Transcript presentation1

COMP2221
Networks
in
Organisations
Richard Henson
February 2012
Week 1: Standards and
Computer Networks

Objectives
– Explain evolution of data transmission
through networks
– Define standards
– Explain how standards work and why they
are so important for digital networks
History of Electricity-based
Communication Networks
 Used
for centuries before
organisations used Computers…

Chronologically:
– Telegraph (1840s)
– Telephone (1910s)
– Telex (1930s)
– Internet/first digital WANs (1970s)
Each network developed its
own standards for…
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Creation of data
Format of transmitted data
Voltage
Error-checking
Receiving, storing, presentation
of transmitted data
National and International
Networks
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Telegraph :transmitted data within a particular
country
– developed National standards
» e.g. in the UK… BS standard
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Telephone:
– initially National standards
– developed International calling
» French-based standards became the Internationally
recognised ones (CCITT)
» Comité Consultatif International Téléphonique et
Télégraphique
A tale of standards…

Roman Empire, AD 0
– urban streets were open sewers
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Created Passing places created
– stone paths across the street
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Needed to leave spaces for
chariot wheels
– how wide?
What width to choose?
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Standard “wheelbase” width agreed (4’ 8½’’)
Used for chariots throughout Roman Empire
Revived in UK as “standard gauge” for
railway tracks (1830s)
– most railways around the world still use the 4’ 8½
standard to this day
– even Space Shuttle was transported on 4’ 8½’’
tracks (!)
Breaking a standard?
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Why stick to standard gauge?
– everyone else uses it!
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Most powerful railway company in the UK
(GWR: The Great Western Railway) tried to
change the standard width of a track to 6’ 0’’
– used the 6’ “Broad Gauge” for all their tracks
– wider carriages, more passenger comfort…
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Other railways maintained 4’ 8½’’ !!!
GWR eventually gave up and converted all
their tracks to the standard gauge
Lessons from this story
Large, powerful organisations try to
make their own standards universal
 Existing standards are difficult to
change
 Once established, standards may well
be adopted world-wide
 Standards therefore need to be right!
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CCITT and Computer
Standards
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In the early days, CCITT laid down the
standard… (like the Romans…)
More recently, CCITT became ITU:
– International Telecommunication Union
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Through ITU, many CCITT standards applied
to computer networks:
– Group 3: protocol for sending fax documents
across (analogue) telephone lines
– Group 4: protocol for sending fax documents over
ISDN networks (more on these later)
– “V” modem standards
Comparison of Computer
& Telecoms Networks
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Information sent is digital (!)
– all prior CCITT etc. standards were
analogue…
– potential range of uses of devices are
much more flexible
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Control doesn’t have to be centralised
– fundamental difference with CCITTstandardised networks
Standards in Computing
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Area of rapid change
Early emerging standard…
– may be eclipsed by new technology
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Standards usually follow many years after the
products themselves have been on the
market
Means they are often based on specific
products (usually the market leader at the
time!)
Standards
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Definition:
– “A standard is an established or accepted model”
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Communication protocols…
– “Elements of a communication system that are
defined by an agreed set of rules, conditions,
parameters or methods”
Type of Standards
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De Facto
– A product or service that is a standard by
virtue of its widespread use by interested
users
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De Jure
– The standard devised by a committee of the
organisation or, a working group of a
subcommittee of a committee of the
organisation
Standards and IT Professionals
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Standards:
– ensure that products can communicate
– identify incompatibilities between products
– provide a check that customers are buying
the correct product
– ensure that customers are not buying a
manufacturer dependent product
ISO (International
Standards Organisation)
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Been providing International
standards for many areas
Even for management systems:
– ISO9001
– ISO14001
– ISO27001
ISO Development Process (1)
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ISO standards panel convened: experts
in the relevant field
1.decide the contents of the definition of draft
standard
2.proposal passed to the parent committee
for ratification before publication as, first, a
draft for discussion (DD)
ISO Development Process (2)
Once ratified, it becomes a draft
international standard
 Once the document has been available
for a certain amount of time…
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– allowing full scrutiny…
– it becomes a full International Standard (an
ISO)
Proprietary Systems
Big computer manufacturers in the
1960s and 1970s worked independently
to produce their own software
 Teams of researchers to develop their
own systems for communicating
between devices
 Different research teams, different
company aims, so products
incompatible
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Proprietary Systems
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Considered to be a good thing by companies
such as IBM and ICL, because it “locked”
customers into their products
Not popular with customers, who wanted to
be able to buy more freely
Also a barrier to communication:
– between companies
– sometimes between different parts of the same
company
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Because they were using incompatible
systems
Open Systems
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ISO aware that the basic infrastructure for
global digital communications was rapidly
emerging in the form of the Internet
ISO decided that the existing proprietary
isolationist stance was not condusive to the
growth of effective digital data
communications on a world-wide basis
ISO agreed that what was needed was open
systems
Open Systems
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Definition:
– “a computer system that is ‘open’ for the purpose
of information exchange”
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Open systems are therefore not restricted to
one particular manufacturers own system of
communicating
Open systems should provide the ability to:
– interchange applications and data
– between systems with different underlying
hardware and software
Open Systems Interconnect (?)
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Historic meetings in Geneva co-ordinated by
ISO (back in 1977, 1978)
Involved proprietary systems manufacturers,
telecomms companies and researchers
Agreed to produce a software model for
open systems
– accepted that this would take years to achieve
– the industry could, however, at least aspire to this
in new developments…
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Model became known as the Open Systems
Interconnection model (OSI model)
LANs, WANs, Standards
The PC changed everything…
 When it became possible to network
PCs, new sets of protocols and
technologies were developed & used
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– new classification required:
» LAN: generally applied to PC/Unix networks
within institutions (IEEE)
» WAN: existing networks that covered longer
distances (CCITT??? ISO???)
OSI Model & WAN standards
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OSI soon caught on
– challenge to CCITT
– teamed up with IEEE (802 standards)
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In 1984, OSI became an International
Standard (!)
– open systems had credibility!!!
– Proprietary systems had competition…
Why link PCs together to
make LANs (revision)
Workshop in small groups
 Each group - four reasons
 Ten minutes
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What makes up a LAN (1)?
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Hardware:
– computers and other network devices
» e.g. printers, web cameras
– transmission media, e.g. cable, radio
waves
– network cards, which link the network
devices to the transmission media
What makes up a LAN (2)?
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Software to (just a sample…)
–
–
–
–
–
send/receive data
provide an even flow of data between devices
make sure sent data goes to the right place
provide a path for data through the network
make sure data is checked for corruption as it
passes through the network
– anything else that may need to be done to the
data e.g. formatting, compression, encryption
Some reasons to keep PCs
“standalone”
Workshops again…
 Another four reasons
 Ten minutes
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Transfer of data
through LANs
Cables designed to transmit high
volumes of digital data
 Network cards provide the computermedium interface:
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– control flow rate and error checking of data
– send/receive data at high, and even
higher… speeds
LAN connections
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Computers physically connected using:
– cabling (or e/m radiation of an appropriate
frequency)
– network cards
– networking software
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If a cabled LAN connection exceeds:
– 100 metres (twisted pair cabling)
– 185 metres (coaxial cabling)
– then a repeater (booster) is needed
More about LANs
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The network card fits inside the computer:
– either as a separate card
– or on the motherboard…
– uses own software
» works with other software that bind together to control the
sending and receiving of data
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If the network is of the client-server type, more
complex server software is needed at the
“server” end
If a peer-peer network, connectivity software is
less sophisticated…
More about LANs
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Other hardware names:
– Nodes: are computers and other intelligent
devices with MAC and IP addresses
– Repeaters: boost weak digital signals
– Hubs: link devices & direct data round a
cabling system more efficiently
» most hubs are also repeaters
– Switches: powerful routers that can
process and filter the data in various ways
way, whilst hubs just send it on
Classification of Networks
by management
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Client-Server Networks
– networked computers either clients or
servers
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Peer-Peer Networks
– networked computers all of equal status
Client-Server Networks
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A client requests services from a server
Client-server interprocess communication
(IPC) fast and reliable
Types of clients:
– computer workstation (“fat” client)
– computer with limited local storage and
processing (“thin” client)
– printer with processing ability
Workstations
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Like a standalone computer in many
respects.
Differences:
– additional hardware
» e.g. network card
– include the basic networking software required:
» to allow connection to the network
» to communicate effectively with other network nodes
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All computers in a peer-peer network are
workstations
Servers
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High-powered computers
– high storage capacity
– a lot of memory
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Provides network services which are access
by users through clients
– requires a highly specialized software called a
Network Operating System (NOS)
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Examples Network Operating Systems:
– Windows NT/2000/XP/2003/Vista
– Netware
– UNIX e.g. Linux
Servers in small networks
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Scenario: a single server is the central
controlling point
The server also looks after security on the
network:
– only allows valid users to log on
– only allows access to resources for users that
have logged on
– stores appropriate “user rights” for access to its
files and directories
Servers in small networks
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This same server offers all the normal
network services:
– Applications
» when a user wants to use an application on the
server, it accesses the software from the
server
– Printing
» the user selects a printer via the server
– File Access
» users with permission directly access files on
the server
Problems with this Scenario?
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Discussion in Groups…
Possible Solutions?
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Further Discussion…
Servers in Larger Networks
Larger networks have MANY servers (the
University ITS network currently has at
least 50)
 functions can be distributed around
different individual servers. Examples:
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– Login Server
– File and Print server
– Applications Server
– Internet Gateway
Login Servers
(the most crucial!)
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Dedicated to logging on users
– database of usernames/passwords
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Only allows a potential user to access the
network if both username and password
exactly correspond with entries in the
database
– In Windows networks known as Domain
Controllers
Peer-Peer networks
Also known as workgroups
 No central server
 Computer nodes can act as both clients
and servers
 No expensive powerful machine
dedicated to providing services
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Peer-Peer networks
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No servers!
All users have the following responsibilities:
– security & network administration
– provide access to their computer’s services
and resources
Advantages & disadvantages
of Client-Server, compared to
Peer-peer
In groups…
 Don’t look at next slides!
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Advantages of a client-server
network, compared to a
workgroup
Centralised security
 Centralised access to resources
 Centralised network administration
 With more than about 10 users, much
easier to manage than a workgroup.
Can handle up to thousands of users
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Disadvantages of clientserver, compared to a
workgroup
Expensive dedicated computer not
accessible to users
 Expensive server operating system
needed
 Network management required
 Reduces user autonomy
 If the server goes down, the network
ceases to function
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Thanks for listening
