Session failures without IMS failure

A session failure not also involving an IMS subsystem failure might occur before IMS returns a requested sync-point response for a response mode or conversational input message.

When the session is reestablished, the DFC state set by IMS using the bind is IMS in-brackets/SEND. The subsequent STSN sequence number recovery might reflect either that the input message has been committed (the transaction has reached a sync point after inserting a reply message) or that the input message has not yet been committed. In either case, IMS being bound as in-brackets/SEND indicates that the input message has been received and the other half session should wait for the reply message. Because session restart resets the original sync-point request, the reply message now becomes an implicit sync-point response to the original input message.

IMS recovers the fact that the session was in conversational mode (and also recovers associated input messages and output replies) across IMS outages. The fact that the session was in response mode (and any associated output replies) is only recovered across an IMS outage if the failure occurs after the transaction sync point that made the response mode reply available.