This document provides an introduction to data communication, outlining key terminology, transmission mediums including guided media like twisted pair, coaxial cable, and fibre optics as well as unguided media like radio waves. It describes twisted pair cables, the differences between shielded twisted pair (STP) and unshielded twisted pair (UTP), and various categories of UTP cable. Other transmission mediums like coaxial cable, fibre optics, wireless networking, infrared, microwave transmission and satellite communication are also summarized.

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
1

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
2

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
3

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
4

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
5

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
6