Logon descriptors

Logon descriptors provide IMS with information about the physical characteristics of the terminals that establish logon sessions.

When you request that ETO descriptors be created during system definition, a logon descriptor is created for each VTAM® TYPE and TERMINAL macro set.

IMS also creates a default logon descriptor during system definition, which reflects the TYPE and TERMINAL macro statements that define the unique characteristics of the largest number of terminals of that type.

For terminals that cannot be represented by the default logon descriptor, IMS creates unique logon descriptors.

IMS does not create ETO logon descriptors for the following terminal types:

  • Any terminal defined as a primary or secondary MTO
  • Any LUTYPE6 terminal defined as the XRF ISC link

You can keep and use the unique logon descriptors that IMS creates or you can discard them. To discard the unique logon descriptors you can:

  • Operate the terminals based on the default logon descriptor
  • Create one or more of your own installation default logon descriptors and code an installation Logon exit routine (DFSLGNX0) to select the required descriptor for logging on to a terminal

The system definition process generates up to 37 default logon descriptors for each device type. The suffix for each descriptor defaults to 0; the last character of the descriptor name ensures that the name is unique. This character is a blank for the most common descriptors, and then 0 through 9, and A through Z, for a total of 37 possible descriptors.

Terminal definitions that do not match the 37 most common terminal definitions generate comment statements with an asterisk in the first position and the rest of the statement is shifted over one position.

All user descriptors created during system definition are generated as comment statements to avoid getting error messages caused by a statically defined LTERM name.

Typically, one generic logon descriptor exists per unique LU type and option configuration. After the descriptor is created, the same descriptor can support any number of logons for the same LU type and option configuration.

The format of a logon descriptor is 
L Descriptor name Parm(1) Parm(2) Parm(3)
L Descriptor name Parm(4) Parm(5) Parm(n)

The parameters that are required for a descriptor cannot fit into one record. You might need to use multiple records with the same descriptor name to define your descriptor.