Chapter 4' Transmission Media

1
Chapter 4. Transmission Media

• Jing Wang
• Towson University

2
4.1. Introduction

• At the lowest level, all computer communication
  involves
• encoding data in a form of energy
• Sending the energy across a transmission medium
• To be transmitted, data must be transformed to
  electromagnetic signals

3
4.2. Copper Wires

• Copper
• Its low resistance to electric current means
  signals can travel farther
• Type of wiring chosen to minimize interference
• Unshielded Twisted Pair (UTP)
• Coaxial Cable
• Shielded Twisted Pair (STP)

4
4.2. Copper Wires (cont.)

• Figure 4.1. Illustration of twisted pair wiring.
  A plastic coating on the surface of each wire
  prevents the metal in one wire from touching the
  metal in the other. The twists help reduce
  interference.

5
4.2. Copper Wires (cont.)

• Twisted-pair network

6
4.2. Copper Wires (cont.)

• 10base5 thick-net
• 10base2 thin-net
• 10baseT
• 10 network operates at 10 Mbps
• base a baseband system
• 2 a given segment lt 200 m
• 5 up to 500 m
• T twisted pair

7
4.2. Copper Wires (cont.)

• 10BaseT Unshielded Twisted Pair (UTP)

8
4.2. Copper Wires (cont.)

• 10BaseT UTP Straight-Through

9
Twisted-Pair Cable
Figure 7-4 and 7-5
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill
10
Figure 7-8
Unshielded Twisted-Pair Cable
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill
11
Figure 7-9
UTP Connectors
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill
12
Figure 7-10
Shielded Twisted-Pair Cable
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill
13
4.2. Copper Wires (cont.)

• Figure 4.2. Enlarged cross-section of a coaxial
  cable with major parts identified. Although a
  coaxial cable is stiffer than a single wire, it
  can be bent.

14
Coaxial Cable
Figure 7-11 and 7-12
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill
15
4.3. Glass Fibers

• Glass fiber
• An optical fiber
• Uses light to transport data
• Transmitter uses LED (light emitting diode) or
  laser to send pulses of light down the fiber
• Receiver uses light sensitive transistor to
  detect pulses

16
Figure 7-20
Fiber Construction
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill
17
4.4. Radio

• Electromagnetic waves
• Radios, TVs, portable phones
• Radio frequency (RF)
• Each participating computer attaches to an
  antenna, which can both transmit and receive RF

18
4.5. Satellites

• Transponder
• Consists of a radio receiver and transmitter
• Accepts incoming radio transmission, amplifies
  it, transmits the amplified signal back toward
  the ground at a different angle

19
4.5. Satellites

• Figure 4.3. Illustration of a satellite used to
  provide communication across an ocean. The
  satellite receives radio signals from one ground
  station, and transmits them to another.

20
4.6. Geosynchronous Satellites

• Geosynchronous or geostationary satellites
• Placed in an orbit that is synchronized with the
  rotation of the earth
• Geostationary Earth Orbit (GEO)
• When viewed from the ground, the satellite
  appears to remain at the same point
• High earth orbit
• Distance required for geosynchronous orbit is 35,
  785 kilometers or 22,236 miles
• 48 degrees, 360-degree circle above the equator
  can only hold 45 to 90 satellites

21
Constants and variables                         
                                        
gravitational constant                         
     mass of Earth                            
  Earth's angular speed     radius of
geosynchronous orbit      orbital speed
       mass of satellite Derivation
                         (centrifugal force
required to maintain circular orbit)
                   (force of gravity from body me
acting on a body of mass ms)                
(equate and cancel previous formulae)         
  (rotational rate in radians per second as a
function of v,r)                         (from
previous two formulae)                         
           (rearrangement of the above formula)
http//www.answers.com/topic/geosynchronous-orbit-
derivation
22
Figure 7-34
Satellite Communication
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill
23
Figure 7-35
Geosynchronous Orbit
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill
24
4.7. Low Earth Orbit Satellites

• Low Earth Orbit (LEO)
• An observer sees such satellites move across the
  sky
• 200 to 400 miles above the earth
• A single satellite can complete an entire orbit
  in 1.5 hrs

25
4.8. Low Earth Orbit Satellite Arrays

• Launch a set of satellites into low earth orbits
• 66 satellites over the entire surface of the
  earth
• At least one satellite overhead at any time
• Transponder ground station
• Radio equipment other satellites
• e.x. Germany-S1-S2-S3-U.S.

26
4.9. Microwave

• Higher frequency version of radio waves
• Can be aimed in a single direction
• Can carry more information
• Cannot penetrate metal structures

27
Figure 7-31
Terrestrial Microwave
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill
28
4.10. Infrared

• Wireless remote controls used with televisions
  and stereos
• Does not require an antenna

29
4.11. Light From A Laser

• The transmitter uses a laser to generate the beam
  of light
• carry data through the air
• Cannot penetrate vegetation or snow or fog

30
4.12. Summary

• Transmission media
• Copper wires, optical fibers, radio and
  microwave, infrared, laser beams
• Each with advantages and costs

31
Supplement

• Behrouz A. Forouzan, Data Communications and
  Networking, http//www.mhhe.com/engcs/compsci/foro
  uzan/

32
Figure 7-1
Electromagnetic Spectrum
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill
33
Figure 7-2
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill
34
Figure 7-3
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill
35
Figure 7-21
Radio Communication Band
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill
36
Figure 7-22
Propagation Types
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill
37
Figure 7-23, 24
VLF
LF
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill
38
Figure 7-25, 26
MF
HF
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill
39
Figure 7-27, 28
VHF
UHF
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill
40
Figure 7-29, 30
SHF
EHF
? The McGraw-Hill Companies, Inc., 1998
WCB/McGraw-Hill