Introduction to Computer Networking Slide 1

Introduction to Data
Communication & Networking
: F J Kiwa

Questions to Answer
Why do we need a network ?
What infrastructure do we need to create
a network ?
Which technologies have been used in
networking ?
Which technology do you consider the
best and why

What is Telecomms
The term telecommunication means
communication at a distance. The word
data refers to information presented in
whatever form is agreed upon by the
parties creating and using the data

What is Data Communication
Data communications are the exchange of data
between two devices via some form of
transmission medium such as a wire cable.
The movement of computer information from
one point to another by means of electrical or
optical transmission systems (called networks).
Improve the day-to-day control of a business
by providing faster information flow.

Communication Systems
 Process describing transfer of information, data, instructions between
one or more systems through some media
 Examples
 people, computers, cell phones, etc.
 Computer communication systems
 Signals passing through the communication channel can be Digital, or
analog
 Analog signals: continuous electrical waves
 Digital signals: individual electrical pulses (bits)
 Receivers and transmitters: desktop computers, mainframe computers,
etc.

1 - 10
Datacom Basics
Broadband Communications
Telecommunications
transmission of voice, video, data,
- imply longer distances
- broader term
Data Communications
movement of computer information
by means of electrical or optical
transmission systems
convergence

What is a Network
A network consists of 2 or more
computers connected together, and
they can communicate and share
resources (e.g. information)

Why Networking?
l Sharing information — i.e. data communication
l Do you prefer these?
l Or this?

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l Sharing hardware or software
l Centralize administration and support
l E.g. print document
l E.g. Internet-based, so everyone can access the same
administrative or support application from their PCs

14
How many kinds of Networks?
l Depending on one’s perspective, we can classify
networks in different ways
l Based on transmission media: Wired (UTP, coaxial cables,
fiber-optic cables) and Wireless
l Based on network size: LAN and WAN (and MAN)
l Based on management method: Peer-to-peer and
Client/Server
l Based on topology (connectivity): Bus, Star, Ring …
:
:

Types of Networks
 Local Area Networks (LANs) - room, building
l a group of PCs that share a circuit.
 Backbone Networks - less than few kms
l a high speed backbone linking the LANs at various
locations.
 Metropolitan Area Networks (MAN) - (< few 10 kms)
l connects LANs and BNs at different locations
l leased lines or other services used to transmit data.
 Wide Area Networks (WANs) - (> few 10 kms)
l Same as MAN except wider scale

17
LAN and WAN
l Local Area Network (LAN)
l Small network, short distance
l A room, a floor, a building
l Limited by no. of computers and distance covered
l Usually one kind of technology throughout the LAN
l Serve a department within an organization
l Examples:
l Network inside the Student Computer Room
l Network inside your home

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l Wide Area Network (WAN)
l A network that uses long-range telecommunication links to
connect 2 or more LANs/computers housed in different
places far apart.
l Towns, states, countries
l Examples:
l Network of our Campus
l Internet
WAN
Student
Computer
Centre
Your home
USA

19
l Example of WAN: Broadband Cable Network
l Cable TV services have been extensively developed in most
modern cities
l Cable TV companies try to make use of their coaxial cable
installed (that are supposed to carry TV signals) to deliver
broadband data services
l Many cable network wiring has been replaced with hybrid
fiber-coax (HFC) ― i.e. use of fiber-optic cable to connect to
the subscribers’ buildings, and then the original coaxial
cable to connect to each household

Intranet
l A LAN that uses the Internet technologies
l Open only those inside the organization
l Example: insurance related information provided to employees over
an intranet
Private networks set up using the same
technology as the Internet (web servers,
Java, HTML) but only open to users
inside an organization are called
intranets

Extranet
l A LAN that uses the Internet technologies
l Open only those invited users outside the organization
l Accessible through the Internet
l Example: Suppliers and customers accessing inventory information
in a company over an extranet
Extranets uses Internet technologies to provide
invited users access to corporate network resources
such as information services and databases.
Extranet access is usually controlled using
passwords, but newer technologies, such as smart
cards, are also being used

22
Five Components of Data
Communication
1.Message
2.Sender
3.Receiver
4.Medium
5.Protocol

23
Direction of data flow
Simplex
Half Duplex
Full Duplex

26
Networks: key issues
 Network criteria
 Performance
 Throughput
 Delay
 Reliability
 Data transmitted are identical to data received.
 Measured by the frequency of failure
 The time it takes a link to recover from a failure
 Security
 Protecting data from unauthorized access

27
Terminology
The throughput or bandwidth of a channel is the
number of bits it can transfer per second
 The latency or delay of a channel is the time that
elapses between sending information and the earliest
possible reception of it

Devices that connect networks
Routers are responsible for forwarding internetwork
packets from one subnet or network to another.
Bridges connect networks of different types. They are
often CPUs or circuit cards in a PC.
Hubs are connectors for broadcast networks such as
Ethernet.
Switches are similar to routers, but connect only LANs,
usually Ethernet.

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Figure 1-1. Components of a Network

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Peer-to-Peer Networks
l Peer-to-peer network is also called workgroup
l No hierarchy among computers  all are equal
l No administrator responsible for the network
Peer-to-peer

33
l Advantages of peer-to-peer networks:
l Low cost
l Simple to configure
l User has full accessibility of the computer
l Disadvantages of peer-to-peer networks:
l May have duplication in resources
l Difficult to uphold security policy
l Difficult to handle uneven loading
l Where peer-to-peer network is appropriate:
l 10 or less users
l No specialized services required
l Security is not an issue
l Only limited growth in the foreseeable future

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Clients and Servers
l Network Clients (Workstation)
l Computers that request network resources or services
l Network Servers
l Computers that manage and provide network resources and
services to clients
l Usually have more processing power, memory and hard disk
space than clients
l Run Network Operating System that can manage not only
data, but also users, groups, security, and applications on
the network
l Servers often have a more stringent requirement on its
performance and reliability

35
l Advantages of client/server networks
l Facilitate resource sharing – centrally administrate and
control
l Facilitate system backup and improve fault tolerance
l Enhance security – only administrator can have access to
Server
l Support more users – difficult to achieve with peer-to-
peer networks
l Disadvantages of client/server networks
l High cost for Servers
l Need expert to configure the network
l Introduce a single point of failure to the system

Network Applications
The network applications environment
consists of several important components:
l Application programs
l Operating systems
l Data communication systems
l Database management systems

Business Data Communication
Applications
Major data communication applications
include:
l E-mail
l Groupware
l Knowledge management systems
l E-commerce and e-business applications
l Wireless applications

Communication Technology
Applications
voice mail Twitter
e-mail
instant
messaging
chat rooms
newsgroups telephony videoconferencing
collaboration groupware global positioning
system (GPS)

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Protocol
protocols define format, order of msgs sent and
received among network entities, and actions taken
on msg transmission, receipt
a human protocol and a computer network protocol:
Hi
Hi
Got the
time?
2:00
TCP connection
req.
TCP connection
reply.
Get http://gaia.cs.umass.edu/index.htm
<file>
time

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Layered Tasks
An example from the everyday life
Hierarchy?
Services

Communication Channels
A channel is a path between two communication devices
Channel capacity: How much data can be passed through
the channel (bit/sec)
 Also called channel bandwidth
 The smaller the pipe the slower data transfer!
Consists of one or more transmission media
 Materials carrying the signal
 Two types:
 Physical: wire cable
 Wireless: Air
destination
network
server
T1
lines
T1
lines
T1
lines
T3
lines

Physical Transmission Media
 A tangible media
 Examples: Twisted-pair cable, coaxial cable, Fiber-optics, etc.
 Twisted-pair cable:
 One or more twisted wires bundled together (why?)
 Made of copper
 Coax-Cable:
 Consists of single copper wire surrounded by three layers of
insulating and metal materials
 Typically used for cable TV
 Fiber-optics:
 Strands of glass or plastic used to transmit light
 Very high capacity, low noise, small size, less suitable to natural
disturbances

plastic outer
coating
woven or
braided metal
insulating
material
copper wire
twisted-pair cable twisted-pair wire
protective
coating
glass cladding
optical fiber
core

44
Unshielded Twisted-Pair (UTP)
l Typically wrapped inside a plastic cover (for mechanical
protection)
l A sample UTP cable with 5 unshielded twisted pairs of wires
Metal
Insulator

45
Shielded Twisted-Pair (STP)
l STP cables are similar to UTP cables, except there is a
metal foil or braided-metal-mesh cover that encases each
pair of insulated wires

Wireless Transmission Media
Broadcast Radio
 Distribute signals through the air over
long distance
 Uses an antenna
 Typically for stationary locations
 Can be short range
Cellular Radio
 A form of broadcast radio used for mobile
communication
 High frequency radio waves to transmit
voice or data
 Utilizes frequency-reuse

Wireless Transmission Media
Microwaves
 Radio waves providing high speed transmission
 They are point-to-point (can’t be obstructed)
 Used for satellite communication
Infrared (IR)
 Wireless transmission media that sends signals
using infrared light- waves - Such as?

100 Mbps is how many bits per sec?
Which is bigger:
10,000 Mbps, 0.01Tbps or 10Gbps?
Wireless channel capacity:

Introduction to Computer Networking Slide 1

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Introduction to Computer Networking Slide 1