The OSI Model – Open System Interconnection Model

This Model define by  International Organization for Standardization (ISO) in 1970.

• This is not a Physical model
• This model divides the network communication process in smaller and simpler component.
• This is very useful tools for network Troubleshooting
• There are seven layers in OSI Model
  • layer 7 – Application Layer
  • layer 6 – Presentation layer
  • layer 5 – Session layer
  • layer 4 – Transport layer
  • layer 3 – Network layer
  • layer 2 – Data Link layer
  • layer 1 – Physical layer
• Layers 7, 6 and 5 (Upper layers) main focus on services to application
• Layers 4,3,2, and 1 (Lower layers) main focus on end to end data delivery
• Data Unit in L4 is called Segment
• Data Unit in L3 is called Packet
• Data Unit in L2 is called Frame
• Data Unit in L1 is called Bits
• Encapsulation – Data moves down (7>6>5>4>3>2>1)
• Decapsulation – Data moves up (1>2>3>4>5>6>7)

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