https://learn.microsoft.com/en-us/previous-versions/office/lync-server-2013/phase-1-plan-your-migration-from-lync-server-2010?redirectedfrom=MSDN
Phase 1: Plan your migration from Lync Server 2010 - Lync Server | Microsoft Learn
Phase 1: Plan your migration from Lync Server 2010.
plan your migrationlync serverphase