Chapter 8 LAN Technologies
and Network Topology
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Direct Point-to-Point Communication
Local Area Networks (LANs)
LAN Topologies
Ethernet
Token Ring
FDDI
LocalTalk
Wireless LAN
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
Local Area Networks (LANs)
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based on sharing the same communications medium.
emerged in 1980’s in local communications as
alternative to expensive, dedicated point-to-point
connections
shared networks confined to local communication
because
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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.
LAN Topologies
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Star network
– all computers attached to a central point such as a hub (fig 8.3)
– Fault tolerant advantage
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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.
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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.
Ethernet Network
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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.
Wireless LAN
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Uses antennas to broadcast RF signals through air
 Carrier Sense Multiple Access with Collision
Avoidance CSMA/CA (fig 8.8)
 IEEE 802.11b
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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
LocalTalk Network
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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)
Token Ring Network
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token passing ring network (fig 8.9)
IBM’s 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.
FDDI Network
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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