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
Layer 7 Application
Layer 6 Presentation
Layer 5
Session
Layer 4 Transport
Layer 3
Network
Layer 2 Data Link
Layer 1
Physical
Function
Provides application services such as file transfer, virtual terminal, and directory services.
Resolves differences in data representation between the communicating applications
Synchronizes communications between applications
Provides reliable data transfer from end node to end node.
Translates physical addresses into logical addresses and routes packets to the destination node.
Places messages into data frames and manages access to the media.
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.
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