Mnemonic to remember all 7 layers in OSI Model is All People Seem To Need Data Processing i.e.

The OSI (Open Systems Interconnection) model is a seven-layer conceptual reference model used to describe the different functions involved in networking. Here is a brief overview of each layer with examples:

• Layer 7 – Application: This layer provides a user interface for the network and supports common application services such as file transfer, email, and web access.
  • Example: File Transfer Protocol (FTP), SSH, Simple Mail Transfer Protocol (SMTP), or Hypertext Transfer Protocol (HTTP).
  • Devices at this layer include web servers, mail servers, and proxy servers.
• Layer 6 – Presentation: This layer provides a common format for data transmission and is responsible for data compression and encryption.
  • Example: Secure Sockets Layer (SSL) or Transport Layer Security (TLS) and character encoding like ASCII vs UTF-8
  • Devices at this layer include SSL accelerators and encryption/decryption devices.
• Layer 5 – Session: This layer establishes and manages communication sessions i.e. point-to-point communication between applications.
  • Example: Remote Procedure Call (RPC)
  • Devices at this layer are not typically found in modern networks, as their functionality has been absorbed by other layers.
• Layer 4 – Transport: This layer provides reliable data transfer between devices, breaking data into segments and reassembling it at the destination.
  • Example: data transfer protocols like TCP (Transmission Control Protocol) and UDP
  • Devices at this layer include network firewalls and load balancers.
• Layer 3 – Network: This layer routes data between networks, providing end-to-end delivery of data packets.
  • Example: network routing protocols like IP (Internet Protocol) and OSPF
  • Devices at this layer include routers, switches with routing capabilities, and firewalls.
• Layer 2 – Data Link: This layer is responsible for transmitting data over a single link of the network, and provides error detection and correction.
  • Example: Protocols that connect the physical layer to the network layer, such as Ethernet, Wi-Fi and ARP, MAC (Media Access Control) addresses
  • Devices at this layer include switches, bridges, and network interface cards (NICs).
• Layer 1 – Physical: This layer defines the physical characteristics of the network, such as the transmission medium is responsible for transmitting raw bits over a physical medium, such as copper wires or optical fibers, voltage levels, and timing.
  • Example: physical components such as Ethernet cable wiring
  • Devices at this layer include network cables, switches, and network interface cards (NICs).

OSI vs TCP/IP model in a nutshell: