Chapter 3 Applications of Data Communications Postacademic Interuniversity

Chapter 3 Applications of Data Communications Postacademic Interuniversity Course in Information Technology – Module C 1 p 1

A three layers model. Networks Layer Postacademic Interuniversity Course in Information Technology – Module C 1 Connectivity Internet & Transport Layer Interoperability Applications Layer p 2

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 C 1 p 3

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 C 1 p 4

File & Print Serving Print server File server Applications server m 4 Connectionless disc serving Connection oriented printer serving Postacademic Interuniversity Course in Information Technology – Module C 1 p 5

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 C 1 p 6

email m 4 is a mail server with a mailbox for each registered user. Connection between mail server and users can be temporary (direct or via internet) m 4 INTERNET d@m 4 a@m 1 b@m 2 Postacademic Interuniversity Course in Information Technology – Module C 1 c@m 4 d@m 4 p 7

Email Protocols pop/imap server Mail Transfer Agent m 4 (X 400) SMTP a@m 1 Exchange http b@m 2 Outlook c@m 4 Netscape Postacademic Interuniversity Course in Information Technology – Module C 1 pop 3 imap d@m 4 User Agent Eudora p 8

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 C 1 p 9

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 – 32 2 629 2905, 32 475 819327 – hierarchy jeopardized by number portability! Postacademic Interuniversity Course in Information Technology – Module C 1 p 10

Flat Addresses • Organizational and geographic hierarchy do not necessarily match • Address values contain no useful information • Example : Internet network ID’s – VUB = 134. 184 ULB = 164. 015 – KUL = 134. 058 KULAK = 193. 190 – RUG = 157. 193 • 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 C 1 p 11

Internet Domains Root uk be fgov vub tiberghien mtv ac vrt info edu com org ieee ulb lvhamme tiberghien@info. vub. ac. be Postacademic Interuniversity Course in Information Technology – Module C 1 p 12

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 C 1 p 13

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 C 1 p 14

Telnet Application X Telnet = C. O. protocol m 4 m 2 INTERNET User of X Remote terminal user Local terminal user Postacademic Interuniversity Course in Information Technology – Module C 1 p 15

Telnet To connect remote users Telnet Application X Operating system INTERNET User of X Remote terminal user Postacademic Interuniversity Course in Information Technology – Module C 1 User of X Local terminal user p 16

Telnet To interconnect application programs Application y Telnet Applications Telnet Application X Operating system INTERNET Postacademic Interuniversity Course in Information Technology – Module C 1 C. O. Telnet link p 17

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 C 1 p 18

File Transfer Protocol m 4 m 2 Internet Direct FTP user Third party FTP user Postacademic Interuniversity Course in Information Technology – Module C 1 p 19

File Transfer Protocol FTP Telnet Applications Telnet FTP Operating system INTERNET Postacademic Interuniversity Course in Information Technology – Module C 1 p 20

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 C 1 p 21

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 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 C 1 p 22

WWW page example Postacademic Interuniversity Course in Information Technology – Module C 1 p 23

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 C 1 p 24

Technically, what is it ? The WEB = Internet + HTML + URL + HTTP 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 Postacademic Interuniversity Course in Information Technology – Module C 1 p 25

Technically, what is it ? The WEB = Internet + HTML + URL + HTTP 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 Postacademic Interuniversity Course in Information Technology – Module C 1 p 26

HTML Hyper. Text 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 C 1 p 27

HTML Hyper. Text Markup Language • Physical Markup 1. (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 C 1 p 28

HTML Hyper. Text Markup Language • Semantic Markup 1. (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 C 1 p 29

Technically, what is it ? The WEB = Internet + HTML + URL + HTTP 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 Postacademic Interuniversity Course in Information Technology – Module C 1 p 30

URL Universal Resource Locator http: //www. info. vub. ac. be: 80 /webpages/info. html • Protocol used to communicate with resource (each protocol further defines URL format) • Internet Resource Address – Domain name • Internet Protocol address of machine (134. 121. 023. 001) • 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) Postacademic Interuniversity Course in Information Technology – Module C 1 p 31

Technically, what is it ? The WEB = Internet + HTML + URL + HTTP 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 Postacademic Interuniversity Course in Information Technology – Module C 1 p 32

HTTP : Hyper. Text 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 C 1 p 33

Inside the Web HTTP Server HTTP Client (Web Browser) HTTP Server HTTP Link transporting HTMLencoded hypertext HTTP Server Other Server Postacademic Interuniversity Course in Information Technology – Module C 1 Other Data Link p 34

HTTP Hypertext Transfer Protocol • Stateless (connectionless) communication protocol • Uses a connection oriented transport protocol. • Typical HTTP 1. 0 transaction: 1. Client HTTP entity opens transport connection with specified Server HTTP entity. 2. Client makes the request to the server. 3. Server sends response. 4. Server 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 C 1 p 35

HTTP Web Server Browser Client HTTP Connectionless protocol Server HTTP Transport entity Connection oriented protocol Transport entity Network Service Postacademic Interuniversity Course in Information Technology – Module C 1 p 36

HTTP is a Stateless Protocol • Benefit : performance of server • Penalty : Server can not keep information about user. Browser Client HTTP > 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 <. . Connectionless protocol Postacademic Interuniversity Course in Information Technology – Module C 1 Web Server HTTP p 37

HTTP Adding state to a Stateless Protocol The state is kept in the messages traveling between server and browser !!! Browser Client HTTP > 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 < Connectionless protocol Postacademic Interuniversity Course in Information Technology – Module C 1 Web Server HTTP p 38

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 C 1 p 39

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 20000 Hz • Perception proportional to logarithm of power Postacademic Interuniversity Course in Information Technology – Module C 1 p 40

Fourier Analysis* Any time dependant signal can be decomposed in a series of sine functions Square. Wave = 1 sin 2. . t + 1 3. 2. . t + 1 5. 2. . t + sin T 3 T 5 T * Students with inadequate mathematical background should skip this slide Postacademic Interuniversity Course in Information Technology – Module C 1 p 41

Sampled Signals F = 2. 5 k. Hz Sampling Frequency = 8 k. Hz Nyquist sampling theorem : Fs > 2 * F Postacademic Interuniversity Course in Information Technology – Module C 1 p 42

Quantization errors 0101 0100 0011 0010 0001 0000 1111 1110 1101 1100 1011 Postacademic Interuniversity Course in Information Technology – Module C 1 p 43

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 C 1 p 44

Sound Communications Common Properties • Throughput requirements (real time) – CD quality = 1. 5 Mb/s – MP 3 - 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 C 1 p 45

Sound Communications Example : MP 3 Music Server WWW and/or FTP Postacademic Interuniversity Course in Information Technology – Module C 1 p 46

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 Postacademic Interuniversity Course in Information Technology – Module C 1 p 47

Internet Telephony Low cost POTS emulation Local PSTN Internet Telephone Gateways Local PSTN Internet + Access through local PSTN - Quality dependant on network load Postacademic Interuniversity Course in Information Technology – Module C 1 p 48

PABX & Intranet for traditional POTS and data PSTN PABX Intranet PABX PSTN PABX needs to be IP compatible (H 323, … ) Postacademic Interuniversity Course in Information Technology – Module C 1 p 49

Intranet Telephony Innovative services welcome ! PSTN Intranet Public gateway PSTN Public gateway Gatekeeper (address translation) Postacademic Interuniversity Course in Information Technology – Module C 1 p 50

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 C 1 p 51

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 C 1 p 52

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 C 1 p 53

A bit map Size = 10 MBytes Postacademic Interuniversity Course in Information Technology – Module C 1 p 54

An other bit map Size = 10 MBytes Postacademic Interuniversity Course in Information Technology – Module C 1 p 55

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 C 1 p 56

A geometric construct Size = 13 KBytes Postacademic Interuniversity Course in Information Technology – Module C 1 p 57

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 C 1 p 58

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 Postacademic Interuniversity Course in Information Technology – Module C 1 p 59