Transcript File - Computing at Campbeltown Grammar School

Higher Computing
Networking
What you need to know about networks:
The transmission media, bandwidth,
geographical spread and functions of
LANs, WANs, intranet and internet
The functions of file, print and web servers
Network topologies
Network hardware and network software
Development trends
Networks and the law
What is a network?
A network is two or more computers linked
together
Programs, data and messages can be
exchanged between the linked computers
Local area networks
Local area network is a computer network
covering a small geographic area, like a
home, office, or group of buildings e.g. a
school.
Local area networks
The defining characteristics of LANs, in
contrast to wide-area networks (WANs),
include:
higher data-transfer rates
Shared peripherals e.g. printers
smaller geographic range
lack of a need for leased
telecommunication lines
Local area networks
Two most common types of connection
Ethernet (over unshielded twisted pair cabling)
Wi-Fi
Others
ARCNET
Token Ring
Ethernet
ARCNET
Token Ring
Network interface card
A network card, network adapter, LAN
Adapter or NIC (network interface card) is
a piece of computer hardware designed to
allow computers to communicate over a
computer network.
Network interface card
Whereas network cards used to be
expansion cards that plug into a computer
bus, the low cost and ubiquity of the
Ethernet standard means that most newer
computers have a network interface built
into the motherboard.
Network interface card
The NIC can provide the computer with a
unique network address
This is the Media Access Control address
(MAC)
Each Mac address is 6 bytes (48 bits)
which allows 248 different addresses
That is 281,474,976,710,656 possible
MAC addresses.
Wireless network interface card
A wireless network interface card allows
computers to communicate with other
computers on the LAN
For a wireless connection the computer
must be within range of the wireless base
station
WiFi is one current standard for wireless
networking
More on WNIC
Wireless hotspots
A hotspot area is an area where network
signals may be received
Hotspots can be in built up areas, parts of
buildings (offices, universities, airports etc)
or even on buses and trains
Unintentional hotspots can also be created
and “illegitimate” users can access the
wireless network
Advantages of wireless networks
Convenience
Mobility
Productivity
Deployment
Expandability
Cost
A full explanation of each advantage
Disadvantages of a wireless network
Security
Range
Reliability
Speed
A full explanation of each disadvantage
Advantages of LAN over stand alone
computers
The sharing of data; quick and convenient
The sharing of peripherals such as printers
will reduce hardware costs
Improved communications due to the
electronic mailing system that can be
implemented
Types of networks LAN
The organisation of a network can be
divided in to two basic types
Client server network
Peer to peer network
Client server network
A method of organisation in which client
workstations make use of resources
available on one or more servers
File servers
Print servers
Web servers
Mail, database and CD-Rom servers
Peer to peer network
Each workstation on a peer to peer
network has its own local storage devices
for programs and data
One node (computer) may act as a file
server, another as a printer server
Each node can also be used as a
workstation
Topology
Topology is a term used to describe
configurations of computer networks
Client server (star)
Peer to peer (full mesh)
Advantages of client server networks
 Security: Each user must log in to server
 Access: Each user can be assigned different
levels of access
 Control: All resources controlled through the
server
 Workgroups: many users can work on the same
document at the same time
 Convenience: Access data from any workstation
 Back up: Back up of all data done centrally
Advantages of peer to peer networks
 Capacity: All clients provide resources and as
more nodes are added and the demand on the
system increases the capacity of the system
also increases
 Cost: than client server as no server or server
software need to be purchased
 Ease of use: Easy to set up using current
computer operating systems (e.g. Windows XP)
 Robustness: The distributed nature of P2P
networks also increases robustness there is no
single point of failure in the system
Disadvantages of client server networks
Adding more clients could mean slower
data transfer for all users
If the file server fails the users cannot
access their data
More expensive than P2P as a server and
server software have to be purchased
Disadvantages of peer to peer networks
No central storage, user must always use
the same machine to access data
No central backup if a machine loses its
data
Less secure as users may not need to log
in
If a station goes down it data and its
assigned purpose (e.g. acting as files
server) is lost
Cost to fully connect all nodes
File server
 Provides central disk storage for user’s
programs and data
 A File server differs from a desktop computer in
that it has:
 More RAM workstations
 Faster or multiple processors
 Higher quality disk drives (more robust)
 Will have a faster connection to the network than
individual nodes (1000Mbps)
 Have a uninterruptible power supply (UPS)
File server software
File servers need specialised software to:
Organise storage of data shared data and
user data
Handle network security
Manage user accounts, including log in
Manage levels of access
Implement back up procedures (may be
separate software)
Backing up - hardware
Shared and users data need to be backed
up
Use Digital Audio Tape (DAT) storing from
1.3 to 72 GB
RAID (Redundant Array of Inexpensive
Disks); a set of hard disks linked together
and used as if they are a single backing
storage device
Backing up - software
Network operating systems can come with
back up software
Backup specific software can be
purchased
Back up schedule for a school:
Once a day, Monday to Friday
Once a week on a Wednesday
Once every four weeks
Once a term and once a year
Print server
Allows all the clients to use a printer
controlled by it
The printer server may have a spooler
program to temporarily store data on its
hard disk
The printer may have RAM which will act
as a buffer
Web server
A web server is a computer that provides
World Wide Web services to a network
A Web server may any computer that has
web server software on it and is connected
to the network
Should provide greater speed of access to
the internet
Keep files server data private
Other types of servers
Mail server
Manages an electronic mailing system
Database server
Manages a large database which may be
accessed by clients
CD-ROM server
Allows clients to access data and programs
from one or more CD-ROMs
The school network
Repeaters and hubs
A repeater is a device which boosts a
signal on a cable
A hub is a repeater with multiple ports
allowing more than one device to share
the same wire
The use of a hub can lead to the slowing
down of the network as all nodes receive
the data not just the node it was intended
for
More on hubs
Switches and routers
A switch is a “smart” hub
Only the intended recipient of data
receives it
The speed of the network is maintained
A router is a device which links two or
more networks e.g. a LAN to the internet
Connecting networks
Switch
Switch
Router
Network topologies
The network topology is the way that the
nodes are connected together
Types of topology:
Bus
Star
Ring
Mesh
Bus topology
Bus network topology is a network
architecture in which a set of clients are
connected via a shared communications
line, called a bus
Bus topology
A terminator at end of the “bus” catches
stray signals and terminates them to stop
them interfering with other signal
Terminator
Terminator
Advantages of bus topology
Easy to implement and extend
Requires less cable length than a star
topology
Well suited for temporary or small
networks not requiring high speeds (quick
setup)
Cheaper than other topologies
Disadvantages of bus topology
If there is a problem with the cable, the
entire network goes down
It works best with limited number of nodes
Disadvantages of bus topology
Performance degrades as additional
computers are added or with heavy traffic
Each bus transaction must be able to
stretch to most distant link
It is slower than the other topologies
Star topology
A network that uses a star topology has all
of the peripheral nodes connected to a
central node
Advantages of star topology
If a node or connection to the node fails it
has no effect on the rest of the network
It is easy to add extra nodes
Advantages of star topology
Speed of communication between any two
nodes is good as data goes from one node
to the other via the central node
Activity on the network can be easily
monitored via the central node
Disadvantages of star topology
A central node failure will result in the
whole network failing
Performance for the entire network is
capped by its throughput especially if a
node needs a significant amount of the
central nodes processing capability
Disadvantages of star topology
The performance and scalability of the
network also depend on the capabilities of
the central node
Network size is limited by the number of
connections that can be made to the
central node (hub)
Ring topology
In a network that uses a ring topology
each node is connected to two other
nodes
Signals are sent around the network from
node to node
Advantages of ring topology
Each node can transmit data
Does not need to go through central node
Can perform better than a star network
under heavy workload
Multistation Access Units allow the
network to function even if a node is down
by bypassing the failed node
Disadvantages of ring topology
If a cable (channel) fails between nodes
the network fails
If a node fails and there is no MAU then
the network fails
Much slower than an Ethernet network
under normal load
Disadvantages of ring topology
If a MAU fails then the network can fail
Network adapter cards and MAU's are
much more expensive than Ethernet cards
and hubs
Mesh topology
A network that uses a mesh topology has
multiple connections between each node
Fully connected mesh topology
If every node is connected to every other
node it is known as a fully connected
mesh
Advantages of mesh topology
Gives alternative routing options in the
event of node or cable failure or if one
particular route of transmission is busy
Example of a mesh topology network is
the Internet
Disadvantages of mesh topology
Expensive to connect every node to every
other node
How the topology effects performance
A bus network provides fast access but as
more nodes are added and compete with
each other to transmit and receive data
the performance of network will decrease
How the topology effects performance
Access to the central node is very fast in a
star topology but its response is
dependent on the central nodes ability to
deal with the overall workload from the
whole network
How the topology effects performance
A mesh network is the best topology in
terms of performance as each node is
directly connected to every other node
How the topology effects performance
Failure
Bus
Star
Ring
Mesh
Node
No effect
on rest of
network
Network
down if
central
node down
Failed node No effect
can be
on rest of
bypassed
network
Channel
Network
down
No effect
on rest of
network
Network
down
No effect
on rest of
network
Mainframe computer
A powerful and reliable computer system
Multi-processor and large amount of RAM
May hundreds of user terminals connected
Know as multi-user or multi-access
systems
Allows multi-tasking and multi
programming
Mainframe computer
Terminals that have no processor and no
local storage are called dumb terminals
Dumb terminals have a keyboard/mouse
and monitor and a connection to the
network
The mainframe computer will carry out all
processing and storage tasks
More on mainframes
Mainframe and Client server networks
Terminals on Mainframe Clients on a client-server
computer network
network
Dumb terminals, no
processing power
Dumb terminals, no
storage facilities
Each client has its own
processor
Each client has its own
storage e.g. hard disk
All processing done
Processing done by
centrally, multi-processing clients
Multi-user, multi access
Single user
Supercomputers
Supercomputers are the fastest and most
powerful of computers
Supercomputers use parallel processors in
order to complete tasks requiring intensive
calculations such as:
Weather forecasting
Digital animation
Climate simulations
Molecular modeling
A comparison of LAN’S, WAN’s,
Intranets and Internetwork
Criteria
LAN
WAN
Intranet
Internetwork
Share data
P
P
P
O
P
O
P
O
E-mail
P
P
P
P
Bandwidth
High
Low
Variable
Variable
Share
peripherals
Channels
owned by
organisation
Geographical Small
spread
Media
Channels Parts owned Parts owned by
owned by by others
others
others
Large
Medium
Large
Bandwidth
Bandwidth is a measure of the quantity of
data which may be carried by a
communications channel at any one time
Home ADSL
(typical)
Home ADSL
(promised)
Ethernet LAN
(client to
server)
LAN
(backbone)
512 Kbps
2-8 Mbps
100 Mbps
1 Gbps
Asymmetric Digital Subscriber Line
Trends
Increasing the bandwidth of networks both
at home and in organisation networks
Wireless communication
WiFi
Bluetooth
Zigbee
Ultra-wideband (UWB)
WiMAX
WiFi v’s WiMax
Bluetooth
Zigbee
Ultra-wideband (UWB)
Technical advances of networks
Hardware
Processors
Main memory capacity
Backing storage
Data transfer rates
Software
Browsers
Network operating systems
Misuse of networks and the law
Types of misuse
Illegal copying (individuals)
Piracy (organizations)
Hacking
Identity theft
Spyware
Phishing
Misuse of networks and the law
The laws
Copyright, Designs and Patent Act 1988
Computer Misuse Act 1990
Data Protection Act 1998
The End
Ethernet over unshielded twisted pair
cabling
 The combination of the twisted pair versions of
Ethernet for connecting end systems to the
network, along with the fiber optic versions for
site backbones, is the most widespread wired
LAN technology. It has been in use from around
1980
 to the present, largely replacing competing LAN
standards such as token ring and ARCNET
 100BASE-T -- A term for any of the three
standard for 100 Mbps Ethernet over twisted pair
cable.
Return
ARCNET
ARCNET Attached Resource Computer
NETwork) is a local area network (LAN)
protocol, similar in purpose to Ethernet or
Token Ring. ARCNET was the first widely
available networking system for
microcomputers and became popular in
the 1980s for office automation tasks
Return
Token Ring
Token ring local area network (LAN)
technology developed for use by IBM in
the 60’ and 70’s
The advent of cheaper Ethernet system
led to its demise. IBM no longer uses or
promotes token ring.
Return
Types of wireless network interface card
The card uses an antenna to communicate
through microwaves. A WNIC in a desktop
computer usually is connected using the
PCI bus. Other connectivity options are
USB and PC card. Integrated WNIC's are
also available, typically in Mini PCI/PCI
Express Mini Card form.
Return
What do the look like?
Wireless Network Interface Card
Peripheral Component Interconnect
PCI expansion slots
Mini PCI/PCI Express Mini Card
Other types
USB
Return
PC card
Advantages of wireless networks
 Convenience: The wireless nature of such networks allows users to access network
resources from nearly any convenient location within their primary networking
environment (home or office). With the increasing saturation of laptop-style
computers, this is particularly relevant.
 Mobility: With the emergence of public wireless networks, users can access the
internet even outside their normal work environment. Most chain coffee shops, for
example, offer their customers a wireless connection to the internet at little or no cost.
 Productivity: Users connected to a wireless network can maintain a nearly constant
affiliation with their desired network as they move from place to place. For a business,
this implies that an employee can potentially be more productive as his or her work
can be accomplished from any convenient location.
 Deployment: Initial setup of an infrastructure-based wireless network requires little
more than a single access point. Wired networks, on the other hand, have the
additional cost and complexity of actual physical cables being run to numerous
locations (which can even be impossible for hard-to-reach locations within a building).
 Expandability: Wireless networks can serve a suddenly-increased number of clients
with the existing equipment. In a wired network, additional clients would require
additional wiring.
 Cost: Wireless networking hardware is at worst a modest increase from wired
counterparts. This potentially increased cost is almost always more than outweighed
by the savings in cost and labor associated to running physical cables.
Return
Continue
Disadvantages of a wireless network
 Security: wireless packets be intercepted by a nearby
computer
 Range: The typical range of a common wireless network
with standard equipment is on the order of tens of
metres. While sufficient for a typical home, it will be
insufficient in a larger structure
 Reliability: Like any radio frequency transmission,
wireless networking signals are subject to a wide variety
of interference. Important network resources such as
servers are rarely connected wirelessly.
 Speed: The speed on most wireless networks (typically
1-108 Mbps) is reasonably slow compared to the slowest
common wired networks (100 Mbps up to several Gbps).
Return
The school network
Client server
File server and web and email server
Central storage of data
Central back up of data
Peer to peer printing so even if the file
server is down all clients can still be used
as stand alone machines and print
Return
Hubs
A network hub or repeater, is a fairly
unsophisticated broadcast device. Hubs
do not manage any of the traffic that
comes through them, and any packet
entering any port is broadcast out on every
other port (other than the port of entry).
Since every packet is being sent out
through every other port, packet collisions
result--which greatly impedes the smooth
flow of traffic.
Return
More on Mainframes
 Modern mainframe computers have abilities not so much
defined by their single task computational speed (MIPS
Millions of Instructions Per Second) as by their:
 redundant internal engineering and resulting high
reliability and security
 extensive input-output facilities
 strict backward compatibility for older software
 a high utilization rates to support massive throughput.
 These machines often run for years without interruption,
with repairs and hardware upgrades taking place during
normal operation.
Return
Bluetooth
 Bluetooth is a wireless protocol utilizing short-range
communications technology facilitating both voice and
data transmissions over short distances from fixed
and/or mobile devices
 Bluetooth differs from Wi-Fi in that the latter provides
higher throughput and covers greater distances, but
requires more expensive hardware and higher power
consumption. They use the same frequency range, but
employ different modulation techniques. While
Bluetooth is a replacement for a variety of applications,
Wi-Fi is a replacement only for local area network
access. Bluetooth can be thought of as wireless,
whereas Wi-Fi is wireless Ethernet
Return
Types of wireless communication
 ZigBee is the name of a specification for a suite
of high level communication protocols using
small, low-power digital radios based on the
IEEE 802.15.4 standard for wireless personal
area networks (WPANs), such as wireless
headphones connecting with cell phones via
short-range radio. The technology is intended to
be simpler and cheaper than other WPANs, such
as Bluetooth. ZigBee is targeted at radiofrequency (RF) applications that require a low
data rate, low power consumption, long battery
life, and secure networking.
Return
UWB
Ultra-wideband (UWB) is a radio
technology. It can be used at very low
energy levels for short-range highbandwidth communications by using a
large portion of the radio spectrum
UWB would allow DVD quality video to be
shared throughout the home
Return
WiMAX
 WiMAX, the Worldwide Interoperability for Microwave
Access, is a telecommunications technology aimed at
providing wireless data over long distances in a variety
of ways, from point-to-point links to full mobile cellular
type access
 WiMAX as "a standards-based technology enabling the
delivery of last mile wireless broadband access as an
alternative to cable and DSL
 Currently, Pakistan has the largest fully functional
nationwide Wimax network in the world
Return
WiFi and WiMAX comparision
 WiMAX is a long-range system, covering many kilometers that typically uses
licensed spectrum (although it is also possible to use unlicensed spectrum) to
deliver a point-to-point connection to the Internet from an ISP to an end user.
Different 802.16 standards provide different types of access, from mobile
(similar to data access via a cellphone) to fixed (an alternative to wired access,
where the end user's wireless termination point is fixed in location.)
 Wi-Fi is a shorter range system, typically hundreds of meters, that uses
unlicensed spectrum to provide access to a network, typically covering only
the network operator's own property. Typically Wi-Fi is used by an end user to
access their own network, which may or may not be connected to the Internet.
If WiMAX provides services analogous to a cellphone, Wi-Fi is more analogous
to a cordless phone.
 WiMAX and Wi-Fi have quite different Quality of Service (QoS) mechanisms.
WiMAX uses a mechanism based on setting up connections between the Base
Station and the user device. Each connection is based on specific scheduling
algorithms, which means that QoS parameters can be guaranteed for each flow.
Wi-Fi has introduced a QoS mechanism similar to fixed Ethernet, where
packets can receive different priorities based on their tags. This means that
QoS is relative between packets/flows, as opposed to guaranteed.
 WiMAX is highly scalable from what are called "femto"-scale remote stations to
multi-sector 'maxi' scale base that handle complex tasks of management and
mobile handoff functions and include MIMO-AAS smart antenna subsystems.
Return