HP-UX SNAplus2 R7 APPC Programmer's Guide

Concepts

Full-Duplex Conversations

Invoking TP Flow Invoked TP

MC_RECEIVE_AND_WAIT (what_rcvd =

AP_DATA_COMPLETE

)

MC_RECEIVE_AND_WAIT (primary_rc

AP_DEALLOC_NORMAL)

<— MC_SEND_DATA

MC_DEALLOCATE

TP_ENDED

MC_RECEIVE_AND_WAIT

(what_rcvd =

AP_DATA_COMPLETE

)

MC_RECEIVE_AND_WAIT

(what_rcvd =

AP_DEALLOC_NORMAL)

TP_ENDED

The characters MC_ at the beginning of many of the verbs stand for mapped conversation. Parameters and results

of APPC verbs are in parentheses.

1.7.1 Starting a Conversation

To start a conversation, the invoking TP issues the following verbs:

• TP_STARTED, which identiﬁes the application to SNAplus2 APPC as an invoking TP

• MC_ALLOCATE, which requests that APPC establish a conversation between the invoking TP and the invoked

TP. The parameters on the MC_ALLOCATE verb specify that the conversation will be full-duplex.

The invoked TP issues the RECEIVE_ALLOCATE verb, which informs APPC that the invoked TP is ready to be-

gin a conversation. SNAplus2 associates the RECEIVE_ALLOCATE verb with the MC_ALLOCATE verb issued

by the invoking TP in order to establish the conversation between the two TPs. The returned parameters on the RE-

CEIVE_ALLOCATE verb specify that the conversation will be full-duplex.

Note

After a full-duplex conversation has been started, the TP must set an additional option in

the opext parameter of all verbs issued in this conversation to operate in full-duplex mode.

See the individual verb descriptions in Chapter 4, APPC Conversation Verbs for details.

1.7.2 Sending Data

The MC_SEND_DATA verb supplies application data to be transmitted to the partner TP. This data is held in the

local LU’s send buffer; it is not transmitted to the partner TP until one of the following events occurs:

• The send buffer ﬁlls up.

• The TP issues a verb that forces APPC to ﬂush the buffer (send data to the partner TP).

In addition to the data, the send buffer also contains the MC_ALLOCATE request (which precedes the data). In this

example, the invoking TP’s second MC_SEND_DATA verb ﬁlls the buffer, forcing the MC_ALLOCATE request

and the data to be transmitted to the partner TP. Other verbs that ﬂush the buffer are MC_DEALLOCATE and

MC_FLUSH.

Because this is a full-duplex conversation, both TPs can send data at the same time. In the example, the invoked

TP sends data before it has received any data sent by the invoking TP.