Postacademic Interuniversity Course in Information Technology – Module C1p1 Chapter 3 Applications of Data Communications

Postacademic Interuniversity Course in Information Technology – Module C1p2 A three layers model. Applications Layer Internet & Transport Layer Networks Layer Connectivity Interoperability

Postacademic Interuniversity Course in Information Technology – Module C1p3 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images

Postacademic Interuniversity Course in Information Technology – Module C1p4 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images

Postacademic Interuniversity Course in Information Technology – Module C1p5 File & Print Serving Print server File server m4 Applications server Connectionless disc serving Connection oriented printer serving

Postacademic Interuniversity Course in Information Technology – Module C1p6 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images

Postacademic Interuniversity Course in Information Technology – Module C1p7 m4 INTERNET m4 is a mail server with a mailbox for each registered user. Connection between mail server and users can be temporary (direct or via internet)

Postacademic Interuniversity Course in Information Technology – Module C1p8 Protocols EudoraOutlookExchangeNetscape m4 SMTP pop3 imap (X400) http pop/imap server Mail Transfer Agent User Agent

Postacademic Interuniversity Course in Information Technology – Module C1p9 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images

Postacademic Interuniversity Course in Information Technology – Module C1p10 Hierarchical Addresses Addresses composed of meaningful fields Address = hierarchical list of domain names A domain is an organizational and/or geographic entity regrouping lower level domains or hosts. Addresses belonging to a given domain are maintained by the authority of that domain. Example : classical telephone numbers – , –hierarchy jeopardized by number portability!

Postacademic Interuniversity Course in Information Technology – Module C1p11 Flat Addresses Organizational and geographic hierarchy do not necessarily match Address values contain no useful information Example : Internet network ID’s –VUB = ULB = –KUL = KULAK= –RUG = Using large set of flat addresses user-unfriendly Solution : Assign a flat and an hierarchical address to every user and maintain a database linking both

Postacademic Interuniversity Course in Information Technology – Module C1p12 Internet Domains uk Root fgovvrt beac ulb lvhamme vub mtv ieee comorgeduinfo tiberghien

Postacademic Interuniversity Course in Information Technology – Module C1p13 Domain Name Servers In Each domain, there is at least one DNS –Name & DNS Address of all subdomains –Name & address of all hosts in the domain –DNS address of, at least, root of DNS system –Names & DNS addresses of frequently used domains Each host must know the address of one DNS Local DNS is locally maintained Caching greatly improves performance of DNS by keeping the translations of most recently accessed domains and hosts

Postacademic Interuniversity Course in Information Technology – Module C1p14 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images

Postacademic Interuniversity Course in Information Technology – Module C1p15 Telnet User of X Application X m4 Remote terminal user m2 INTERNET User of X Local terminal user Telnet = C.O. protocol

Postacademic Interuniversity Course in Information Technology – Module C1p16 Telnet To connect remote users User of X Application X Remote terminal user User of X Local terminal user Telnet INTERNET Applications Operating system

Postacademic Interuniversity Course in Information Technology – Module C1p17 Telnet To interconnect application programs Application X Telnet INTERNET Applications Operating system Application y C.O. Telnet link

Postacademic Interuniversity Course in Information Technology – Module C1p18 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images

Postacademic Interuniversity Course in Information Technology – Module C1p19 File Transfer Protocol m4 m2 Internet Direct FTP user Third party FTP user

Postacademic Interuniversity Course in Information Technology – Module C1p20 File Transfer Protocol FTPTelnet INTERNET Applications Operating system FTP

Postacademic Interuniversity Course in Information Technology – Module C1p21 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images

Postacademic Interuniversity Course in Information Technology – Module C1p22 World Wide Web Uniform hypertext based, user friendly interface for distributed databases. Inexpensive, high quality, browsers available for almost all computers. Sophisticated and application specific user’s interactivity by downloading programs to be executed on client’s workstation (Java applets). Already over 500,000,000 pages available worldwide, mainly for public relations, publicity and, to some extent, electronic commerce. Electronic commerce still restrained by security concerns.

Postacademic Interuniversity Course in Information Technology – Module C1p23 WWW page example

Postacademic Interuniversity Course in Information Technology – Module C1p24 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

Postacademic Interuniversity Course in Information Technology – Module C1p25 Technically, what is it ? HTML : hypertext Markup Language. –Hypertext = multimedia information(containing even executable programs) with references to other pieces of hypertexts. URL : Universal Resource Locator. –The address where a piece of hypertext (or other resources) can be obtained HTTP : Hypertext Transfer Protocol. - Conventions to transfer hypertexts between computers The WEB = Internet + HTML + URL + HTTP

Postacademic Interuniversity Course in Information Technology – Module C1p26 Technically, what is it ? HTML : hypertext Markup Language. –Hypertext = multimedia information(containing even executable programs) with references to other pieces of hypertexts. URL : Universal Resource Locator. –The address where a piece of hypertext (or other resources) can be obtained HTTP : Hypertext Transfer Protocol. - Conventions to transfer hypertexts between computers The WEB = Internet + HTML + URL + HTTP

Postacademic Interuniversity Course in Information Technology – Module C1p27 HTML HyperText Markup Language Hypertext –Multimedia document Normal text Graphics and images (stored in separate files) Sound (stored in separate files) Executable programs ( = applets in Java code) –References to other hypertext documents (“Anchors”) “clickable” normal text or image (icon) address (URL) where the corresponding document can be found

Postacademic Interuniversity Course in Information Technology – Module C1p28 HTML HyperText Markup Language Physical Markup (used for textprocessors, not in “pure” HTML) –Functional role of contents is not mentioned –Describes how the document should look “new page”; “use font ‘Times-Roman 24’ “ “Print ‘Teleprocessing’ page-centered” –Presentation imposed by author of document –What You See Is What You Get (WYSIWYG)

Postacademic Interuniversity Course in Information Technology – Module C1p29 HTML HyperText Markup Language Semantic Markup (used in original HTML) –Functional role of contents is described “Main Title ‘Teleprocessing’ “ –Presentation defined by interpreter settings Text only / graphics, Black & white / color,... Braille. –What You Get Is What You Meant (WYGIWYM)

Postacademic Interuniversity Course in Information Technology – Module C1p30 Technically, what is it ? HTML : hypertext Markup Language. –Hypertext = multimedia information(containing even executable programs) with references to other pieces of hypertexts. URL : Universal Resource Locator. –The address where a piece of hypertext (or other resources) can be obtained HTTP : Hypertext Transfer Protocol. - Conventions to transfer hypertexts between computers The WEB = Internet + HTML + URL + HTTP

Postacademic Interuniversity Course in Information Technology – Module C1p31 URL Universal Resource Locator Protocol used to communicate with resource (each protocol further defines URL format) Internet Resource Address –Domain name Internet Protocol address of machine ( ) Domain Server Name of machine (infoweb.vub.ac.be) –Port number on machine Optional : Each protocol has a default port number Resource details (protocol specific) (i.e. directory and filename of an HTML page) http: 80 //

Postacademic Interuniversity Course in Information Technology – Module C1p32 Technically, what is it ? HTML : hypertext Markup Language. –Hypertext = multimedia information(containing even executable programs) with references to other pieces of hypertexts. URL : Universal Resource Locator. –The address where a piece of hypertext (or other resources) can be obtained HTTP : Hypertext Transfer Protocol. - Conventions to transfer hypertexts between computers The WEB = Internet + HTML + URL + HTTP

Postacademic Interuniversity Course in Information Technology – Module C1p33 HTTP HTTP : HyperText Transfer Protocol. –HTTP Client : a Web Browser Presenting information encoded in HTML. Translating user interactions into the HTTP. –HTTP Server : a process interpreting client requests Sending pieces of hypertext stored in HTML Translating information available in other formats acquiring information from outside the Web.

Postacademic Interuniversity Course in Information Technology – Module C1p34 Inside the Web HTTP Client (Web Browser) HTTP Server Other ServerHTTP Server HTTP Link transporting HTML- encoded hypertext Other Data Link

Postacademic Interuniversity Course in Information Technology – Module C1p35 HTTP Hypertext Transfer Protocol Stateless (connectionless) communication protocol Uses a connection oriented transport protocol. Typical HTTP 1.0 transaction: 1Client HTTP entity opens transport connection with specified Server HTTP entity. 2Client makes the request to the server. 3Server sends response. 4Server closes transport connection. Some HTTP implementations allow looping through steps 2 and 3 (Keep-alive) to transfer entire hypertext pages with images and sound in one HTTP transaction.

Postacademic Interuniversity Course in Information Technology – Module C1p36 HTTP Network Service Transport entity Transport entity Connection oriented protocol Server HTTP Connectionless protocol Client HTTP Browser Web Server

Postacademic Interuniversity Course in Information Technology – Module C1p37 HTTP is a Stateless Protocol Benefit : performance of server Penalty : Server can not keep information about user. > show me my bank transactions Give your name and password < > XYZ, ****** OK, what do you want < > show me my bank transactions Give your name and password <.... Server HTTP Connectionless protocol Client HTTP Browser Web Server

Postacademic Interuniversity Course in Information Technology – Module C1p38 HTTP Adding state to a Stateless Protocol The state is kept in the messages traveling between server and browser !!! Server HTTP Connectionless protocol Client HTTP Browser Web Server > I want to log into the server Give your name and password < > XYZ, ****** OK, here is your key 478 < > show me my bank records, my key is 478. Here are your bank records < $$$$$$$$$ < If you need more use key 953 <

Postacademic Interuniversity Course in Information Technology – Module C1p39 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images

Postacademic Interuniversity Course in Information Technology – Module C1p40 Digital Sound Sound= variation in air pressure Air pressure= continuous time function To digitize sound the pressure function is sampled periodically and the corresponding pressure memorized Any sound= sum of sine waves (pure sounds) Human ear can perceive pressure variations in the frequency range 25 Hz to Hz Perception proportional to logarithm of power

Postacademic Interuniversity Course in Information Technology – Module C1p41 Fourier Analysis* Any time dependant signal can be decomposed in a series of sine functions  T 5.2. .t sin 5 1 T 3.2. .t sin 3 1 T 2. .t 1 sinSquareWave * Students with inadequate mathematical background should skip this slide

Postacademic Interuniversity Course in Information Technology – Module C1p42 Sampled Signals F = 2.5 kHzSampling Frequency = 8 kHz Nyquist sampling theorem : Fs > 2 * F

Postacademic Interuniversity Course in Information Technology – Module C1p43 Quantization errors

Postacademic Interuniversity Course in Information Technology – Module C1p44 Speech Redundancies Time domain redundancies –Nonuniform amplitude distributions –Sample-to sample correlation (~0.85) –Cycle-to-cycle correlation (= periodicity) –Pitch interval to pitch interval correlation –Inactivity factors (Speech pauses ~ 40%) Frequency domain redundancies –Non uniform long term spectral densities –Sound specific short term spectral densities

Postacademic Interuniversity Course in Information Technology – Module C1p45 Sound Communications Common Properties Throughput requirements (real time) –CD quality = 1.5 Mb/s –MP3 - CD quality= 128 Kb/s –Classical telephony = 64 Kb/s –GSM telephony= 13 Kb/s –Synthetic voice= 2.4 Kb/s Transmission errors almost harmless Full duplex communications –Connection oriented application –Very sensitive to delays One way communications –Connectionless or connection oriented –Sensitive to delay jitter if listening in real time

Postacademic Interuniversity Course in Information Technology – Module C1p46 Sound Communications Example : MP3 Music Server WWW and/or FTP

Postacademic Interuniversity Course in Information Technology – Module C1p47 Voice over the Internet The initial goal : free international calls Internet Sound enabled PC (full duplex) -To communicate, precise appointments need to be made,... by phone ?!? -Voice quality dependent from network delays -Acceptable if network not overloaded Sound enabled PC (full duplex)

Postacademic Interuniversity Course in Information Technology – Module C1p48 Internet Telephony Internet +Access through local PSTN -Quality dependant on network load Local PSTN Local PSTN Internet Telephone Gateways Low cost POTS emulation

Postacademic Interuniversity Course in Information Technology – Module C1p49 PABX & Intranet for traditional POTS and data Intranet PABX PSTN PABX needs to be IP compatible (H323, … )

Postacademic Interuniversity Course in Information Technology – Module C1p50 Intranet Telephony Innovative services welcome ! Intranet Gatekeeper (address translation) Public gateway PSTN Public gateway PSTN

Postacademic Interuniversity Course in Information Technology – Module C1p51 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images

Postacademic Interuniversity Course in Information Technology – Module C1p52 Image Sampling Images decomposed into matrix of pixels A pixel has a uniform color and luminosity Size of pixel < size of smallest detail of image Too large pixels => spatial aliasing Finite resolution for color and luminosity => Quantization errors. For communication purposes, properties of pixels are transmitted sequentially.

Postacademic Interuniversity Course in Information Technology – Module C1p53 Graphical encoding Bit Maps (.bmp files in DOS) –Luminosity and color of each point of a regular raster is encoded –Very versatile but requires a lot of memory. Geometric coding : –Straight lines between two points –circle with given center, radius, color and intensity –Very efficient for computer generated images Conversions –Geometric coding > bit maps : OK –Bit maps > Geometric coding : Very Difficult: =Tif, gif, jpeg, mpeg,...

Postacademic Interuniversity Course in Information Technology – Module C1p54 A bit map Size = 10 MBytes

Postacademic Interuniversity Course in Information Technology – Module C1p55 An other bit map Size = 10 MBytes

Postacademic Interuniversity Course in Information Technology – Module C1p56 Graphical encoding Bit Maps (.bmp files in DOS) –Luminosity and color of each point of a regular raster is encoded –Very versatile but requires a lot of memory. Geometric coding : –Straight lines between two points –circle with given center, radius, color and intensity –Very efficient for computer generated images Conversions –Geometric coding > bit maps : OK –Bit maps > Geometric coding : Very Difficult: =Tif, gif, jpeg, mpeg,...

Postacademic Interuniversity Course in Information Technology – Module C1p57 A geometric construct Size = 13 KBytes

Postacademic Interuniversity Course in Information Technology – Module C1p58 Graphical encoding Bit Maps (.bmp files in DOS) –Luminosity and color of each point of a regular raster is encoded –Very versatile but requires a lot of memory. Geometric coding : –Straight lines between two points –circle with given center, radius, color and intensity –Very efficient for computer generated images Conversions –Geometric coding > bit maps : OK –Bit maps > Geometric coding : Very Difficult: =Tif, gif, jpeg, mpeg,...

Postacademic Interuniversity Course in Information Technology – Module C1p59 Introduced concepts File and printer serving Telnet = tool for interactively using remote computers FTP = tool for transferring files WWW = Interface for accessing distributed databases –Hypertext –Universal Resource Locator Multi-media applications –Sufficient Sampling frequency in time or space –Sufficient resolution –Contents dependant data compression possible