Content Server Selection (CSS) is a StarOS function that defines how traffic will be handled based on the "content" of the data presented by a mobile subscriber (or to a mobile subscriber). CSS is a broad term that includes features such as load balancing, NAT, HTTP redirection, and DNS redirection.
The content server (services) can be either external to the platform or integrated inside the platform.
CSS uses Access Control Lists (ACLs) to redirect subscriber traffic flows. ACLs control the flow of packets into and out of the system. ACLs consist of "rules" (ACL rules) or filters that control the action taken on packets matching the filter criteria.
ACLs are configurable on a per-context basis and applies to a subscriber through either a subscriber profile (or an APN profile in the destination context. For additional information, refer to the Access Control Lists chapter.