MSIS 4523 Ch7.Transmission Media

8/3/2019 MSIS 4523 Ch7.Transmission Media

1/39

Data Communications SystemsCh 7: Transmission Media

JinKyu Lee, Ph.D.

[email protected]

Include the course code (MSIS4523) in every email subject!!


2/39

Topics

Transmission Media

Guided

Twisted Pair

Coaxial Fiber-optic

Unguided

Air / Space

Wireless Transmission Electromagnetic spectrum

Categories of wireless Transmission

Propagation Methods


3/39

Transmission medium and physical layer


4/39

Classes of Transmission Media

Medium sets signal characteristics and quality Key concerns are data rate and distance

Conducted (guided) media

use a conductor such as a wire or a fiber optic cable to move thesignal from sender to receiver

The medium is more important

Wireless (unguided) media

use radio waves of different frequencies and do not need a wireor cable conductor to transmit signals

Bandwidth produced by the antenna is more important


5/39

Design Factors for Transmission Media

Bandwidth All other factors remaining constant, the greater the bandwidth of

a signal, the higher the data rate that can be achieved

Transmission impairments Attenuation limits the distance a signal can travel

Interference Competing signals in overlapping frequency bands can distort or

wipe out a signal

Number of receivers & splices Each attachment introduces some attenuation and distortion,

limiting distance and/or data rate


6/39

Guided Media - Twisted Pair Wires

Consists of two insulated copper wires arranged in a

regular spiral pattern to minimize the electro-magneticinterference between adjacent pairs Often "bundled" into cables

Often used at customer facilities and also over distances

to carry voice as well as data communications Limited distance

Analog requires an amplifier every 5km to 6km

Digital requires a repeater every 2km or 3km

Limited bandwidth (1MHz)

Limited data rate (100MHz)


7/39

Types of Twisted Pair

UTP (unshielded twisted pair)

Most common, least expensive medium

Suffers from external EM interference

Very easy to install

STP (shielded twisted pair)

the pair is wrapped with metallic foil or braid to insulate the pairfrom electromagnetic interference

More expensive and harder to handle (thick, heavy)

Used for local area networks (LAN)


8/39

Twisted-pair cable


9/39


10/39

Ratings of Twisted Pair

Traditional UTP

2 & 3 pairs of wires

Core of telephone service

Used by 80-90% of businessand 99+% of existingresidences

Up to 2500 pair cables used bytelephone companies

Category 3 UTP

4 pr of wires - 8 conductors

Twist length of 7.5 to 10 cm

Data rates of up to 16Mbps Provides voice to offices

Category 5, 5E UTP

4 pr of wires - 8 conductors

Twist length 0.6 to 0.85 cm

Data rates of up to 100Mbps

More expensive, but betterperformance

Installed in star config. in allnew buildings by FCC rule

STP

More expensive, harder towork with

Can go to 1Gbps over shortdistances


11/39

RJ-45 Ethernet UTP Connector


12/39

UTP performance


13/39

Guided Media - Coaxial Cable (or Coax)

Solid inner conductor covered by a braided mesh

Separated by insulating material

Inner conductor is wire

Both conductors share a common center axis

Hence the term co-axial

Transmission Characteristics of Coax

Up to 750MHz

Analog requires amplifiers every few km

Digital requires repeaters every 1km

Closer for higher data rates


14/39

Coaxial Cable & Connectors


15/39

Categories of Coaxial Cables

Category Impedance Use

RG-59 75 Cable TV

RG-58 50 Thin Ethernet

RG-11 50 Thick Ethernet


16/39

Coaxial cable performance


17/39

Coax Advantages & Disadvantages

Advantages

Higher bandwidth

400 to 750Mhz

up to 10,800 voiceconversations

Can be tapped easily(pros and cons)

Much less susceptible tointerference than twisted

pair

Disadvantages

High attenuation ratemakes it expensive overlong distance

Bulky and somewhat

harder to work with


18/39

Coaxial Cable Applications

Television distribution

From Antenna to TV

Cable TV

Long distance telephone transmission

Can carry 10,000 voice calls simultaneously Being replaced by fiber optic

Short distance computer systems links

Local area networks


19/39

Guided Media - Fiber Optic Cable

Relatively new (late 1960s) transmission medium used by telephone

companies in long-distance trunk lines Now standard feeder for new commercial buildings

Common in feeder plant to neighborhood service points

Fiber to the Home (FTTH) or Premise (FTTP) being installed selectivelytoday expensive

Also used by private companies in implementing local datacommunications networks

Require a light source with injection laser diode (ILD) or light-emitting diodes (LED)


20/39

Bending of light ray


21/39

Fiber Optic Types

Multimode step-index fiber

The reflective walls of the fiber move the light pulsesto the receiver

Multimode graded-index fiber

Acts to refract the light toward the center of the fiberby variations in the density

Single mode fiber

The light is guided down the center of an extremely

narrow core


22/39

Optical Fiber Modes


23/39

Categories of Fiber

Type Core Cladding Mode

50/125 50 125 Multimode, graded-index

62.5/125 62.5 125 Multimode, graded-index

100/125 100 125 Multimode, graded-index

7/125 7 125 Single-mode


24/39

Fiber Optic Cable (cont.)
http://www.tigerdirect.com/applications/category/category_slc.asp?CatId=429&Nav=|c:74|&Sort=0&Recs=10


25/39

Fiber Construction


26/39

Fiber-Optic Cable Connectors


27/39

Transmission Characteristics of OpticalFiber

Act as wave guide for 1014 to 1015 Hz light

Portions of infrared and visible spectrum

Transmitters

Light Emitting Diode (LED) Injection Laser Diode (ILD)

Multiple channels with Wavelength DivisionMultiplexing (WDM)


28/39

Optical fiber Performance

m


29/39

Fiber Optic Advantages

Greater capacity (bandwidth up to 2 Tbps)

Existing systems can deliver 40 Gbps/wavelength

Dense Wave-division multiplexing (DWM) systems can multiplexup to 160 wavelengths per fiber

Smaller size and lighter weight

Lower attenuation Repeater spacing 10s of km at least

Immunity to environmental interference

Electromagnetic isolation

Highly secure due to tap difficulty and lack of signalradiation


30/39

Fiber Optic Disadvantages

Expensive over short distance

Requires highly skilled installers

More susceptible to vibration and physicaldamage

Adding additional nodes is difficult


31/39

Conducted Media


32/39

Unguided Media - Wireless transmission

Categories:

Electromagnetic spectrum for communication:

Infrared signals can be used for short-range communicationin a closed area using line-of-sight propagation


33/39

Propagation methods


34/39

Wireless Frequency Bands

Band Range Propagation Application

VLF 330 KHz Ground Long-range radio navigation

LF 30300 KHz GroundRadio beacons andnavigational locators

MF 300 KHz3 MHz Sky AM radio

HF 330 MHz SkyCitizens band (CB),

ship/aircraft communication

VHF 30300 MHzSky and

line-of-sightVHF TV, FM radio

UHF 300 MHz3 GHz Line-of-sight UHF TV, cellular phones,paging, satellite

SHF 330 GHz Line-of-sight Satellite communication

EHF 30300 GHz Line-of-sight Long-range radio navigation


35/39

Useful Electromagnetic Spectrum


36/39

Wireless Media

Radio, satellite transmissions, and infrared light are all different

forms of electromagnetic waves


37/39

Wireless transmission Categories

Infrared signals can be used for short-range communication in a closed area

using line-of-sight propagation


38/39

Radios Use Omnidirectional Antennas

Radio waves are usedfor multicast

communications, such

as radio and television,and paging systems


39/39

Microwave Radios Use UnidirectionalAntennas

Microwaves are used for unicastcommunication such as cellular telephones,

satellite networks, and wireless LANs

MSIS 4523 Ch7.Transmission Media

Documents

Transcript of MSIS 4523 Ch7.Transmission Media