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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