CS/IS 465 Data Communications and Networks Lecture 28

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CS/IS 465Data Communications and
NetworksLecture 28

• Martin van Bommel

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High-Speed Wireless LANs

• Why?
• Extraordinary growth in speed, power, and storage
  capacity of PCs
• Increasing use of LANs as computing platforms
• Low speed not capable of supporting requirements
• Examples
• Server farms - multiple centralized servers
• Power work groups - e.g. CAD company
• High-speed backbones

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LAN Generations

• First - CSMA/CD and Token Ring
• terminal-to-host connnectivity
• client-server at moderate data rates
• Second - FDDI and others
• backbone LANs and high-performance stations
• Third - ATM LANs
• multiple guaranteed high-speed classes of service
• multimedia applications

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Fast Ethernet

• CSMA/CD operating at 100 Mbps
• Easy to integrate with existing systems
• 100BASE-X - two simplex links b/w nodes
• Can use UTP (100BASE-TX) but requires two lines
  between stations
• Can use Fiber (100BASE-FX)

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Fast Ethernet Configuration

• 100BASE-T uses star-wire topology
• All stations connected to central point using
  multiport repeater (broadcast method)
• Repeater, not stations, detects collisions and
  sends jam signal on all ports
• Repeaters connected with bridges

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Fast Ethernet Full-duplex Mode

• Traditional Ethernet is half-duplex
• Two links b/w stations allows full-duplex
• NICs must support full-duplex mode
• Switched hub must be used - determines path for
  frame
• No collisions ever occur

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Mixed Ethernet

• Can mix 10-Mbps and 100-Mbps LANs
• Slow stations attach to 10-Mbps hubs
• Hubs connected to 100-Mbps hubs
• High-speed servers connected to 100-Mbps
• See Figure 15.4

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Gigabit Ethernet

• Still under development (started late 1995)
• Retains CSMA/CD protocol and Ethernet format,
  ensuring smooth upgrade path
• Uses optical fiber over short distances
• 1-Gbps switching hub provides backbone
  connectivity for central servers and high-speed
  workgroup hubs - Figure 10-5

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FDDI

• Fiber Distributed Data Interface
• Oldest high-speed LAN standard
• Token ring MAC protocol with early token release
  (frame occupies only small part of ring with
  high-speed)
• Piggy-back frames by claiming early-release token

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FDDI (2)

• 100 Mbps optical fiber
• 100 Mbps category 5 UTP or STP
• Respectable market share
• ATM LANs better suited to multimedia traffic and
  to integrate with ATM WANs

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ATM LANs

• Several types
• Gateway to ATM WAN
• ATM switch acts as router to ATM WAN
• Backbone ATM switch
• ATM switch(es) interconnect other LANs
• Workgroup ATM
• high-performance stations connect directly to ATM
  switch
• Mixture of types on internet

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Backbone ATM LAN

• Local ATM network consists of switches
  interconneted with high-speed point-to-point
  links running ATM rates of 155 622 Mbps
• LANs directly connect to ATM switches
• ATM switch performs buffering, speed and protocol
  conversion
• Figure
• End systems still limited by shared mediums

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ATM Hub

• Each ATM hub includes number of ports
• Ports operate at different rates and protocols
• Each end system has dedicated point-to-point link
  with hub - Figure
• Existing LAN hardware can be used on LAN systems
  while introducing ATM LAN
• Hub requires complex protocol conversions

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Pure ATM LAN

• End systems attach directly to ATM network
• ATM protocols implemented
• No conversions required

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ATM Compatibility Issues

• Interaction between ATM-based station and
  legacy-based station
• Interaction between two stations using same
  legacy protocol but communicating via ATM
• Interaction between two stations using different
  legacy protocols via ATM
• Solution - bridge or router type ATM switch