The document provides an overview of transmission media, categorizing them into guided (wired) and unguided (wireless) types. It discusses characteristics and quality determinants, including bandwidth, attenuation, and interference for various mediums such as twisted pair cables, coaxial cables, and optical fibers. Additionally, it highlights the advantages and disadvantages of each medium along with their applications in telecommunications.

1. Notes #4
Transmission Media

2. Overview
Transmission media is divided into two categories:
➢ Guided – wired, also known as bounded media
➢ Unguided – wireless, also referred to as unbounded
media
Characteristics and quality of transmission is determined
by medium and signal
For guided, the medium is more important
For unguided, the bandwidth produced by the antenna
is more important
In wireless transmission, we make use of some form of
antenna
Key concerns are data rate and distance

3. Transmission medium Design
Factors
Bandwidth
Higher bandwidth gives higher data rate
Transmission impairments
Attenuation, noise, etc
Attenuation is the decay/falling off/degradation of a
signal as the distance increases.
Interference especially electromagnetic
interference.
Number of receivers
In guided media
More receivers (multi-point) introduce more
attenuation

4. Electromagnetic Spectrum

5. Guided Transmission Media
Twisted Pair cable
Coaxial cable
Optical fiber

6. Twisted Pair

7. Twisted Pair - Applications
Most common medium
Telephone network
Between house and local exchange (subscriber
loop/local loop connection/last mile connection)
Within buildings
To private branch exchange (PBX)/switch
For local area networks (LAN)-Ethernet cable
10Mbps or 100Mbps

8. Twisted Pair - Pros and Cons
Pros/Adv/Merits
➢ Cheap
➢ Easy to work with
❑Cons/Disadv/Demerits
➢ Low data rate
➢ Short transmission range

9. Twisted Pair - Transmission
Characteristics
Analog
Amplifiers every 5km to 6km
Digital
Use either analog or digital signals
repeater every 2km or 3km
Limited distance-range
Limited bandwidth (1MHz)
Limited data rate (100Mbps)-1Gbps
Susceptible/Prone to interference and noise

10. Unshielded and Shielded TP
Unshielded Twisted Pair (UTP)
Ordinary telephone wire
Cheapest-It does not have an outer cover/shield
Easiest to install
Suffers from external EM interference
Shielded Twisted Pair (STP)
Metal braid or sheathing (outer covering) that
reduces interference
More expensive-Extra material for the cover
Harder to handle (thick, heavy)

11. UTP Categories
Cat 3
up to 16MHz
Voice grade 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

12. Near End Crosstalk-
Interference
Coupling of signal from one pair to another
Coupling takes place when transmit signal
entering the link couples back to receiving pair
i.e. near transmitted signal is picked up by near
receiving pair

13. Coaxial Cable

14. Coaxial Cable Applications
Most versatile medium
Television distribution
Ariel 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

15. Coaxial Cable - Transmission
Characteristics
Analog
Amplifiers every few km
Closer if higher frequency
Up to 500MHz
Digital
Repeater every 1km
Closer for higher data rates

16. Optical Fiber

17. Optical Fiber - Benefits
Greater capacity
Data rates of hundreds of Gbps
Smaller size & weight-Easy to handle
Lower attenuation
Electromagnetic isolation-No interference
Greater repeater spacing-Less repeater is used.
10s of km at least

18. Optical Fiber - Applications
Long-haul trunks/Long distance backbone
transmission (High capacity transmission) E.g
SEACOM and TEAMS cable interconnecting the
different continents.
Metropolitan trunks-within cities E.g “Faiba”
from Jamii Telecoms in Kenya
Rural exchange trunks-Local switch
interconnections
Subscriber loops-To the Home/customer
LANs: But is will be expensive.

19. Optical Fiber - Transmission
Characteristics
Act as wave guide for 1014 to 1015 Hz
Portions of infrared and visible spectrum
Two Optical (fiber) signal sources:
➢ Light Emitting Diode (LED)
Cheaper
Wider operating temp range
Last longer
➢ Injection Laser Diode (ILD)
More expensive
More efficient
Greater data rate
Wavelength Division Multiplexing (WDM)-Dense WDM

20. Optical Fiber Transmission Modes
(Modes=Number of simultaneous
signals transmitted)

21. Wireless Transmission
Unguided media-No physical cable or wire
Transmission and reception via antenna
Directional antenna
Focused beam
Careful alignment required-Line of sight (LOS)
Omnidirectional
Signal spreads in all directions
Can be received by many antennae

22. Frequencies
2GHz to 40GHz
Microwave transmission
Highly directional-LOS requirement
Point to point
Satellite
30MHz to 1GHz
Omnidirectional
Broadcast radio
3 x 1011 to 2 x 1014
Infrared-Short links
Local

23. Terrestrial Microwave
Transmission (1)
Parabolic dish
Focused beam
Line of sight
Long haul telecommunications
Higher frequencies give higher data rates

24. Terrestrial
Microwave Transmission(2)
uses the radio frequency spectrum, commonly
from 2 to 40 Ghz
transmitter is a parabolic dish, mounted as high
as possible
used by common carriers as well as by private
networks
requires unobstructed line of sight between
source and receiver
curvature of the earth requires stations (called
repeaters) to be ~30 miles apart

25. Satellite Microwave
Satellite is relay station-Mounted on the Orbit
Satellite receives on one frequency, amplifies or
repeats signal and transmits on another
frequency-Different uplink and down link
frequencies
Requires geo-stationary orbit
Height of 35,784km (22,300 miles)
Television-DSTV
Long distance telephone-Satellite-Suraya
Private business networks-E.g Remote Site
connections for mobile telephone service

26. dish
dish
uplink station downlink station
satellite
transponder
22,300 miles
Satellite Transmission Process

27. Principal Satellite Transmission
Bands
C band: 4(downlink) - 6(uplink) GHz
the first to be designated
Ku band: 12(downlink) -14(uplink) GHz
rain interference is the major problem
Ka band: 19(downlink) - 29(uplink) GHz
equipment needed to use the band is still very
expensive

28. Broadcast Radio
Omnidirectional-
FM radio
UHF and VHF television
Line of sight-Clear of obstacles and avoid signal
reflections on different surfaces e.g. walls
Suffers from multipath interference
Reflections

29. Infrared
Modulate noncoherent infrared light
Line of sight (or reflections will occur)
Blocked by walls
e.g. TV remote control, IRD port

30. Required Reading
Stallings Chapter 4