OSI/TS Configuration and Management Manual

Introduction
OSI/TS Configuration and Management Manual—424831-001
1-3
OSI/TS Features
Figure 1-2 shows the relationship between end systems and intermediate systems.
OSI/TS Features
The OSI/TS subsystem implements the Transport Layer of the OSI Reference Model. It
conforms to the ISO 8072 service definitions and to the ISO 8073 protocol specification.
OSI/TS implements protocol classes 0, 1, 2, 3, and 4. It initiates and responds to
connect-request transport protocol data units (CR-TPDUs). OSI/TS also implements
internet protocol (IP), including the inactive subset, ES-IS routing exchange protocol (to
allow end systems to dynamically exchange routing information), and subnetwork
dependence convergence function, SNDCF (to allow the IP to operate over X.25 wide
area subnetworks).
OSI/TS sends TPDUs as normal data requests to the network. Network Layer expedited
data transfer is not used. In class 1, OSI/TS sends acknowledgment TPDUs (AK-
TPDUs) to acknowledge outstanding TPDUs. In class 2, OSI/TS always uses flow
control; there is no provision for disabling flow control. In class 4, OSI/TS does not
split a transport connection over multiple network connections.
The OSI/TS subsystem has a standard Compaq file-system interface. It supports both
wait and nowait file-system I/O calls.
Hardware Components
OSI/TS runs on K-series and S-series hardware. K-series hardware is supported by
D-series software; S-series hardware is supported by G-series software.
Figure 1-2. OSI End Systems and Intermediate Systems
102CDT .CDD
Subnetwork
Layer
Application
Presentation
Session
Transport
Network
Data Link
Physical
• • •
• • •
• • •
Intermediate
System
Intermediate
System
End
System
End
System