HP-UX SNAplus2 R7 APPC Programmer's Guide

Concepts
Conversation States (half-duplex)
available, APPC can return the status information about this verb in addition to the data. The verb returns with
a
what_rcvd parameter of AP_DATA_COMPLETE_CONFIRM, which indicates that the invoking TP sent data and
then requested confirmation. The first two MC_RECEIVE_AND_WAIT verbs have the rtn_status parameter set to
AP_NO, so APPC does not return status information with the data; the first verb receives the data, and the second
receives the status information.
1.5 Conversation States (half-duplex)
In a half-duplex conversation, APPC operates as a half-duplex process, which means that only one of the two TPs
is permitted to send data at any time. In general, one TP will send a certain amount of data, and then do one of
the following:
• Ask the other TP to confirm receipt of the data
• Allow the other TP to send
At any one time, the TP regards the conversation as being in a particular conversation state; the conversation
state governs which APPC verbs can be issued by a TP at a particular time. For example, a TP cannot issue the
MC_SEND_DATA verb if the conversation is not in Send or Send-Pending state. For more information about the
APPC verbs that can be issued in each state, see Appendix C, APPC State Changes.
Following is a list of possible conversation states:
Confirm
The TP has received a request for confirmation of receipt of data; it must respond positively or send error
information to the partner TP.
Confirm-Deallocate
The TP has received a request for confirmation and must respond positively or send error information. If the
TP responds positively, the partner TP deallocates the conversation.
Confirm-Send
The TP has received a request for confirmation; it must respond positively or send error information. After
responding, the TP can begin to send data.
Pending-Post
The TP is receiving data asynchronously. The TP can perform other processing not related to this conversation.
When the TP finishes receiving data, the state is usually Receive.
Receive
The TP can receive application data and status information from the partner TP. When the conversation is in
Receive state, the TP can also send error information and request permission to send data.
Reset
The conversation has not started or has been terminated.
Send
The TP can send data to the partner TP and request confirmation. When the conversation is in Send state,
the TP can also begin to receive data, which causes the state to change to Receive.
Send-Pending
The TP has received data together with a SEND indication from the partner TP. This state is similar to Send
state, except that the TP can use an extra parameter on the [MC_]SEND_ERROR verb to indicate the source
of a detected error.
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