1、1,Internet & Home networking,Prof. J. Won-Ki Hong jwkhongpostech.ac.krDept. of Computer Science & Engineering POSTECH,2,Contents,Data Communication NetworkInternet & World Wide WebHome Networking,3,Data Communication Network,4,1960s “How can we transmit bits across a communication medium efficiently
2、 and reliably?”1970s “How can we transmit packets across a communication medium efficiently and reliably?”1980s “How can we provide communication services across a series of interconnected networks?,Brief History of Computer Networks,5,1990s “How can we provide high-speed, broadband communication se
3、rvices to support high-performance computing and multimedia applications across the globe?”2000s What do you think will dominate in the next 10 years?,6,A Communication Model,7,Common Communication Tasks,Data encoding: the process of transforming input data or signals into signals that can be transm
4、ittedSignal generation: generating appropriate electro-magnetic signals to be transmitted over a transmission mediumSynchronization: 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
5、 transmission errors are detected and correctedFlow control: ensuring that the source does not overwhelm the destination by sending data faster than the receiver can handleMultiplexing: a technique used to make more efficient use of a transmission facility. This technique is used at different levels
6、 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 managemen
7、t: 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 mediaExample devices are: mainframes, minicomputers, supercomputers workst
8、ations, 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 sat
9、ellite 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 cal
10、led “store-and-forward” or “pack-switched” some topologies: star, ring, tree,13,Broadcast Networkshave 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,Loc
11、al 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)
12、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 transmissi
13、on 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 i
14、n 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 actionComputer Network a collection of computers interconnected via a communication network,24,Protocol agreement re
15、quired 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 sequencingCommunications Architecture a structured set of modules that implements the commun
16、ication function,25,ISO-OSI Reference Model,International Standards Organization (ISO) Open Systems Interconnection (OSI) Reference model is a framework for connecting computers on a networkMotivation? to reduce the complexity of networking software as a step towards international standardization of
17、 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,App
18、lication,Presentation,Session,Transport,Network,Data Link,Physical,OSI Stack,Application,Presentation,Session,Transport,Network,Data Link,Physical,OSI Stack,Application,Presentation,Session,Transport,Network,Data Link,Physical,OSI Stack,28,Functions of the OSI Layers 1. Physical layer responsible fo
19、r 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 subn
20、etworks 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 manag
21、ing 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 Communicat
22、ion Takes Place Between the Layerscommunication 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,31,32,On the sending side: a layer receives a PDU (Protocol Dat
23、a 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 smalle
24、r 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 t
25、he 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 PCsThe TCP/IP Model only 5 layers exist used mostly in Internet network applications,35,36,Communication Service T
26、ypes,Connection-oriented servicemodeled 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 servicemodeled after the
27、 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 (Internatio
28、nal 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)
29、 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,Inter
30、net 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 ter
31、m “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 networksBased on TCP/IP (Transmission Control Protocol/Internet Protocol)A variety of services and tools,43,Network of networks,a group of
32、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 todays computers are connected via Internet,44,Based on TCP/IP,TCP/IP enables the different types of machines on separate netw
33、orks 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
34、 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, s
35、ounds, 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 Inte
36、rnet, 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 users computer The browser can be graphical or text-based and can make the Internet easier to use
37、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 an
38、d 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 structur
39、e 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. stand
40、ardized 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 I
41、nternet 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.,51,URL,a standardized addressing scheme for Int
42、ernet resources used to link documents on the Internet the browser knows where to go to get the document basic format of an URL type-of-resource:/ domain.address:port/path/filename ftp:/ftp.postech.ac.kr/pub/welcome.txt file:/C|/My Documents/resume.htm news:han.protocol.http telnet:/vision.postech.a
43、c.kr http:/www.postech.ac.kr/index.html,52,Home Networking,53,Definition,the collection of technologies and services that make it possible to connect PCs Network devices Appliances Security equipment,54,Why now?,Building “Internet” into consumer products is now possible Standardization has occurred
44、Costs are low Low-cost, high-speed LAN and routers Ethernet, IEEE 1394, Phone Wire, PLC, RF, etc. Video rate networks - IEEE 1394,Gigabit Ethernet Modem and broadband networking are becoming ubiquitous,Golden age of networking,55,Technology Enablers,ADSL and HFC (cable) networks Enable broadband Int
45、ernet to the home LANs, power line carrier, phone line networks, and wireless Enable ubiquitous connectivity Internet connection sharing Brings the Internet to everything in the home The communications software infrastructure has been determined:,The Web and TCP/IP,56,Analogous History,Single to mul
46、tiple cars per family One to multiple phones per household Multiple phone lines per house One to multiple TVs per house,MegaTrend: From one Internet device per home to MANY,57,Roles for Home Networking,Data Extension of current use of Internet by PDAs, tablets, multiple PCs Communications Telephony,
47、 videophone, chat, conferencing Entertainment Games, TV, high-fidelity audio Control Lights, HVAC, security, appliances,58,Connecting Everything,59,Challenges for deployment of home network,Ease of installation There are no Net admins at homeNetwork configuration has to be automatic There are no Net
48、 admins at homeNetwork health and recovery There are no Net admins at home,60,Home Network Architecture,Public networks,PSTN, Internet,Camera,Printer,Internet Connection Sharing,61,Architecture for The Future,Great standards exist today IETF: TCP/IP, DNS, DHCP, HTTP, SSL, LDAP, IPSEC W3C: HTML, XML
49、Great services exist today Today: eCommerce, search Early Stages: Internet audio/video, IP Telephony - much like early 1950s TV Billions of Web hits served daily,Leveraging Web technologies,Internet exists and it works,62,TCP/IP and Web is the software infrastructure,Web is evolving HTTP v1.1 for performance improvements XML extends Web for software applications “Pages” can now be simply data Internet Explorer 5.0 has XML support Easy to wrap existing programs/tools/systems in Web Programming language neutral Contents neutral Operating system neutral,
