Logical unit connection test (IBMTEST)

You can enter the IBMTEST command from a terminal to find out whether that terminal can communicate with its owning SSCP. When you use the IBMTEST command, an unformatted RU is sent through the network path supporting the LU-SSCP session. This RU contains the IBMTEST command followed by the number of times the SSCP is to return (echo) the data to the logical unit and optional data (up to 247 bytes) being sent to the SSCP.

You can increase the possibility of repeating an intermittent error that is hard to re-create by using IBMTEST, because you can request up to 255 echoes. You can also use it to determine whether a suspended LU-LU session is caused by either a hardware problem or by a problem with VTAM® or an application program.

Start this test with the following command:

IBMTEST [n][,data]

n: Specifies the number of times the test data should be returned to the terminal. Specify n as a decimal number in the range 1–255. If no value is specified, a value of 10 is used by default.
data: Specifies the test data to be returned. Specify a character string of up to 247 characters, or the maximum message length of the terminal, whichever is smaller. If no test data is supplied, VTAM returns the following alphanumeric sequence:
ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789

The IBMTEST command is valid only for terminals that use the USS LOGON format. The IBMTEST command must be defined in the USS table for that terminal.

Note: This echo check does not verify that a terminal can establish a session with an application program in the host, because the session request may specify a different network path than the one supporting the terminal's LU-SSCP session. If the requested path is unavailable, the session request is rejected, even though another path is available.

If there are any errors, the VTAM operator receives a message that contains the logical unit name associated with the terminal, the number of echoes that took place before the I/O error, and the error sense code.