OSI/TS Configuration and Management Manual

OSI Transport Services
OSI/TS Configuration and Management Manual—424831-001
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Resynchronizing the Data
is confirmed, OSI/TS considers the transport connection released and informs users by
issuing file-system error 140.
The OSI/TS Subsystem as Responder
As the responder, the OSI/TS subsystem does not try to reassign the transport
connection, but waits for reassignment from the peer entity that initiated the connection.
On receipt of a disconnect indication, OSI/TS starts the timer TWR. TWR determines
the length of time that OSI/TS waits to receive a valid TPDU on the connection. If a
valid TPDU is received, TWR is stopped and OSI/TS begins the resynchronization
procedure.
If no valid TPDU is received before TWR expires, OSI/TS considers the connection
released and informs users by issuing file-system error 140. In either case, if
reassignment is successful, OSI/TS resynchronizes the data on the new transport
connection.
Resynchronizing the Data
OSI/TS resynchronizes data in protocol classes 1 and 3 whenever the subnetwork issues
a reset indication or the transport connection is reassigned to a new network connection.
The resynchronization protocol defines both an active and a passive procedure for the
corresponding transport entities. The initiator of the connection performs the active
procedure, and the responder performs the passive procedure.
The OSI/TS Subsystem as Initiator
The OSI/TS subsystem begins the active-resynchronization procedure by starting the
TTR timer. If an outstanding request for connection establishment or connection release
remains unacknowledged, OSI/TS re-sends it. If there are no outstanding requests,
OSI/TS re-sends any unacknowledged expedited data TPDUs (ED-TPDU). It then
sends a reject TPDU (RJ-TPDU) to the corresponding peer. The RJ-TPDU indicates the
next TPDU that OSI/TS expects to receive, and causes the remote peer to retransmit any
TPDUs that might have been lost when the connection was disrupted. OSI/TS then re-
sends any unacknowledged DT-TPDUs.
If the subnetwork issues a disconnect during the resynchronization procedure, OSI/TS
attempts to reassign the transport connection according to the reassignment procedure
described above. If reassignment is successful, OSI/TS again attempts to resynchronize
the data. The TTR timer is used to avoid an endless loop between these two procedures,
as follows:
•
The TTR timer is set once, either at the beginning of reassignment or at the
beginning of resynchronization.
•
During the reassignment procedure, if TTR times out before reassignment is
complete, OSI/TS releases the transport connection.
•
If OSI/TS receives a subnetwork disconnect indication during resynchronization,
reassignment is attempted only if TTR has not timed out. Otherwise, OSI/TS
releases the transport connection.