Internet Applications

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1 Internet Applications รศ.ดร. อน นต ผลเพ ม Assoc. Prof. Anan Phonphoem, Ph.D. Computer Engineering Department Kasetsart University, Bangkok, Thailand 1

2 Outline Client-Server WWW DNS 2

3 Application Layer Examples Hypertext Transfer Protocol (HTTP) Domain Name System (DNS) Telnet File Transfer Protocol (FTP) Trivial File Transfer Protocol (TFTP) Simple Mail Transport Protocol (SMTP) Simple Network Management Protocol (SNMP) 3

4 Responsibilities of Application Layer Identifying and establishing the availability of intended communication partners Synchronizing cooperating applications Establishing agreement on procedures for error recovery Controlling data integrity 4

5 Application Definition Programs run on behalf of users serve specific service requests Application types self-contained (take input show output) remote interaction (send-receive info.) client receive instruction from user server react/service as requested 5

6 Application-Layer Protocols 2 broad types of application-layer protocols (depend on the intended use) Private communication proprietary, limited scope Standardized service standard, Internetwide: Web server, FTP, etc. Standards for the Internet are known as Request for Comments (RFCs) 6

7 Representation And Transfer Application-layer protocols specify two aspects of interaction: Representation Transfer 7

8 Client-Server Architecture Most network application Server use well-known port numbers (i.e. a part of shop address) run all the time Client use an ephemeral port number (i.e. a part of user address) terminate after the service. 8

9 Client-Server Client Application Client Application Daemon Server Application Client Internet Server Client Application Connection: TCP or UDP and Ports 9

10 Connectionless Iterative Server Legend Datagram from client 1 Datagram from client 2 Datagram from client 3 10

11 Connection-Oriented Concurrent Server 11

12 TCP/IP protocol suite and OS 12

13 Sockets Basic Concepts 13

14 Sockets Basic Concepts 14

15 Connectionless Iterative: using UDP 15

16 Connection-Oriented Concurrent: TCP Client Server 16

17 Connection-Oriented Concurrent: TCP Client Server Connection handshake 17

18 Connection-Oriented Concurrent: TCP Client Server 18

19 Parent / Child Process c. After folk 19

20 World Wide Web

21 Web Protocols The World Wide Web (WWW) is one of the most widely used services in the Internet 21

22 Markup Language Method of presenting document in common character set (ASCII) Using tag for formatting instruction embedded in the text inform application how to display document font, indentation, text color, etc. e.g. word processor 22

23 Hypertext A collection of documents containing cross-references or "links" Use in interactive browser program allow reader to move easily from one document to another point-and-click references between doc. 23

24 Hypertext 24

25 Hypertext Markup Language (HTML) Coded format language used for creating hypertext documents on WWW controlling how Web pages appear HTML documents are written in plain text with the addition of tags Example tag ANCHOR <A> tag create link <A HREF=" Welcome page</a> 25

26 General Form of HTML Document <HTML> <HEAD> <TITLE> Intelligent Wireless Network Group </TITLE> </HEAD> <BODY> <A HREF=" University Page</A> </BODY> </HTML> Whitespaces do not matter <HTML><HEAD><TITLE>Intelligent Wireless Network Group</TITLE></HEAD><BODY>Kasetsart University</BODY> </HTML> 26

27 Universal Resource Locators (URLs) Address identifies the location of a Web page A way of specifying the location of something on the Internet Indicate service used to access the resource mailto://<username>@<hostname> 27

28 Hypertext Transfer Protocol (HTTP) Most extensively used in the Internet Communication between web browsers and web server Standard access protocol to allow applications to get and send document and files across Internet 28

29 Hypertext Transfer Protocol (HTTP) A browser is a client that extracts a server name from a URL and contacts the server Most URLs contain an explicit protocol reference of or omit the protocol altogether (HTTP is assumed) HTTP is hidden behind web browser GUI TCP connection with well-known port 80 29

30 HTTP transaction request/response message use HTTP message header followed by MIME MIME: Multipurpose Internet Mail Extensions 30

HTTP Once it establishes a connection a browser sends an HTTP request to the

32 Request Message Method indicates what to be performed on the resource identified by the Request-URL Ex.: GET, PUT, HEAD HTTP Example: GET HTTP/1.1 32

33 Response Message Status code: Same format as FTP responses (three digits) Example: HTTP/ OK Status Code 200 The request has succeeded 33

34 Headers Example: Accept: image/gif 34

35 Example: Retrieve Document GET method request line Header Status line GET method to retrieve an image with the path 35

36 Example: Retrieve Document HEAD method HEAD method to retrieve information about an HTML document 36

37 Example: POST method POST method to send input data to the server 37

38 Web Browser Architecture A browser must understand HTTP (at least) A browser also provides support for other protocols Knows how to interact with a server and how to interpret responses E.g., a browser must know how to access the FTP (File Transfer Protocol) service Knows what external program to launch for particular protocol code 38

39 Domain Name System (DNS) 39

40 Naming Purpose Addresses are used to locate objects Names are easier to remember than numbers To get to the address or other objects prefer using a name 40

41 Domain Name System (DNS) System used for translating names of domains into IP addresses using lookup mechanism Domain names comprise a hierarchy (tree) unique easy to remember DNS can use the services of UDP or TCP using the well-known port

42 DNS Mapping Process User 1 Host name 2 Host name 6 IP address Transport layer 5 IP address 3 Query Response 4 42

43 IP Address Mapping Example name server 2 สอบถามช อโดเมน nontri.ku.ac.th ผ ใช 1 ใช ช อโดเมน telnet nontri.ku.ac.th TELNET ตอบไอพ แอดเดรส TCP IP 43

44 DNS Features A globally distributed maintain data locally, but retrievable globally No single computer has all DNS data Loosely coherent replicate changes (timing set by the zone admin) Scalable not limited size not limited # of query Reliable (data replicate) Dynamic database 44

45 DNS Concept Domain names can be mapped to a tree New branches at the dots No restriction to the amount of branches www ftp ripe ws1 disi net ws2 isi edu sun com www tislabs moon google 45

46 Top-Level Domains (TLDs) The most significant segment of each domain name is called a top-level domain (TLD) Controlled by the Internet Corporation for Assigned Names and Numbers (ICANN) ICANN designates one or more domain registrars to administer a given top-level domain and approve specific names 46

47 DNS in Internet ราก arpa com edu gov int mil net org de th uk in-addr mit usu ac go or cc ku mua nectec โดเมนท วไป nontri mis nucleus cc.usu.edu. 2 โดเมนผกผ น nontri.ku.ac.th. nucleus.nectec.or.th. โดเมนระด บประเทศ in-addr.arpa. = ม ต นไม ย อยได อ ก 47

48 Standard Name Space (Top Level) com edu gov mil net org th commercial education goverment military network operator organization country New.aero.biz.coop.info.name.pro 48

49 Inverse Domain in-addr arpa ราก in-addr.arpa nontri.ku.ac.th 49

50 Hostname Structure Sequence of labels separated by periods each label can be up to 63 characters total name can be at most 255 characters Examples: iwing.cpe.ku.ac.th 50

51 Domain Name and Label Absolute Domain Name challenger.atc.fhda.edu. Relative Domain Name atc atc.fhda.edu. 51

52 Domain Concept 52

53 Domain ku.ac.th ราก th Node ku.ac.th go ac Domain ku.ac.th ku 53

54 Sub-Domain ราก th Domain cpc.ku.ac.th go ac ku Domain ku.ac.th Domain sci.ku.ac.th cpc eng lib sci Domain eng.ku.ac.th ce ie me Domain lib.ku.ac.th 54

55 Delegation Administrator can create sub-domains according to geography, affiliation or other criterion Domain Admin may delegate responsibility for managing a sub-domain Parent domain retains links to delegated sub-domain parent domain remembers who it delegated the sub-domain to 55

56 Zones and Domains 56

57 Zones and Delegations Zones are administrative spaces Zone administrators are responsible for portion of a domain s name space Authority is delegated from a parent and to a child net zone net domain ripe.net zone disi.ripe.net zone ripe net www disi ftp ws2 edu isi ws1 com sun moon google tislabs www 57

58 Zone and Domain ราก th go ac ku Zone ku Domain ku cpc eng lib sci ce ie me 58

59 Zone and Domain ราก th go ac ku Zone ku Domain ku Domain eng Zone eng cpc ce ie eng me lib sci Domain lib Zone lib 59

60 Name Servers Name servers answer DNS questions Several types of name servers Authoritative servers master (primary) slave (secondary) (Caching) recursive servers also caching forwarders Mixture of functionality 60

61 Authoritative Name Servers Give authoritative answers for one or more zones Master server loads data from zone file Slave server replicates data from master via a zone transfer slave master slave 61

62 Recursive Name Server Perform actual lookups ask questions to DNS on behalf of clients Answers are obtained from authoritative servers but answers forwarded to clients are marked as not authoritative Answers are stored for future reference in cache 62

63 Resolver Ask questions to DNS system on behalf of the application Normally implemented in a system library (e.g, libc) gethostbyname (char *name); gethostbyaddr (char *addr, int len, type); 63

64 ไคลเอ นต nontri.ku.ac.th Browser OS's resolver DNS process Recursive Query 1 jaguar.lcs Add to cache.mit.edu jaguar.lcs.mit.edu 2 3 w20ns.mit.edu, jaguar.lcs.mit.edu 4 mintaka.lcs.mit.edu, ns.ku.ac.th Recursive Server (nomally) Iterative Query jaguar.lcs.mit.edu 6 7 jaguar.lcs.mit.edu, ร ทเนมเซ ร ฟเวอร Always Iterative Server เนมเซ ร ฟเวอร mit.edu w20ns.mit.edu เนมเซ ร ฟเวอร lcs.mit.edu mintaka.lcs.mit.edu

65 DNS process ไคลเอ นต nontri.ku.ac.th ร ทเนมเซ ร ฟเวอร Always Iterative Server Browser 1 jaguar.lcs.mit.edu เนมเซ ร ฟเวอร mit.edu OS's resolver ns.ku.ac.th 5 w20ns.mit.edu Add to cache Iterative Server 6, เนมเซ ร ฟเวอร lcs.mit.edu mintaka.lcs.mit.edu

66 DNS Message 68

67 Query Record Format (Question) admin.atc.fhda.edu. 69

68 DNS Exchange ftp.nectec.or.th เนมเซ ร ฟเวอร 1 2 ku.ac.th ku.or.th ftp.nectec.or.th เนมเซ ร ฟเวอร nectec.or.th nontri.ku.ac.th ftp.nectec.or.th, 4 ns.ku.ac.th ns.nectec.or.th

69 nontri.ku.ac.th ns.ku.ac.th ftp.nectec.or.th เนมเซ ร ฟเวอร 1 2 ku.or.th ku.ac.th ftp.nectec.or.th เนมเซ ร ฟเวอร nectec.or.th ftp.nectec.or.th, nontri.ku.ac.th 4 ns.ku.ac.th ns.nectec.or.th ไอพ เฮดเดอร (บางส วน) destination= identification=10 source= query, standard, recursive ด เอ นเอสเฮดเดอร number of questions = 1 number of answers RRs = 0 number of authority RRs = 0 numberof additional RRs = 0 ส วนค าถาม name=ftp.nectec.or.th., type=a, class=in Type A = indicate that VALUE is an IP Add Class IN = indicate Internet 71

70 ns.ku.ac.th ns.nectec.or.th ftp.nectec.or.th เนมเซ ร ฟเวอร 1 2 ku.or.th ku.ac.th ftp.nectec.or.th เนมเซ ร ฟเวอร nectec.or.th ftp.nectec.or.th, nontri.ku.ac.th 4 ns.ku.ac.th ns.nectec.or.th destination= identification=20 source= query, standard, recursive ด เอ นเอสเฮดเดอร number of questions = 1 number of answers RRs = 0 number of authority RRs = 0 numberof additional RRs = 0 ส วนคาถาม name=ftp.nectec.or.th., type=a, class=in 72

71 DNS File Example BIND (Berkeley Internet Name Domain) Unix use daemon named ns มาสเตอร เนมเซ ร ฟเวอร /etc/named.conf /usr/local//named/db.ku /usr/local/named/db.rev /usr/local/named/db.local /usr/local/named/db.cache ns2 สเลฟเนมเซ ร ฟเวอร /etc/named.conf /usr/local/named/db.ku * /usr/local/named/db.rev * /usr/local/named/db.local /usr/local/named/db.cache www mail nontri omega sigma 73

72 nslookup Interactive resolver allows user to communicate directly with a DNS server 74

73 dig 75

74 References TCP/IP Protocol Suite, 2nd Edition, Behrouz A. Forouzan Introduction to the DNS system, Olaf M. Kolkman CCNA 1 v3.0 Module 11 TCP/IP Transport and Application Layers, cisco.com Address Conversion Functions and The Domain Name System, Anonymous ส รศ กด สงวนพงษ, ท ซ พ ไอพ 76

Application Protocols

Application Protocols รศ.ดร. อน นต ผลเพ ม Asso. Prof. Anan Phonphoem, Ph.D. anan.p@ku.ac.th http://www.cpe.ku.ac.th/~anan Computer Engineering Department Kasetsart University, Bangkok, Thailand 1 Outline