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OSI Model

https://www.youtube.com/watch?v=nFnLPGk8WjA

Layers

Layer Name Mnemonic Mnemonic Mnemonic
7 Application All All Away
6 Presentation People People Pizza
5 Session Seem Should Sausage
4 Transport To Try Throw
3 Network Need New Not
2 Data Link Domino Dr. Do
1 Physical Pizza Pepper Please

Physical Path

  1. Sending device starts with Application (Layer 7)
  2. Data moves down Layers from 7 => 1
  3. Data moves along Network medium
  4. Data moves up Layers from 1 => 7 to receiving device

Logical Path

Layer Sender Receiver
Application Generates Data Receives Data
Presentation Encrpyts/Compresses Decrypts/Decompresses
Session
Transport Chops into Segments Puts segments together
Network Makes Packets Opens Packets
Data Link Makes Frames Opens Frames
Physical

Layer Notes

Application (Layer 7)

  • non-technical
    • About user's application
      • Chrome/Firefox/Outlook/etc
  • technically
    • refers to application protocols
      • HTTP, SMTP, POP3, IMAP4, etc
      • facilitate communications between application and operating system
  • Application data generated here

Presentation (Layer 6)

  • Provides variety of coding/conversion functions on application data
  • Ensures information sent from app layer of client is understood by app layer of server
  • trys to translate app data into certain format that every system can understand

Session (Layer 5)

  • Establish, manage, terminate connectiosn between sender and receiver

Transport (Layer 4)

  • Accepts data from Session
  • Chops data into smaller segments
  • Adds Header information
    • Destination Port Number
    • Source Port Number
    • Sequence Number
      • used by receiver to put segments back in order
  • Main Protocols:
    • TCP (dominant protocol)
    • UDP

Network (Layer 3)

  • Primary Protocol: IP
  • Takes segments and adds actual header information
    • Senders IP address
    • Receivers IP address
    • Packets are created
  • All about IP address and routing
  • More Header information added
    • Adds Frame Header
      • Source MAC Address
      • Desination MAC Address
    • Adds Trailing FCS
  • Exists @ NIC

Physical (Layer 1)

  • Accepts Frames from Data Link layers
  • Generates Bits
    • Bits made of electrical pulses or light
      • depends on medium (copper vs fiber etc)