Status-Acknowledge messages are the basic mechanism used to enforce inbound and outbound data acknowledgment protocols on all three connections. See Outbound Data and Inbound Data for details of the use of Status-Acknowledge messages.
For a 3270 emulation application, Status-Acknowledge messages sent from the application to the local node (acknowledging outbound data from the host) can also carry information on host response times. This allows the local node to maintain response time statistics for sending to the host when required. See Response Time Monitor Data for details.