1CSIE,NTUT,TAIWAN
Underlying Technologies
Chuan-Ming Liu
CSIE,NTUT
Spring ’04,TAIWAN
CSIE,NTUT,TAIWAN 2
CONTENTS
LANS
POINT-TO-POINT WANS
SWITCHED WANS
CONNECTING DEVICES
CSIE,NTUT,TAIWAN 3Figure 3-1
Internet model
CSIE,NTUT,TAIWAN 4
LOCAL AREA
NETWORKS
(LANS)
3.1
CSIE,NTUT,TAIWAN 5
Local Area networks (LANs)
Data communication system in a limited
geographic area such as a single department,a
single building,or a campus.
Popular LANs include
– Ethernet LANs
– Token Ring LANs
– Wireless LANs
– ATM LANs
CSIE,NTUT,TAIWAN 6
Ethernet
Most widely used LAN protocol
Bus or star topology
Traditional Ethernet
– 10 Mbps
– Carrier Sense Multiple Access with Collision
Detection (CSMA/CD)
Minimum frame length
Transmission rate
Collision domain (maximum network distance)
CSIE,NTUT,TAIWAN 7Figure 3-2
CSMA/CD
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Minimum frame length/Transmission rate
is proportional to
Collision domain / Propagation speed
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Ethernet Data Link Layer
Logical link control (LLC)
– Flow control
– Error control
Media access control (MAC)
operation of the CSMA/CD access method
CSIE,NTUT,TAIWAN 10Figure 3-3
Ethernet Layers
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Ethernet Frame
Preamble
Start frame delimiter (SFD)
Destination address (DA)
Source address (SA)
Length/type
Data
Cycle Redundancy Check (CRC)
CSIE,NTUT,TAIWAN 12Figure 3-4
Ethernet Frame
CSIE,NTUT,TAIWAN 13Figure 3-5:a
Ethernet Implementation
CSIE,NTUT,TAIWAN 14Figure 3-5:b
Ethernet Implementation
CSIE,NTUT,TAIWAN 15Figure 3-5:c
Ethernet Implementation
CSIE,NTUT,TAIWAN 16Figure 3-5:d
Ethernet Implementation
CSIE,NTUT,TAIWAN 17
Fast Ethernet
CSMA/CD
Transmission rate from 10 to 100 Mbps
Options to implement
– Increasing the minimum frame length
– Decrease the collision domain
Collision domain decreases from 2500 to
250m
CSIE,NTUT,TAIWAN 18Figure 3-6:a
Fast Ethernet Implementation
CSIE,NTUT,TAIWAN 19Figure 3-6:b
Fast Ethernet Implementation
CSIE,NTUT,TAIWAN 20Figure 3-6:c
Fast Ethernet Implementation
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Gigabit Ethernet
Data rate is from 100 to 1000 Mbps
Using CSMA/CD and increasing the minimum
length of the frame
Dropping CSMA/CD – full-duplex with no
collision
CSIE,NTUT,TAIWAN 22Figure 3-7:a
Gigabit Ethernet Implementation
CSIE,NTUT,TAIWAN 23Figure 3-7:b
Gigabit Ethernet Implementation
CSIE,NTUT,TAIWAN 24
Token Ring
Using a token passing access method
Two layers
– LLC
– MAC
CSIE,NTUT,TAIWAN 25Figure 3-8:a
Token Passing
CSIE,NTUT,TAIWAN 26Figure 3-8:b
Token Passing
CSIE,NTUT,TAIWAN 27Figure 3-8:c
Token Passing
CSIE,NTUT,TAIWAN 28Figure 3-8:d
Token Passing
CSIE,NTUT,TAIWAN 29Figure 3-9
Data frame
CSIE,NTUT,TAIWAN 30
Figure 3-10 MAU
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Wireless LANs
One of the fastest growing technologies
Spread Spectrum
– Frequency hopping
– Direct sequence
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Frequency Hopping Spread
Spectrum
Action
– One carrier frequency for a short period of time
– Hopping to another carrier frequency for the same
amount of time
– Hopping again for the same amount of time
After N hops,the cycle is repeated.
If the bandwidth (spectrum) of the original
signal is B,the spread spectrum needed is
BN?
CSIE,NTUT,TAIWAN 33Figure 3-11:a
Frequency Hopping Spread Spectrum
CSIE,NTUT,TAIWAN 34
Direct Sequence Spread
Spectrum
Each bit sent is replaced by a chip code (a
sequence of bits)
If N is the number of bits in a chip code,and
the data rate of the original bit stream is B,the
spread spectrum is
BN?
CSIE,NTUT,TAIWAN 35Figure 3-11:b
Direct Sequence Spread Spectrum
CSIE,NTUT,TAIWAN 36Figure 3-12
ISM bands
CSIE,NTUT,TAIWAN 37
Architectures
By IEEE 802.11 standard
Two services
– Basic Service Set (BSS)
Stationary or mobile wireless stations
An optional central base station (BS),known as the
access point (AP)
BSS without an AP is an ad hoc architecture
– Extended Service Set (ESS)
Two or more (stationary or mobile) BSSs with APs
APs are connected usually to a wired LAN
Forming a distributed system
AP may be shared by stations
CSIE,NTUT,TAIWAN 38Figure 3-13
BSSs
CSIE,NTUT,TAIWAN 39Figure 3-14
ESS
CSIE,NTUT,TAIWAN 40
Access Method
Carrier sense multiple access with collision
avoidance (CSMA/CA)
Collision detection is not applicable
Hidden terminal problem – due to being
unable to detect collision
CSIE,NTUT,TAIWAN 41Figure 3-15
CSMA/CA
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CONNECTING
DEVICES
3.4
CSIE,NTUT,TAIWAN 61
Connecting Devices
Tools to join the LANs and WANs
Kinds of devices:
– Repeater
– Hub
– Bridge
– Router
– Switch
CSIE,NTUT,TAIWAN 62Figure 3-26
Connecting Devices
CSIE,NTUT,TAIWAN 63Figure 3-27
Repeater
CSIE,NTUT,TAIWAN 64
A repeater connects segments of a
LAN together.
CSIE,NTUT,TAIWAN 65
A repeater forwards every packet; it has no
filtering capability.
CSIE,NTUT,TAIWAN 66Figure 3-28
Hubs
CSIE,NTUT,TAIWAN 67
A hub is actually a multiport repeater.
CSIE,NTUT,TAIWAN 68Figure 3-29
Bridge
CSIE,NTUT,TAIWAN 69
A bridge has a table used in filtering
decisions.
CSIE,NTUT,TAIWAN 70
A bridge connects segments of a LAN
together.
CSIE,NTUT,TAIWAN 71
A router is a three-layer (physical,data
link,and network) device.
Routers
CSIE,NTUT,TAIWAN 72
A repeater or a bridge connects segments
of a LAN,
A router connects independent LANs or
WANs to create an internetwork (internet).
CSIE,NTUT,TAIWAN 73Figure 3-30
Routing Example
CSIE,NTUT,TAIWAN 74
A router changes the physical addresses in
a packet,
CSIE,NTUT,TAIWAN 75
Switches
Note the level at which the device operates
Switches
– Two layer switch
a bridge
– Three layer switch
a router