1. CS 1302- Data Communications & Networking
Topic 5 – Transmission Media

2. Relation to Internet Model
Actually located below the physical layer
Directly controlled by the physical layer

3. Introduction
Data must be converted into electromagnetic signals to be transmitted from device to device
Signals can travel through a vacuum, air, or other media
May be in the form of power, voice, radio waves, infrared light, and gamma rays
Each of these forms constitutes a portion of the electromagnetic spectrum

4. Categories of Media Broad categories:
Guided Media – media with a physical boundary
Twisted pair, coaxial, and fiber-optic
Unguided Media – no physical boundaries
Radio waves, infrared light, visible light and gamma rays
Sent by microwave, satellite, and cellular transmission

5. Classes of Transmission Media

6. Guided Media Provides a conduit from one device to another
Signal is directed and contained by physical limits of medium
Twisted-pair and coaxial use copper conductors to accept and transport signals in form of electrical current
Optical fiber is glass cable that accepts and transports signals in form of light

7. Twisted-Pair Cable Two conductors surrounded by insulating material
One wire used to carry signals; other used as a ground reference
Twisting wires reduces the effect of noise interference or crosstalk since both wires will likely be equally affected
More twists = better quality
Limits interfences
No. of twists / unit length determines the quality of the cable

8. Unshielded Twisted Pair (UTP)
Most common type; suitable for both voice and data transmission
Categories are determined by cable quality
Cat 3 commonly used for telephone systems (up to 10 Mbps Base T)
Cat 5 usually used for data networks (up to 100 Mbps – 100 Base T)
Performance is measured by attenuation versus frequency and distance
Adv: cheaper, flexible, easy to install
UTP connectors - RJ45

9. Categories of UTP cables
Category
Bandwidth
Data Rate
Digital/Analog
Use 1
very low
< 100 kbps
Analog
Telephone 2
< 2 MHz
2 Mbps
Analog/digital
T-1 lines 3
16 MHz
10 Mbps
Digital
LANs 4
20 MHz
20 Mbps 5
100 MHz
100 Mbps
6 (draft)
200 MHz
200 Mbps
7 (draft)
600 MHz
600 Mbps

10. UTP example

11. Shielded Twisted Pair (STP)
A metal foil or braided-mesh covering encases each pair of insulated conductors to prevent electromagnetic noise called crosstalk
Crosstalk occurs when one line picks up some of the signals traveling over another line
Uses RJ-45 connectors
More expensive but less susceptible to noise
Supports high Bandwidth over long distances

12. Coaxial Cable
Has a central core conductor enclosed in an insulating sheath, encased in an outer conductor of metal foil
RG numbers denote physical specs such as wire gauge, thickness and type of insulator, construction of shield and size/type of outer casing
RG-8, RG-9, and RG-11 used in thick Ethernet
RG-58 used in thin Ethernet
RG-59 used for TV

13. Coaxial Cable Connectors
Most common is barrel connector (BNC)
T-connectors are used to branch off to secondary cables
Terminators are required for bus topologies to prevent echoing of signals

14. Coaxial Applications & Performance
Analog and digital phone networks
Cable TV networks
Traditional Ethernet LANs
Home Networks-phone line , power line.
Higher bandwidth than twisted-pair
Attenuation is higher and requires frequent use of repeaters
Single coax carries voice signals & digital data upto 600 Mbps.

15. Fiber-Optic Cable
Made of glass; signals are transmitted as light pulses from an LED or laser
Light is also a form of electromagnetic energy
Speed depends on density of medium it is traveling through; fastest when in a vacuum, 186,000 miles/second

16. Refraction and Reflection
Refraction often occurs when light bends as it passes from one medium to another less dense medium
When this angle results in a refraction great enough, reflection occurs and the light no longer passes into the less dense medium

17. Reflection
Optical fibers use reflection to guide light through a channel
Information is encoded onto a beam of light as a series of on-off pulses representing 1s and 0s

18. Propagation Modes Method for transmitting optical signals: Multimode
Multimode step-index fiber
Multimode graded-index fiber
Single Mode

19. Multimode
Multiple beams from light source move through core at different paths
Multimode step-index fiber
Density remains constant from center to edges
Light moves in a straight line until it reaches the cladding
Some beams penetrate the cladding and are lost, while others are reflected down the channel to the destination

20. Multimode (cont)
As a result, beams reach the destination at different times and the signal may not be the same as that which was transmitted
To address this problem and to allow for more precise transmissions, multimode graded-index fiber may be used
Index refers to the index of refraction
Graded-index refers to varying densities of the fiber; highest at center and decreases at edge

21. Multimode Graded-Index Fiber (cont)
Since the core density decreases with distance from the center, the light beams refract into a curve
Eliminates problem with some of the signals penetrating the cladding and being lost
Also signals intersect at regular intervals

22. Single Mode
Only one beam from a light source is transmitted using a smaller range of angles
Smaller diameter and lower density
Makes propagation of beams almost horizontal; delays are negligible
All beams arrive together and can be recombined without signal distortion
Uses stepped index fiber

23. Propagation Modes

24. Light Sources & Connectors
Light source is light-emitting diode (LED) or a laser
LEDs are cheaper but not as precise (unfocused); limited to short-distance use
Lasers can have a narrow range, better control over angle
Receiving device needs a photosensitive cell (photodiode) capable of receiving the signal
Uses SC- Subscriber channel & ST-straight tip connectors

25. Applications of Fiber Optics
Backbone networks due to wide bandwidth and cost effectiveness
Cable TV
LANS
100Base-FX (Fast Ethernet)
1000Base-X

26. Advantages of Fiber Optics
Higher bandwidth than twisted-pair and coaxial cable; not limited by medium, but by equipment used to generate and receive signals
Noise resistance
Less signal attenuation
More resistant to corrosive materials
Lightweight
Greater security

27. Disadvantages of Fiber Optics
Installation/maintenance
Unidirectional
Cost

28. 7.2 Unguided Media: Wireless
Wireless communication; transporting electromagnetic waves without a physical conductor

29. Wireless Propagation Methods
Ground – radio waves travel through lowest portion of atmosphere, hugging the Earth
Distance depends on power of signal
Sky – higher-frequency radio waves radiate upward into ionosphere and then reflect back to Earth
Line-of-sight – high-frequency signals transmitted in straight lines directly from antenna to antenna

30. Propagation Methods

31. Wireless Transmission Waves
Radio Waves
Microwave
Infrared

32. Radio Waves Frequency ranges: 3 KHz to 1 GHz Omni directional
Susceptible to interference by other antennas using same frequency or band
Ideal for long-distance broadcasting
May penetrate walls
Propagate in SKY mode
Used for multicast communication such as radio, TV etc

33. Bands Band Range Propagation Application VLF 3–30 KHz Ground
Long-range radio navigation LF
30–300 KHz
Radio beacons and navigational locators MF
300 KHz–3 MHz
Sky
AM radio HF
3–30 MHz
Citizens band (CB), ship/aircraft communication
VHF
30–300 MHz
Sky and line-of-sight
VHF TV, FM radio
UHF
300 MHz–3 GHz
Line-of-sight
UHF TV, cellular phones, paging, satellite
SHF
3–30 GHz
Satellite communication
EHF
30–300 GHz
Radar, satellite communication

34. Microwaves Frequencies between 1 and 300 GHz Unidirectional
Narrow focus requires sending and receiving antennas to be aligned
Issues:
Line-of-sight (curvature of the Earth; obstacles)
Cannot penetrate walls

35. Parabolic Dish Antenna
Incoming signals - Signal bounces off of dish and is directed to focus
Outgoing signals – transmission is broadcast through horn aimed at dish and are deflected outward

36. Horn Antenna
Outgoing transmissions broadcast through a stem and deflected outward
Received transmissions collected by a scooped part of the horn and deflected downward into the stem

37. Microwave Applications
Unicasting – one-to-one communication between sender and receiver
Cellular phones
Satellite networks
Wireless LANs

38. Infrared Frequencies between 300 GHz and 400 THz
Short-range communication
High frequencies cannot penetrate walls
Requires line-of-sight propagation
Adv: prevents interference between systems in adjacent rooms
Disadv: cannot use for long-range communication or outside a building due to sun’s rays

39. Infrared Applications
Wide bandwidth available for data transmission
Communication between keyboards, mice, PCs, and printers

40. Media selection
Each media has advantages and disadvantages. Some of the advantage or disadvantage comparisons concern the following:
Cable length
Cost
Ease of installation
Susceptibility to interference

41. Ethernet Media standard
The cables and connector specifications used to support Ethernet implementations are derived from the Electronic Industries Association and the Telecommunications Industry Association (EIA/TIA) standards body.
The categories of cabling defined for Ethernet are derived from the EIA/TIA-568 (SP-2840) Commercial Building Telecommunications Wiring Standards.

42. Lab on Cable connectorization
EIA/TIA specifies an RJ-45 connector for unshielded twisted-pair (UTP) cable. The letters RJ stand for registered jack, and the number 45 refers to a specific wiring sequence.

43. Straight through Cable
Maintain the pin connection all the way through the cable.
Wire connected to pin 1 is the same on both ends.
Used to connect such devices as PCs or routers to other devices such as hubs or switches.

44. Cross over cable
Cross the critical pair to properly align, transmit, and receive signals on devices with like connections.
Pin 1 connected to pin 3, pin 2 connected to pin 6.
Used to connect similar devices: switch to switch, switch to hub, hub to hub, router to router, PC to PC.

45. Connectorization