With the release of Exchange 2013 CU1, we can finally deploy the Unified Contact Store (UCS) into an existing Exchange2010 SP3 environment. This is because Exchange2013 is required for UCS and the GTM version of Exchange2013 did not support coexistence with previous versions of Exchange. To recap, UCS enables users to store all contact information in Exchange 2013 so that the information is available globally across Lync, Exchange, Outlook, and Outlook Web Access. Without UCS, Lync2013 clients cannot change or upload their photos. Below is the UCS architecture diagram for reference:
Deploying Exchange2013 CU1 itself is beyond the scope of this article and the steps are provided in Technet. For existing Exchange2010 environments as in the case of this lab setup, upgrading to Exchange2010 SP3 is required which also performs the prepare AD schema, thereby eliminating the need to run setup.exe /PrepareSchema using Exchange2013. After deploying Exchange2013 we also need to run the post-install steps as described in here. Most notably would be the need to assign a CA issued certificate for the CAS role as Exchange2013, like it's predecessors, by default uses a self-signed cert which Lync2013 will not recognize. Once the prerequisites are done, enabling unified contact store in Lync Server 2013 does not require any topology settings. All that's needed is that the Unified contact store policy is enabled (default is enabled), user's mailboxes have been migrated to Exchange2013, and user log in with using the Lync 2013 rich client at least once.