Internet & Home networking

1. Internet & Home networking Prof. J. Won-Ki Hong jwkhong@postech.ac.kr Dept. of Computer Science & Engineering POSTECH

2. Contents • Data Communication Network • Internet & World Wide Web • Home Networking

3. Data Communication Network

4. Brief History of Computer Networks • 1960’s – “How can we transmit bits across a communication medium efficiently and reliably?” • 1970’s – “How can we transmit packets across a communication medium efficiently and reliably?” • 1980’s – “How can we provide communication services across a series of interconnected networks?

5. 1990’s – “How can we provide high-speed, broadband communication services to support high-performance computing and multimedia applications across the globe?” • 2000's – What do you think will dominate in the next 10 years?

6. 1 2 3 4 5 6 Input Information m Input data g or signal g(t) Transmitted signal s(t) Received signal r(t) Output data g’ or signal g’(t) Output Information m’ ’ Transmission Input Output Sender Receiver Transmitter Receiver Device medium Device Source System Destination System A Communication Model

7. Common Communication Tasks • Data encoding: the process of transforming input data or signals into signals that can be transmitted • Signal generation: generating appropriate electro-magnetic signals to be transmitted over a transmission medium • Synchronization: timing of signals between the transmitter and receiver ; when a signal begins and when it ends; duration of each signal

8. Error detection and correction: ensuring that transmission errors are detected and corrected • Flow control: ensuring that the source does not overwhelm the destination by sending data faster than the receiver can handle • Multiplexing: a technique used to make more efficient use of a transmission facility. This technique is used at different levels of communication

9. Addressing: indicating the identity of the intended destination • Routing: selecting appropriate paths for data being transmitted • Message formatting: conforming to the appropriate format of the message to be exchanged • Security: ensuring secure message transmission • Systems management: configuring the system, monitoring its status, reacting to failures and overloads, and planning for future growth

10. Communication Network • A communication network is a collection of devices connected by some communications media • Example devices are: • mainframes, minicomputers, supercomputers • workstations, personal computers • printers, disk servers, robots • X-terminals • Gateways, switches, routers, bridges • Cellular phone, Pager, TRS • Refrigerator, Television, Video Tape Recorder

11. Communications Media • twisted pairs • coaxial cables • line-of-sight transmission: lasers, infra-red, microwave, radio • satellite links • fiber optics • Power line

12. Network Structures • Point-to-Point Networks • each communication line connects a pair of nodes • a packet (or message) is transmitted from one node to another • intermediate nodes, in general, receive and store entire packet and then forward to the next node • also called “store-and-forward” or “pack-switched” • some topologies: star, ring, tree

13. Broadcast Networks • have a single communication line shared by all computers on the network • packets sent by a host are received by all computers • some topologies: bus, satellite, radio

14. Types of Communication Networks • Local Area Networks (LANs) • < a few km • high data transmission rate (at least several Mbps) • ownership usually by a single organization • e. g., Ethernet, IBM Token Ring, Token Bus, FDDI, Fast Ethernet, ATM, Gigabit Ethernet

15. POSTECH LAN (1998.6)

16. POSTECH LAN (1999. 3)

17. Metropolitan Area Networks (MANs) • up to 50 km • fibre optics is a popular technology for MANs • may be private or public • may involve a number of organizations • e.g., cable TV networks (CATV), ATM networks

18. Wide Area Networks (WANs) • a few km to thousands of km • point-to-point networks (also called long-haul networks) • lower data transmission rate than LANs • fiber optics is a popular technology for MANs ownership usually by more than a single organization • e.g., ARPANET, MILNET (US military), CA*NET, NSFNET, KREONET, BoraNet, KORNET, INET, Internet

19. Internet in Korea (1995.5)

20. Internet in Korea (1999.6)

21. Growth of Internet Users in Korea

22. Growth of Internet Hosts in Korea

23. Computer Communication Architecture • Computer Communication – the exchange of information between computers for the purpose of cooperative action • Computer Network – a collection of computers interconnected via a communication network

24. Protocol – agreement required between the communication entities and consists of three components: Syntax: data format and signal levels Semantics: control information for coordination and error handling Timing: speed matching and sequencing • Communications Architecture – a structured set of modules that implements the communication function

25. ISO-OSI Reference Model • International Standards Organization (ISO) – Open Systems Interconnection (OSI) Reference model is a framework for connecting computers on a network • Motivation? • to reduce the complexity of networking software • as a step towards international standardization of the various protocols

26. The main principles applied to the OSI layered architecture are • each layer represents a layer of abstraction, • each performs a set of well-defined functions, • implementation of a layer should not affect adjacent layers, and inter-layer communication should be minimized

27. OSI Stack OSI Stack OSI Stack Application Application Application Presentation Presentation Presentation Session Session Session Transport Transport Transport Network Network Network Data Link Data Link Data Link Physical Physical Physical

28. Functions of the OSI Layers 1. Physical layer – responsible for the electro-mechanical interface to the communications media 2. Data link layer – responsible for transmission, framing and error control over a single communications link. 3. Network layer – responsible for data transfer across the network, independent of both the media comprising the underlying subnetworks and the topology of those subnetworks.

29. 4. Transport layer – responsible for reliability and multiplexing of data transfer across the network (over and above that provided by the network layer) to the level required by the application. 5. Session layer – responsible for establishing,, and managing sessions between cooperating applications. 6. Presentation layer – responsible for providing independence to the application process from differences in data representation (syntax). 7. Application layer – ultimately responsible for managing the communications between applications.

30. How Communication Takes Place Between the Layers • communication takes place between peer entities. • a layer provides services to the layer above it. • services are available at SAPs (Service Access Points) – analogous to telephone numbers and street addresses

31. Relation Between Layers at an Interface IDU Layer N + 1 ICI SDU SAP Interface Layer N entities exchange N-PDUs in their layer N Protocol Layer N ICI SDU SAP = Service Access Point IDU = Interface Data Unit SDU = Service Data Unit PDU = Protocol Data Unit ICI = Interface Control Information SDU Header

32. On the sending side: • a layer receives a PDU (Protocol Data Unit) from the layer above it, with some ICI (Interface Control Information) (such as address, data size, etc.). • the layer ads some PCI (Protocol control Information) to the APDU and passes the enlarged PDU to the layer below along with more ICI. • A layer may also fragment a PDU into several smaller pieces to be passed separately to the layer below (in this case, the peer entity at the receiving end will reassemble the fragments).

33. At the receiving end: • a layer receives a PDU from the layer below. • The layer strips off the PCI added by its peer, and passes the PDU to the layer above it. • If the sending layer fragmented a PDU, its peer is responsible for reassembling it before passing it up.

34. Other Communication Models • The Anarchistic Network Model • have been used mostly in PCs • The TCP/IP Model • only 5 layers exist • used mostly in Internet network applications

35. The Anarchistic Network Model The OSI Model The TCP/IP Model Application Application Application Presentation Session Operating System Transport Transport Network Network Data Link Controller Data Link Physical Physical Physical the network

36. Communication Service Types • Connection-oriented service • modeled after the telephone system • must establish a connection before use, and terminates the connection when finished. • FIFO guaranteed. • the path from the sender to receiver is fixed. • resources are pre-allocated at setup time

37. Connectionless service • modeled after the postal system • no connection required, but instead full addressing required in each message • FIFO not guaranteed. • the path is not fixed • resources are dynamically allocated

38. Standards Organizations • ITU-T (International Telecommunication Union - Telecommunications Sector) - formerly CCITT (International Telegraph and Telephone Consultative Committee), a committee within ITU, a United Nations agency, responsible for X.25, X.21, X.400, X.500, X.700, X.900, etc. • ISO (International Standards Organization): ISO 8073 (connection-oriented transport protocol) • ANSI (American National Standard Institute) • IEEE (Inst. of Electrical and Electronics Engineers): IEEE 802

39. IETF (Internet Engineering Task Force): TCP/IP, FTP, SNMP • W3C (World-Wide Web Consortium): HTTP, HTML, XML • ATMF (ATM Forum) - ATM related standards • TMF (TeleManagement Forum) - formerly known as NMF, Network Management Forum

40. Internet and World Wide Web

41. History of the Internet • 1969 - Researchers at four US campuses create the first hosts of the ARPANET • 1971 - The ARPANET grows to 23 hosts connecting universities and research centers • 1973 - The ARPANET goes international with connections to England and Norway • 1982 - The term "Internet" is used for the first time and TCP/IP is created • 1992 - Internet Society is chartered. World-Wide Web released by CERN.

42. Definitions • A network of networks • Based on TCP/IP (Transmission Control Protocol/Internet Protocol) • A variety of services and tools

43. Network of networks • a group of two or more networks that are : • interconnected physically • capable of communicating and sharing data with each other • able to act together as a single network • virtually all of today’s computers are connected via Internet

44. Based on TCP/IP • TCP/IP enables the different types of machines on separate networks to communicate and exchange information. • TCP/IP is • A suite of protocols • Rules for sending and receiving data across networks • Addressing • Management and verification

45. Variety of services or tools • The Internet offer access to data, graphics, sound, software, text, and people through a variety of services and tools for communication and data exchange • E-Mail • Usenet • FTP • Gopher • Telnet • World Wide Web

46. World Wide Web • A way to provide and access information resources on the Internet • Using Web Browser & Web Server • Based on HTML and HTTP • Multimedia • Hypertext "links" can lead to other documents, sounds, images, databases (like library catalogs), e-mail addresses, etc. • Non-Linear • There is no top, there is no bottom. Non-linear means you do not have to follow a hierarchical path to information resources.

47. Web Browser • a piece of software that acts as an interface between the user and the Internet, specifically the World Wide Web • The browser acts on behalf of the user. The browser: • contacts a web server and sends a request for information • receives the information and then displays it on the user's computer • The browser can be graphical or text-based and can make the Internet easier to use and more intuitive • The helper applications are automatically invoked by the browser when a user selects a link to a resource that requires them • A Web browser can be used on most of computers

48. Web Server • Also known as HTTP Server or HTTP Daemon • The repository of web pages of which types are HTML and any application data with MIME type • Listens for HTTP requests from the web browsers, serves those requests • Designed to communicate with web browsers using HTTP protocol • Typically runs on general purpose computer

49. HTML • consists of standardized codes,or "tags", that are used to define the structure of information on a web page • defines several aspects of a web page including heading levels, bold, italics, images, paragraph breaks and hypertext links to other resources. • a sub-language of SGML (Standard Generalized Markup Language) that defines and standardizes the structure of documents. • standardized and portable: A document that has been prepared using HTML can be viewed using a variety of web browsers, such as Netscape and Lynx

50. HTTP • the set of rules, or protocol, that governs the transfer of hypertext between two or more computers. • Based on Client/Server paradigm • Convey variety of Internet resources: HTML documents, text files, graphics, animation and sound • HTTP also provides access to other Internet protocols, among them: • File Transfer Protocol (FTP) • Simple Mail Transfer Protocol (SMTP) • Network News Transfer Protocol (NNTP) • etc.