CTI 2572 Technical Overview Manual
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CHAPTER 3. ETHERNET OVERVIEW
3.1 ISO Reference Model
Modern network implementations separate data communication functions into layers. Each layer
performs a specific set of services and interacts with layers above and below in a well defined
way.
In 1984 the International Standards Organization published the Open Systems Interconnection
(OSI) Reference model. Although there are few, if any, strict implementations of the entire
seven layer model, it is commonly used as a conceptual reference when discussing networking
software. The OSI model is briefly described below:
Layer Function
Layer 7
Application
Provides application services such as file transfer,
virtual terminal, and directory services.
Layer 6
Presentation
Resolves differences in data representation between
the communicating applications
Layer 5
Session
Synchronizes communications between applications
Layer 4
Transport
Provides reliable data transfer from end node to end
node.
Layer 3
Network
Translates physical addresses into logical addresses
and routes packets to the destination node.
Layer 2
Data Link
Places messages into data frames and manages access
to the media.
Layer 1
Physical
Defines the electrical and mechanical characteristics
of the transmission media .
The Ethernet specifications describe both the Physical layer (cabling, connectors, and
topology) as well as the Data Link (Medium Access) layer. As a result of this complete
specification, Ethernet equipment from various vendors can be used on the same network.
Ethernet is the most widely used local area network in the world and it is continuing to gain
market share due to its low cost and flexibility. One of the fastest growing areas in Ethernet
installations is the factory floor.
