A SIP server can be deployed in a two-tier architecture, including an engine tier for processing of SIP communications and a state tier for maintaining the state associated with these communications. The state tier can include RAM-based replicas that provide data to the engines. Some of the SIP session...http://www.google.com/patents/US8078737?utm_source=gb-gplus-sharePatent US8078737 - System and method for efficient storage of long-lived session state in a SIP server
