Selecting session parameters for the logon mode table

When a logical unit requests a session with an application program, it uses a symbolic logon mode name, either directly or by default, to suggest the session protocols. Session protocols are a set of rules that describe how the session is conducted. For example, one protocol might specify the application program uses chaining for SNA requests. Another might require the logical unit does not send end-bracket indicators to the application program. For a complete description of the session protocols available in VTAM®, see z/OS Communications Server: SNA Programming.

Session protocols are expressed as a string of characters called session parameters, usually specified in the logon mode table. A set of session parameters for a session is also called its logon mode. VTAM contains an IBM®-supplied logon mode table, ISTINCLM. This table contains a set of generally accepted session parameters for a basic list of IBM device types, but it might not completely meet your needs. You can create supplementary logon mode tables and associate them with device type logical units or application programs using the MODETAB operands on the definition statements defining them.

To create the logon mode table:

Modify the IBM-supplied table.
Create supplementary tables and associate them with device-type LUs or application programs using the MODETAB operands in the definition statements defining them. You can use the DLOGMOD operand on the appropriate definition statements to indicate the specific logon mode entry in the table that contains the session parameters to be used by default. The LOGMODE operand can also be specified on VARY LOGON commands to specify a logon mode table entry.
Associate a supplementary table with dynamic CDRSCs using the DYNMODTB start option. You can also use the DYNDLGMD start option to indicate the default logon mode entry for dynamic CDRSCs. The value for DYNMODTB can be changed using the DYNMODTB operand on the MODIFY VTAMOPTS command, or by using the MODIFY TABLE,OPTION=LOAD command to replace the existing table that is being used by dynamic CDRSCs. You can change the default logon mode entry for dynamic CDRSCs using the DYNDLGMD operand on the MODIFY VTAMOPTS command. You can also override this value for a specific dynamic CDRSC using the MODIFY DEFAULTS or MODIFY RESOURCE commands.
When VTAM builds a dynamic CDRSC, it uses the DYNMODTB value (if specified; otherwise ISTINCLM) to associate a logon mode table to the dynamic CDRSC. It also uses the DYNLOGMD value, if specified, to assign a default logon mode table entry to the dynamic CDRSC. Changing the value of these start options does not change the value for dynamic CDRSCs that have already been built.

Logon mode names are always resolved using the logon mode table associated with the secondary logical unit (SLU). For more information about which node performs the mode resolution, see Resolving logon mode names to subarea and APPN Classes of Service.

Logon mode tables are created or modified using MODETAB, MODEENT, and MODEEND macro instructions. The z/OS Communications Server: SNA Resource Definition Reference describes the contents of the IBM-supplied logon mode table. It also describes how TSO can query for the logon mode being used by a terminal in place of supplying the LOGMODE during the logon. Figure 1 shows the sequence in which MODETAB, MODEENT, and MODEEND macros are coded to define a logon mode table.

Figure 1. Macroinstructions for logon mode table

Diagram that shows the sequence in which MODETAB, MODEENT, and MODEEND macros are coded to define a logon mode table.

The various ways of specifying session parameters are illustrated in Table 1.

Table 1. How session parameters are identified
Request source	Request form	How session parameters are identified
Request source	Request form	Logon mode table entry	Logon mode table
Dependent Logical Unit	Initiated Self request Interpret table character string representing logon Character-coded logon	Field in Initiate Self request containing mode name used to search logon mode table Parameter in a character-coded logon that translates into LOGMODE (name) DLOGMOD operand on LU definition statement Default entry ISTCOSDF, if the ISTCOSDF start option allows its use for dependent LUs First entry in logon mode table named in MODETAB operand on LU definition statement First entry in IBM-supplied logon mode table	MODETAB operand on LU definition statement IBM-supplied logon mode table
Independent Logical Unit	BIND Cross-domain initiate	Field in BIND or cross-domain initiate request containing mode name used to search logon mode table DLOGMOD operand on CDRSC definition statement, or DYNDLGMD start option value (for dynamic CDRSCs) Default entry ISTCOSDF, if the ISTCOSDF start option allows its use for independent LUs First entry in logon mode table named in MODETAB operand on CDRSC definition statement or DYNMODTB start option value (for dynamic CDRSCs) First entry in IBM-supplied logon mode table	MODETAB operand on CDRSC definition statement or DYNMODTB start option value (for dynamic CDRSCs) IBM-supplied logon mode table
Application Program	Application program issuing VTAM macros, such as SIMLOGON or REQSESS	Name of logon mode table entry specified in the NIB DLOGMOD operand on LU definition statement Default entry ISTCOSDF, if the ISTCOSDF start option allows its use for application programs First entry in logon mode table named in MODETAB operand on LU definition statement First entry in IBM-supplied logon mode table
Automatic logon	Initiate Other request	DLOGMOD operand on LU or CDRSC definition statement or DYNDLGMD start option value for dynamic CDRSCs Default entry ISTCOSDF, if the ISTCOSDF start option allows its use First entry in logon mode table named in MODETAB operand on LU or CDRSC definition statement, or DYNMODTB start option value for dynamic CDRSC First entry in IBM-supplied logon mode table
VTAM operator	VARY LOGON command	LOGMODE operand in VARY LOGON command LOGMODE operand in previous VARY LOGON command DLOGMOD operand on LU or CDRSC definition statement, or DYNDLGMD start option value for dynamic CDRSCs Default entry ISTCOSDF, if the ISTCOSDF start option allows its use First entry in logon mode table named in MODETAB operand on LU or CDRSC definition statement, or DYNDLGMD start option value for dynamic CDRSCs First entry in IBM-supplied logon mode table

Regardless of the source of the logon or what session parameters are associated with the logon, the application program decides which session parameters are used for the session. It can decide to use the session parameters associated with the pending logon, or it can choose a different set of parameters. When the application program issues a macro to initiate a session with a logical unit, the application program indicates the logon mode name or session parameters to be used during the session. The logon mode table from which the session parameters are selected is always the one associated with the SLU, or, if a table is not associated with the logical unit, it is the IBM-supplied default logon mode table in the VTAM that owns the SLU.

If the specified logon mode entry does not exist in the logon mode table associated with the secondary logical unit, the default logon mode (ISTCOSDF) is used if it is found in the table and its use is allowed as determined by the ISTCOSDF start option.

You can modify or replace the IBM-supplied logon mode table, provided that the modified or replacement table has the same name as the IBM-supplied table and that the IBM-supplied table is deleted. However, because the IBM-supplied table might be needed for problem determination, you should create supplementary tables instead of deleting the IBM-supplied table.

As part of the session-establishment procedures, an application program acting as the PLU can:

Supply a logon mode name associated with the SLU. The session parameters associated with the logon mode name in the domain of the SLU are used.
Directly supply the session parameters to be used.
Use the session parameters associated with the pending logon.

z/OS Communications Server: SNA Programming describes in more detail how the application program handles session parameters.

Figure 2 shows a summary of the algorithm VTAM uses to obtain session parameters.

Figure 2. How session parameters are obtained from a logon mode table