Transcript network1 - Warilla High School Intranet

Illawarra Grammar School
• Computing networks at first consisted of a mainframe computer
connected to dumb terminals which had no processing power
themselves. Users shared the mainframe’s CPU, disk storage and other
resources. The mainframe did all the work and this is referred to as a
Shared Processor System and Centralised Processing.
• Due to advancements of the personal PC and falling costs, companies
have replaced their mainframes & minicomputers with networks of
PCs. Each PC operates separately of the others, yet any PC can share
files, printers and other resources with any other PC on the network.
Referred to as Distributed Processing
• An emerging technology is the attempt to combine the best of
distributed computing and centralised computing (a hybrid of both).
By storing all the programs and data on a central server, network
administrators regain control over the organisations’ computing
resources. Because users can’t install programs on their own
machines, they can run only authorised software - this great reduces
the risk of computer viruses and copyright infringements
• PCs have their own processor, graphical display and disk storage.
Special PCs (file servers) allow individual client PCs to use the shared
disk, printers etc. This provides excellent performance and flexibility
but at a high cost in equipment, software and ongoing maintenance.
• Thin clients are PCs with no disk storage. This clients must load all
their software from a central server and must save their work on the
server. Users can’t install their own programs or make configuration
changes. It combines the nature of mainframe computing with the
power and graphical interface of personal computers.
• A Network Model consists of:
• Network Operating System (NOS). Consists of a suite of programs that
run in networked computers. Some programs allow the sharing of files
and printers. Computers that share resources are called servers. Both
client and server software run at the same time.
• Networked peripherals: Include printers & modems. Networked
peripherals have internal specialised processors to run networking
server software so they don’t have to be directly attached to a
computer.
• A Network Model consists of:
• Network Interface Card (NIC or LAN adaptor): A network interface card
changes the computer signals into more powerful signals that can
cross a network cable. The NIC takes the data from the computer,
packages the data for transmission and acts as a gatekeeper to control
access to the shared network cable.
• Network Cabling: electrical pulses can be sent over copper cable,
pulses of light over fibre-optic or through the air using radio or light
waves. Cabling installations use a wiring hub to isolate cable
problems and improve reliability.
Modem- Networked Device
Networking Software
Wiring
Hub
Printer- Networked Device
Network Interface Card
Networking Software
• Networking software can be a separate product one adds to a system
such as Novell’s Netware. Modern operating systems include inbuilt
networking functions [Windows 95, 98, 2000, XP]. Apple Macintosh
computers come with networking software that allows them to operate
on Netware or Windows based networks.
• Network Interface Cards links a computer to the cable system. It
controls the flow of data between the computer’s internal data bus and
the serial stream of data on the network cable. Some computers now
come with their NIC built into the main circuit board.
Printer- Networked Device
Modem- Networked Device
• Devices such as printers and modems can have their own network
attachments. The networking software makes it possible to use these
shared devices as if they were locally attached.
Wiring Hub
• One can choose from a variety of network cable types and arrange the
cable in several ways. Cabling is a hidden cost that many people fail to
consider when planning a network installation. One’s network is only
as good as the cabling.
• Client Computer: is not a server;
its networking client software
allows application programs to
use disk drives, printers, etc. as
if they were directly attached to
the computer. In this case an
application program
(spreadsheet) has a print job.
The print job goes from the
application to Windows with
instructions to print on a specific
port such as LPT2. Windows
send any print jobs addressed to
LPT2 to a specific networked
printer.
• Redirector: the principle element of the client software. The redirector
captures service request it has been programmed to recognise and routes
them out of the PC and across the network for service. Typically,
redirector software is a built-in part of the client’s operating system
• Network communications protocols package the requests from the client
computers and send the requests across the network. Protocols handle
the nitty-gritty details of addressing, routing, ensuring delivery and
ensuring accuracy. Typical protocols include Apple File Protocol (Apple),
Microsoft’s NetBIOS Extended User Interface (NetBEUI), & Novell’s
Sequental Packet Exchange and Internetwork Packet Exchange (SPX and
IPX. Because the Internet is based on the TCP/IP protocol, many
companies have adopted TCP/IP as their standard corporate networking
protocol. TCP/IP is very flexible, and it can transport data on behalf of
other protocols such as NETBIOS.
• The driver software works between the network interface card
and the network’s communications software. If an adaptor
manufacturer supplies drivers conforming to Microsoft
Network Driver Interface Standard (NDIS) or Novell’s Open
Data-Link Interface (ODI), one can use the adaptor with a
variety of network operating systems.
• Netware Dedicated File Server: It
can’t run applications. When a
request for file access is made,
the server software checks to
make sure the person placing the
request has been granted access
to the file. Once validated, the
request goes to the file server
software. This software coordinates simultaneous requests
for the same data, finds the data,
and sends it back to the
requesting client computer.
• Client Computer & Print Server:
The networking software in this
computer gives it the ability to
act as a client, so it can request
files & send print jobs to other
server computers, but it can also
act as a print server. It can
accept print jobs from other
client computers and print them
on its locally attached printer.
• Client Computer: is running an
application program, a database,
that needs access to a file. The
application sends to Windows
the filename, along with the
specified disk drive name, eg. F:.
Windows reroutes any request
for data on the F: drive to the file
server.
• Network operating
systems package
requests from the
keyboard & from
applications in a
succession of data
envelopes for
transmission across
the network. In this
example, Novell’s
NetWare packages a
file request in an IPX
packet, and the LAN
adaptor packages the
IPX request into an
Ethernet frame. Each
data envelope contains
its own addressing &
error control
information
RJ-45 Connector
twisted pair wire
Connector for
Transceiver
BNC coaxial
connector
Expansion bus connectors
• RJ-45 Connector
Unshielded Twisted Pair
• BNC connector Coaxial Cable
• IBM data connector
Shielded Twisted Pair
• ST fibre-optic connector
• Network cabling should be at least Category 5
• LAN cables come in many physical configurations. One needs
to consider resistance to crosstalk - electric currents between
pairs of wires in the same cable - resistance to outside electrical
fields caused by power lines, motors, relays, radio transmitters,
other devices; and ease of installation.
• Fibre-optic cables uses pulses of light and have total immunity
from electrical noise. Fibre-optic cables carry signals faster and
farther than any other type of cable. Cables with outside shields
of copper braid or foil, such as coaxial and shielded twisted pair,
offer good resistance to electrical noise, but because they are
thicker, they are difficult to pull through the wiring conduits &
walls. The thin, unshielded twisted-pair is easier to install but
offers less resistance to electrical noise. This fibre-optic cable
doesn’t fill conduits, but installers need special training and
equipment.
Internet
Access point A
Access point B
Router
Laptop with
wireless card
• Wireless LANs are
used to provide
LAN connections
for portable PCs.
Each laptop has a
wireless access
card.
Server
Printer
• Bluetooth: named for a Viking king, Bluetooth is a new
wireless protocol that promises to link virtually any type of
communications equipment into a portable, small network.
• Bluetooth uses radio technology similar to the 802.11
wireless LAN standard, but at a very much lower power level.
The low power level allows Bluetooth devices to be very
small, and it also reduces interference from other close
Bluetooth devices.
• Bluetooth devices have a range of about 10 metres and can
operate at speeds up to about 700bps.
• Think of Bluetooth as a wireless replacement for all the
cables in your office. All Bluetooth devices can talk to each
other, allowing them to exchange information wirelessly.
Typical applications include wireless links among cell
phones, laptop / handheld computers, scanners, keyboards,
mice, and digital cameras.
• Each client computer
runs its own application
programs, & networking
software in each machine
redirects requests for file
& print services to the file
server. Files created by
the applications and
perhaps the applications
themselves, cross the
network from the file
server.
• This is designed to act as a
central server, is equipped with
multiple hard drives, a tape
drive (backup), CD-ROM drive.
It uses specialised multitasking
operating system and runs
many management / monitoring
programs
• A non-windows Network
computer (NC) terminal for
mainframes or a NC to carry out
web services or Java or other
specialist services written in a
specific langauge. The
programs are executed in the
clients but the data / files are
sent by the file server.
• Windows machines where they
are used for input & output. The
programs are actually executed
at the shared CPU Server.
• A thin network client solution
reduces the number of user induced problems.
• Any computer on the network can share its drives & printers
while running application programs. Here different computers
share their hard drives, tape drive & CD-ROM drive. Easy to
install and economical.
How Networks Work
Derfler, Freed
QUE publishers, ISBN: 0 7897 2445 6