To define subarea classes of service, create a class-of-service table with entries containing lists of routes grouped together on the basis of characteristics such as security, transmission priority, and bandwidth. The characteristics of a particular list determine a class of service. For example, you could place the fastest routes in one list for use in interactive sessions and slower routes in another list for use by batch jobs. If a session involves the transmission of sensitive data, you would place only secure routes in the list used for that session. By specifying the name of an entry from the CoS table in the logon mode table associated with a session, you can select the list of routes you want to be used for the session.
VTAM® does not provide a default subarea CoS table. However, you can define a default CoS in the logon mode table by specifying ISTCOSDF on the LOGMODE operand of the MODEENT macroinstruction. You can modify the session characteristics in ISTCOSDF, though if you do, it is recommended that you put ISTCOSDF in a separate table rather than modifying it in the IBM-supplied default logon mode table, ISTINCLM.
VTAM also offers a default list of virtual routes that is used if you do not create a CoS table. This default list is used if you do not name a Class of Service in the logon mode table for a session. It is also used if you specify ISTVTCOS as the Class of Service in the logon mode table and there is no explicit Virtual Route List defined for ISTVTCOS. You can replace this default list by creating a CoS table with an unnamed (blank) CoS entry containing the new list. This new default list is then used if you do not name a Class of Service in the logon mode table for a session, or if you specify ISTVTCOS as the Class of Service in the logon mode table and there is no explicit Virtual Route List defined for ISTVTCOS.
In addition to coding an unnamed CoS entry in your CoS table, you might also want to code an entry for use in SSCP sessions (SSCP-SSCP, SSCP-PU, and SSCP-LU). You can specify the routes used for SSCP sessions by including an entry named ISTVTCOS in the CoS table.