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OSI Model

  • Application Layer
  • Presentation Layer
  • Session Layer
  • Transport Layer
  • Network Layer
  • Data link Layer
  • Physical Layer

Application Layer

  • Provide network services directly to the user/application
  • example: Web Browsers, email clients, file transfer apps
  • Protocols:
    • HTTP
    • HTTPS
    • SMTP
    • FTP
    • DNS

Presentation Layer

  • Translates, Compresses or encrypts data so application can understand it
  • Functions:
    • Data format conversions -> JPEG, MP4, PDF
    • Encryption, Decryption -> SSL, TLS
    • Compression -> ZIP, MPEG

Session Layer

  • Manages session between two systems
  • Functions:
    • Establishing, maintaining and ending sessions
    • Synchronization in data transfer
  • Protocols:
    • NetBIOS
    • RPC

Transport Layer

  • Ensure end-to-end communication with reliability and error-checking
  • Functions:
    • Split data into Segments
    • Re-transmit if data is lost
    • Error detection
    • Can be connection oriented(TCP) or connection less(UDP)
  • Protocols
    • TCP
    • UDP

Networks Layer

  • Handles logical addressing and routing
  • Functions:
    • Assign IP addresses
    • Finds the best path for data (routing)
    • Delivers packets to the correct device on a different network
  • Protocols:
    • IP(IPv4, IPv6)
    • ARP
  • Devices:
    • Router
  • Handles physical addressing (MAC) and error detection on a single local link.
  • Functions:
    • Frames the raw bits into meaningful chunks (from physical layer to networks layer)
    • Uses MAC addresses to deliver data to the right device on the same network
    • Error detection with checksums
  • Protocols:
    • Ethernet
    • PPP
    • WiFi
  • Devices:
    • Switches
    • Bridges

Physical Layer

  • Concerned with raw transmission of bits over physical media
  • Functions:
    • Deals with cables, signals, voltages, wireless frequencies
    • Defines connectors, pin layout and transmission rates
  • Protocols / Tech:
    • Ethernet cable
    • Fiber optics
    • WiFi signals
    • Bluetooth
  • Devices:
    • Hubs
    • Repeaters
    • Cables

For instance => When we open a website - Application -> Browser requests web page using HTTP/S - Presentation -> Data encryption, compression and translation with SSL/TLS etc - Session -> Session started between the browser and server - Transport -> TCP ensures reliable delivery of packets - Network -> IP decides where the packet should go in the network - Data link -> Within a local network, ensures delivery to the correct MAC Address. Frame the raw bits - Physical -> Bits travel as electrical signals

Network Devices