The Timing mark scan interval and the Timing mark interval are used together to determine if a connection has been lost. Whenever data is received from the client, the TN3270 server records the time. The server checks all connections at regular intervals defined by the scan interval value. Each connection is checked to see if any data has been received from the client in the past timing mark period of time. If no data has been received, the server sends a TN3270 TIMEMARK command to the client, which acts as an "are you there?" and the server remembers that it sent this TIMEMARK. During the next check at the scan interval, each connection is again checked to see if any data has been received from the client. If not, and a TIMEMARK had been sent on the previous scan interval check, then the connection is dropped.
For example, assume the values for scan interval and timing mark interval are 1800 and 10800, respectively. That means every 30 minutes, all connections are checked to see if any data has been received in the last 3 hours. If not, a TIMEMARK is sent to the client. Thirty minutes later, the server checks the connections again. If the client responded to the TIMEMARK or sent in actual data, the server leaves the connection active. If nothing has been received the server drops the connection.
Caution must be used in setting these timers.
Setting the scan interval too low could cause excessive CPU usage.
Setting the timing mark interval too low could cause excessive flooding of the network with TIMEMARK commands.
For
example, these timers should take into account extended breaks such as lunch. If the timing mark interval is smaller
than the lunch break time, the network may be flooded with TIMEMARK commands around the lunch hour.