1. Introduction Outline
to n Terminology
Data Communication n Transmission medium
n Guided media
Unguided media
DCS201- Computer Science
n
By:
Dilum Bandara
Data Communication Terminology
n Is the process of transmitting data from n Bit rate
one computer to another n Number of bits per second
Given in bps
Focus is on the transmission medium,
n
n
n Baud rate
different signal levels & data coding
n Number of signal variations per second
n Given in bauds per sec
n Bandwidth
n Maximum frequency supported by the medium
Transmission Medium Guided media
n Provides the path for data n Copper wires
communication n Twisted Pair
n Allows a bit stream to be transported n UTP – Unshielded Twisted Pair
STP - Shielded Twisted Pair
from one machine to another n
Coaxial cables
Can be categorised as
n
n
n Guided media
n Fibre
n Unguided media
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2. Unguided media Twisted pair
n Radio waves n Pairs of insulated copper wires twisted
n Microwave links together
n for the reduction of Electro Magnetic
n IR – Infra Red Interference
n Covered with an outer insulating jacket
n Two types
n Shielded twisted-pair (STP)
n Unshielded twisted-pair (UTP)
Twisted pair cont… STP & UTP
n One or more pairs of wire
n Twisted around one another
n Resistant to interference
n A parallel set of wires forms an antenna
but twisted pair does not
n Limits signals influence on other pair
n Referred as Crosstalk
UTP Pros & Cons
n UTP cables are grouped in several n Inexpensive
categorises n Easy to work with
n Category 1 – Voicegrade telephone cabling n Can run up to several Kilometres
n Category 2 – up to 4 Mbps 4 pairs without amplification
n Category 3 – up to 10 Mbps 4 pairs n For long distances repeaters are needed
Category 4 – up to 16 Mbps 4 pairs
n
n With the distance bandwidth reduces
n Category 5 – up to 100 Mbps 4 pairs
Category 5e – up to 1 Gbps 4 pairs
n High number of twists per meter
reduces the crosstalk
n
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3. Coaxial cables Types of cables
n In early days of networking these types n 50 O - Baseband Coaxial Cable
of cables were heavily used
n Used in digital transmission
n 75 O - Broadband Coaxial Cable
n Used for analog transmission
n Used for TV antennas & Cable TV
Advantages of Coaxial cables Disadvantages of Coaxial cables
n Easy to install n Higher cost compared to twisted pair
n Inexpensive n Harder to work with & cable easily get
n Since it is shielded can span a higher damaged
distance at higher speed than twisted
pair
n High bandwidth
n Excellent noise immunity
Fibre optics Fibre optics cont…
n Bundle of glass or plastic fibres
n Sends signals on pulses of light
n Based on the concept of Total Internal
Reflection
n Immune to Electro Magnetic & other
interferences
n High bandwidth, speed, long distance
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4. Components of a fibre system Components of a fibre system cont…
n Light source n Light Source
n Transmission medium n Converts electrical signals to optical signals
n Light detector n Transmission Medium
n Transmits the light signal from one point to
another
n Detector
n Detects the light signal & converts it back to
electrical signals
Light source
Light detector
Types of fibre Types of fibre cont…
Jacket (Plastic) Core (Glass)
n Single Mode fibre
n Harder to manufactory so high cost
n High speed
Single Mode fibre
n Long distance (up to 100Km)
n Multi Mode fibre Cladding (Glass)
n Low cost
n Low speed
n Lower distance (2 Km) Multi Mode fibre
Radio Transmission Wireless Networking
n Unguided transmission - Intangible media n Use is increasing with the introduction
n Easy to generate of mobile devices
n Travel long distances n Cost is decreasing
n Penetrate buildings easily n Hybrid networks use cable & wireless
n Omni directional
n At high frequencies they travel in straight lines
n Absorbed by rain
n Reflected by ionosphere
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5. Wireless LAN Technologies Infrared (IR)
n Infrared (IR) n Uses IR signals transmit data
n Laser or light wave n Used for short range communication
n Do not pass through solid objects
n Microwave Transmission
n Simple to develop & cost effective
n Satellite Communications
n Low speed
n Cannot be used outdoor
n Used in remote controllers, hand held
devices, laptops, etc.
Light wave Transmission Microwave Transmission
n Can be used to interconnect LANs in 2 n Above 100MHz, waves travel in straight lines
different buildings n Can be narrowly focused
n Highly focused & coherent n Can be concentrated to a small beam using
parabolic antennae
n Requires very high degree of alignment
n Antennas at transmitter & receiver must be
between transmitter & detector
aligned (Line of Sight)
n Cannot penetrate rain or thick fog n Long distance links must have repeaters
n Does not penetrate through objects
Satellite Communication UTP Cat 5e Cables
n Make use of geosynchronous Satellites n Used with 10/100/1000 Ethernet
n Orbiting the earth at a distance of 36000 n Most heavily used cabling types
km above the equator
n Are connected to networking devices
n Period of the satellite is 24 hours through RJ45 Jacks
n Uses different bands for different
purposes
n Telecommunication, TV braodcasting
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6. RJ45 cabling Types of RJ45 cabling
n Has 8 wires n Straight Cables
n But only 4 are used n Cross Cables
n 2 for transmitting data n Rollover cables
n 2 for receiving data
Straight Cable Cross Cable
Wire pairs
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