SCANINTERVAL and TIMEMARK are used together to determine if a connection has been lost. These parameters can be specified in TELNETGLOBALS, TELNETPARMS, and PARMSGROUP. The smallest SCANINTERVAL value is used to define how often the connections are checked. If the SCANINTERVAL value is greater than the TIMEMARK value, the SCANINTERVAL value is reset to the TIMEMARK value. Whenever data is received from the client, Telnet records the time. Telnet checks all connections at regular intervals defined by the SCANINTERVAL value. Each connection is checked to see if any data has been received from the client in the past TIMEMARK period of time. If not, a TIMEMARK command is sent to the client which acts as an "are you there" and Telnet remembers a TIMEMARK was sent to this client. During the next check at SCANINTERVAL time later, each connection is again checked to see if any data has been received from the client. If not, and a TIMEMARK was sent on the previous check, the connection is dropped with DEBUG SUMMARY message CONN DROP reason TIMEMARK.
For example, assume the values for SCANINTERVAL and TIMEMARK 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. 30 minutes later Telnet checks the connections again. If the client responded to the TIMEMARK or sent in actual data of some type Telnet leaves the connection active. If nothing has been received Telnet drops the connection.
A SCANINTERVAL check could occur just before the last data received is old enough to trigger sending a TIMEMARK. The connection remains active until the next SCANINTERVAL is made. Then a TIMEMARK is sent, and at the next SCANINTERVAL the connection is dropped.
Using the example above, SCANINTERVAL checks a connection that received data 2 hours, 59 minutes ago. No TIMEMARK is sent. The next SCANINTERVAL runs 30 minutes later. Now the data received time is greater than 3 hours and a TIMEMARK is sent. At the next SCANINTERVAL, the connection is dropped. The connection's last activity was 3 hours 59 minutes ago.