The Phone Participants activity selects a session engine based on a percent loaded value reported by each available session engine. Phone Participants then connects to least-loaded engine and uses the engine throughout the session. If the engine should fail (is no longer available), Phone Participants will select a new session engine. This new session engine can be on the same (or different) physical computer from the original session engine. When the failed session engine is restarted it starts up, without any history, as a new session engine. Your dialing components will need to handle a situation where an interviewer does not log out (due to a communication failure or crash) but then proceeds to log in to a new session engine.

In addition, any sample records associated with a failed session engine should be returned as not dialed or passed off to a new session engine. Sample records are moved to the ACTIVE queue when sent to the dialer and cannot be retrieved by another session engine until they are returned. To meet this requirement, your dialing components can pool sample records so that they are not associated with a particular session engine or they could support a recovery step where records that are associated with a now failed engine can be recovered. These are only recommendations. You may choose a different implementation based on your dialer's features and architecture.