Pipeline context properties

what is actually the difference between  “routeDirectToTP” and “loopback” pipleine context properties??

this is the description…

//Defines whether the message should be submitted into the

//server for a loop back execution. In loop back execution,

//the request message is published into the MessageBox database

//where it is routed directly to the receive adapter as a response.

RouteDirectToTP routeDirectToTP = new BTS.RouteDirectToTP();