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The OSI Reference Model
Basically, the ISO is pretty much the Emily Post of the network protocol world. Just as Ms.
Post wrote the book setting the standards—or protocols—for human social interaction, the
ISO developed the OSI reference model as the precedent and guide for an open network protocol
set. Defining the etiquette of communication models, it remains today the most popular
means of comparison for protocol suites.
The OSI reference model has seven layers:
- Application layer (layer 7)
- Presentation layer (layer 6)
- Session layer (layer 5)
- Transport layer (layer 4)
- Network layer (layer 3)
- Data Link layer (layer 2)
- Physical layer (layer 1)
The OSI layers are divided into two groups. The top three layers define how the applications
within the end stations communicate with each other and with users. The bottom four
layers define how data is transmitted end to end.
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