| HP LoadRunner Protocol SDK Overview > About LoadRunner Protocols |
A LoadRunner protocol is a set of dynamic link libraries, resources, and configuration files used by LoadRunner to emulate a client application's interactions with its server application. Protocols participate in:
All LoadRunner protocols provide services for running scripts during test run. Most protocols provide services to support recording sessions and code generation.
Note that this version of the SDK enables you to create protocols that support only test run. For information about the services you can provide in your custom protocol, see Features Supported by the SDK and Features Not Supported by the SDK.
During a recording session, a user (most commonly a software developer or tester) performs a business process on a client application while LoadRunner traps the requests sent by the client and the servers' responses. A protocol can provide specialized functions, called hook functions, to trap requests and responses of interest to the protocol. The recorded communication events are saved.
When session recording is complete, LoadRunner performs code generation, during which it scans the recorded events and creates a test script that can be used to replay the recorded session. A protocol can provide specialized functions to process the events of interest to the protocol. When the events are processed, LoadRunner translates them into test steps and writes the script. The user can edit the script and add various checks and correlations to make the recorded script a usable test. The user can also invoke code generation manually at any time after recording.
During test run, LoadRunner creates virtual users (Vusers). Each Vuser reads the functions in the script and calls the implementations of the script functions in the protocols' libraries. The protocol performs the appropriate actions so that the server application responds as though it were working with an instance of the client application. The server's responses are evaluated to determine if application errors occurred and to evaluate the server application's performance under load.
For more information, see the HP LoadRunner Virtual User Generator User's Guide.