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OSI model

Just like a doctor tells his/her patient “There is something wrong with your XYZ.”, computer needs a frame of reference for the doctor(or someone who fix the computer) to discuss the issues. Hence, we created a conceptual model called the Open Systems Interconnection(OSI) model.

OSI model and protocols

OSI model defines how information is passed between hardware devices and user applications. It divides network communication into seven layers: Application layer, Presentation layer, Session layer, Transport layer, Network layer, Data link layer and Physical layer, each layer is associated with a packet of protocols(sets of rules, like a language).

OSI model and protocols

Layer7: Application layer

application layer

Application layer is the layer closet to the end user and is used by network application like Chrome, Outlook, etc. Some examples of protocols in this layer are:

Layer6: Presentation layer

presentation layer

Presentation layer translates, compresses, encrypt/decrypt the data.

layer5: Session layer

session layer

Session layer manages each session(a temporary and interactive information interchange between two or more communicating devices), it is responsible for:

layer4: Transport layer

transport layer

Transport layer controls the reliability of communication through:

There are two protocols for two types of transmission:

layer3: Network layer

network layer

Network layer performs:

data link layer

Data Link layer has two sublayers: Logical Link Control(LLC) sublayer and Media Access Control(MAC) sublayer. It allows data for accessing the media through framing, and controls how data is placed and received from the media through Media Access Control and Error Detection.

layer1: Physical layer

physical layer

Physical layer controls the rules of data transmission, including signals, types of cables, and transmission speed.

Other models

We uses OSI model to describe other models, for example:

TCP/IP model

TCP/IP model, also known as DoD model. It has four layers, omitting the physical layer.

Internet model

Internet model, collapses the top three OSI layers into one.