To accommodate LU 6.2 implementations on different processors and in different languages, SNA LU 6.2 architecture defines how application programs request LU 6.2 services in generic terms. This generic interface is called an LU protocol boundary. Protocol boundaries offered to user application programs are defined in terms of verbs.

For example, the function of sending data somewhere else in the network is defined in the LU 6.2 architecture by the verb SEND_DATA. The SNA definition for this verb further specifies the format the data must be in, what parameters can be supplied on the request, and what parameters can be returned to the application program. The APPCCMD CONTROL=SEND, QUALIFY=DATA macroinstruction conforms to this definition by allowing application programs to specify the input parameters required by the architecture and by returning the required output parameters.

Through LU 6.2 support, VTAM® provides an API that enables its application programs to implement an LU protocol boundary. The application program takes advantage of the VTAM API by using the APPCCMD macroinstruction. The various forms of the APPCCMD macroinstruction offer the functions of verbs defined in the architecture.

By using these verb functions, an application program on one end of the network can initiate a transaction with another application program or device on the network, send and receive data as required by the transaction, and terminate the transaction. All of this can be done without the application program being aware of the configuration of the network or even of the SNA protocols used to establish connections and transmit data across the network.

VTAM offers its application programs both conversation verbs and control operator verbs. VTAM does not support all the conversation verbs defined in the architecture. However, it does support a large subset of the base set and many key optional layers. For more information on VTAM verbs, see LU 6.2 verbs.

Control operator verbs are used to request services to control the LU. These services include establishing limits for the number and types of sessions the LU can have.