Horizon conversation states and statements

Overview

The communication statements (verbs) that an application program may issue at any given point in the conversation depend upon the current state of the conversation. The Model 204 Horizon conversation states are described briefly below. Statement and state dependencies lists the Horizon statements that can be issued in each state.

Conversation states

The following conversation states are used in Horizon:

Reset	The application program may allocate a conversation (open a process).
Send	The application program may send data, request confirmation, or (stop sending and) receive data.
Receive	The application program may receive data from the partner application program or request permission to send.
Confirm	The application program may comply with the request for confirmation. (It may also request permission to send later, after the confirmation.)
Close	The application program may deallocate the conversation (close the process) with the remote application program.

Conversation Statement/State Dependencies

The matrix in the following table lists the Horizon statements that can be issued in a given conversation state.

• "No" means that a state check is incurred because the statement is not valid in that state. State checks are issued only when a process is already open.
• The dashes in the matrix mean that some error other than a state check is incurred.
• N/A's (not applicable) are entered for TEST RECEIPT and WAIT FOR RECEIPT because they are not state dependent.

Statement and state dependencies

Reset	Send	Receive	Confirm	Close
OPEN PROCESS	Yes	-	-	-
CONFIRM	-	Yes	No	No
CONFIRMED	-	No	No	Yes
CLOSE PROCESS	-	Yes	Yes	Yes
FLUSH	-	Yes	No	No
INVITE	-	Yes	No	No
QUERY PROCESS	Yes	Yes	Yes	Yes
RECEIVE	-	Yes	Yes	No
SIGNAL	-	No	Yes	Yes
SEND	-	Yes	No	No
SEND ERROR	-	Yes	Yes	Yes
TEST RECEIPT	N/A	N/A	N/A	N/A
WAIT FOR RECEIPT	N/A	N/A	N/A	N/A