Transcript Networks - Burgate ICT

Network Structure
www.ICT-Teacher.com
• Students should be aware of what is
available in order to
– create and use an ICT network:
• communication devices
• networking software
• data transfer media
• standards and procedures
• ICT networks for different geographical
scales and uses should be considered.
Links
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Local Area Networks & Wide Area Networks.
Software.
Topology.
Peer to Peer, Client Server.
Hardware.
Transmission Media.
Ethernet & Token Ring.
A Network System
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There are three parts to a network system:
1. a sender of information;
2. a communications link;
3. a receiver of information.
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Types
• There are two types of computer network:
• 1. a wide area network (WAN) – computers are
linked city to city, or country to country.
• 2. a local area network (LAN) – computers are
linked from office to office, or building to building.
• 3. a metropolitan area network (MAN) – not a
WAN but may link computers in different parts of
a city, not a LAN but may link computers from
building to building.
Networked Computers in a Call-Centre
Typical Network
Configuration
Local Area Network
• A local area network (LAN) is normally used for
sharing of resources such as a printer or files of
data.
• LAN’s are usually confined to a single site, such
as a school, but may extend to groups of
buildings stretched across a city, such as a
university campus.
• Each computer (workstation) on the network is
linked by cable to a central server using one of a
number of systems.
Wide Area Network
• A wide area network is normally used to link
groups of computers across long distances.
• A multinational company in New York will have
its own LAN, but to link with its Japanese offices
LAN, it will need to make use of a WAN.
• The WAN will be made up of telephone lines,
radio and satellite links, all run by the local
public providers. These will have their own
charges.
• Alternatively the company may pay for a
permanent link between offices, known as a
leased line. The company pays a fixed rate for
the permanently open connection.
Advantages of Networks
1. A common pool of data is shared among all the
users, without duplication.
– Consider a catalogue telephone sales dept.
– What is the system for entering sales into a
database from 50 operatives all using
connected workstations?
– What is the system for entering sales into a
database from 50 operatives all using stand
alone PC’s?
2. Sharing of hardware resources such as
printers, scanners, fax etc.
- Consider a school where many students
need to print off their coursework.
- How would a whole class print off all their
work in a single lesson from 24 networked
workstations?
- How would a whole class print off all their
work in a single lesson if only one PC is
connected to the printer?
- Would an option of connecting a printer to
each computer be feasible?
3. Software with a licence for x number of
workstations on a network is available cheaper
than single use licences. Most programs can be
downloaded onto workstations from the server,
saving time and money.
4. The back-up of data is done centrally by a
network manager, daily or weekly, and copies
kept for some time.
- What are the consequences if left to
individuals?
5. Better communication is achieved between
users, the system may be linked to the Internet.
- What is a company Intranet?
- How would users communicate to each
other?
6. Improved security from theft, destruction,
spying.
- Where are the data files kept on a networked
system?
- Where are the data files kept on a PC?
- How can some networked workstations
operate without a hard drive?
7. As programs are kept on the server, upgrading
and maintenance becomes one operation for all
workstations that access these programs.
Advantages of Stand Alone PC’s
1. The setup of a stand alone system is cheaper,
there are no special software, connections and
cabling required.
2. The IT manager requires less knowledge than
a network administrator.
3. Security problems are isolated such as a virus
introduced by an infected floppy disk.
4. The system is not dependant on the running
and maintenance of a central server, therefore
is less expensive to run.
Network Software
• Special software is required to run the network.
• Microsoft Windows NT Server 4.0 is a multipurpose
server operating system. A multipurpose operating
system integrates a variety of network services. The
services it provides are designed to address customer
requirements and are managed in a single way.
• http://www.microsoft.com/ntserver/ProductInfo/features/Features.asp
• X11 for Mac OS X is another server operating system
based on UNIX for Apple Macs.
• http://www.apple.com/macosx/newfeatures/
Topology
• Topology is the way devices are linked in a
certain design either physically and / or
logically.
• There are different topologies:
– Bus;
– Ring;
– Star;
– Mesh.
• There are different types of network:
– Peer to Peer;
– Client Server.
Bus Network
Workstations,
File Server,
Printer.
Terminal
Central Cable
• Data is sent from the sender to all other devices
(nodes), this may be the server or a workstation.
• There is no computer in control but there may be
a server that stores the data files.
• Advantages: simple, reliable, cheap, short cabling.
• Disadvantage: slow when busy or a large network,
as only one computer at a time can transmit data.
Bus Network
What would happen to the network if a workstation
breaks down?
X
Ring Network
• Data is sent from the
sender, it goes around
the ring being read by
Workstations
each computer, if it is
with In and Out
not for that one, it gets
Connections.
sent to the next, until it
File server and
reaches its destination.
Printer.
• Data has to wait its turn
before sending, special
software (token) writes
an address for sender
and destination.
Token Ring
Ring Network
What would happen to the
network if a workstation
breaks down?
Advantage: all nodes
can access the Token
equally, high speed.
Disadvantage: all on
one path, therefore
maintenance is high
for faults and failures.
X
Star Network
Data is controlled by
a central server,
messages sent and
received are read by
the controller.
Each workstation has
Its own dedicated link.
Advantages: fast with
high volumes of data,
extra nodes added without
any disconnections.
Central
Controller
Node
Workstations
Star Network
What would happen to the
network if a workstation
breaks down?
X
Disadvantages: if the
Central controller fails the
whole system is down,
large amounts of cable
are required, so it may
get expensive.
Mesh Network
Data sent from node to
node goes by a direct link.
Possible to leave out
some paths as there are
many alternative routes.
Advantages: very fast,
and fault tolerant.
Disadvantages: very large
amounts of cabling, resulting
In higher maintenance costs.
Mesh Network
What would happen to the
network if a
workstation breaks
down?
X
Peer to Peer Network
• File storage and printing facilities are not
accessed from the central server, but from any
of the computers on the network.
• Any workstation can use the others facilities, i.e.
hard disk, CD drive, printer, etc.
• These networks are easy to install and run, but
become slow if being used for a large network of
over 20 stations.
• These networks need a network interface card
(nic), cable, and network operating system
software to work.
Peer to Peer
• Advantages:
– ordinary equipment only,
– no need for an administrator,
– easy to get started,
– cheap to connect,
– user sets up their own defaults, more
personal,
– user controls their own resources,
– no costly maintenance and repair, no reliance
on one main computer.
Peer to Peer
• Disadvantages:
– no central organisation of data, bit are kept on
different hard disks, archiving haphazard,
– back-ups are done individually each of the
users, not done in one go centrally,
– users have to run their own computers in line
with company policy, need more skills,
– security may be more easily compromised
without a user name and password system.
Peer to Peer
How does the
laptop user print
out her work?
Client Server Network
• The server is a powerful computer containing the
files, the programs, the maintenance, the printer
and other resources.
• The server contains high processing power
(some have several CPU’s), and high storage
capacity, with back up facilities.
• A hub or switch is needed to control the flow of
traffic in the network so that signals do not
interfere with each other.
• The software is a network operating system
capable of Internet gateway facilities.
Data Control
• Files are stored on the central server, where
they are available for everyone with access to
use.
• Some parts of the file are kept on the server,
other parts are available for the client, these are
the parts that can be read, written, amended,
deleted etc.
• The updated file is then returned to the server
when saved.
• The amount of data that is sent and returned is
kept to a minimum allowing other users file
transfer time.
The Clients
• The client is the workstation being used to
access the data held on the server.
• All the client computers work independently from
each other, so any that are faulty or taken off the
network for maintenance do not affect the
performance of the system.
Advantages
• Advantages over peer to peer:
– speed of transfer as only part of the files need
be sent by dedicated servers,
– all users work on the same piece of data,
– the running and maintenance is done by a
specialist, users don’t need this knowledge,
– security is centralised through user access
and passwords, and files are stored centrally,
– back-up of files are done for all files regularly
and centrally.
Disadvantages
• Disadvantages:
– Entirely dependant on the server, the system
is down if the server has a fault.
– a more costly system to run, with expensive
equipment, needing a specialist network
administrator,
– software is more expensive as it is dedicated
to network use.
Client Server
How many devices
have access to the
printer?