OSI Model

1
OSI Model

• Shawn Shuoh-Ren Tsai
• Cisco Academy Training Center
• David Ta-Wei Shih
• CGUIC

2
Media

• telephone wires
• Category 5 UTP (used for 10BASE-T Ethernet)
• coaxial cables (used for cable TV)
• optical fibers (thin glass fibers that carry
  light)

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Why a Layered Network Model

• Reduces complexity
• Standardize interfaces
• Facilitate modular engineering
• Ensure interoperable technology
• Accelerate evolution
• Simplifies teaching and learning

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Seven Layers of OSI Model

• The seven layers of the OSI reference model are
• Layer 7 The application layerLayer 6 The
  presentation layerLayer 5 The session
  layerLayer 4 The transport layerLayer 3 The
  network layerLayer 2 The data link layerLayer
  1 The physical layer

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Data Encapsulation

• Build the data.
• Package the data for end-to-end transport.
• Add the network address (IP) to the header
• Add the local address (MAC) to the data link
  header
• Convert to bits for transmission

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Protocol Data Units (PDUs)

• Data
• Application, Presentation, and Session Layers
• Segment
• Transport layer
• Packet (datagram)
• Network layer
• Frame
• Data Link Layer
• Bit
• Physical Layer

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TCP /IP Model

• TCP/IP model has four layers
• the application layer, the transport layer, the
  Internet layer, and the network access layer.

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TCP/IP Model (Cont.)

• Differences
• TCP/IP combines the presentation and session
  layer issues into its application layer
• TCP/IP combines the OSI data link and physical
  layers into one layer
• TCP/IP appears simpler because it has fewer
  layers
• TCP/IP protocols are the standards around which
  the Internet developed, so the TCP/IP model gains
  credibility just because of its protocols. In
  contrast, typically networks aren't built on the
  OSI protocol, even though the OSI model is used
  as a guide.

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