gtps2m3pACF/SNA Data Communications Reference


Appendix A. Logical Unit Status (LUSTAT)

Note:
The logical unit status information described in this section does not apply to LU 6.2; see IBM Systems Network Architecture Format and Protocol Reference Manual: Architecture Logic for LU Type 6.2 for this information.

A logical unit sends status information to its session partner via a mechanism called logical unit status (LUSTAT). The format of the SNA request unit (RU) when status information is sent is as follows:

Byte


0 = X'04' Indicates this is LUSTAT
1-2 = X'0001' Indicates component is now available

= X'0002' Component failure: Permanent error

= X'0003' Component failure: Insufficient resource
3-4

User field; these two bytes may be used as an extension to bytes 1-2.

TPF only receives LUSTAT messages; it does not send them. Further, TPF does not receive LUSTAT messages from the following logical units:

LUSTAT messages from 3274/3276 attached logical units are passed to TPF's output message transmission (OMT) program. TPF needs this status information to perform error processing. LUSTAT messages received from these logical units are listed below. The term primary, as used here, refers to a display station. The term secondary refers to a printer.

X'00010000' Component now available
X'0001B000' Secondary component now available
X'0001D000' Primary component now available
X'00020000' Component has no data to send
X'081CD000' Component failure: Permanent error in primary device
X'081CB000' Component failure: Permanent error in secondary device
X'082B0000' Temporary error; component available
X'08310000' Component powered off or disconnected

LUSTAT messages from all other logical units are passed to the application in the associated message block on data level 0. In order to let the application program distinguish between an SNA command and user data, the Expanded RCPL GDA area will contain the RH combined with the Sequence Number. The RH contains the RU category to distinguish between user data (FMD) and SNA commands (NC, DFC, SC). SIGNAL messages are handled in the same manner.