Telnet Keep-Alive Time-Out Parameter
The TCP protocol utilizes a mechanism to probe if the client is still
active. The TCP keep-alive parameter (TCPKEEPALV) specifies at which
intervals the protocol begins to probe the client. When the value in
this parameter has been reached, the TCP protocol will send a TCP
keep-alive request to the client. If the client does not respond to the
first request, the protocol will re-send the request until the client
responds or until the tenth request has been sent. If the client does
not respond to any of these requests, the protocol will assume the
client is no longer active (for example, PC hanging or re-booting,
network drop, and so on).
The Telnet server takes advantage of the TCP keep-alive functionality
with its Session keep-alive parameter (TIMMRKTIMO). For Telnet, the
recovery action depends on the type of virtual device associated with
the user's interactive job. If it is an auto-selected virtual device
(for example, QPADEV0002), then the interactive job is always ended. If
it is a named virtual device, (for example, PC52S1), then the action
specified in the system value QDEVRCYACN is taken. Once action has been
taken on the interactive job, the virtual device is recovered to a VARY
ON PENDING status to allow a new connection.
Whereas the Telnet Session keep-alive parameter is used to detect and
act upon clients no longer responding, the system value QINACTITV is
used to act upon inactivity by the user (for example, user went to lunch
still logged onto the session). The QINACTITV value defines the length
of time an interactive job can be in DSPW status before action is taken.
For auto-selected virtual devices (for example, QPADEV0003), the
interactive job is always ended. For named virtual devices (for example,
PC52S1), the system value QINACTMSGQ defines what action is to be taken
with the interactive job. The virtual device then goes into a SIGNON
DISPLAY status and the user is presented with the sign-on screen. For
further information on system value QINACTITV, refer to document
12822845, QINACTITV System Value Explained . To link to 12822845
immediately, click here
How to Access the Parameters and Values
The TCP keep-alive parameter (TCPKEEPALV) can be set using the Change
TCP Attributes ( CHGTCPA ) command. The value defaults to 120 minutes.
Changes to the TCP Attributes take affect immediately.
The Telnet Session keep-alive parameter (TIMMRKTIMO) can be set using
the Change Telnet Attributes ( CHGTELNA ) command. The value defaults to
*CALC (on most systems this equates to 600 seconds).
System values can be displayed and changed using the appropriate options
from the Work with System Values screen. This screen can be accessed
with the WRKSYSVAL command: