OSI/TS Configuration and Management Manual

OSI/TS Configuration and Management Manual—424831-001
6-1
6
Managing a Transport Connection
The management of a transport connection is divided into three protocol phases:
Connection establishment
Data transfer
Connection release
During each phase, transport peer entities coordinate their activities and provide services
by exchanging messages through subnetwork connections. These messages are
transport protocol data units (TPDUs).
This section describes these three protocol phases. Connection establishment is
described twice because the OSI/TS subsystem acts differently depending on whether it
is the initiator or the responder.
As Table 6-1
illustrates, the type of TPDU determines its use in one of the transport
protocol phases. OSI/TS supports the TPDU types shown.
Connection Establishment: OSI/TS as Initiator
A transport service user initiates the connection-establishment phase by issuing a
T-CONNECT request service primitive to a local transport entity. The transport entity
then determines the subnetwork address of the remote peer entity and requests a
subnetwork connection. The corresponding transport peer entities exchange a sequence
of TPDUs over the subnetwork connection. Control information in these TPDUs
determines which services peer entities provide. See Section 7, NonStop Kernel File-
System Interface for information about choosing whether the OSI/TS subsystem or the
application handles the transport protocol.
Table 6-1. TPDU Types in Each Connection Phase
Connection Phase TPDU Type Function
Connection
establishment
CR-TPDU
CC-TPDU
Request a transport connection
Confirm a CR-TPDU
Data transfer DT-TPDU
AK-TPDU
ED-TPDU
EA-TPDU
RJ-TPDU
Transfer transport user data
Acknowledge one or more DT-TPDUs
Expedite transfer of user data
Acknowledge an ED-TPDU
Reject TPDU (classes 1 and 3)
Connection release DR-TPDU
DC-TPDU
Request a connection release
Confirm a DR-TPDU
Any ER-TPDU Error TPDU