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The purpose of the OSI model

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					   The purpose of the
     OSI model (1)

• It breaks network
  communication into smaller
  simpler parts
• It standardizes network
  components to allow multiple-
  vendor development and
  support
• It allows different types of
  network hardware and software
  to communicate with each other
    The purpose of the
      OSI model (2)
• It prevents changes in one layer
  from affecting the other layers,
  so that they can develop more
  quickly
• It breaks network
  communication into smaller
  parts, to make learning it easier
  to understand
 Use the OSI model to
      visualize how
    information (data
  packets) travels from
   applications on one
   computer, through
networking media, to an
 application on another
        computer
         The 7 Layers

•   Layer 7:   Application
•   Layer 6:   Presentation
•   Layer 5:   Session
•   Layer 4:   Transport
•   Layer 3:   Network
•   Layer 2:   Data Link
•   Layer 1:   Physical


All People Seem To Need Data
           Processing
7. The Application Layer

• Closest to user
• Provides network services to
  user’s applications
• Only provides services to
  applications outside the OSI
  model
• Establishes availability of
  communication partners
• Synchronizes and agrees on
  error recovery procedures and
  control of data integrity
• BROWSERS
6. The Presentation Layer

• Ensures that data sent by the
  application layer of one system
  is readable by the application
  layer of another system
• If needed, translates between
  multiple data formats using a
  COMMON DATA FORMAT
  5. The Session Layer
• Establishes, manages, and
  terminates sessions between
  applications
• Provides services to the
  presentation layer
• Synchronizes dialogue between
  hosts’ presentation layers and
  manages their data exchange
• Provides efficient data transfer,
  class of service, and exception
  reporting for layers 5, 6, & 7
• DIALOGUES &
  CONVERSATIONS
 4. The Transport Layer
• Segments data from the sending
  host & reassembles data on the
  receiving host
• Shielding boundary between
  upper 3 layers (application
  issues) & lower 3 layers (data
  transport issues)
• Establishes, maintains, and
  terminates virtual circuits
• Error detection-and-recovery
• Information flow control
• QUALITY OF SERVICE,
  RELIABILITY
 3. The Network Layer

• Provides connectivity and best
  path selection between two end
  systems
• Domain of routing
• PATH SELECTION,
  ROUTING, ADDRESSING
2. The Data Link Layer

• Provides reliable transfer of
  data across a physical link
  (media)
• Physical (vs. logical)addressing
• Network topology, access
• Error notification
• Ordered delivery of frames
• Flow control
• FRAMES, MEDIA ACCESS
  CONTROL
 1. The Physical Layer

• Defines the electrical,
  mechanical, procedural,
  functional specifications for the
  physical link
• Wires, connectors, voltages,
  data rates
• SIGNALS, MEDIA
       Encapsulation
• Packaging of data for
  transmission
• Data flows down the levels of
  the source and then up the
  levels of the destination
• 5 encapsulation steps:
  – Build data
  – Transport layer segments data
  – Network layers puts data into a
    packet with header information
  – Data Link layer puts packet into a
    frame
  – Physical Layer converts frame to
    bits
   Protocol Data Units
• Different layers in the OSI
  model have different groupings
  for data
• Each layer has a protocol data
  unit, or PDU
• Transport layer deals with
  segments
• Network layer encapsulates
  segments into packets
• Data Link layer encapsulates
  packets into frames
• Physical layer converts frames
  to bit streams

				
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