Specifications

4
Schneider Electric
Local Area Networks
Local Area Networks have been standardized according to the OSI model.
Definition: OSI, Open Systems Interconnection.
This standard includes seven layers:
This document describes in detail the characteristics of the communication medium
used for "Power Logic System" products. The following aspects will be discussed:
b Physical implementation (Layer 1)
b The Modbus protocol supported by this medium, which can be classified in layer 2
of the OSI model.
Some aspects of the application layer are discussed in Chapter 3 (Implementing
products), but the application layer is directed more towards the application software,
which is not the subject of this guide.
Concerning the other layers:
b Layer 3, the "Network" layer, manages the interconnection of local area networks
(layers 1, 2 and 7).
b Layer 4, the "Transport" layer, compensates for problems that may be encountered
in layer 3.
b Layers 5 and 6, "Session" and "Presentation", deal with the Operating System.
They manage the synchronization of messages, priorities, language, security
aspects, etc.
E52411
7 - Application
The 7 OSI layers
Factory LANs use only 3 layers
6 - Presentation
5 - Session
4 - Transport
3 -
Network
2 - Data Link
1 - Physical
7 - Application
2 -
Data Link
1 - Physical
Introduction