HP-UX SNAplus2 R7 APPC Programmer's Guide

Concepts

Conﬁrmation Processing (half-duplex)

1.2.4 Ending a Conversation

To end a conversation, one of the TPs issues the MC_DEALLOCATE verb, which causes APPC to deallocate the

conversation between the two TPs.

After this conversation is deallocated, each TP either issues another [MC_]ALLOCATE or RECEIVE_ALLOCATE

verb to start another conversation (with this or another partner TP), or issues the TP_ENDED verb.

A TP can participate in multiple conversations simultaneously. In this case, the TP issues the TP_ENDED verb

when all conversations have been deallocated.

1.3 Conﬁrmation Processing (half-duplex)

Using conﬁrmation processing, a TP sends a conﬁrmation request with the data; the receiving TP conﬁrms receipt

of the data or indicates that an error occurred. Each time the two TPs exchange a conﬁrmation request and response,

they are synchronized.

The example of conﬁrmation processing in Table 1–2, Conﬁrmation Processing shows two ways of conﬁrming the

transfer of data: requesting conﬁrmation after sending the data (by using the CONFIRM verb), and requesting

conﬁrmation at the end of a transaction (by requesting conﬁrmation on the DEALLOCATE verb). Conﬁrmation can

also be requested on the PREPARE_TO_RECEIVE verb; this asks the partner TP to conﬁrm receipt of data, and

then begin to send data itself. For more information, see Section 1.5.2, State Changes. A pair of TPs may choose

to use only one of these mechanisms; in the following example, the invoked TP uses the PREPARE_TO_RECEIVE

verb without requesting conﬁrmation; this simply tells the partner TP to send data.

Table 1–2 Conﬁrmation Processing

Invoking TP Flow Invoked TP

TP_STARTED

MC_ALLOCATE (sync_level =

AP_CONFIRM_SYNC_LEVEL)

MC_SEND_DATA

MC_CONFIRM

—>

RECEIVE_ALLOCATE

MC_RECEIVE_AND_WAIT (primary_rc =

AP_OK)(what_rcvd = AP_DATA_COMPLETE

)

MC_RECEIVE_AND_WAIT (primary_rc=

AP_OK)(what_rcvd =

AP_CONFIRM)

MC_SEND_ERROR

<—

(MC_CONFIRM returns, primary_rc =

AP_PROG_ERROR_PURGING)

MC_PREPARE_TO_RECEIVE (ptr_type =

AP_FLUSH)

<—