Integrity tables

The following tables show the message integrity of conversations, results of processing when integrity is compromised, and how IMS recovers APPC messages.

The following table shows the results, from the viewpoint of the IMS partner system, of normal conversation completion, abnormal conversation completion due to a session failure, and abnormal conversation completion due to non-session failures. These results apply to asynchronous and synchronous conversations and both input and output. This table also shows the outcome of the message, and the action that the partner system takes when it detects the failure. An example of an action, under LU 6.2 Session Failure, is a programmable work station (PWS) resend.

Table 1. Message integrity of conversations
Conversation attributes	Normal	LU 6.2 session failure¹	Other failure²
Synchronous Sync_level=NONE	Input: Reliable Output: Reliable	Input: PWS resend Output: PWS resend	Input: Reliable Output: Reliable
Synchronous Sync_level=CONFIRM	Input: Reliable Output: Reliable	Input: PWS resend Output: Reliable	Input: Reliable Output: Reliable
Synchronous Sync_level=SYNCPT	Input: Reliable Output: Reliable	Input: PWS resend Output: Reliable	Input: Reliable Output: Reliable
Asynchronous Sync_level=NONE	Input: Ambiguous Output: Reliable	Input: Undetectable Output: Reliable	Input: Undetectable Output: Reliable
Asynchronous Sync_level=CONFIRM	Input: Reliable Output: Reliable	Input: PWS resend Output: Reliable	Input: Reliable Output: Reliable
Asynchronous Sync_level=SYNCPT	Input: Reliable Output: Reliable	Input: PWS resend Output: Reliable	Input: Reliable Output: Reliable
Notes: A session failure is a network-connectivity breakage. A non-session failure is any other kind of failure, such as invalid security authorization. IMS resends asynchronous output if CONFIRM is lost; therefore, the PWS must tolerate duplicate output.

The following table shows the specifics of the processing windows when integrity is compromised (the message is either lost or its state is ambiguous). The table indicates the relative probability of an occurrence of each window and whether output is lost or duplicated.

A Sync_level value of NONE does not apply to asynchronous output, because IMS always uses Sync_level=CONFIRM for such output.

Table 2. Results of processing when integrity is compromised
Conversation attributes	State of window₁ before accepting transaction	Probability of window state	Possible action while sending response	Probability of action while sending response
Synchronous Sync_level=NONE	ALLOCATE to PREPARE_TO_ RECEIVE return	Medium	Can lose or send duplicate output.	Medium
Synchronous Sync_level=CONFIRM	PREPARE_TO_ RECEIVE to PREPARE_TO_ RECEIVE return	Small	CONFIRM to IMS receipt. Can cause duplicate output.	Small
Synchronous Sync_level=SYNCPT	PREPARE_TO_ RECEIVE to PREPARE_TO_ RECEIVE return	Small	CONFIRM to IMS receipt. Can cause duplicate output.	Small
Asynchronous Sync_level=NONE	Allocate to Deallocate	High	CONFIRMED to IMS receipt. Can cause duplicate output.	Small
Asynchronous Sync_level=CONFIRM	PREPARE_TO_ RECEIVE to PREPARE_TO_ RECEIVE return	Small²	CONFIRMED to IMS receipt. Can cause duplicate output.	Small
Asynchronous Sync_level=SYNCPT	PREPARE_TO_ RECEIVE to PREPARE_TO_ RECEIVE return	Small²	CONFIRMED to IMS receipt. Can cause duplicate output.
Notes: The term window refers to a period of time when certain events can occur, such as the consequences described in this table. Can be recoverable.

The following table indicates how IMS recovers APPC transactions across IMS warm starts, XRF takeovers, APPC session failures, and MSC link failures.

Table 3. Recovering APPC messages
Message type	IMS warm start (NRE or ERE)	XRF takeover	APPC (LU 6.2) session fail	MSC LINK failure
Local Recoverable Tran., Non Resp., Non Conversation - APPC Sync. Conv. Mode - APPC Async. Conv. Mode	Discarded (2) Recovered	Discarded (4) Recovered	Discarded (6) Recovered (1)	N/A (9) N/A (9)
Local Recoverable Tran., Conv. or Resp. mode - APPC Sync. Conv. Mode - APPC Async. Conv. Mode	Discarded (2) N/A (8)	Discarded (4) N/A (8)	Discarded (6) N/A (8)	N/A (9) N/A (8,9)
Local Non Recoverable Tran., - APPC Sync. Conv. Mode - APPC Async. Conv. Mode	Discarded (2) Discarded (2)	Discarded (4)	Discarded (6) Recovered (1)	N/A (9) N/A (9)
Remote Recoverable Tran., Non Resp., Non Conv. - APPC Sync. Conv. Mode - APPC Async. Conv. Mode	Discarded (2,5) Recovered	Discarded (3,5) Recovered	Recovered (1) Recovered (1)	Recovered (7) Recovered (7)
Remote Recoverable Tran., Conv. or Resp. mode - APPC Sync. Conv. Mode - APPC Async. Conv. Mode	Discarded (2,5) N/A (8)	Discarded (3,5) N/A (8)	Recovered (1) N/A (8)	Recovered (7) N/A (8)
Remote Non Recoverable Tran., - APPC Sync. Conv. Mode - APPC Async. Conv. Mode	Discarded (2,5) Discarded (2,5)	Discarded (3,5) Discarded (3,5)	Recovered (1) Recovered (1)	Recovered (7) Recovered (7)
Note: This recovery scenario assumes the message was enqueued before failure; otherwise, the message is discarded. The message is discarded during IMS warm-start processing. The message is discarded when the MSC link is restarted and when the message is taken off the queue (for sending across the link). The message is discarded when the message region is started and when the message is taken off the queue (for processing by the application program). For all remote MSC APPC transactions, if the message has already been sent across the MSC link to the remote system when the failure occurs in the local IMS, the message is processed. After the message is processed by the remote application program and a response message is sent back to the local system, it is enqueued to the DFSASYNC TP name of the LU 6.2 device or program that submitted the original transaction. At sync point, the User Message Control Error exit routine (DFSCMUX0) can prevent the transaction from being aborted and the output message can be rerouted (recovered). For more information about this exit routine, see IMS Version 15.3 Exit Routines. The standard MSC Link recovery protocol recovers all messages that are queued or are in the process of being sent across the MSC link when the link fails. IMS conversational-mode and response-mode transactions cannot be submitted from APPC asynchronous conversation sessions. APPC synchronous conversation-mode must be used. MSC link failures do not affect local transactions.