Device identification

If the exit returns the begin vector with the dynamic build bit set, VTAM® queues the XID vector to the exit whenever any of the following attempts to dial in:

An unknown switched PU type 1, 2, 2.1 device
An unknown switched PU type 2 or 2.1 for DLUR-supported devices
A casually connected PU type 4 or 5 device

The exit uses the information provided in the XID vector to construct a build vector and any necessary resource entry blocks.

The exit needs a way to identify the unknown device. A device allowed to participate in dynamic builds can have its definition in either a created CPNDEF or NIDDEF definition file. If the device is identified by a CPNAME, its definition is in the CPNDEF file. If the device is identified by a NODEID (IDBLK and IDNUM), its definition is in the NIDDEF file.

Both the NIDDEF and the CPNDEF definition file names must match your exit name.

The exit searches for a valid, unique name for the unknown device. The exit checks the X'10' bit, which indicates that VTAM received from the dependent LU requester (DLUR) a PU name on the REQACTPU in a X'0E' vector and did not find a defined PU with that name. If the bit is set, the exit will use this PU name to build a resource entry block for the device. (See Table 1 for bit and PU name offsets.) If the bit is not set, the exit then attempts to find a CPNAME field. If there is no CPNAME field, the exit attempts to find a NODEID field. If the unknown device does not have either a CPNAME field or a NODEID field, the exit invokes the name generation function.

If the exit finds a valid CPNAME field or NODEID field for the device, the exit searches for the device's definition in either the CPNDEF or NIDDEF file. If the exit does not find a definition in CPNDEF or NIDDEF, the exit invokes the name generation function.

If the exit finds the device's definition in either the CPNDEF or the NIDDEF definition file, the exit looks for a complete resource name or model name pair for the device. If the exit finds a complete resource name or model name pair, the exit builds a resource entry block for the device. The exit then puts the build vector header and flag information in front of the list of resource entry blocks and returns to VTAM. If the exit does not find a complete resource name or model name pair for the device, the exit denies the REQCONT (or REQACTPU) from the unknown device and returns to VTAM.

The CPNDEF implementation supplied with the sample exit routine ISTEXCCS can define a single PU 2.1 connection to a CP by using CPNAME. Any subsequent attempt to define a dynamic PU for a connection by using the same CPNAME will fail because the name returned to use for the dynamic PU is already in use by VTAM.

If the name generation function cannot construct a name for the device, the exit returns to VTAM. The X'80' bit in byte 0 of the build vector is set to indicate to VTAM that it is to deny the REQCONT (or REQACTPU).