OSI Model TryHackMe

OSI Model

Open Systems Interconnection Model is an essential model that provides a framework dictating how all networked devices will send, receive and interpret data.

Layers of OSI Model

7. Appliction

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link

1. Physical

Physical Layer (Layer 1)

References the physical components of the hardware used in networking. Ethernet Cables and computer components.

Data Link Layer (Layer 2)

The physical addressing of the transmission (MAC). It receives a packet from the network layer including IP address and adds the physical MAC address of the receiving endpoint.

Also the job of this layer to present the data in a format suitable for transmission.

Network Layer (Layer 3)

Layer where routing & re-assembly of data takes place.

Routing typically done using protocols OSPF (Open Shortest Path First) and RIP (Routing Information Protocol).

• What path is the shortest?

• What path is the most reliable?

• Which path has the faster physical connection?

At this layer, everything is dealt with via IP addresses.

Transport Layer (Layer 4)

It ensures that data arrives at the correct application, in the correct order, and without errors.

When data is sent between devices, it follows one of two different protocols that are decided based upon several factors:

• TCP

• UDP

TCP (Transmission Control Protocol)

This protocol is designed with reliability and guarantee in mind.

This protocol reserves a constant connection between the two devices.

Portocol can guarantee that data sent in small chunks has then been received and reassembled in the same order.

UDP (User Datagram Protocol)

Transmission protocol that is lightweight and quick without error checking and reliability.

It's designed for speed and efficiency, making it suitable for real-time applications where occasional packet loss is acceptable, such as online gaming, video streaming.

Session Layer (Layer 5)

Layer will begin to create and maintain the connection to other computer for which the data is destined.

Presentaion Layer (Layer 6)

The layer in which standardisation of data starts to take place.

Because software developers can develop any software differently, the data still needs to be handled in the same way.

Layer acts as a translator for data to and from the application layer.

Applicaion Layer (Layer 7)

The layer is the interface between users and software applications, typically providing a GUI for users to interact with data. Example services like web browsing, email, and file transfer.