1. Datornätverk A – lektion 14: Applikationslagret Kap 24: Sockets Kapitel 25: DNS Kapitel 26: SMTP och FTP Kapitel 27: HTTP och WWW

2. Application Layer PART VI

3. Position of application layer

4. Chapter 24 Client-Server Model: Socket Interface

5. Figure 22.5 Socket address A socket is a data flow between two processes that is identified by its socket address pair, i.e. a unique combination of: - Transport protocol (UDP or TCP). - Source IP address and port number. - Destination IP address and port number.

6. Figure 24.2 Client-server relationship

7. Figure 24.3 Connectionless iterative server

8. Figure 24.4 Connection-oriented concurrent server

9. Figure 24.6 Socket types

10. Figure 24.7 Socket interface for connectionless iterative server

11. Figure 24.8 Socket interface for connection-oriented concurrent server

12. Chapter 25 DNS = Domain Name System

13. Figure 25.1 Domain name space

14. Domain Name System - DNS En distribuerad databas som används till att koppla IP- nummer till textbaserade internetadresser. Ex www.gb.se 195.7.73.37 Varje sökning utgår från någon av rootservrarna som håller ordning på toppdomänerna. (.com.edu.se m fl) All information rörande en domän ligger i den ”Name Server” som hanterar domänen. För att lägga upp en ny domän krävs ”tillstånd” från närmast högre

15. Figure 25.2 Domain names and labels

16. Figure 25.4 Domains

17. Figure 25.5 Hierarchy of name servers

18. A primary DNS server loads all information from the disk file; the secondary server loads all information from the primary server. Note:

19. Figure 25.7 DNS in the Internet

20. Table 25.1 Generic domain labels LabelDescription.comCommercial organizations.eduEducational institutions.govGovernment institutions.intInternational organizations.milMilitary groups.netNetwork support centers.orgNonprofit organizations

21. Table 25.2 New generic domain labels LabelDescription.aeroAirlines and aerospace companies.bizBusinesses or firms (similar to com).coopCooperative business organizations.infoInformation service providers.museumMuseums and other nonprofit organizations.namePersonal names (individuals).proProfessional individual organizations

22. Figure 25.9 Country domains

23. Figure 25.10 Inverse domain

24. Figure 25.11 Recursive resolution

25. Figure 25.12 Iterative resolution

26. Figure 25.13 Query and response messages

27. Figure 25.14 Header format

28. DNS can use the services of UDP or TCP, using the well-known port 53. Note:

29. Elektronisk Postvia SMTP, POP eller IMAP Konferenssystem via USENET News och NNTP Fildelningvia t.ex NFS Filöverföringvia t.ex FTP Skrivardelning World Wide Webvia HTTP MassutsändningarMbone- Multicast Backbone LAN Tjänster

30. Chapter 26 Internet E-mail

31. Figure 26.10 Email delivery

32. Figure 26.11 POP3

33. Figure 26.1 Format of an email

34. Figure 26.2 Email address

35. Figure 26.3 User agent

36. Figure 26.4 MIME

37. Figure 26.5 MIME header

38. Table 26.1Data types and subtypes in MIME TypeSubtypeDescription TextPlainUnformatted text Multiport MixedBody contains ordered parts of different data types ParallelSame as above, but no order DigestSimilar to mixed, but the default is message/RFC822 AlternativeParts are different versions of the same message Message RFC822Body is an encapsulated message PartialBody is a fragment of a bigger message Ext. BodyBody is a reference to another message Image JPEGImage is in JPEG GIFImage is in GIF format VideoMPEGVideo is in MPEG format AudioBasicSingle-channel encoding of voice at 8 KHz Application PostScriptAdobe PostScript Octet-StreamGeneral binary data (8-bit bytes)

39. Table 26.2 Content-transfer encoding CategoryDescription Type ASCII characters and short lines 7bitNon-ASCII characters and short lines 8bitNon-ASCII characters with unlimited-length lines Binary6-bit blocks of data are encoded into 8-bit ASCII characters Base64Non-ASCII characters are encoded as an equal sign followed by an ASCII code

40. Figure 26. 6 Base64

41. Table 26.3 Base64 encoding table ValueCodeValueCodeValueCodeValueCodeValueCodeValueCode 0A11L22W33h44s 55 3 1B12M23X34i45t 56 4 2C13N24Y35j46u 57 5 3D14O25Z36k47v 58 6 4E15P26a37l48w 59 7 5F16Q27b38m49x 60 8 6G17R28c39n50y 61 9 7H18S29d40o51z 62 + 8I19T30e41p520 63 / 9J20U31f42q531 10K21V32g43r542

42. Figure 26.7 Quoted-printable

43. Figure 26.8 Email client and server

44. 26.2 File Transfer Connections Communication File Transfer User Interface Anonymous

45. FTP uses the services of TCP. It needs two TCP connections. The well-known port 21 is used for the control connection, and the well-known port 20 is used for the data connection. Note:

46. Figure 26.12 FTP

47. Figure 26.13 Using the control connection

48. Figure 26.14 Using the data connection

49. Figure 26.15 File transfer

50. Example 1 Figure 26.16 (next slide) shows an example of how a file is stored. 1.The control connection is created, and several control commands and responses are exchanged. 2.Data are transferred record by record. 3.A few commands and responses are exchanged to close the connection.

51. Figure 26.16 Example 1

52. Table 26.4 List of FTP commands in UNIX Commands !, $, account, append, ascii, bell, binary, bye, case, cd, cdup, close, cr, delete, debug, dir, discount, form, get, glob, hash, help, lcd, ls, macdef, mdelete, mdir, mget, mkdir, mls, mode, mput, nmap, ntrans, open, prompt, proxy, sendport, put, pwd, quit, quote, recv, remotehelp, rename, reset, rmdir, runique, send, status, struct, sunique, tenex, trace, type, user, verbose,?

53. Example 2 We show some of the user interface commands that accomplish the same task as in Example 1. The user input is shown in boldface. As shown below, some of the commands are provided automatically by the interface. The user receives a prompt and provides only the arguments. $ ftp challenger.atc.fhda.edu Connected to challenger.atc.fhda.edu 220 Server ready Name: forouzan Password: xxxxxxx ftp > ls /usr/user/report 200 OK 150 Opening ASCII mode........... 226 transfer complete ftp > close 221 Goodbye ftp > quit

54. Example 3 We show an example of using anonymous FTP. We connect to internic.net, where we assume there are some public data available. $ ftp internic.net Connected to internic.net 220 Server ready Name: anonymous 331 Guest login OK, send "guest" as password Password: guest ftp > pwd 257 '/' is current directory ftp > ls 200 OK 150 Opening ASCII mode bin... ftp > close 221 Goodbye ftp > quit

55. Chapter 27 HTTP and WWW

56. HTTP uses the services of TCP on well-known port 80. Note:

57. Figure 27.1 HTTP transaction

58. Figure 27.9 Example 1

59. Example 1 This example retrieves a document. We use the GET method to retrieve an image with the path /usr/bin/image1. The request line shows the method (GET), the URL, and the HTTP version (1.1). The header has two lines that show that the client can accept images in GIF and JPEG format. The request does not have a body. The response message contains the status line and four lines of header. The header lines define the date, server, MIME version, and length of the document. The body of the document follows the header (see Fig. 27.9, next slide).

60. Figure 27.3 Request line

61. Figure 27.4 URL

62. Figure 27.6 Status line

63. Figure 27.7 Header format

64. Figure 27.10 Example 2

65. Example 2 This example retrieves information about a document. We use the HEAD method to retrieve information about an HTML document (see the next section). The request line shows the method (HEAD), URL, and HTTP version (1.1). The header is one line showing that the client can accept the document in any format (wild card). The request does not have a body. The response message contains the status line and five lines of header. The header lines define the date, server, MIME version, type of document, and length of the document (see Fig. 27.10, next slide). Note that the response message does not contain a body.

66. HTTP version 1.1 specifies a persistent connection by default. Note:

67. Figure 27.12 Hypertext

68. Figure 27.11 WWW Hyperlinks

69. Figure 27.13 Browser architecture