Yes, refer to the SRND deployment models chapter for clustering over the WAN requirements and call processing chapter for platform capacities.
Unified CM Capacity Planning
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/8x/callpros.html#wp1156290
If you're not using 8.x refer to the applicable SRND for your version, same chapters.
HTH
java
if this helps, please rate
www.cisco.com/go/pdihelpdesk
HTH
java
if this helps, please rate