Inside the link service setup scripts, the components that need to be installed are listed as options. Two types of options used are main options and additional options. The main option usually represents the link service itself, and the additional options represent the subcomponents that are needed (such as device drivers or other system services). For example, in the IBM DFT install script, the main option is IBMDFTLS (IBM DFT link service) and the only additional option is IBMDFTDD (IBM DFT device driver). These names are arbitrary, but should be chosen to reflect what is being installed. Each option has a number of other attributes, such as a title (in the example, IBM DFT Link Service Support), and a version, (for example, 2.3).
At link service install time, main SNA Server Setup enumerates all the .INF files (link service setup scripts) in a certain directory and calls each one in turn. Each script provides its main options and attributes. The titles from each main option are presented to the user in a list box. When the user selects a title, main Setup calls that setup script to install its main and additional options.
Each component can be configured to permit installation of one or many instances of itself, depending on the needs of the link service. This allows a device driver to be installed once and have only one link service running on it, as is the case for IBM DFT support, or to have several instances of a link service on one device driver, as is done for IBM SDLC support. You can also have one link service using several device drivers.
An SNA Server link service setup script usually requires three files to work properly: the script itself (.INF), the Setup Resource Library (.SRL), and the online Help (.HLP). The Setup Resource Library is a special DLL that contains the dialog boxes, icons, and other resources needed by a particular script. The online Help file is a standard Windows Help file, meant to be used with the Windows Help Engine. References to these files can be removed from the scripts if they are not needed; however, it is recommended that you place stubs for these files rather than removing the references.