When you install an app agent, the agent detects incoming calls and registers transactions based on the default transaction detection rules. Automatic detection rules describe entry points for transactions based on supported frameworks.

Typically, more than one tier participates in the processing of a transaction. A request to the originating tier may invoke services on:

• Another instrumented tier – called a downstream tier.
• Remote services that are not instrumented.

Outbound requests from an instrumented application tier are called exit points. Downstream tiers may, in turn, have exit points that invoke other services or backend requests.

App agents tag exit point calls with metadata describing the existing transaction. When an agent on a downstream tier detects an entry point that includes transaction metadata from another app agent, it treats the entry point as a continuation of the transaction initiated on the upstream tier. This linking of upstream exit points to downstream entry points is called correlation. Correlation maintains the client request context as it is processed by various tiers in your business application.