1. Chapter 4 Transmission Media
Overview
Guided – wire (twisted pair, coaxial cable, optical fiber)
Unguided – wireless (broadcast radio, terrestrial microwave, satellite)
Characteristics & quality of data transmission is determined by medium & signal
For guided medium, the medium itself is more important in determining the transmission limitations
For unguided medium, the bandwidth produced by the antenna is more important
Key concerns are data rate and distance in the design of trans. sys.

2. Design Factors Bandwidth: Transmission impairments: e.g. Attenuation
Higher bandwidth (HZ) gives higher data rate (bps)
Transmission impairments: e.g. Attenuation
Limits the transmission distance
Twisted pair -> coaxial cable -> optical fiber
Interference: from competing signals in overlapping frequency bands can distort or wipe out a signal.
Number of receivers: In guided media
Point-to-point link or share link with multiple attachment: each attachment introduce some attenuation & distortion on the line, limiting distance and/or data rate

3. Electromagnetic Spectrum for Telecom

4. Guided Transmission Media
Twisted Pair
Coaxial cable
Optical fiber

5. Twisted Pair & Applications
Most common medium: least expensive
Telephone network
Between house and local exchange (subscriber loop)
Within buildings
To private branch exchange (PBX)
For local area networks (LAN)
10Mbps or 100Mbps

6. Twisted Pair - Transmission Characteristics
Pros and Cons
Cheap; Easy to work with
Low data rate; Short distance <- bigger attenuation
Analog Signal: Amplifiers every 5km to 6km
Digital Transmission: repeater every 2km or 3km
Limited distance
Limited bandwidth (1MHz)
Limited data rate (100Mbp)
Susceptible to interference and noise

7. Unshielded and Shielded TP
Unshielded Twisted Pair (UTP)
Ordinary telephone wire
Cheapest
Easiest to install
Suffers from external EM interference
Shielded Twisted Pair (STP)
Metal braid or sheathing that reduces interference
More expensive
Harder to handle (thick, heavy)

8. UTP Categories Cat 3 Cat 4 Cat 5 up to 16MHz
Voice-grade cable found in most offices
Twist length of 7.5 cm to 10 cm
Cat 4
up to 20 MHz
Cat 5
up to 100MHz
Commonly pre-installed in new office buildings
Twist length 0.6 cm to 0.85 cm

9. Coaxial Cable

10. Applications & Transmission Characteristics
Television distribution : Cable TV
Long distance telephone transmission
Can carry 10,000 voice calls simultaneously (via FDM)
Being replaced by fiber optic
Short distance links between computer devices
Transmission Characteristics:
Analog
Amplifiers every few km; Closer if higher frequency
Up to 500MHz
Digital: Repeater every 1km; Closer for higher data rates

11. Optical Fiber - Transmission Characteristics
Optical Fiber: transmit a signal-encoded beam of light by means of total internal reflection
Act as waveguide for freq. of 1014 to 1015 Hz
Portions of infrared and visible spectrum
Three Transmission Modes:
Step-index multimode; Graded-index multimode; Single-mode
Two Type of Light Sources:
Light Emitting Diode (LED)
Cheaper; Wider operating temp range; Last longer
Injection Laser Diode (ILD): More efficient; Greater data rate
WDM: multiple beams of light at different freq. are transmitted on the same fiber. This is a form of FDM.

12. Optical Fiber Transmission Modes

13. Optical Fiber - Properties & Applications
Greater capacity: in the unit of Gbps, Tbps
Smaller size & lighter weight
Lower Attenuation
EM Isolation: not affected by external EM interference
Greater Repeater Spacing: every hundreds of km
Applications:
Long-haul trunks ; Metropolitan trunks; LANs
Rural exchange trunks
Subscriber loops

14. Wireless Transmission
Unguided media
Transmission & reception via antenna
Directional
Focused beam
Careful alignment required
Omnidirectional
Signal spreads in all directions
Can be received by many antennae

15. 3 Frequency Ranges 30MHz to 1GHz: 2GHz to 40GHz: Microwave frequency
Suitable to Omnidirectional app.
Refer to as broadcast radio range
2GHz to 40GHz: Microwave frequency
Highly directional beams are possible
Suitable to point- to-point transmission
Can also be used for satellite comm.
3 x 1011 to 2 x 1014
Infrared portion of the spectrum
Local apps. Within confined areas, e.g. a single room

16. Terrestrial Microwave
Physical Description: the most common type of antenna is the parabolic “dish”
Focuses a narrow beam: to achieve line-of-sight trans. to the receiving antenna
Apps.: Long haul telecommunications
Higher frequencies give higher data rates
common freq : 2 – 40 GHZ

17. Satellite Microwave Satellite is a microwave relay station
Satellite receives on one frequency, amplifies or repeats signal and transmits on another frequency
Requires geo-stationary orbit
Height of 35,784km
Applications:
Television
Long distance telephone
Private business networks

18. Broadcast Radio Omnidirectional Freq: 30 MHZ to 1GHZ
FM radio
UHF and VHF television
Trans. is limited to the line of sight
Suffers from multipath interference

19. Infrared Transceivers modulate noncoherent infrared light
Two parties must be within line of sight (or reflection)
Blocked by walls
e.g. TV remote control