You can provide geographical redundancy by clustering application servers over WAN. Also called disaster recovery, this configuration protects you in the event of disruption of service at a location due to a network or power outage or a natural disaster. In the following illustration, the company has a redundant telephony system and redundant application servers. The degree and kind of survivability in this case depends on how much system capacity is being actively used. If Location Atlanta is running at or near 200 port capacity and the location is struck by a hurricane, the Location Atlanta DR site would take over, and there would be no loss of service. If Location Atlanta is using only 100 ports, Location Atlanta could survive a complete network or power outage at its main location, plus a failure of one of the application servers at the DR location.
