Extending LANs: Fiber Modems, Repeaters, Bridges, and Switches

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Extending LANs Fiber Modems, Repeaters,
Bridges, and Switches

• Keng Siau
• University of Nebraska-Lincoln

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LAN Extensions

• Several techniques extend diameter of LAN medium
• Most techniques use additional hardware
• Fiber Modems
• Repeaters
• Bridges
• Switches

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Fiber Optic Extensions

• Insert fiber modems and fiber optic cable into
  AUI cable
• Fiber modems
• Convert AUI signals to digital signal
• Transmit digital signals via fiber optic cable to
  other modem
• Most often used to connect LANs on different
  buildings

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Fiber Optic Extensions
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Repeaters

• Bidirectional, analog amplifier that retransmits
  analog signals
• One repeater can effectively double the length of
  an LAN segment

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Limits on Repeaters

• Can't extend Ethernet with repeaters indefinitely
  
• CSMA/CD requires low delay if medium is too
  long, CSMA/CD won't work
• Ethernet standard includes limit of 4 repeaters
  between any two Ethernet stations

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Repeaters used to Connect Ethernet Segments
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Bridges

• Connect two LAN segments
• Retransmits frames from one segment on other
  segment(s)
• Handles complete frame
• Uses NIC like any other station
• Performs some processing on frame
• does not forward interference or other problems
• Invisible to other attached computers

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Bridges
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Frame Filtering

• Only forward frames where necessary
• Bridge performs frame filtering and forwards
  frames along LAN segments to destination
• Learns location of stations by watching frames
• Forwards all broadcast and multicast packets

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Switches

• Hardware includes an electronic device that
  connects to one or more computers and allows them
  to send and receive data
• With switching, multiple stations can transmit
  simultaneously
• Provides much higher aggregate bandwidth

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Switches
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Summary

• Optical fiber and modems can be used to extend
  AUI for single station
• Repeater acts as amplifier and retransmits analog
  signals
• Bridge accepts entire incoming frame and
  retransmits
• Switches provide full LAN speed to each port by
  simulating separate LAN segments