1. 09-07-K.Steenhaut & J.Tiberghien - VUB 1 Telecommunications Concepts Chapter 1.3 Some Applications

2. 09-07-K.Steenhaut & J.Tiberghien - VUB 2 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images Side Tracks –Data compression –Person to person communications

3. 09-07-K.Steenhaut & J.Tiberghien - VUB 3 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images Side Tracks –Data compression –Person to person communications

4. 09-07-K.Steenhaut & J.Tiberghien - VUB 4 Applications, File & Print Serving Print server File server m4 Applications server

5. 09-07-K.Steenhaut & J.Tiberghien - VUB 5 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images Side Tracks –Data compression –Person to person communications

6. 09-07-K.Steenhaut & J.Tiberghien - VUB 6 email a@m1 d@m4c@m4 b@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 (direct or via internet)

7. 09-07-K.Steenhaut & J.Tiberghien - VUB 7 Email Protocols Eudora Outlook Exchange Netscape a@m1 d@m4 c@m4 b@m2 m4 SMTP pop3 imap (X400) http Pop/imap server Mail Transfer Agent (X400) User Agent

8. 09-07-K.Steenhaut & J.Tiberghien - VUB 8 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images Side Tracks –Data compression –Person to person communications

9. 09-07-K.Steenhaut & J.Tiberghien - VUB 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!

10. 09-07-K.Steenhaut & J.Tiberghien - VUB 10 Flat Addresses Organizational and geographic hierarchy do not necessarily match Address values contain no useful information Example : Internet network ID’s –VUB = 134.184ULB = 164.15 –KUL = 134.58 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

11. 09-07-K.Steenhaut & J.Tiberghien - VUB 11 Internet Domains uk Rootibm vrt beac ulb dhondt vub mtv ieee comorgedu tiberghien@info.vub.ac.be etro tiberghien

12. 09-07-K.Steenhaut & J.Tiberghien - VUB 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 Address resolution can be done recursively or by successive calls to different DNS Local DNS is locally maintained Caching greatly improves performance of DNS by keeping the translations of most recently accessed domains and hosts

13. 09-07-K.Steenhaut & J.Tiberghien - VUB 13 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images Side Tracks –Data compression –Person to person communications

14. 09-07-K.Steenhaut & J.Tiberghien - VUB 14 Telnet User of X Application X m4 Remote terminal user m2 INTERNET User of X Local terminal user Telnet

15. 09-07-K.Steenhaut & J.Tiberghien - VUB 15 Telnet To connect remote users User of X Application X Remote terminal user User of X Local terminal user Telnet INTERNET Applications Operating system

16. 09-07-K.Steenhaut & J.Tiberghien - VUB 16 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images Side Tracks –Data compression –Person to person communications

17. 09-07-K.Steenhaut & J.Tiberghien - VUB 17 File Transfer Protocol m4 m2 Internet Direct FTP user Third party FTP user

18. 09-07-K.Steenhaut & J.Tiberghien - VUB 18 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images Side Tracks –Data compression –Person to person communications

19. 09-07-K.Steenhaut & J.Tiberghien - VUB 19 World Wide Web Uniform, hypertext based, user friendly interface for distributed databases. Inexpensive, high quality, browsers available for almost all computers. Well over 10 9 pages available worldwide, mainly for public relations, publicity and electronic commerce. Electronic commerce still somewhat restrained by security concerns and by logistics.

20. 09-07-K.Steenhaut & J.Tiberghien - VUB 20 Technically, what is the Web ? The WEB = Internet + HTML + URL + HTTP HTML = Hypertext Mark-up language –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

21. 09-07-K.Steenhaut & J.Tiberghien - VUB 21 Technically, what is the Web ? The WEB = Internet + HTML + URL + HTTP 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 (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) http: 80 //infoweb.vub.ac.be:80/webpages/info.html

22. 09-07-K.Steenhaut & J.Tiberghien - VUB 22 Inside the Web HTTP Client (Web Browser) HTTP Server Other Server HTTP Server HTTP Link transporting HTML- encoded hypertext Other Data Link

23. 09-07-K.Steenhaut & J.Tiberghien - VUB 23 Technically, what is the Web ? 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. –Stateless (connectionless) communication protocol –Uses a connection oriented transport protocol. The WEB = Internet + HTML + URL + HTTP

24. 09-07-K.Steenhaut & J.Tiberghien - VUB 24 HTTP Hypertext Transfer Protocol Network Service Transport entity Transport entity Connection oriented protocol Client HTTP Server HTTP Connectionless protocol Browser Web Server

25. 09-07-K.Steenhaut & J.Tiberghien - VUB 25 HTTP is a Stateless Protocol Benefit : performance of server Penalty : Server can not keep information about user. Client HTTP Server HTTP Connectionless protocol Browser Web Server > 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 <....

26. 09-07-K.Steenhaut & J.Tiberghien - VUB 26 HTTP is a Stateless Protocol Logging in a stateless server : Client HTTP Browser Server HTTP 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 <....

27. 09-07-K.Steenhaut & J.Tiberghien - VUB 27 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 some indexing services. Many sites use tricks to be favorably presented by search engines

28. 09-07-K.Steenhaut & J.Tiberghien - VUB 28 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images Side Tracks –Data compression –Person to person communications

29. 09-07-K.Steenhaut & J.Tiberghien - VUB 29 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 Time functions= sum of sine functions Human ear can perceive pressure variations in the frequency range 25 Hz to 20000 Hz Perception proportional to logarithm of power

30. 09-07-K.Steenhaut & J.Tiberghien - VUB 30 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

31. 09-07-K.Steenhaut & J.Tiberghien - VUB 31 Sampled Signals F = 2.5 kHzSampling Frequency = 8 kHz Nyquist sampling theorem : Fs > 2 * F

32. 09-07-K.Steenhaut & J.Tiberghien - VUB 32 Sampled Signals F = 2.5 kHzSampling Frequency = 8 kHz Nyquist sampling theorem : Fs > 2 * F

33. 09-07-K.Steenhaut & J.Tiberghien - VUB 33 Aliasing F1 = 2.5 kHz F2 = 5.5 kHz Sampling frequency = 8 kHz Undersampling causes irrecoverable frequency shifts called “aliasing errors”.

34. 09-07-K.Steenhaut & J.Tiberghien - VUB 34 A to D conversion x 8 kHz sampling clock AD Anti- aliasing filter Cut-off frequency < 4 KHz

35. 09-07-K.Steenhaut & J.Tiberghien - VUB 35 Quantization errors 0101 0100 0011 0010 0001 0000 1111 1110 1101 1100 1011

36. 09-07-K.Steenhaut & J.Tiberghien - VUB 36 Data rates for sound Based on subjective quality tests High quality stereo music (CD) : 1.5 Mb/s –Sampling = 44 100 Hz, 2 * 16 bits / sample. Standard telephony (ISDN) : 64 Kb/s –Sampling = 8 000 Hz, 8 bits / sample. Voice and music contain redundancies –Data-compression techniques applicable »Music MP3, CD quality = 128 Kb/s »GSM telephony = 13 Kb/s –Dedicated compression techniques cause serious distortion if applied to other signals.

37. 09-07-K.Steenhaut & J.Tiberghien - VUB 37 Sound Communications Example : MP3 Music Server http and/or FTP Transmission delays cause no harm !

38. 09-07-K.Steenhaut & J.Tiberghien - VUB 38 Internet Telephony (Skype) Internet -Free if both ends on the Internet -Local call charges if one end on PSTN -Voice quality dependent on network delays -Acceptable if network not overloaded Pots Gateway PSTN

39. 09-07-K.Steenhaut & J.Tiberghien - VUB 39 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images Side Tracks –Data compression –Person to person communications

40. 09-07-K.Steenhaut & J.Tiberghien - VUB 40 Names vs. Addresses A name identifies a service –The mail service of a specific person (mailbox) –The web service of a specific company An address specifies a host on which services are available Several names can be linked with a single address – jacques.tiberghien@ulb.ac.bejacques.tiberghien@ulb.ac.be – tiberghien@vub.ac.betiberghien@vub.ac.be Several addresses can be linked with a single name –Redundant web servers DNS assumes stable links between names and addresses –Machines offering services have stable addresses

41. 09-07-K.Steenhaut & J.Tiberghien - VUB 41 Beyond DNS For some applications DNS is insufficient –Internet telephony = person to person service –At different times, people are at different locations –Personal computers seldom have a unique address –One person can be reached through different devices, with different service levels. Session Initiation Protocol (SIP, RFC 3261) –A SIP server is an agent that handles multi-media services for one or several people: »As any server, it has a stable address »It knows the present address of the people it works for »It establishes and manages connections between multi- media communicating applications.

42. 09-07-K.Steenhaut & J.Tiberghien - VUB 42 Session Initiation Protocol Cathy@info.vub.ac.be The SIP server can handle both diversity in terminals and mobility of terminals

43. 09-07-K.Steenhaut & J.Tiberghien - VUB 43 Home network Visited network SIP in Redirection mode Callers network SIP Redirection server Mobility management Session set-up Actual Data transfer Most efficient data transfer Caller has access to actual called address

44. 09-07-K.Steenhaut & J.Tiberghien - VUB 44 Home network Visited network SIP in Proxy mode Callers network SIP Proxy server Mobility management Session set-up Actual Data transfer Longer transmission delays SIP server can be bottleneck Caller has no access to the actually called address

45. 09-07-K.Steenhaut & J.Tiberghien - VUB 45 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images Side Tracks –Data compression –Person to person communications

46. 09-07-K.Steenhaut & J.Tiberghien - VUB 46 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 moving pictures, spatial and temporal aliasing can occur (e.g. wheel revolving in wrong direction).

47. 09-07-K.Steenhaut & J.Tiberghien - VUB 47 Bit Maps Luminosity and color of each point of a regular raster is encoded Very versatile but requires a lot of memory. In MS Windows, files with a.bmp suffix are bit maps. Size = 10 MBytes

48. 09-07-K.Steenhaut & J.Tiberghien - VUB 48 Geometric coding of images Straight lines between two points circle with given center, radius, color and intensity … Very efficient for computer generated images Size = 280 KBytesSize = 13 KBytes

49. 09-07-K.Steenhaut & J.Tiberghien - VUB 49 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 Geometric coding > bit maps : simple Bit maps > Geometric coding : Complex feature extracting algorithms: jpeg, mpeg,...

50. 09-07-K.Steenhaut & J.Tiberghien - VUB 50 Contents Data Communications Applications –File & print serving –Mail –Domain Name Server –Telnet –File Transfer Protocol –World Wide Web Multi-media Applications –Voice –Images Side Tracks –Data compression –Person to person communications

51. 09-07-K.Steenhaut & J.Tiberghien - VUB 51 frequencycodenbr of bitscodenbr of bits red50%0010000500 yellow12.5%11250111375 blue25%0150010500 green12.5%10250110375 Data Compression total20001750 Four colors encoding 1000 colors, non-uniform distribution

52. 09-07-K.Steenhaut & J.Tiberghien - VUB 52 frequencycodenbr of bitscodenbr of bits red25%005000 yellow25%11500111 blue25%0150010 green25%10500110 250 750 500 750 Data Compression total20002250 Four colors encoding 1000 colors, uniform distribution

53. 09-07-K.Steenhaut & J.Tiberghien - VUB 53 Data Compression Shannon’s Law Minimal Number of bits per symbol : n min = -  i p i log 2 p i In the four colors example: Non-uniform: Uniform: 0.5 + 0.5 + 0.375 + 0.375 = 1.75 0.5 + 0.5 + 0.5 + 0.5 = 2.00

54. 09-07-K.Steenhaut & J.Tiberghien - VUB 54 Data Compression Entropy coding : –based on symbol frequency –No loss of information –used for data compression and storage –Examples »Huffman coding : variable length codes See colors example »run length encoding : repetition factors 123333320000000123333333311111112234 >12#532#7012#83#712234 Example : Zip - Unzip

55. 09-07-K.Steenhaut & J.Tiberghien - VUB 55 Data Compression Source coding : –based on meaning of data –acceptable loss of information –used for data compression and storage –spectacular compression rates –Examples »GSM vocoders : only for human voice 64 Kb/s > 13 Kb/s or 6.5 Kb/s »JPEG : still images, compression 1:20 »MPEG : TV images, compression 1:100

56. 09-07-K.Steenhaut & J.Tiberghien - VUB 56 Introduced concepts Distributed address management Person to person vs. address to address Universal Resource Locator Hypertext Fourier : any function = sum sine functions Nyquist : –F sampling >= 2 * F max In analog signal –Aliasing occurs if F sampling < 2 * F max Shannon : –Data compression possible if redundant information