OSI/TS Configuration and Management Manual

OSI/TS Configuration and Management Manual—424831-001
5-1
5
OSI Transport Services
In an OSI network, the Transport Layer provides application processes with host-to-host
data-transfer services. To provide these services, the Transport Layer uses the services
provided by the Network Layer. This section explains how the OSI/TS subsystem uses
and augments the services provided by the Network Layer.
This section includes the following topics:
•
Transport service primitives exchanged between the OSI/TS subsystem and the
transport user
•
The five transport protocol classes
•
OSI/TS error-detection and recovery mechanisms
•
OSI/TS addressing and multiplexing schemes
•
Relationships between CR-TPDU parameters: called address and calling address,
and SRC-REF and DST-REF
Functions Supported by OSI/TS
OSI/TS performs all functions listed as mandatory functions in the ISO standards. The
following optional functions are not available:
•
Ability to disable explicit flow control in class 2
•
Confirmation-receipt variant of retention until acknowledgment of TPDUs
•
Network-expedited data transfer
OSI/TS supports extended format numbering for data TPDUs.
Transport Service Primitives
Table 5-1 lists Transport Layer service primitives that OSI/TS supports. These
primitives represent the Transport Layer's view of messages that a transport user and an
OSI/TS transport entity exchange at a transport service access point (TSAP).
The transport user's view of these messages, however, is mediated through the file
system.
Reception of a service primitive by the transport entity is associated with the completion
of a file-system request issued to the local subdevice by the transport user. Refer to
Section 4, Performing Monitoring and Troubleshooting Guide
for a description of the
file-system interface to OSI/TS.