Creating a USS table

The following macro instructions are used to create the USS table. Telnet USS function supports almost all VTAM® session-level USS message and command definitions. See z/OS Communications Server: IP Configuration Reference for macro details.

USSTAB indicates the beginning of the USS table.
USSCMD defines commands accepted by Telnet.
USSPARM defines each operand or positional parameter that can be specified on the USSCMD macro instruction. It also defines default values for the operand or positional parameter. Multiple USSPARM macro instructions can be associated with a USSCMD macro instruction. For each operand or positional parameter code a USSPARM macro instruction.
USSMSG defines messages sent from Telnet.
USSEND indicates the end of the USS table.

The following rules are some of the more common rules to consider when you are coding a new USS table. Also, see the samples in SEZAINST(EZBTPUST) and SEZAINST(EZBTPSCS) as a guide. Considerations when using mixed-case passwords describes general table rules.

If a DEFAULTAPPL application is mapped at the same Client Identifier level as a USS table, or an LUMAP-DEFAPPL application is mapped, the USS table is used only to return error messages and optionally after the first session logoff. FIRSTONLY or LOGAPPL options on DEFAULTAPPL will cause Telnet to send a USSMSG10 after the first session logoff. DEFAULTAPPL without the FIRSTONLY or LOGAPPL options will cause Telnet to request a session with the default application after every session logoff.
Both the 3270 data stream and the SNA character stream (SCS) formats are supported. For more information, see 3270 Data Stream Programmer's Reference and the table samples.
If a user-defined table is coded as part of another module, code an assembler EXTRN definition statement for the table name in that module so the table will be known externally and can be accessed by other modules.

Below are message related rules.

3270 format USSMSGs must contain the 3270 data stream write control characters (WCCs).
All character substitutions (@@'s) substitute the same number of characters. Any character substitution that is VTAM-specific will be translated to blanks. If the substituted value is smaller, the field is padded to the right with blanks. The parameter LUNAME or SCAN must be coded on the USSMSG macro instruction for Telnet to perform character substitutions. For a complete list of character substitutions, see z/OS Communications Server: IP Configuration Reference for Telnet and z/OS Communications Server: SNA Resource Definition Reference for VTAM. Telnet supports multiple USSPARMs with the DATA keyword. This method can be used to pass multiple data parameters to the host application. For example, two DATA USSPARMs allow the user to type 'TSO USER1 PROC001' and have both the user ID and the Procname passed to TSO as data. Telnet also supports the system symbolics substitution, padding to the right when the substituted value is smaller than the symbolic. VTAM USS processing does not support system symbolic substitution.

Below are command related rules.

LOGON command format
PL1 - logon applid(tso) logmode(snx32702) data(user1)

BAL - logon applid=tso,logmode=snx32702,data=user1
Any application defined in a USSCMD macro instruction must also be specified on either an ALLOWAPPL or a RESTRICTAPPL statement in the Telnet profile.
If the USS Command rules in z/OS Communications Server: IP Configuration Reference cannot be followed, use an interpret table to convert the character-coded command into a formatted SNA request.