Transcript Networks - cutestteacherever

Importance
of
Communication
What is a network?
Networks
What is a network?
• A network consists of
two or more
computers that are
linked in order to:
• share resources (such
as printers and CDROMs),
• exchange files, or
• allow electronic
communications
ADVANTAGES of NETWORKS
• A network makes it easier to communicate
(between computers)
• Eg an email is faster than ‘normal mail’
• There are 2 major ways networks
advantage people and organisations
1. Save money by sharing resources
2. Remote services
ADVANTAGES of NETWORKS
1.
Save money by sharing resources
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•
Sharing internet connection resources
•
•
Many people able to use one connection
Sharing printing resources
•
•
E.g. teacher sends notes via email instead of printing,
photocopying, collating, stapling & handing out
Many people able to use one printer
Sharing other resources
•
Like faxes, CD-ROM towers, network storage & directory services
ADVANTAGES of NETWORKS
2. Remote services
•
•
Eg customers ordering over the internet
Eg business to business transactions
•
•
Gives customers more control (and reduces 3rd
party errors/ human errors)
Eg ATMs
USING NETWORKS
• The cost of equipment used to connect
a computer to a network is now
relatively cheap
• The software used to control networks
has developed and improved so that
most users do not know there is
software handling such tasks
• The use of networks has become
“transparent” to the user
How are they linked?
• Computers on a
network may be
linked through:
• cables,
• telephone lines,
• radio waves, satellites
or
• wireless technologies
COMMON NETWORKS
• Cable TV
• (traffic is just one way)
• Telephone system
• (traffic is two-way)
• Mobile phones
• (use radio waves rather than cables or wires)
The two basic types of networks
include:
• Local Area
Networks
(LAN)
• Wide Area
Networks
(WAN)
LAN
WAN
Local area networks
• LANs are confined to a relatively small area
such as a school or a building
• LANs usually have one computer designated
as the file server
• Other computers are connected to the
network by cables connecting network
interface cards in each computer
Wide Area Networks
• WANs connect larger
areas, such as whole
states, or even the
world.
• Transoceanic cables
and satellites are used
to connect WANs
Protocol
• A protocol is a set of
rules that governs the
communications
between computers on
a network
• These rules include
guidelines that regulate
the method of access,
types of cabling and
speed of data transfer
PROTOCOL =
SET OF RULES ABOUT
COMMUNICATIONS
BETWEEN
NETWORKS!
The most common protocols are:
• Ethernet
• Token
Ring
• TCP/IP
Protocol = a formal
description of a set of
rules and conventions
that govern how
devices on a network
exchange information
Ethernet
• Most widely used
• Uses an access method
called CSMA/CD (Carrier
Sense Multiple
Access/Collision
Detection
What does that mean?
• Each computer in the
network ‘listens’ to the
cable before sending
anything through the
network. If the network is
clear, the computer will
transmit.
• If another computer is
already transmitting on
the cable, the computer
will wait and try again
when the line is clear
A bit like waiting for
your younger sister to
get off the telephone
perhaps?
Ethernet (continued)
• Sometimes, two computers
attempt to transmit at the same
instant. When this happens, a
collision occurs. Each computer
then backs off and waits a
random amount of time before
attempting to retransmit. It is
normal to have collisions using
this method, but the delays
caused by collisions and
transmissions is small, and does
not effect speed of transmission
on the network
CSMA/CD =Carrier
Sense Multiple
Access /Collision
Detection
Fast Ethernet
• To allow for faster
transmission, the
Ethernet protocol has
developed a new
standard that supports
100 Mbps
• Fast Ethernet requires
the use of more
expensive equipment
and network cards
Token Ring
• Token ring
protocol involves
‘token-passing’.
• It is not as popular
as Ethernet
protocol
A single electronic ‘token’
moves around the ring from
one computer to the next. If a
computer wishes to transit
and receives an empty token,
it attaches data to the token
which then proceeds around
the ring until it comes to the
computer the data is meant
for.
ATM
• Stands for Asynchronous
Transfer Mode
• Transmit data at a speed of
155 Mbps and higher
• Works by transmitting all
data in small packets of
fixed size (other protocols
transfer variable size
packets)
• Like FDDI , is most often
used to connect two or
more LANs
Where does TCP/IP fit into all
this???
• TCP/IP is the protocol that is used for the
transmission of information over the Internet
• IP (Internet Protocol) - the main delivery system for
information over the Internet
• TCP (Transport Control Protocol) - used to break
apart and rebuild information that travels over the
Internet
Network Hardware
• Network hardware
includes:
•
•
•
•
Computers
Peripherals
Interface cards and
Other equipment
needed to perform
data processing and
communications
within the network
File servers
• A very fast computer
with a large amount
of RAM and storage
space along with a
fast network interface
card
• The network
operating system
software resides on
this computer
Workstations
• All computers
connected to the file
server on a network
are called
workstations
Network interface cards
• The network interface card
(NIC) provides the physical
connection between the
network and the computer
workstation.
• Most NICs are internal with
the card fitting into an
expansion slot in the
computer.
• Three common network
interface connections are
Ethernet cards, Local Talk
connectors and Token Ring
cards
Ethernet cards
• The most common
Network Interface
Cards are Ethernet
cards
• They contain
connections for either
coaxial or twisted pair
cables, or both
Co-axial
cable
Twisted
pair cable
Concentrators / Hubs
• A concentrator is a device that
provides a central connection point
for cables from workstations,
servers and peripherals
• Hubs are multi-slot concentrators
• A hub is a device that takes any
incoming signal and re-broadcasts
it down all the outgoing wires
connected to it
• Hubs can have from 5 ports to 128
ports
• Can transmit & receive at up to
100Mbps
Switches
• While hubs provide an easy
way to scale up and shorten
the distance that the packets
must travel to get from one
node to another, they do not
break up the actual network
into discrete segments. That
is where switches come in.
• An alternative to hubs are switches
• A switch stores the address of every device down each wire leading from
the switch
• Usually found in larger networks
Switches (continued)
• A vital difference between a hub and a switch is that
all the nodes connected to a hub share the bandwidth
among themselves, while a device connected to a
switch port has the full bandwidth all to itself.
• Think of a switch as a ‘clever’ hub
Routers (continued)
Modems
• A modem is a device that is used to send a
computer’s digital signal over a telephone
line – where the signal must be changed to
analog.
• Different types of modems:
• Dial-up
• Integrated Services Digital Network (IDSN or
DSL)
• Cable
Cabling
• Network cabling is the
medium through which
information usually
moves from one
network device to
another
• There are several
different types of cable
commonly used in
LANS
• Some networks use a
variety of cable types
within the one network
Unshielded Twisted Pair (UTP)
Cable
• Twisted pair cables
come in two varieties:
shielded and unshielded.
Unshielded (UTP) is the
most popular
• Shielded twisted pair is
used only in
environments where
there may be electrical
interference
UTP (continued)
• UTP has four pairs of wires inside the jacket
• Each pair is twisted with a different number of twists per
inch to help eliminate interference from adjacent pairs
UTP Connector
• The standard
connector for UTP
cabling is an RJ-45. It
looks like a telephone
style connection
Coaxial cable
• Coaxial cable has a single copper conductor at its
centre with a plastic layer between the centre
conductor and the braided metal shield
• Although coaxial cabling is difficult to install, it is
highly resistant to signal interference
Coaxial cable connectors
• Carries data at 10Mbps over 185metres
• Carries signal both directions, usually used when no
hubs or switches
• The most common type of connector used with coaxial
cables is the BNC connector
Fiber Optic Cable
• Fiber optic cabling consists of a center glass core
surrounded by several layers of protective
materials
• It transmits light rather than electronic signals
• It is the standard for connecting networks between
buildings, due to its immunity to the effects of
moisture and light
Fiber Optic (continued)
• Fiber optic cable has the ability to transmit signals over
much longer distances than coaxial or twisted pair
• It can also carry information at vastly greater speeds
(Transmits light pulses up to 2km & over 1000
frequencies can be transmitted along a strand at one
time)
• Fiber optic cable is more difficult to install than other
cabling & is expensive
Wireless LANS
• Wireless networks use high frequency radio signals to
communicate between the workstations and the
fileserver or hubs.
• Disadvantages of wireless networks are:
•
•
•
•
they are expensive (relatively),
provide poor security,
are susceptible to interference and
are slower than cabled networks
Wireless Transmission
• Wireless transmission includes the use of:
• Radio waves
• Bluetooth
• Microwaves
• Satellite
• Infra-Red
Network Operating Software
• Network operating systems
co-ordinate the activities of
multiple computers across a
network
• The two major types of
network OS are:
• Peer-to-peer
• Client/server
Peer to peer network OS
• In peer to peer network OS, there
is no file server or central
management source; all
computers are considered equal
• Peer to peer networks are design
primarily for small to medium
LANS
• AppleShare and Windows for
Workgroups are examples of
programs that can function as peer
to peer
Client/Server network OS
• Client/server network OS
centralise functions and
applications in one or more
dedicated file servers.
• The file server provides access
to resources and provides
security
• Novelle Netware and Windows
NT Server are examples of
client/server network
operating systems
Network Operating Systems
• There are 3 major network operating systems used
with personal computers
• Windows (2000 then XP now - Vista)
• Novell
• Apple
• The network operating system is software that
controls traffic on the network and defines how
well we communicate with each other
• Having all machines in a network use the same
operating system is preferable, especially for
instructions & maintenance
Topology
• The physical topology of a network refers to the
configuration of cables, computers and other
peripherals.
• The main types of network topologies are:
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•
•
•
Linear Bus
Star
Ring
Tree or Hybrid
Linear Bus
• A linear bus topology consists of a main run of
cable with a terminator at each end. All servers
workstations and peripherals are connected to the
linear cable
Star
• A star network is
designed with each
node (file server,
workstation,
peripheral)
connected directly
to a central network
hub or server
Ring
• A ring network is one
where all
workstations and
other devices are
connected in a
continuous loop.
There is no central
server
Tree or hybrid
• A tree or hybrid
topology combines
characteristics of
linear bus and star
and/or ring
topologies.
• It consists of groups
of star-configured
workstations
connected to a linear
bus backbone cable
IMPROVEMENTS THROUGH
USING NETWORKS
1. Improvements in efficiency
• Save time (single resource, many users – no
queues)
• Save money (single resource, many users)
• Save effort (don’t need to move from machine
to machine)
• Communication is simpler & faster (instant – in
‘real time’
IMPROVEMENTS THROUGH USING
NETWORKS (cont)
2. Improvements in effectiveness
•
•
Because communication is easier & faster, people are
more likely to communicate
As well as improved quantity & speed, quality has also
been improved (eg group work & instant updates &
less duplication)
IMPROVEMENTS THROUGH USING
NETWORKS (cont)
3. Improvements in information systems
•
•
•
Networks allow data to be shared among users and
enables users to retrieve information from more than
one source
This synchronisation avoids data duplication
Data manipulation can be spread over a number of
computers, speeding up processing
IMPROVEMENTS THROUGH USING
NETWORKS (cont)
4. Improvements in meeting organisational goals
•
•
•
Save time by having multiple users working on same
data set simultaneously
Also when passing on data to other workers, there is
very little time & effort involved if networks are used
for the data movement
Improved productivity thanks to improved efficiency
& effectiveness
Network Security
Encryption Software
• Makes normally readable plain text a mixture of
characters
• This ‘scrambling’ is done using algorithms
Eg Chris may become…
Hsirc
Or
3818919
Or
#+*’?
Network Security
Usernames &
Passwords
• Network policies, profiles –Many organisations
now use networks to enable employees to access
data stored in different locations
• To enable employees to gain access to some files but
not others, a network administrator will establish a
series of network policies and profiles
• For example, needing a username and password
Network Security
Firewalls
• Firewalls are based on a combination of hardware and
software that only allow authorised network traffic to pass
through the ‘gate’ which they protect
Network Security
Anti-Virus & Malware Protection
• Protects computers by
detecting the presence
of viruses as the
machine boots up
• Scans files for virus
signatures, or virus-like
activity
• Can be automatically
removed or a warning
flashed to the user
Logical Design of a Network
• Logical Design Factors:
• Ability to fulfil required functions
• Software Interface
• Ease of Hardware Use
• Procedures
•
•
•
•
Applications
Cost
Security
Access to required information & resources
• Inclusiveness
• LAN protocol
• Expansion potential
• Compatibility of components
Physical Design of Networks
• Often networks can become very
complicated
• A way of visually showing the physical
devices & communication lines present
in a network is with a network diagram
Network Diagram