Transcript Computer Networks

Introduction to Computer
Networks For ECE1001
Dr. Taek Mu Kwon
Department of Electrical and Computer
Engineering, UMD
Outline

ECE 4321
 Networks Today
 Optical Fiber Technology
 Wireless Technology
 Conclusion
ECE 4321 Computer Networks
• ECE Technical Elective Course
• 3 Credits
• Network Lab (MWAH 60)
• Network Programming Project (3 – 4)
• Written Exams
• Course Objective: To learn about the characteristics of network
transmission media, OSI model, TCP/IP, data link protocols,
routing algorithms, various LAN technologies, WAN
technologies, and network programming.
Integrated Digital Service Revolution
(2000 - )
1. No boundary between public and private networks
(security through virtual private network)
2. Single mode of transmission for data/voice/video:
high speed multimedia
3. No difference between wired and wireless
Multipurpose global network that can be accessed any time,
anywhere
Required Technology Advances for
Digital Service Revolution
Elimination of present multiple, complex, costly networks
and integrate them into one high speed multipurpose network.

 Always ON: accessible anytime from anywhere
 Improved mobility by reliable wireless/wired technology
 High definition multimedia to any connection
 Smart network that works like power plug
 High speed optical network to home and office
Why Optical Fiber?

1 lb of optical fiber can transmit
information equivalent to 2 metric tons of
copper
 A single optical fiber can carry 60 million
simultaneous phone calls
 Can transmit the entire 30 volume
Encyclopedia Britannica within a fraction
second from NY to CA.
Transmission Characteristics of Guided Media
Twisted pair
(with
loading)
Twisted pairs
(multi-pair
cables)
Coaxial cable
Optical fiber
Frequency
Range
0 to 3.5 kHz
Typical
Attenuation
0.2 dB/km @
1 kHz
Typical
Delay
50 µs/km
Repeater
Spacing
2 km
0 to 1 MHz
0.7 dB/km @
1 kHz
5 µs/km
2 km
0 to 500 MHz
7 dB/km @
10 MHz
0.2 to 0.5
dB/km
4 µs/km
1 to 9 km
5 µs/km
40 km
186 to 370
THz
Attenuation of Typical Guided Media
Who invented Optical Fiber?

Invented in Aug. 1970 by Dow Corning
Scientists: Dr. Donald Keck, Dr. Bob
Maurer and Dr. Peter Schultz
 Invention was motivated by space limitation
of telephone wires
First Large Commercial Use

Nationwide long-distance telephone
network by MCI using single-mode optical
fiber, 1983
 Since then more than 300 million km of
optical fiber lines have been deployed
worldwide.
What is Optical Fiber?

A thin flexible medium capable of
conducting an optical ray. The basic
material consists of silicon dioxide, silica,
and plastic.
Snell’s Law
qt
Cladding
Refractive index = n2
qi
Fused Silica
Refractive index = n1
sin q t n1

sin q i n 2
Internal Structure of Optical Fiber
Optical Fiber Types

Multimode (Orange Color)
* Stepped index
* Grade index
 Singlemode (Yellow Color)
The fiber diameter is one wavelength of
light (1um)
Wavelength Division Multiplexing
(WDM)

Multiple beams of different wavelengths are
transmitted over the same fiber
 Transmission of one Tbps was achieved by
100 beams each operating at 10 Gbps (1997
Bell Lab)
Wavelengths Used in Optical Fiber
Wavelength (in
vacuum) range
(nm)
Frequency
range (THz)
820 to 900
366 to 333
1280 to 1350
234 to 222
1528 to 1561
1561 to 1620
Band
label
Fiber type
Application
Multimode
LAN
S
Single mode
Various
196 to 192
C
Single mode
WDM
185 to 192
L
Single mode
WDM
Next Revolution of Optical Fiber

Optical switching and routing
 High bandwidth all-optical network
 Fiber To The Home (FTTH)
Free Space Optics
Characteristic Summary of Optical
Fiber

Greater bandwidth
 Smaller size and light weight
 Lower attenuation
 E&M isolation
 Greater repeater spacing
 Greater security
Wireless Networks

Provide mobility with true any time any
where access.
Wireless Transmission
Frequencies

2GHz to 40GHz
– Microwave
– Highly directional
– Point to point
– Satellite

30MHz to 1GHz
– Omnidirectional
– Broadcast radio

3 x 1011 to 2 x 1014
– Infrared
– Local
Terrestrial Microwave

Parabolic dish
 Focused beam
 Line of sight
 Long haul telecommunications
 Higher frequencies give higher data rates
Satellite Point to Point Link
Satellite Broadcast Link
Wireless Propagation

Ground wave




Sky wave




Follows contour of earth
Up to 2MHz
AM radio
Amateur radio, BBC world service, Voice of America
Signal reflected from ionosphere layer of upper atmosphere
(Actually refracted)
Line of sight


Above 30Mhz
May be further than optical line of sight due to refraction
Ground Wave Propagation
Sky Wave Propagation
Line of Sight Propagation
Line of Sight Transmission (1)

Atmospheric Absorption
– Water vapour and oxygen absorb radio
signals
– Water absorption: greatest at 22GHz, less
below 15GHz
– Oxygen absorption: greater at 60GHz, less
below 30GHz
– Rain and fog scatters radio waves

Free space loss
– Signal disperses with distance
– Greater for lower frequencies (longer
wavelengths)
Optical and Radio Horizons
Line of Sight Transmission (2)

Multipath
– Better to get line of sight if possible
– Signal can be reflected causing multiple
copies to be received
– May be no direct signal at all
– May reinforce or cancel direct signal

Refraction
– May result in partial or total loss of signal
at receiver
Multipath Interference
Concluding Remark

In order to advance to the next generation of
always ON, anytime, anywhere access, to
data/voice/video, today’s diverse complex
network and protocols must be unified to a
multipurpose, multimedia network.
 More bandwidth and significant improvement
in wireless technology are needed.
 Evolution on computer networks will
continue providing many opportunities