chapter 1.3 computer networks. client-server systems the question : within a large organization,...
TRANSCRIPT
Chapter 1.3
Computer Networks
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
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
Centralized Data Processing
Star Network
Mainframe Computer
Dumb Terminals
Benefits :
Professional Data Management
Enforceable Security
Simple Access to Common Data
Well Defined Cost
Full control by EDP people
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
Technical arguments against
Central ComputersProcessing Power of a single CPU
can not grow indefinitely
Transmission capacity neededbetween
processor and terminalhas become enormous
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
Technical arguments against
Central ComputersProcessing Power of a single CPU
can not grow indefinitely
Transmission capacity neededbetween
processor and terminalhas become enormous
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
Independent Personal Computers
The Reaction :
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 !
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
Client - Server Systems
Many computers
with characteristics matching
their specific usage
interconnected by means of
a network
Client - Server Systems
Interconnection Network
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)
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
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 !!!
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
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
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
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)
Network TechnologyData Transmission over the
Public Switched Telephone Network
PSTN<=
30Kb/s
Network TechnologyData Transmission over the
Integrated Services Digital Network
ISDN=
64Kb/s
Network TechnologyInternet Service Provider Access
over an Hybrid Network
ISDN=
64Kb/s
56Kb/s
ISP ISP
Network TechnologyData Transmission over Data Networks
PrivateAccessPublic
Access
PSTN
Private Data Network(Banksys,...)
The Early ARPANET (1976)
Hawaii
London
Satellite link
56 Kbps terrestrial link
The INTERNETCooperative interconnection of
local area networks
BELNET
RESULBVUBNET
RUGNET KULNET
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
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 ???
A D S Lfor residential Internet
access
ROUTER
ADSL ADSL
SW
Subscriber's line
600 Kb/s6 Mb/s
Analog Voice
Co-locatedequipment
Data over Cable TV
frequency
VTM RTBF BRTN RTLReturn
7-8 MHz
Data
Cablemodem
Cablemodem
ROUTER
SW
Co-locatedequipment
TVCablehead
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
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.
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
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
Internet Domains(= internet distributed
directory)
uk
Root
be brtn
be
ac
ulb
lvhamme
vub
mtv ieee
com orgedu
info
tiberghien
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
IRC
Internet
Telnet
User of X
Application X
m4
Remote terminal user
m2
INTERNET
User of X
Local terminal user
Telnet
File Transfer Protocol
m4m2
Internet
Direct FTP userThird party FTP user
Internet Telephony
Internet
+ Access through local PSTN- Quality dependant from network load
LocalPSTN
LocalPSTN
Internet TelephoneGateways
Low costPOTS
emulation
Network File System
Intranet
Sharedfilesystem