This figure provides a high-level view of the layers in an Oracle Application Server active-active topology. The layers from top to bottom are:

- clients

- firewall

- external load balancer

- OracleAS Web Cache from Release 2 (10.1.2)

- Oracle HTTP Server from Release 2 (10.1.2) or Release 3 (10.1.3)

- middle-tiers from Release 3 (10.1.3). This includes OC4J and middle-tier applications.

- Oracle Identity Management from Release 2 (10.1.2). This includes Oracle HTTP Server, OC4J Security (to run OracleAS Single Sign-On and Oracle Delegated Administration Services), Oracle Internet Directory, and OracleAS Infrastructure database.

- Customer database

Middle-tier applications can access the Oracle Identity Management and the customer database. From the Oracle HTTP Server, mod_plsql can also access the customer database.