Abstract: A session-oriented network application dependent on reliable transport of messages on a first system communicates in a new form of connectionless, session-oriented communication called Sideband over a network with a second similar application on a second system. Sideband transport is not guaranteed; Some types of messages and those which are lost must be sent on a reliable, non-Sideband transport. The LAN application contains means to track whether Sideband is both available and enabled on its session with the second application. The application determines whether to disable or reenable the Sideband in its session based on network reliability. As Sideband is fast, but unreliable, the application must be selective about which messages to send Sideband. Messages which would change the state of the receiving system if received twice due to retry of an apparently lost message should not be sent Sideband.