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 : s/instruction : d < 30 cm 1 TIPS : s/instruction : d < 0.3 mm

Technical arguments against Central Computers Processing Power of a single CPU can not grow indefinitely Transmission capacity needed between processor and terminal has 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 Computers Processing Power of a single CPU can not grow indefinitely Transmission capacity needed between processor and terminal has 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 Networks In a room, a building, a campus High throughput, low delays, low cost VUBNET: Mbit/s in buildings Twisted pairs / coaxial cables 1 Gbit/s between buildings Optical Fibers

Network Technology Wide Area Networks All over the world Low throughput, high delays, high cost Leased lines: From Brussels to 64 Kb/s 2 Mb/s Antwerp Paris New York (Indicative prices in Euro per month)

Network Technology Data Transmission over the Public Switched Telephone Network PSTN <= 30Kb/s

Network Technology Data Transmission over the Integrated Services Digital Network ISDN = 64Kb/s

Network Technology Internet Service Provider Access over an Hybrid Network ISDN = 64Kb/s 56Kb/s ISP

Network Technology Data Transmission over Data Networks Private Access Public Access PSTN Private Data Network (Banksys,...)

The Early ARPANET (1976) Hawaii London Satellite link 56 Kbps terrestrial link

The INTERNET Cooperative interconnection of local area networks BELNET RESULB VUBNET 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 NL Belnet eunet Skynet Planet 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 L for residential Internet access ROUTER ADSL SW Subscriber's line 600 Kb/s 6 Mb/s Analog Voice Co-located equipment

Data over Cable TV frequency VTMRTBFBRTNRTLReturn 7-8 MHz Data Cable modem Cable modem ROUTERSW Co-located equipment TV Cablehead

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.

HTML HyperText 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 Rootbe brtn beac ulb lvhamme vub mtv ieee comorgedu info tiberghien

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 m4 m2 Internet Direct FTP user Third party FTP user

Internet Telephony Internet +Access through local PSTN -Quality dependant from network load Local PSTN Local PSTN Internet Telephone Gateways Low cost POTS emulation

Network File System Intranet Shared file system