Defining a program operator

A VTAM® application program can be authorized to issue VTAM operator commands to:

Display the status of the network
Control the status of the network
Receive messages from VTAM
Reply to VTAM messages.

Such an application program is called a program operator, or a program operator application (POA), and permits a user to:

Enter operator commands from any LU in the network (for example, from a terminal)
Monitor and control elements in the network at program execution speed
Specialize network control by dividing the network among several application programs
Define specialized commands (for example, to display the status of the entire network with a single command)
Reformat replies received for VTAM commands (for example, to reformat the status display of a part of the network to fit on a 3270 display screen)
Coordinate control of different domains in a multiple-domain network.

A program operator can:

Issue a DISPLAY, MODIFY, or VARY command by using a SENDCMD macroinstruction. The format of the command is the same as though it were issued from the system console.
Receive messages from VTAM by using a RCVCMD macroinstruction.
Reply to a VTAM message by using a SENDCMD macroinstruction to send a REPLY command.

Figure 1 shows how the system console operator and a program operator send VTAM operator commands and receive VTAM operator messages to control the VTAM domain. OPNDST, SEND, RECEIVE, and CLSDST are examples of session-establishment and communication macroinstructions.

Figure 1. VTAM operator control of a VTAM domain

The diagram shows how a VTAM operator controls a VTAM domain. The VTAM operator commands and the VTAM operator messages are sent through a host processor.

The NetView® program provides many of the facilities listed in the preceding section while also providing a base for communication network management functions.

In a multiple-domain network, program operators in different domains can communicate by means of VTAM macroinstructions to allow a program operator or an operator at a terminal to monitor and control elements in other domains. Figure 2 shows an example of how a multiple-domain network can be controlled using two program operators.

Figure 2. VTAM operator control of a multiple-domain VTAM network

To activate an element in domain 2:

An operator at a terminal in domain 1 sends a command to program operator 1.
Program operator 1 determines that the command is for domain 2 and sends it to program operator 2.
Program operator 2 sends the command to VTAM (using a SENDCMD macroinstruction), where the command is processed.
Program operator 2 sends any replies back to program operator 1, which, in turn, sends them to the terminal.

Another way to activate an element in domain 2 is to have a terminal establish a session directly with program operator 2.

Two levels of authorization for an application program determine the type of messages that the program can receive. A program can be authorized to:

Receive only messages that are in reply to VTAM operator commands issued by a program operator (solicited messages). Such an application program is called a secondary program operator (SPO).
Receive messages whether they are in reply to VTAM operator commands that the program operator issued (solicited messages) or are as a result of unexpected events in the network (unsolicited messages), for example, losing contact with a terminal. Such an application program is called a primary program operator (PPO).

Only one primary program operator can be active at a time; however, one or more secondary program operators can also be active.

Note: If a primary program operator is active, the systems' operations console does not receive unsolicited messages.