chapter 1.3 computer networks. client-server systems the question : within a large organization,...

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

tiberghien@info.vub.ac.be

info

tiberghien

email

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