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Description of the Architecture

Introduction to PROFIBUS on Industrial PC

C79000-G8976-C068

3.1 The ISO/OSI Reference Model

As the user of powerful automation components such as host

computers, programmable logic controllers, printers, data servers etc.,

you expect trouble-free interaction between these devices and control

systems and features such as:

•

Use of communication systems without time-consuming

configuration and programming.

•

Independence from any one particular vendor.

•

Flexible modification of plant structures without affecting

communication.

•

The highest possible reliability in data transmission.

•

Long-term planning and use of equipment (today’s devices should

be able to communicate with those of tomorrow).

The answer to such requirements is a

heterogeneous network of

automation components

, in which devices from a variety of vendors

can communicate (

open communication

). In contrast, in a

homogeneous network, only devices of one vendor can communicate

with each other.

The International Standards Organization (ISO) defined a reference

model for open system communication for heterogeneous networks.

This ISO/OSI reference model provides a guideline for standardization

of communications procedures. It provides a framework for

standardizing communications procedures in seven layers. All

manufacturers of automation components or generally of data terminal

equipment, not only for industry, today base their products on the

ISO/OSI reference model (Figure 3.1).

The Layers and Their Tasks

7 Application layer Provides uniform access

to specific services.

6 Presentation layer Establishes transfer syntax.

5 Session layer Establishes, maintains, terminates

4 Transport layer Transfers “raw” information

3 Network layer Provides network connections.

2 Data link layer Establishes and terminates

1 Physical layer Regulates physical connections

communication sessions

links.

for bit transfer.

reliably.

Figure 3.1 The Seven Layers of the ISO/OSI Reference Model

Trouble-Free

Interaction

Open

Communication

The ISO/OSI

Reference Model

The Seven Layers

of the ISO/OSI

Model

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 ... 35 36

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