1. Network Technologies (I)
Data Transmission
Transmission Media
Cabling Systems
LAN Technologies
Ethernet
Token Ring
FDDI

2. Data Transmission Message Source XMTR Modulator Channel RCVR Noise
Interference
Distortion

3. Data Transmission Transmission of data depends on
Quality of signal
Characteristics of medium
Need to do signal processing
Need to measure quality of received signal
Analog: signal-to-noise ratio
Digital: probability of symbol error
To transmit bits (0’s or 1’s) we need to map them into electromagnetic waves. Modulation techniques.

4. Data Transmission Transmitted signals are
Attenuated
Distorted
Corrupted by noise
Attenuation and distortion depend on
Type of transmission medium
Bit rate
Distance
Medium determines
Data rate
Bandwidth of channel

5. Data Transmission Medium: Direct link: point-to-point or guided
Guided: twisted pair, coaxial cable, optical fiber
Unguided: radio, satellite, infrared, microwave
Direct link: point-to-point or guided
Two devices share the medium (intermediate repeaters, amplifiers)
Indirect link: multipoint or broadcast
More than two devices share the medium
Transmission modes: simplex, half-duplex, full-duplex
Frequency, spectrum, bandwidth
Time-domain vs. frequency domain

6. Data Transmission
Bandwidth: several criteria, choice depends on application (3dB or 50% power; fraction of signal power)
Nyquist formula
Maximum data rate as a function of channel bandwidth (BW)
if BW=B then max. data rate is 2B
2 levels per signaling element
General
C = 2B log2 (M) [bps], M = levels per signaling element

7. Data Transmission
Attenuation: strength of signal falls off with distance; increases as a function of frequency
Delay distortion: propagation velocity varies with frequency; different frequency components arrive at different times
Noise: thermal, intermodulation, crosstalk, quantization, impulse
Data rate: C = B log2 (1 + S/N) [bps]

8. Transmission Medium
Twisted pair
Coaxial cable
Optical fiber
Wireless

9. Transmission Medium Twisted pair (UTP, STP)
two insulated copper wires arranged in a spiral fashion
wire pair acts as a single communication link
twist length varies from 2-6 inches
thickness varies from to inches
used in telephone networks
used within buildings
inexpensive compared to other media
easy to work with
poor noise and interference immunity
twisted to avoid crosstalk

10. Transmission Medium Twisted pair (UTP, STP)
analog signal amplifiers required every 5 to 6 km
digital signal repeaters required every 2 to 3 km
interference reduced by sheating
UTP: ordinary telephone wire, cheapest media for LANs, subject to interference
STP: less prone to interference, more expensive, harder to work with
EIA-568-A standard recognizes
category 3 UTP capable of 16MHz
category 4 UTP capable of 20 MHz
category 5 UTP capable of 100MHz

11. Data Rate Capacity of UTP Cables
Capacity Mb/s
1000
NEXT - Dominated
Environment
800
Category 5
600
Category 4
400
Category 3
200
100m
Horizontal Link (ft)
100
200
300
400
500
600
700
800

12. Transmission Medium Coaxial cable
hollow outer cylindrical conductor surrounding a single inner wire
regularly spaced insulating dielectric hold inner conductor in place
jacket or shield covers the outer conductor
diameter 0.4 to 1 inch
television distribution: CATV
long distance telephone transmission
short run computer I/O channels
LANs
better frequency characteristics, higher data rates, and more immune to interference than twisted pair

13. Transmission Medium Optical fiber 2 to 124 um flexible medium
conducts and optical ray
core: innermost section; cladding: middle section forms a plastic coating over the core; jacket: the outer most section covering the cladding
data rates of 2Gbps over tens of km
significantly low attenuation
not susceptible to interference or crosstalk
used for: long haul, metropolitan, and rural trunks, subscriber loops and LANs

14. Transmission Medium Optical fiber Multimode transmission
rays entering the core reflect and propagate along the fiber
Single mode transmission
radius of core reduced to one wavelength
only a single angle of reflection is allowed
provides superior transmission
XMTR: light-emitting diode (LED) or injection laser diode (ILD)
RCVR: photodiode or photo transistor

15. Transmission Medium Wireless terrestrial microwave satellite microwave
broadcast radio
infrared
laser

16. Transmission Medium Terrestrial microwave requires line of sight
requires fewer amplifiers or repeaters
long haul telecommunication services
voice and TV transmission
point-to-point links between buildings

17. Transmission Medium Satellite microwave
relays used to link ground stations
functions as an amplifier or a repeater
can provide point-to-point to point-to-multipoint connectivity
television distribution
long distance telephone transmission
private business networks

18. Transmission Medium Broadcast radio omnidirectional
does not require complex antennas
antennas need not be precisely aligned
FM radio
VHF and UHF television
data networks

19. Transmission Medium Infrared
XMTR/RCVR (transceivers) modulate non-coherent infrared light
line of sight is needed
no frequency allocation is needed
provides point-to-point connectivity

20. Cabling Systems Evolution
1980’s View, Dedicated Application Proprietary Wiring, Central Processing, Voice and Data Separate
1990’s View, Integrated Open Architecture Wiring System, Voice/Data/Image/Video
Need for High-Speed Transmission, 100/155 Mbps and Higher, Require Significantly more Bandwidth

21. Cable Systems Evolution1G
Data Rate bps
622 Mb/s
100M
TP-PMD
ATM
10BASE-T
16M Token Ring
10M
4M Token Ring
Baseband
Video
IBM 3270 1M
StarLAN 1
100K
DCP
10K
EIA-232 1K
1975
1980
1985
1990
1995
2000
Year

22. Cabling Systems Evolution
Cable systems must be developed to address:
Non Compatible
Non Standard
Conventional Type Wiring Plans
Designed to ease the introduction of new computer systems, LANs and PBXs

23. Cabling Systems Concerns
Installing and Maintaining a Reliable Cable Plant is Essential to the Well-Being of Today’s Mission Critical LANs
Category 5 UTP is Today’s Preferred Choice for LAN Cabling
Why is Category 5 UTP the Best Bet for Horizontal Wiring?
How Does it Handle 100/155 Mbps + Data Rates?
How Do You Maximize the Performance of Your UTP Installation?

24. Cabling Systems Concerns
Voice: Wiring system placed by PBX vendor or telephony networks to all identified work locations
Data: Wiring placed by data networks on an as needed basis
Proprietary Application Media (Coax, Dual Coax, Shielded)
Data Processing Systems - Mainframe (IBM 3270, IBM System 36/38 AS 400, etc..)
PC - Stand alone

25. Cabling Systems Concerns
LAN electronics vendors estimate cabling problems account for 50% of all LAN failures and problems
LAN Technology stated that 70% of downtime is attributed to cable related problems
A Communications Week study in January 1992 Found network downtime cost small companies $3, per hour
Infonectics Corporation study in October 1993 found network downtime cost Fortune 1000 companies an average of $62,500 per hour.

26. Network Costs 34% 5% 7% LAN Wiring Intelligent Workstation Wiring LAN
Attachment 5%
LAN
Attachment 7%
Software &
Mainframe
Intelligent
Workstation
54%
Software & Mainframe

27. Cabling Systems Trends
100 Mbps over Copper, solutions for UTP already exist
100 Mbps over Fiber, Momentum has Slowed
Fast Ethernet* 100 Mbps, on both CAT3 and CAT5 Cables
ATM 155 Mbps do-able
Theoretical limits of some manufactures CAT5 cables is more than 950 Mbps at 100 Meters.

28. Cabling Systems Properties
Open Architecture
Integrated Distribution Plan
Standards Compliant
Cost Effective
End-to-End Offering
Full Functionality and Flexibility
Manageable Growth
Investment Protection

29. Network cabling
Networking supports transmission and reception of data.
Network cabling provides the physical path for transmission and reception of data. 1

30. Overview Transmission media typically used Bounded media
Electrical conductors (eg coaxial cable, twisted wire pairs).
Optical conductors (eg Optical Fiber ).
Waveguides (air is the transmission medium but the waveguide confines or “binds” the transmission).
Unbounded media
Transmission of electromagnetic waves or light through air or space.

31. Bounded media Also known as guided media.
Bounded transmission media constrain and guide communication signals.
Media using electrical signals are
Single conductor
Paired cable and
Coaxial cable

32. Bounded media ( Cont.) Media using light signals
Optical fiber
Media using electromagnetic waves
Waveguides

33. Single conductor
A single conductor is used to provide a path for an electric current.
The earth provides the return path ( since a circuit needs to be complete for current to flow).
Today, used for short distances, like on a circuit board or on a silicon chip.

34. Paired cable
Two Conductors are used, with second conductor providing the return path for the signal current.
Two cables can be
Open wire pair (parallel to each other ).
Unshielded twisted pair ( twisted ).
Shielded twisted pair (seldom used today).
Open wires are susceptible to to cross talk and electromagnetic interference and are seldom used.

35. Paired cable (Cont.)
To avoid cross talk and interference the pairs of conductors are twisted.
A twisted pair consists of 2 insulated copper wires twisted together.
Usually number of these pairs are bundled together into a cable. Long distance cables may contain hundreds of pairs (eg telephone cables).

36. Paired cable (Cont.)
Twisting decreases the cross talk interference between adjacent cables by confining the electromagnetic field.
Twisted pair can be used for short distances ( usually less than 10 miles).
Longer distances require repeaters to regenerate the signal.

37. Paired cable (Cont.)
It has bandwidth limitations, when used over long distances.
It is susceptible to noise since not all interference is eliminated.
It is widely used for local telephone and data transmission.

38. Paired cable (Cont.)
It provides the “local loop” for telephone but the bandwidth is limited.
It can support 155Mbps transmission over short (less than 30ft) distances.
It is therefore widely used for network cabling within buildings (intrabuilding cabling).

39. Coaxial cable Coaxial cable consists of two conductors.
An inner conductor is completely sorrounded by an outer conductor.
The two conductors are separated by high quality insulation.
The outer conductor is sorrounded by a protective sheath.

40. Coaxial cable (Cont.)
Coaxial cables can be used for transmission of high frequency signals.
Using frequency or time division multiplexing (FDM or TDM) many channels can be supported by single cable.
It is widely used for cable TV.

41. Coaxial cable (Cont.)
It was widely used for (thick and thin cable) ethernets but it is being rapidly displaced by unshielded twisted pairs for this purpose.

42. Waveguides
A waveguide is a rectangular or circular pipe, usually made of some conductor such as copper.
It confines and guides very high frequency radio waves between two locations.
Waveguides are used for signals in the range of gigahertz (GHz) frequencies where twisted pair or even coaxial cables are not effective.

43. Optical fibers
Optical fiber is a thin, flexible glass or plastic fiber through which light energy is transmitted.
An optical fiber is actually a waveguide that guides the propogation of optical frequency waves through total internal reflection.

44. Optical fibers (Cont.)
Since most of the data that need to be transmitted are in the form of electrical signals, these signals must be converted to light signals before they can be transmitted by optical fibers.

45. Optical fiber communication system
Transmitter
Optical
Fiber
Optical
Receiver
Information
Information
Multiplexer
Optical
Receiver
Optical
Repeater
Optical
Transmitter
Multiplexer
FIG. 1. Typical optical fiber communication system.

46. Optical fibers (Cont.)
Fiber optic transmission systems have transmitters which use
LED (Light emitting diode) used primarily for short distances (< 2km) transmission or
LASER diodes used primarily for longer distance transmission
to convert electrical signals to light signals.

47. Optical fibers (Cont.)
The receiver uses a photo diode to convert the light signals back to electrical signals.
It offers large bandwidth.
Signal loss is very low.
Fibers are immune to electromagnetic interference.

48. Optical fibers (Cont.)
A basic optical fiber consists of two concentric layers, the inner core and the outer cladding which has a specific refractive index lower than the core.
There are 2 types of refractive index profiles, step and graded
For a step profile fiber, the inner core’s refractive index is uniform, for a graded fiber, the profile inner core’s refractive index is not uniform.

49. Characteristics of optical fiber

50. Optical fibers (Cont.) There are 3 basic types of fibers In multimode
Single mode.
Multimode graded index.
In multimode
Inner core diameter is relatively large (50 to 62.5 microns).
Light travels in different modes.

51. Optical fibers (Cont.) In single mode fibers
Used for short or medium distances ( < 2km).
Cheap compared to other types.
Supports medium to high bandwidths.
In single mode fibers
Inner diameter is very small, typically 0.8 to 1 micron.
Light travels in single mode.
Used for medium and long distances (> 2km).
More costly than multimode fiber.
Can support very high bandwidths (6 Gbps).

52. Optical fibers (Cont.) In multimode graded index fibers
Core is relatively large but difficult to manufacture.
Properties are intermediate between single and multimode fibers.
Because of difficulty in manufacture, such fibers are seldom used in data networking.

53. Unbounded media No physical connection is required.
Space or air is the transmission medium for electromagnetic waves.
Source and destination can be static or mobile.
Broad spectrum from low to high bandwidth is available.
Can be quickly implemented.

54. Unbounded media (Cont.)
It is prone to interference.
Transmission spectrum has to be shared and must be controlled to prevent interference in any given location.
Different unbounded communication systems
Broadcast radio and television.
Terrestrial microwave.
Satellite.
Infra red.

55. Network cabling Transmission media of interest for network cabling
Twisted pair
Coaxial
Fiber
Wireless

56. Twisted pair Least expensive. Flexible Easy to install Widely used.
There are two varieties
UTP ( Unshielded twisted pair ).
STP ( Shielded twisted pair ).

57. UTP Least expensive and popular. It is light and flexible.
Easy to install.
It is not shielded by external conductors.
It is subject to electromagnetic interference and external noise.
Twisting minimizes electromagnetic interference.

58. UTP (Cont.)
For data transmission 3 categories of UTP cabling can be used
Category 3 (cat 3 is for data rates upto 16 Mbps)
Category 4 (cat 4 is for data rates upto 20 Mbps)
Category 5 (cat 5 is for data rates upto 100 Mbps and even 155Mbps for limited distances)

59. UTP (Cont.) Cat 3 and Cat5 are used extensively
Cat3 is voice grade cable and widely used for telephone.
It has 3 to 4 twists per foot.
Cat 5 is data grade cable and widely used for data networking.

60. UTP (Cont.) It has 6 to 12 twists per inch.
Tighter twisting provides better performance but is more expensive.
Characteristic impedance of both cat 3 and cat 5 is 100 Ohms.
Cat5 is recommended, for data since it can support higher bandwidths.

61. STP
Twisted pairs of copper wire are sorrounded with metallic braid or sheathing.
Interference is reduced due to sheathing.
Characteristic impedance is 150 Ohms.
At lower data rates STP provides better performance than UTP.
It creates less electrical noise.
It is more expensive.

62. STP (Cont.) It is bulky. Less flexible.
Installation is more expensive.
Difficult to work with compared to UTP.

63. Coaxial cable
It consists of single copper conductor at its center surrounded by a hollow cylindrical outer conductor, with the 2 conductors separated by a dielectric medium.
Outer conductor provides a shield.
Coaxial cable is highly resistant to signal interference because the electromagnetic field is confined between the inner and outer conductors.

64. Coaxial cable (Cont.)
Less susceptible to cross talk than twisted pair cable.
It can support greater cable lengths between network devices than twisted pair cables.
It can support much larger bandwidths than twisted cable pairs.
It is bulky.

65. Coaxial cable (Cont.)
More difficult to install and work with than twisted pair cables.
It is more expensive than twisted pairs.
Coaxial cable was used in thin ethernet (10Base-2) and thick ethernet (10Base-5), but is now largely being replaced by cat5 UTP.

66. Fiber optic cable
An optical fiber is a thin (0.8 to 125 µm), flexible medium capable of conducting light.
It has the ability to transmit signals over much longer distances than coaxial and twisted pair cables.
Very high data rates (gigabits per second ) can be achieved over optical fiber.

67. Fiber optic cable (Cont.)
Theoretically 50Gbps are possible over fiber optic.
Data rates of 4.8 Gbps over tens of kilometers have been demonstrated.
Current dat rates are limited by the electronics and the optical transmitter/receivers.
Optical fiber has the advantage of being thinner and lighter over coax or a bundle of twisted pair cables.

68. Fiber optic cable (Cont.)
It has lower attenuation than coax and twisted pair cables.
Since it transmits light, the problem of electrical interference is eliminated.
It is also immune to the environmental (eg. moisture, lightening) disturbances.

69. Fiber optic cable (Cont.)
The advantage of optical fiber over coax and twisted pair will be more compelling as the demand for greater bandwidth increases.
It is highly secure medium, because it is difficult for any break to go undetected.
The main disadvantage is it is very expensive
Installation is expensive.

70. Fiber optic cable (Cont.)
Cannot tolerate small bending radius.
Difficult to work with because it is delicate.

71. Wireless
Wireless media has the benefit of relatively inexpensive installation in an environment where users are mobile.
It can also be beneficial in extending the network without rewiring the existing network.
The 3 ways in use as of now are
Microwave
Spread spectrum
Infrared

72. Microwave signals
Uses a highly directional antenna to minimize interference.
Frequencies used for transfer of information are dedicated.
Usually suports point to point transmission.
FCC regulates the bandwidth allocation.

73. Microwave signals (Cont.)
Has the disadvantage of using only part of the total available bandwidth.
Microwave signals can cross through walls and physical barriers.
Prone to interference from other sources of microwave signals.

74. Microwave signals (Cont.)
In general, it is relatively expensive but it may be the cheapest form of transmission over rough and mountainous terrain.
Requires high power.
Data rates upto 500 Mbps are possible.
Exposure to microwave radiation may be risky (health wise).

75. Spread spectrum It doesn’t require FCC license.
In this method each node has a radio transceiver.
Each node uses an antenna to send and receive information.
The signal to be transmitted is spread over a broad range of frequencies, so that signals look like noise.

76. Spread spectrum (Cont.)
The receiving station extracts its message, thus allowing a greater number of users to share the bandwidth.
There are 2 ways to do this
Frequency hopping.
Direct Sequence.

77. Spread spectrum (Cont.)
In frequency hoping the transmission frequency is made to hop (change) rapidly. The receiver also hops in synchronism with transmitter and picks up the message.
In direct sequence method, each bit is chipped into multiple bits using a bit pattern (thus spreading the signal over wider frequencies), with the help of same bit pattern receiver detects the bits.
Data rates of upto 1-2Mbps are achievable.

78. Infrared In this method infrared light is modulated by transmitter.
Transceivers must be in line of sight either directly or via reflection from a light colored surface such as a ceiling of a room.
Data rates of upto 20Mbps are possible.
No security or interference problems, as infrared transmission does not penetrate the walls.

79. Infrared (Cont.) License is not required.
Short range, point to point and potential eye damage if exposed to IR rays are the main disadvantages of infrared transmission.

80. Standards based cabling
Unstructured cabling
No single standard is followed for interconnection
Low initial cost, more expenses later.
Difficulties in the long run with developing technologies.
Difficulty in maintenance and scalability
Structured cabling increases initial cost but can avoid the problems and future expenses.

81. Standards based cabling (Cont.)
Telecommunications industry and the users realized the need for cost effective, efficient cabling systems.

82. Standards based cabling (Cont.)
Electronic Industries Association (EIA), Telecommunications Industry Association (TIA) and other leading telecommunication companies worked cooperatively to create ANSI/TIA/EIA-568-A standard for commercial buildings.
This standard defines structured cabling, a telecommunication cabling system that can support virtually any voice, imaging or data applications that an end user chooses.

83. TIA/EIA 568-A standard EIA/TIA 568-A specifications address
Recognized media.
Topology.
Cabling distances.
User interfaces.
Cabling and Connecting hardware performance.
Installation practices.
Link performances.

84. Cabling elements Horizontal Cabling. Backbone Cabling. Work Area (WA).
Telecommunications closet (TC).
Equipment Room (ER).
Entrance Facility (EF).

85. Horizontal cabling
It extends from the telecommunications outlet in the work area to the horizontal cross connect in the telecommunications closet.
Terminal
Work Area
Telecommunications
Closet

86. Horizontal cabling (Cont.)
It includes
The outlet.
Horizontal cables.
Mechanical terminations and Patch cords (or jumpers) that comprise the horizontal cross connect (each outlet in work area is connected to a horizontal cross connect in the telecommunications closet) .

87. Horizontal cabling (Cont.)
Specifications here are about
Proximity to EMI.
No. of outlets for each individual workarea.
UTP, STP and Fiber are recognized.
Coax is recognized but not recommended for new cabling installations.
Horizontal cabling shall be configured in star topology.
Other such issues.

88. Backbone cabling
The backbone cabling system provides interconnections between
Telecommunication closets.
Equipment rooms.
Entrance facilities.
It also includes the vertical wiring between floors, hence also known as vertical wiring.
Backbone also extends between buildings in a campus environment.

89. Backbone cabling (Cont.)
The specifications include
Backbone cables.
Intermediate and main cross connects including mechanical terminations.
Patch cords or jumpers used for backbone to backbone cross connections.
Recognized cables here are UTP, STP, Multimode and single mode fiber.

90. Work area Work area specifications consist of
Cable connecting user station to wall plate.
Devices connecting the user station to the wall plate.
Work area wiring is typically UTP or STP.

91. Telecommunication closet
Also known as wiring closet.
One on each floor (typically, depending on the floor space and special requirements number may vary).
Standards complaint connecting hardware should be used.
Specifications about short cables (patch chords) are made.

92. Equipment room
In large office buildings, there will be centralized equipment rooms to house servers, hubs, modems etc.
It is the central interconnection point for network cabling.
Main cross connections are specified here.

93. Entrance facility It is the network entry point of the building.
Within the network entrance facility, a cross connect device provides a termination point for all the cables.
Interfaces are specified.
Interconnection for cross connect devices and network devices are specified.

94. Other specifications
In addition to the cabling elements in TIA-568-A, there are specifications (connectors, cables, color coding etc) for
UTP cabling.
Fiber Optic cabling.
STP cabling.

95. Design considerations
Structured wiring is the way to go.
Highest quality connectors should be used.
While connecting twisted pair cables to punch down blocks, care must be taken not exceed the bend radius of the cable (otherwise there can be signal leaks, leading to interference).
Copper cables should not be run very close to power lines or parallel to them, otherwise there can be interference.

96. Design considerations(Cont.)
The end of the cable should not be untwisted more than needed, as this may result in excessive cross talk.
Plenum grade cable must be used where there is a possibility of fire (like area above the suspended ceilings).
NEC specifications for fire safety of cable installation should be followed .

97. Design considerations(Cont.)
While splicing fiber optic cable care must be raken to splice it perfectly at right angles.
The connection of fiber to the optical connector must be perfect.
Fiber should not be bent beyond its bending radius (several inches).
Have patch cables as short as possible.

98. Design considerations(Cont.)
Label all the cables and connectors.
Maintain an accurate wiring plan.
Avoid using already installed telephone cable (since it is not a data grade cable).