This exit routine provides a way for you to give VTAM® information to create dynamic representations of switched devices without disrupting your switched network. You can also use the exit to specify to VTAM the name of the dynamic switched major node under which the dynamic devices are to be placed. Because the exit allows dynamic definition capability, you do not have to explicitly define a switched device to VTAM before the device attempts to dial in.

You can also use the exit to record connection and disconnection times of switched devices including subarea connection (with VTAM as PU type 5 and NCP as PU type 4).

This exit can also be called for switched devices that are already defined to VTAM. If the exit is called for a known device, you can code the exit to indicate to VTAM that it is to either process or deny requests for contact (REQCONT, or REQACTPU for devices supported by DLUS) from the known switched device.

Before you decide to use a configuration services XID exit routine for dynamic definition, keep in mind that there might be some devices you do not want to define dynamically. For example, if connection time for a particular PU is extremely important, you might want to define the PU in a switched major node. Likewise, you might not want to define dynamically a switched device that makes many connections in a short time.

An important difference between devices defined dynamically and devices defined statically is that when you deactivate a PU defined dynamically, both the device and its subnodes are deleted from VTAM. When a device is deleted from VTAM, you cannot reactivate that device with operator commands. There is one exception—you can deactivate a dependent LU defined dynamically and later activate that same LU with operator commands so long as its PU stays active. You cannot use this exit to define independent LUs dynamically.

VTAM supplies a functional configuration services XID exit routine named ISTEXCCS. The source for this sample exit routine is stored in SYS1.SAMPLIB. The exit runs under a subtask of VTAM. This allows VTAM's main task to continue running while the exit is running. See Sample configuration services XID exit routine for the ISTEXCCS source code.

You can use the sample or write your own configuration services XID exit routine. Whether you use the sample or write your own routine, assemble and link-edit the routine into the appropriate VTAM library.

VTAM sequentially queues REQCONTs or REQACTPUs to the exit. When the exit receives a REQCONT or a REQACTPU, the exit has the opportunity to define the resource dynamically.

VTAM sequentially queues REQCONTs or REQACTPUs to the exit. When the exit receives a REQCONT or a REQACTPU, the exit has the opportunity to indicate to VTAM that it is to process or deny the REQCONT.

If the exit is coded to support connection status reporting, VTAM calls the exit whenever the connection status of a switched PU changes.

If the configuration services XID exit routine abends while processing, VTAM purges all outstanding REQCONTs or REQACTPUs and deactivates the exit; you can use the MODIFY EXIT,OPT=ACT command to reactivate the exit.

You can use the DISPLAY EXIT command to display information regarding a configuration services XID exit. You also can use a MODIFY EXIT command to activate, deactivate, or replace the configuration services XID exit routine without interrupting VTAM processing. See z/OS Communications Server: SNA Operation for more information about these commands.

If you use the MODIFY EXIT,OPT=REPL command to replace your current exit, the level of support specified in the begin vector of the replacement exit must be the same as the level of support specified in the begin vector of the current exit. If you want a different level of support in the replacement exit, deactivate the current exit (MODIFY EXIT,OPT=INACT) and activate the replacement exit (MODIFY EXIT,OPT=ACT).

If you need to trace information relative to configuration services XID exit routine activity, use the MODIFY TRACE and MODIFY NOTRACE commands. These commands allow you to trace the configuration services XID exit's input and output. You can specify which exit functions to trace on the OPTIONS operand of the MODIFY TRACE and MODIFY NOTRACE commands. To display the trace, use the DISPLAY TRACES command.

For information about trace output, see z/OS Communications Server: SNA Diagnosis Vol 1, Techniques and Procedures. For information about the MODIFY TRACE command, the MODIFY NOTRACE command, and the DISPLAY TRACES command, see z/OS Communications Server: SNA Operation.

The following topics contain information that will help you use the sample configuration services XID exit. They also contain information you need to write your own configuration services XID exit routine. You might also want to see Sample configuration services XID exit routine.