Every connection must be represented by an LU name before a session can be initiated. The time of LU assignment depends on the connection type. In general, for TN3270E clients, the LU name is assigned early during connection negotiation before an application name is known. For all other types of clients, the LU name is assigned immediately after application name selection. For details and exceptions to this rule, see Advanced LU name mapping topics. Mapping statements define which LU name is assigned to the connection.