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Unit03

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Unit03 Unit03 Presentation Transcript

  • Unit03: The OSI Model
  • Overview
    • Open Systems Interconnection
    • Encapsulation
    • Physical
    • Data-link
    • Network
    • Transport
    • Session
    • Presentation
    • Application
  • Open Systems Interconnection
    • Proposed by the International Organization for Standardization (IOS) and released in 1984
    • Decidedly structured set of seven protocol layers interconnecting as a stack
    • Developed to maintain the ability to connect diverse types of computers
    • Valuable as a teaching and development tool
  • OSI
  • Encapsulation The sending station converts data into increasingly smaller capsules until they are mere bits Puts those bits back together into increasingly larger capsules at the receiving station
  •  
  • Physical Layer
    • Transmission of raw data in the form of a stream of bits across physical media
    • Physical Layer conveys the bit stream data through electrical impulses, light, or radio signals
    • The connections that are supported at the physical layer are either multipoint or point-to-point
  • Physical Layer
  • Data Link Layer
    • It is the only layer with two sublayers: Media Access Control (MAC) and Logical Link Control (LLC).
    • The data-link layer supplies hardware addresses, identifies errors, and manages flow control.
    • Bit stream received from the physical layer is assembled into larger pieces, called frames
    • Able to insert control information into a frame header
    • Source and destination of the frame on that network segment
  • Data Link Layer
    • Media Access Control (MAC)
      • This sublayer defines how devices are able to gain access to the media
      • maintains the hardware address for the device
    • The three types of MACs are:
      • Contention
      • Polling
      • Token passing
  • Data Link Layer
    • MAC Address
      • also called the hardware address
      • MAC address is unique to each interface
  • Data Link Layer
    • Logical Link Control
      • second data-link sublayer
      • Responsible for logical link functions of single or multiple connections
      • LLC provides services to the higher-level network layer
      • The LLC primarily provides flow control and frame sequencing services
  • Network Layer
    • Providing an address for each network segment
    • Providing a logical address for each device that is separate from the MAC address
    • Routing and forwarding data
    • Selecting a route if there are multiple routes to the same network segment
    • Discovering the routes to other network segments
    • Error handling, congestion control, and packet sequencing
  • Network Layer
  • Network Layer
    • RIP
      • Distance Vector routing protocols periodically broadcast the entire routing table to neighboring routers
    • OSPF
      • These advanced protocols use a hello process to announce a new router on the network
      • the time it takes for the new routes to be added to the network is greatly reduced
  • Transport Layer
    • Provides for a transparent transfer of data between the sender and receiver nodes
    • Control information provides end-to-end recovery and flow control
    • Ensures that the data is completely transferred
  • Transport Layer
    • Connection Orientation
      • Connection-oriented
        • TCP
        • Reliable Transfer
        • use of acknowledgments (ACK)
      • Connectionless
        • UDP
        • Does not use ACK
        • Smaller headers and less time needed
  • Session Layer
    • Establishes a connection between applications and manages that connection until it terminates.
    • Also terminate a session in an orderly manner
    • Remote procedure calls (RPCs) function at the session layer
    • Example : Telnet and Citrix MetaFrame ICA sessions
    • Data is transmitted in a session in three ways
      • Simplex.
      • Half-duplex..
      • Full-duplex.
  • Presentation Layer
    • Provides the way for data to be presented to the application
    • Encryption/decryption and data compression/expansion are handled at this layer
    • provide formatting data
    • Bit order
    • Byte order
    • Character code
    • File syntax.
  • Application Layer
    • Supports end-user processes
    • Specific to the application being used.
    • Application-layer protocols connect across the internetwork in three ways
      • Collaborative computing
      • Operating system call interception
      • Remote operation