If a session is full-duplex, conversations on that session can be full-duplex or half-duplex. If a session is half-duplex, conversations on that session must be half-duplex. In full-duplex conversations, an LU can send and receive data simultaneously. In half-duplex conversations, only one LU can send data at a given time. One transaction program in the conversation must be designated as the sender and the other as the receiver. Sessions between logical unit partners are designated as contention-winner or contention-loser sessions. If the two LU partners attempt to use a session simultaneously, the designated contention winner for the session has priority for the use of the session. An application program can allocate a conversation over a session for which it is designated the contention loser, but the logical unit partner must give the application program permission.