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/The Open Systems Interconnection (OSI) Model
The Open Systems Interconnection (OSI) Model
The OSI layer model will help us to understand the overall picture of how computer networks work without getting into too many low-level details.
Common Models
There are several models along which computer networks are organized. The two most common ones are the Open Systems Interconnection (OSI) model and the Transmission Control Protocol/Internet Protocol (TCP/IP) model.
We will discuss each model and the differences between the two in detail starting with the OSI model.
The OSI Model
The OSI Model was developed in the '70s by the Organization for Standardization (ISO). At this time, the Internet was in its infancy and its protocols had not fully matured. The OSI model provides a standard for different computer systems to be able to communicate with each other.
The Layers of the OSI Model
The model splits up a communication system into 7 abstract layers, stacked upon each other.
Here are the seven layers of the OSI Model.
Mnemonic
A good mnemonic device to help remember these layers is:
Network protocols are implemented in software, hardware or a combination of both, and their hardware and software components are organized into these layers. So the main purpose of this ‘network stack’ is to understand how the components of these protocols fit into the stack and work with each other.
Here are some key responsibilities of each layer. Note that we are listing only some of the responsibilities of each layer. The exhaustive discussion is deferred to later chapters.