Layer 7 – Application Layer
The Application Layer contains the business logic and functionality of applications, serving as the interface for users to interact with network services. Most developers build applications at this layer, where the complexities of the underlying layers are abstracted away.
Examples of Layer 7 Applications:
- HTTP (Hypertext Transfer Protocol): Facilitates access to web applications.
- FTP (File Transfer Protocol): Enables users to transfer files.
- SNMP (Simple Network Management Protocol): A protocol used to read and modify network device configurations.
Many applications utilize these protocols, including Google Chrome, Microsoft Skype, and FileZilla.
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Layer 6 – Presentation Layer
Typically an invisible layer, it is responsible for adapting, transforming, and translating data to ensure that the application and the layers below can communicate effectively.
- Encoding Schemes: Used to represent text and data, such as ASCII (American Standard Code for Information Interchange) and UTF (Unicode Transformation Format).
- Encryption Services: For securing data, including SSL (Secure Sockets Layer) and TLS (Transport Layer Security).
- Compression: Techniques like GZip, commonly used in various HTTP implementations.
Layer 5 – Session Layer
This layer is responsible for managing connections between the application and the layers below, which includes establishing, maintaining, and terminating sessions.
Common protocols that exemplify the Session Layer include:
- SOCKS: A protocol for routing packets through a proxy server.
- NetBIOS: An older Windows protocol for establishing sessions and resolving names.
- SIP (Session Initiation Protocol): Used for initiating VOIP (Voice Over IP) communications.
Layer 4 – Transport
The layer that enables applications to be represented on the network.
Some well-known protocols at this layer include:
- TCP (Transmission Control Protocol): Utilized by many applications to ensure stability, control the amount of data sent at any time, and provide reliability.
- UDP (User Datagram Protocol): A lightweight and fast protocol used for various services.
- QUIC (Quick UDP Internet Connections): A protocol designed for faster connections that complements HTTP/2.
Layer 3 – Network
A layer responsible for routing packets between networks using routers.
The following protocols operate at this layer:
- IP (Internet Protocol): Commonly used for accessing the Internet, available in two versions: IPv4 and IPv6.
- ICMP (Internet Control Message Protocol): Employed by network devices and operators for diagnosing network connections and facilitating error reporting.
- IPSec (Internet Protocol Security): Enables encrypted and secure connections between two network devices.
Layer 2 – Link
The Link Layer consists of protocols designed to transmit packets through the physical connections between network nodes, effectively moving data from physical to logical (network layer) levels.
Protocols at this layer include:
- Ethernet: A fundamental protocol widely used by operating systems for wired network connections.
- Wi-Fi (Wireless Fidelity): Enables network access via radio signals, utilizing a family of protocols known as IEEE 802.11.xx.
- NDP (Neighbor Discovery Protocol): Used by IPv6 on the Link Layer to collect necessary information for IPv6 communication.
Layer 1 – Physical
The Physical Layer encompasses the signaling that enables the transfer of bits and bytes over a physical medium, which can occur through radio waves, electrical signals, or light (such as fiber optics).
Examples of Physical Layer protocols include:
- CAN Bus (Controller Area Network): Used in microcontrollers and other devices for communication with similar devices, typically without involving a computer; commonly utilized in Industrial Control Systems (ICS).
- Ethernet Physical Layer: Utilized by Ethernet to transmit signals at speeds reaching several gigabits per second.
- Bluetooth Physical Layer: Bluetooth has specific standards for the transmission and reception of radio signals.
