Chapter 8 LAN Technologies and Network Topology

1
Chapter 8 LAN Technologies and Network Topology

• Direct Point-to-Point Communication
• Local Area Networks (LANs)
• LAN Topologies
• Ethernet
• Token Ring
• FDDI
• LocalTalk
• Wireless LAN

2
Direct Point-to-Point Communication

• used in early computer communications systems
• Advantages
• - Each point-to-point connection can use
  different network hardware, frame format, and
  bandwidth (fig 8.1)
• - Each point-to-point connection has exclusive
  access
• - Easy to enforce security and privacy
• Disadvantages
• - fully meshed network becomes exponentially
  expensive as number of nodes increases (fig 8.2)
• - number of direct connections required (N2
  - N) / 2

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Local Area Networks (LANs)

• based on sharing the same communications medium.
• emerged in 1980s in local communications as
  alternative to expensive, dedicated
  point-to-point connections
• shared networks confined to local communication
  because
• more time would be spent coordinating the of
  sharing of network and less time spent actually
  transmitting data if two nodes are separated
  farther apart
• Cost of providing high bandwidth is more
  expensive over long distance than over short
  distance
• Locality of reference computers usually
  communicate to another nearby computer.

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LAN Topologies

• Star network
• all computers attached to a central point such as
  a hub (fig 8.3)
• Fault tolerant advantage
• Ring network
• computers are logically arranged in circular loop
  (fig 8.4)
• Physical orientation may be different ( offices
  on various floors using token ring).
• One bad cable may disable the entire ring.
• Token ring may be logical ring but physical
  star.
• Bus network
• usually consist of a single shared long cable to
  which computers attach (fig 8.5)
• One bad cable may cripple the entire bus.
• Ethernet network can be logical bus but physical
  star.

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Ethernet Network

• Manchester Encoding (fig 8.6)
• Originally a bus network (ANIM06_1.MOV) in which
  multiple computers share a single transmission
  medium.
• While one computer transmits a frame, all other
  computers must wait (fig 8.7)
• Uses CSMA (carrier sense multiple access with
  collision detect) (ANIM06_2.MOV)
• Uses binary exponential backup in recovering from
  collision. Delay time is doubled after each
  successive collision.

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Wireless LAN

• Uses antennas to broadcast RF signals through air
• Carrier Sense Multiple Access with Collision
  Avoidance CSMA/CA (fig 8.8)
• IEEE 802.11b
• Up to 11 Mbps
• frequency hopping spread spectrum (FHSP)
• direct sequence spread spectrum (DSSS)
• radio frequencies in range of 2.4 GHz - 2.483 GHz
• IEEE 802.11a
• Up to 50 Mbps
• radio frequencies in range of 5 GHz

7
LocalTalk Network

• bus network designed by Apple.
• Uses modified CSMA/CA (a short message is sent to
  reserve the medium before transmitting a large
  message)
• Limited to 230 kbps
• Easy to install daisy-chain computers (fig 10.9)

8
Token Ring Network

• token passing ring network (fig 8.9)
• IBMs token ring operate at 16Mbps
• token is a special bit pattern or message
  different from normal data frames (bit stuffing
  of data may be used)
• only one token circulates the ring at any time.
  To send data, computer waits for token to arrive,
  transmit one frame, and then pass token to next
  node (ANIM06_3.MOV)
• guarantees fair access because nodes take turns.

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FDDI Network

• Fiber Distributed Data Interconnect (FDDI)
• token ring technology operating at 100 Mbps using
  fiber.
• Uses counter rotating ring for fault tolerance
  (fig 8.10)
• Self healing
• Ring is still up if there is one break in the
  ring