System sense information indicates one of the five major classes of system-defined errors. The five major classes are described in Table 1.

System-sense modifier information indicates one of many specific causes of the error indicated by the system-sense information. Like RTNCD and FDB2, the system-sense and its modifier information together form a specific type of error condition within a general class of error conditions. See the SNA Formats and z/OS Communications Server: IP and SNA Codes for more information.

User-sense information is generally used when the error condition is detected by the user-written program itself. In general, no particular codes or values are defined by IBM® to indicate types of errors. The logical unit must generate its own user-sense information that is understood by other logical units.

The SNA defined values for the sense fields can be found in SNA Formats Additional information is contained in SNA Format and Protocol Reference Manual: Architectural Logic, and SNA Sessions between Logical Units

These three types of sense information—system, system modifier, and user—are set in RPL fields. Three fields (one for each type of sense information) are set by the application program when it sends a negative response or LUSTAT request to the logical unit. Three other fields are set by VTAM® when the application program receives an exception request, a negative response, or LUSTAT request from the logical unit. These are the names of the six fields, as they would be used on a manipulative or RPL macroinstruction: