03-11-2016, 10:34 AM
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INTRODUCTION
Open Systems Interconnection
Standard Model for Data Communications
Specified by International Standards Organization (ISO)
Adopted by CCITT/ITU
Official Model Explained in X.200 Series
In 1984, the OSI reference model was approved as an international standard for communication architecture.
International standard organisation (ISO) established a committee
in 1977 to develop an architecture for computer communication.
What is “THE MODEL?”
Commonly referred to as the OSI reference model.
The OSI model
is a theoretical blueprint that helps us understand how data gets from one user’s computer to another.
It is also a model that helps develop standards so that all of our hardware and software talks nicely to each other.
It aids standardization of networking technologies by providing an organized structure for hardware and software developers to follow, to insure there products are compatible with current and future technologies.
The OSI Model
Layered Approach to Communications
Seven Layers Altogether
Each Layer Performs a Unique Function
Each Layer Has Its Own Protocol
Protocol Messages in Upper Layer is Data to Layer Below
Physical Layer
Representation of bits
Begin Can Be Flag
End Can Be Flag
End May Include Check Sum (CRC)
Data Transparency
Data Link Layer
Link Layer Header Has Frame Type
Sequence and Acknowledgement Numbers
Error Recovery Procedures
Limited to Local Wire or Circuit
Transport Layer
Transport Header Has Packet Type
Sequence and Acknowledgement Numbers
Error Recovery Is End to End
Upper Layers Can Count on Reliability