An application program can obtain information about a
conversation before initiating the conversation
by issuing the APPCCMD CONTROL=PREALLOC macroinstruction. This puts
the conversation in PENDING_ALLOCATE state. VTAM® returns a conversation identifier (CONVID)
and related information for the pending conversation.
VTAM may also return information
in the VTAM-APPCCMD vector list, which can be requested by the application
by specifying a vector list area (VTRINA) and the length of that area
(VTRINL) on an APPCCMD macroinstruction. Applications should examine
the VTAM-APPCCMD vector list when using any of the following functions:
- Password Substitution
- Applications that implement LU 6.2 option set 223 for password
substitution must examine the following vectors:
- Local-nonce vector (ISTAPC13)
- Partner's-nonce vector (ISTAPC14)
- Send-FMH_5-sequence-number vector (ISTAPC15)
- Receive-FMH_5-sequence-number vector (ISTAPC16)
- Partner-application-capabilities vector (ISTAPC1A)
- Extended Security Sense Codes
- Applications that implement LU 6.2 option set 225 should examine
the partner-application-capabilities vector (ISTAPC1A) to determine
whether the partner can interpret the extended security sense codes.
- DCE Security
- Applications that implement LU 6.2 option sets 230 and 231 should
examine the partner's-DCE-capability vector (ISTAPC12).
- High Performance Data Transfer (HPDT)
- Applications using the HPDT interface should examine the session-information
vector (ISTAPC19).
To establish a conversation reserved by the APPCCMD CONTROL=PREALLOC
macroinstruction, the application issues the APPCCMD CONTROL=SENDFMH5
macroinstruction specifying the CONVID of the pending conversation.
This places the FMH-5 in the SEND buffer destined for the partner
LU. For conversations whose preallocated sessions are full-duplex-capable,
the FMH-5 is not buffered, but sent immediately. For conversations
whose preallocated sessions are half-duplex-capable, the FMH-5 is
not sent until one of the following conditions occurs:
- The application program issues an APPCCMD macroinstruction that
flushes the SEND buffer.
- The application program sends enough additional data to cause VTAM to flush the buffer.
The application program uses the AREA
parameter on the macroinstruction to point to the FMH-5. The RECLEN
parameter specifies the length of the FMH-5.
On the APPCCMD CONTROL=PREALLOC macroinstruction, applications
can specify any of the QUALIFY values that are available for the APPCCMD
CONTROL=ALLOC macroinstruction. See Table 1 for more information about
these QUALIFY values.
To deallocate a conversation reserved by the APPCCMD CONTROL=PREALLOC
macroinstruction, use one of the following macroinstructions:
- APPCCMD CONTROL=DEALLOC, QUALIFY=ABNDPROG
- APPCCMD CONTROL=DEALLOC, QUALIFY=ABNDSERV
- APPCCMD CONTROL=DEALLOC, QUALIFY=ABNDTIME
- APPCCMD CONTROL=DEALLOC, QUALIFY=ABNDUSER
- APPCCMD CONTROL=DEALLOCQ