OSI Model: Understanding the Layers of Network Communication

I always forget the specific layers of the OSI model so I'd thought I'd share it here for myself to go back to.

Here are the OSI models and a general description of what they represent.

Layer 7 Application

At the top of the OSI model is the Application layer, responsible for high-level interactions between user applications and the network. Here, requests are made, such as a GET request, containing HTTP headers, cookies, and content-type information.

Layer 6 Presentation (optional, used for encryption)

The Presentation layer, though optional, plays a vital role in encryption and decryption. It ensures data compatibility between systems and encrypts data if necessary, often utilized by protocols like TLS for secure communication.

Layer 5 Session

Establishing and maintaining communication sessions between devices is the task of the Session layer. Each session is tagged with a unique session ID number, facilitating encryption and data tagging.

Layer 4 Transport

The Transport layer segments data into manageable chunks for transmission. It also adds crucial information like port numbers and source ports to each segment for efficient communication.

Layer 3 Network

In the Network layer, data packets are routed based on logical addressing (IP addresses). Each packet contains source and destination IP addresses, enabling seamless transmission across networks.

Layer 2 Data Link

Data packets are transformed into frames in the Data Link layer. Frames are equipped with MAC addresses, identifying source and destination devices. Additionally, Address Resolution Protocol (ARP) converts IP addresses to MAC addresses for communication.

Layer 1 Physical

The Physical layer deals with the transmission of raw binary data over physical mediums like wires or wireless signals. It ensures reliable transmission of data bits from one device to another.

Summary

The OSI model provides a structured approach to understanding network communication. From the physical transmission of data to high-level application interactions, each layer plays a crucial role in the seamless exchange of information across networks.

Layer 1 Physical: Transmits binary data via physical mediums.

Layer 2 Data Link: Converts data into frames with MAC addresses.

Layer 3 Network: Routes data based on IP addresses.

Layer 4 Transport: Segments data and adds port information.

Layer 5 Session: Establishes and maintains communication sessions.

Layer 6 Presentation: Encrypts and decrypts data for secure transmission.

Layer 7 Application: Facilitates high-level interactions between user applications and the network.