chapter 1.3 computer networks. client-server systems the question : within a large organization,...
TRANSCRIPT
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Chapter 1.3
Computer Networks
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Client-Server systems
• The question :
Within a large organization, what is the optimal localization of
– Processing power
– Data storage
• The possibilities :– In a global computer center
– In local computer centers
– With the user
– Any combination of the three previous solutions
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Client-Server systems
• The question :
What is the optimal localization of– Processing power
– Data storage
• The possibilities :– In a global computer center
– In local computer centers
– With the user
– Any combination of the three previous solutions
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Centralized Data Processing
Star Network
Mainframe Computer
Dumb Terminals
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Benefits :
Professional Data Management
Enforceable Security
Simple Access to Common Data
Well Defined Cost
Full control by EDP people
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But...
Mainframe Computer
Processing power limited by physics !
1 GIPS : 10-9 s/instruction : d < 30 cm
1 TIPS : 10-12 s/instruction : d < 0.3 mm
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Technical arguments against
Central ComputersProcessing Power of a single CPU
can not grow indefinitely
Transmission capacity neededbetween
processor and terminalhas become enormous
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But...
Graphic User Interfaces put extreme
stress on communications !
This screen = 892,800 bytes
transmitting it at 56 Kb/s takes 124 s.
Mainframe Computer
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Technical arguments against
Central ComputersProcessing Power of a single CPU
can not grow indefinitely
Transmission capacity neededbetween
processor and terminalhas become enormous
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Client-Server systems
• The question :
What is the optimal localization of– Processing power
– Data storage
• The possibilities :– In a global computer center
– In local computer centers
– With the user
– Any combination of the three previous solutions
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Independent Personal Computers
The Reaction :
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But ...
Access to common data ???
Risk of loss of data !
Cost of some peripheral equipment
Software Maintenance !
Limited processing power
And many other hidden costs !
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Client-Server systems
• The question :
What is the optimal localization of– Processing power
– Data storage
• The possibilities :– In a global computer center
– In local computer centers
– With the user
– Any combination of the three previous solutions
![Page 14: Chapter 1.3 Computer Networks. Client-Server systems The question : Within a large organization, what is the optimal localization of –Processing power](https://reader036.vdocument.in/reader036/viewer/2022070409/56649e7e5503460f94b82193/html5/thumbnails/14.jpg)
Client - Server Systems
Many computers
with characteristics matching
their specific usage
interconnected by means of
a network
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Client - Server Systems
Interconnection Network
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Networked Computers Benefits
Sharing of disk space(= access to common data & programs)
(= centralized disk back-up facilities)
Sharing of processing power
Sharing of expensive peripherals(Spooling required)
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Client Server Systems
Minimal integration:
“Terminal Emulation”Very User Unfriendly
Full Integration:
“Virtual Mainframe”The user has the feeling all resources
of all networked computers are
part of her/his personal computer
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Terminal Emulation
= sub-minimal Client-server system
• The personal workstations are used
– as stand alone computers
– as terminals connected to other computers
• The user has to mentally switch between widely
different user interfaces and operating systems.
• Transferring data between local and remote
applications is far from trivial
• Terminal emulation is very user unfriendly !!!
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Client Server Systems
Minimal integration:
“Terminal Emulation”Very User Unfriendly
Full Integration:
“Virtual Mainframe”The user has the feeling all resources
of all networked computers are
part of her/his personal computer
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Virtual Mainframe= true Client-Server
system• The users interface of all applications runs on the
personal workstations.
• For some applications, the workstation requests help from specialized servers. The user remains unaware of such requests.
• Servers can be optimized for specific tasks
• Virtual Mainframes can be
– Very user friendly
– cost effective
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Network Technology
Local Area NetworksIn a room, a building, a campus
High throughput, low delays, low cost
VUBNET:
10-100 Mbit/s in buildings
Twisted pairs / coaxial cables
1 Gbit/s between buildings
Optical Fibers
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Network Technology
Wide Area NetworksAll over the world
Low throughput, high delays, high cost
Leased lines:
From Brussels to
64 Kb/s2 Mb/s
Antwerp
4005 000
Paris
1.60020.000
New York
2.50030.000
(Indicative prices in Euro per month)
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Network TechnologyData Transmission over the
Public Switched Telephone Network
PSTN<=
30Kb/s
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Network TechnologyData Transmission over the
Integrated Services Digital Network
ISDN=
64Kb/s
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Network TechnologyInternet Service Provider Access
over an Hybrid Network
ISDN=
64Kb/s
56Kb/s
ISP ISP
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Network TechnologyData Transmission over Data Networks
PrivateAccessPublic
Access
PSTN
Private Data Network(Banksys,...)
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The Early ARPANET (1976)
Hawaii
London
Satellite link
56 Kbps terrestrial link
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The INTERNETCooperative interconnection of
local area networks
BELNET
RESULBVUBNET
RUGNET KULNET
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Internet Cost Structure
RARE
- Backbone infrastructure and neutral interconnects paid by interconnected networks, proportional to their access bandwidth.- Cost of direct interconnects shared by partners.- Not ACTUAL but POTENTIAL traffic is charged.
USA
Surfnet
Planet
Uunet
NLBelnet
eunet
SkynetPlanet
Uunet
BE
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Private Internet Access• Via Internet Service Provider
• Main problem : local access line– Via PSTN or ISDN• Low throughput• time based charges• conflicting with phone and fax
– Via ADSL or Cable TV• High throughput• Volume based charges• No Conflict with phone, fax or TV
– Via Wireless link• GSM : slow & expensive• GPRS : much better but not yet widely used• UMTS : the wireless paradise ???
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A D S Lfor residential Internet
access
ROUTER
ADSL ADSL
SW
Subscriber's line
600 Kb/s6 Mb/s
Analog Voice
Co-locatedequipment
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Data over Cable TV
frequency
VTM RTBF BRTN RTLReturn
7-8 MHz
Data
Cablemodem
Cablemodem
ROUTER
SW
Co-locatedequipment
TVCablehead
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Internet Usage
Electronic Mail
Remote Login (TELNET)
File transfers (FTP)
Access to distributed multimedia databases (World Wide Web)
Internet Real-time Chat
Network File System
Internet Telephony
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World Wide Web
• Uniform hypertext based users friendly interface for distributed databases.
• Inexpensive, high quality, browsers available for almost all computers.
• Sophisticated and application specific users interactivity possible by downloading programs to be executed on client’s workstation (Java).
• Already over 200,000,000 pages available worldwide, mainly for public relations, publicity and, to some extent, electronic commerce.
• Electronic commerce still restrained by security concerns.
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HTMLHyperText Markup
Language • Hypertext
– Multimedia document
» Normal text
» Graphics and images (stored in separate files)
» Sound (stored in separate files)
» Executable programs (Java Applets)
– References of other hypertext documents (“Anchors”)
» “clickable” normal text or image (icon)
» address (URL) where the corresponding document can be found
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Search Engines
• Finding information becomes more and more
difficult due to the amount of information.
• Automated indexing services, searching all
available databases on the Internet and setting up
keyword databases are very popular.
• Good ranking of keywords can be purchased from
indexing services.
• Many sites use tricks to be favorably presented by
search engines
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Internet Domains(= internet distributed
directory)
uk
Root
be brtn
be
ac
ulb
lvhamme
vub
mtv ieee
com orgedu
info
tiberghien
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a@m1 d@m4c@m4b@m2
m4
d@m4
INTERNET
m4 is a “pop server”, with a mailbox for each registered user.
Connection between pop server and users can be temporary
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IRC
Internet
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Telnet
User of X
Application X
m4
Remote terminal user
m2
INTERNET
User of X
Local terminal user
Telnet
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File Transfer Protocol
m4m2
Internet
Direct FTP userThird party FTP user
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Internet Telephony
Internet
+ Access through local PSTN- Quality dependant from network load
LocalPSTN
LocalPSTN
Internet TelephoneGateways
Low costPOTS
emulation
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Network File System
Intranet
Sharedfilesystem