SNAP-IX APPC Programmer's Guide - 1.6 Changing Conversation States

1.6 Changing Conversation States

In Using APPC Verbs to Change Conversation States, the conversation states appear in the left and right margins. This table shows how APPC verbs can change the state of the conversation from Send to Receive and from Receive to Send.

Using APPC Verbs to Change Conversation States

State	Invoking TP	Flow	Invoked TP	State
	TP_STARTED
Reset
	MC_ALLOCATE(sync_level = AP_CONFIRM_SYNC_LEVEL)
Send
	MC_SEND_DATA
	MC_PREPARE_TO_RECEIVE (ptr_type = AP_SYNC_LEVEL)
		->
				Reset
			RECEIVE_ALLOCATE
				Receive
			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_SEND)
				Confirm-Send
			MC_CONFIRMED
				Send
		<-
	(MC_PREPARE_TO_RECEIVE returns, primary_rc = AP_OK)
Receive
			MC_SEND_DATA
			MC_CONFIRM
		<-
	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)
Confirm
	MC_REQUEST_TO_SEND
	MC_CONFIRMED
Receive
		->
			(MC_CONFIRM returns, primary_rc = AP_OK, rts_rcvd = AP_YES)
				Send
			MC_PREPARE_TO_RECEIVE (ptr_type = AP_SYNC_LEVEL)
		<-
	MC_RECEIVE_AND_WAIT (primary_rc = AP_OK) (what_rcvd = AP_CONFIRM_SEND)
Confirm-Send
	MC_CONFIRMED
		->
			(MC_PREPARE_TO_RECEIVE returns, primary_rc = AP_OK)
				Receive
Send
	MC_SEND_DATA
	MC_DEALLOCATE (dealloc_type = AP_SYNC_LEVEL)
		->
			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_DEALLOCATE)
				Confirm-Deallocate
			MC_CONFIRMED
		<-
			(MC_DEALLOCATE returns, primary_rc = AP_OK)
Reset				Reset
	TP_ENDED		TP_ENDED

1.6.1 Initial States

Before the conversation is allocated, the state is Reset for both TPs. After the conversation is allocated, the initial state is Send for the invoking TP and Receive for the invoked TP.

1.6.2 Changing to Receive State

The MC_PREPARE_TO_RECEIVE verb enables a TP to change the conversation from Send to Receive state. This verb does the following:

Flushes the local LU's send buffer.
Sends the AP_CONFIRM_SEND indicator to the partner TP through the what_rcvd parameter of a receive verb. This indicator tells the partner TP that an MC_CONFIRMED response is expected before the partner TP can begin to send data.
Performs confirmation processing because the following conditions are true:
- The synchronization level of the conversation is set to AP_CONFIRM_SYNC_LEVEL.
- The parameter ptr_type is set to AP_SYNC_LEVEL.

Issuing the MC_RECEIVE_AND_WAIT verb while the conversation is in Send state also flushes the LU's send buffer and changes the conversation state to Receive. Changing the conversation state in this manner does not support confirmation processing.

1.6.3 Changing to Send State

The MC_REQUEST_TO_SEND verb informs the partner TP (for which the conversation is in Send state) that the local TP (for which the conversation is in Receive state) wants to send data.

This request is communicated to the partner TP through the rts_rcvd parameter of the MC_CONFIRM verb. (The rts_rcvd parameter is also returned to MC_SEND_DATA and other verbs.)

When the partner TP issues the MC_PREPARE_TO_RECEIVE verb, the conversation state changes to Receive for the partner TP, making it possible for the local TP to send data.

Issuing the MC_REQUEST_TO_SEND verb does not change the state of the conversation. Upon receiving a request to send, the partner TP is not required to change the conversation state; it can ignore the request.