Lync 2010 client does not login in Lync 2013 server

ISSUE:  Lync 2010 client does not login in Lync 2013 server.


CAUSE:  The cause may be following one from 3.

i.   Client version filter in Lync SERVER
ii.  Network Security: Minimum session security in Lync SERVER



SOLUTION:

i.   Client version filter in Lync SERVER :  Here

ii.  Network Security: Minimum session security in Lync SERVER :  Here