-CsUserServicesConfiguration cmdlet provides a way for administrators to modify information about any (or all) of the User Services configuration settings currently in use.
After some testing and review, it seems that the default value for one key parameter was either set by another admin, or carried over from a legacy Lync Server 2010 deployment. To ensure a better user experience, I recommend changing the bellow parameter and I'll explain shortly:
Set-CsUserServicesConfiguration -Identity "Global" -AnonymousUserGracePeriod 10:00:00
The default value for the AnonymousUserGracePeriod is 01:30:00; meaning that anonymous users can join a scheduled Lync meeting through the dial in access number without an authenticated (or Lync user) present for a maximum of 1hour and 30 minutes. I found we had this setting adjusted to 30 minutes only. In this situation I've set above a period of 10 hours allowing for a rather long meeting time, although-when conducting web conferencing sessions and you have users dialling in, you don't want to have to re-create new sessions once you start.
Ideally users that are authenticated, that is internal Lync users who setup the conference, should be dialled in through their respective Lync client and not simply using the dial in access number. This ensures that you don't have the problem of the anonymous user grace period parameter kicking in. Circumstances, user preference among other reasons come into play though and this should be used as a backup measure only. The default of 90minutes is fine for most situations.
Personally I would set it to 3 hours, double the default, which enough time for the majority of Lync conferences where an authenticated user might dial in not via their Lync client.