Performing the resynchronization

When a session is reestablished (or established for the first time), the state of each flow is represented by the sequence numbers that are available for synchronization in each half session.

The sequence numbers available for synchronization in each half session can represent the following states for each flow:
  • COLD

    This session has no sequence numbers to send or to compare. The primary half session indicates this by resetting the sequence number indicator bit in the BIND request. If the BIND is negotiable, the secondary half session indicates this by the same bit setting in the BIND response. If STSN is required (as for nonnegotiable BIND), the primary half session sends a SET AND TEST action code with zeros as the sequence number values.

  • NOT PENDING

    This session has no work units that are indoubt (that is, waiting to be committed)

  • PENDING

    One work unit is in doubt (waiting to be committed). The sequence numbers available to the session are the committed number (the sequence number of the last message to be committed) and the potential number (the sequence number of the last message to be issued).

  • DECISION TO COMMIT

    An indoubt work unit is committed during the session outage. Potential and committed numbers are still available. (A decision to commit occurs only as the result of a /DEQ command being issued during a session outage.)

  • DECISION TO BACK OUT

    An indoubt work unit is backed out during the session outage. Potential and committed numbers are still available. (IMS does not back out work units, but other session partners might).

  • INVALID

    Invalid sequence numbers are detected. (An invalid sequence number is one that should not occur, as, for example, a sequence number sent on the secondary-to-primary flow that does not match the committed or potential numbers saved by the STSN receiver.) This type of condition usually indicates an incorrect log data set; the master terminal operator must intervene to recover the session.

  • RECEIVED PENDING (Sync-Point Response Lost)

    The receiver of this flow receives the entire work unit that the sender sends and generates a DR2 that might be lost in the network.

  • NOT RECEIVED PENDING (Sync-Point Response Not Lost)

    The receiver of this flow never receives the RQ*2 that the sender sends and therefore backs out the work unit that the sender is pending on.

The half sessions exchange information on their respective states by using bind negotiation and the action codes in the STSN request and response.