VTAM conversations

Although application programs do not control LU 6.2 sessions, they do explicitly start and stop conversations. The macroinstructions used to do this are APPCCMD CONTROL=ALLOC and APPCCMD CONTROL=DEALLOC. Allocation and deallocation can cause VTAM® to activate or deactivate sessions between the application program and its partner LU, depending on the session limits and number of sessions in use. (See Managing sessions for a detailed description.)

The way application programs use conversations is analogous to the way they use non-LU 6.2 sessions. When conversations are allocated, VTAM assigns an identifier that application programs can find in the CONVID field in the RPL extension. (When the APPCCMD CONTROL=ALLOC or CONTROL=RCVFMH5 macroinstructions complete successfully, CONVID is returned.) The application programs can use the CONVID value to specify particular conversations on APPCCMD macroinstructions.

The application program uses the APPCCMD macroinstruction to control a particular conversation. For example, macroinstructions used to send data or deallocate a conversation all specify a particular conversation. Application programs can request that VTAM do the following for a particular conversation:

Send or receive data and control information over the conversation.
Deallocate a conversation.
Change the role of one of the conversation partners on a half-duplex conversation from sender to receiver.
Change how data is received from a partner.
Return status information about an active conversation to the application.

All of these options are discussed in detail in Managing sessions through Sending and receiving data using high performance data transfer. For basic information about conversations, see Conversations.