Determining the destination of the input message
Non-SNA terminals are dedicated to the z/TPF system. This means that all input flows directly to the z/TPF system. However, non-SNA terminals can either select (through a special input message called LOGON) the application in the z/TPF system they are to be connected with or be permanently logged into one specific application. The application is the destination of the message.
SNA devices are shared resources, which means that SNA devices are associated with more than one host. A LOGON input message specifies the host and application to be connected (that is, associated) with an SNA device. If an SNA device is always associated with the same application in a host, it can be permanently logged. Again, the application is the destination of the message.
Figure 1 shows the tables used to locate the application package necessary to process an input message. A routing control parameter list (RCPL) is constructed in the ECB with fields to hold the origin and destination of the message and the characteristics of the message.
- For a terminal or workstation on an SNA network,
- The resource vector table (RVT) if the destination application is a new application
- The terminal address table (WGTA) if the destination application is an old application
- For a terminal or workstation on a non-SNA network, the terminal address table (WGTA).
A terminal identification table is indexed (accessed) based on the origin of the input message, and the origin is dependent on the communication protocol involved. The tables contain a pointer for each user terminal and workstation and are used to locate the application that the user selected previously.
A program called the log processor is used to interpret a logon input message, which permits a terminal or workstation user (who is the source of input) to select an application package, such as the Airlines Reservation Application Package (). In this information, application packages refers to installation-produced software. The log processor sets up the pointer in the appropriate terminal identification table (RVT or WGTA).
The pointer in the appropriate terminal identification table locates an item in the application name table (ANT), which has a field to hold an application name (such as RES0) to which the user is connected, and another field to point to an item in the routing control application table (RCAT). The RCAT item holds the online linkage to an application program segment. A large application, such as RES0, consists of many program segments, (ranging from hundreds to thousands), only one of which is identified in the RCAT.
