Networks Internet WWW q Reading Materials v

Networks, Internet & WWW q Reading Materials: v Ch 7 of [SG 3] v Additional Notes: (from web-site) q Contents: v Motivation for Networks v Types of Networks and Their Structure v Communication Protocols – routing info v Network Services / Applications v Internet and WWW Hon Wai Leong, NUS (UIT 2201, Networks) Page 1 Copyright © 2007 by Leong Hon Wai

Networks, Internet, WWW q Context so far… v Use algorithm to solve problem v Database used to organize massive data v Algorithms implemented using hardware Educational Goals for this Chapter: q The computer as a tool for v Communication and Collaboration v Information Sharing v Resource Sharing v Shared Services Hon Wai Leong, NUS (UIT 2201, Networks) Page 2 Copyright © 2007 by Leong Hon Wai

Introduction to Computer Network q What is a Computer Network v Computers connected together v Why: Share information and resources v What kind of information u data files (pictures, videos, audio), programs u movies, tv and radio signals v What kind of services u a shared printer u a shared software application Hon Wai Leong, NUS (UIT 2201, Networks) Page 3 Copyright © 2007 by Leong Hon Wai

Basic Networking Concepts q A Computer Network v A set of independent computer systems u connected by telecommunication links v Purpose: u sharing information and resources v Nodes, hosts, or end systems u individual computers on a network Hon Wai Leong, NUS (UIT 2201, Networks) Page 4 Copyright © 2007 by Leong Hon Wai

The Ever-changing Internet Different colors based on IP address http: //research. lumeta. com/ches/map

What is the Internet? n n n n WWW Video conferencing ftp telnet Email Instant messaging …

What is the Internet? n n n n WWW Video conferencing ftp telnet Email Instant messaging A communication infrastructure … Usefulness is in exchanging information

“On-line interactive communities. . . will be communities not of common location, but of common interest. . the total number of users. . . will be large enough to support extensive general purpose [computers]. All of these will be interconnected by telecommunications channels. . . [to] constitute a labile network of networks--ever changing in both content and configuration. ” J. C. R. Licklider

Communicating Via the Internet

A Brief History of the Internet and the World Wide Web: The Internet q August 1962: First proposal for building a computer network v Made by J. C. R. Licklider of MIT q ARPANET v Built by the Advanced Research Projects Agency (ARPA) in the 1960 s v Grew quickly during the early 1970 s Hon Wai Leong, NUS (UIT 2201, Networks) Page 10 Copyright © 2007 by Leong Hon Wai

The Internet (continued) q NSFNet: A national network built by the National Science Foundation (NSF) q October 24, 1995: Formal acceptance of the term Internet q Internet service providers start offering Internet access once provided by the ARPANET and NSFNet Hon Wai Leong, NUS (UIT 2201, Networks) Page 11 Copyright © 2007 by Leong Hon Wai

ARPANET, 1980 http: //mappa. mundi. net/maps_001/

Figure 7. 20 State of Networking in the Late 1980 s Hon Wai Leong, NUS (UIT 2201, Networks) Page 13 Copyright © 2007 by Leong Hon Wai

The World Wide Web q Development completed in May 1991 q Designed and built by Tim Berners-Lee q Components v Hypertext u. A collection of documents interconnected by pointers called links v URL (Uniform Resource Locator) u. The worldwide identification of a Web page located on a specific host computer Hon Wai Leong, NUS (UIT 2201, Networks) Page 14 Copyright © 2007 by Leong Hon Wai

History of the Internet n Tim Berners-Lee at CERN in 1989 n n n Proposal for WWW in 1990 First web page on November 13, 1990 Hypertext - Text that contains links to other text. n n Ted Nelson’s Xanadu Vannevar Bush’s Memex (http: //www. theatlantic. com/unbound/flashbks/computer/bushf. htm) n W 3 C Get more info at: http: //www. isoc. org/internet/history/

History of the Internet Hosts Stage 1 DARPA Experiment, operation Stage 2 Enterprise Internets, R&A scaling l Kahn poses internet challenge 2 Q 73 l Cerf-Kahn sketch gateway and TCP in 2 Q 1973 l Cerf-Kahn paper published May 1974 l Cerf team full spec - Dec 1974 Stage 3 Universality 1995 -NSFNet ceases, non-USA nets >50% 1992 -Internet Society created 1990 -ARPANet ceases 1989 -first public commercial Internets created 1986 -NSFNet created 1984 -DNS created, DARPA divests Jan. Internet 1983 -ARPANet adopts TCP/IP, CSNet created, first real Internet begins ARPANet 1981 -Bitnet created copyright © 1995 A. M. Rutkowski & Internet Society

Babel n Internet consists of many different types of networks n n Ethernet Token ring Different types of operating systems and other software How do they work together? n Standards

The Basic Communication Link q Dial-up telephone line, v A circuit is temporarily established ubetween caller and callee v Analog medium (analog signals) v Requires modem at both ends to transmit information produced by a computer u. Computer produces digital information Hon Wai Leong, NUS (UIT 2201, Networks) Page 18 Copyright © 2007 by Leong Hon Wai

Analog vs Digital Signals Figure 7. 1 Two Forms of Information Representation Hon Wai Leong, NUS (UIT 2201, Networks) Page 19 Copyright © 2007 by Leong Hon Wai

Analog Digital Conversion Figure 7. 2: Modulation of a Carrier to Encode Binary Information Hon Wai Leong, NUS (UIT 2201, Networks) Page 20 Copyright © 2007 by Leong Hon Wai

The Communication Link (cont…) q Dial-up phone links v Transmission rate: 56 Kbps q Broadband v Transmission rate: > 256 Kbps Home Use: * DSL * Cable modem Hon Wai Leong, NUS Office & Commercial Use: * Ethernet * Fast Ethernet * Gigabit Ethernet (UIT 2201, Networks) Page 21 Copyright © 2007 by Leong Hon Wai

Comparison of Transmission Speed Figure 7. 3: Transmission Time of an Image at Different Transmission Speeds Hon Wai Leong, NUS (UIT 2201, Networks) Page 22 Copyright © 2007 by Leong Hon Wai

Communication Links (continued) q Wireless Data Communication v Uses radio-wave, microwave, infrared v Enables “mobile computing” v Two types: u Wireless Local Access Network u Wireless Wide-area Access Network Hon Wai Leong, NUS (UIT 2201, Networks) Page 23 Copyright © 2007 by Leong Hon Wai

Local Area Networks q Local Area Networks (LAN) v Used to connects computers in a small area (say, in a building) q Common LAN topologies Hon Wai Leong, NUS (UIT 2201, Networks) Page 24 Copyright © 2007 by Leong Hon Wai

Local Area Networks (cont…) q Most commonly wired by Ethernet v Using bus topology v Two ways to wire-up an Ethernet LAN Hub Shared Cable Hon Wai Leong, NUS (UIT 2201, Networks) Page 25 Copyright © 2007 by Leong Hon Wai

Ethernet n n Bob Metcalfe at Xerox PARC Used for local area networks (LANs) n n n Physically near one another 200 computers within 100 meters Broadcast medium n Single wire connects all computers n n n Each computer has unique 48 -bit MAC address All computers constantly listen “Carrier Sense, Multiple Access with Collision Detect” n n Sender waits until wire unused before sending If hears collision, stops, waits random time, retransmits

Ethernet

Ethernet Variations

Ethernet Properties Shared n Distributed (not Centralized) n Insecure n Unpredictable Latency & Bandwidth n But it works! n n Under light load (<30%), appears to be point-topoint

Alternative to Ethernet: Token Ring Alternative introduced by IBM (1980 s) n “Passing the Conch Shell” n

Wide Area Networks q To connect across town, country, ocean q Dedicated point-to-point lines q Expensive. v By major service providers (SP) v Users buy services from SP q Uses different protocol: v Store-and-forward, packet-switched tech. Hon Wai Leong, NUS (UIT 2201, Networks) Page 31 Copyright © 2007 by Leong Hon Wai

Wide Area Networks q To connect across town, country, ocean Figure 7. 7: Typical Structure of a Wide Area Network Hon Wai Leong, NUS (UIT 2201, Networks) Page 32 Copyright © 2007 by Leong Hon Wai

Overall Structure of the Internet q All real-world networks, including the Internet, are a mix of LANs and WANs v Example: A company or a college u One or more LANs connecting its local computers u. Individual LANs interconnected into a wide-area company network Hon Wai Leong, NUS (UIT 2201, Networks) Page 33 Copyright © 2007 by Leong Hon Wai

Structure of Large Network q Large networks contains hybrid… Figure 7. 8(a): Structure of a Typical Company Network Hon Wai Leong, NUS (UIT 2201, Networks) Page 34 Copyright © 2007 by Leong Hon Wai

Figure 7. 8(b): Structure of a Network Using an ISP Hon Wai Leong, NUS (UIT 2201, Networks) Page 35 Copyright © 2007 by Leong Hon Wai

Figure 7. 8(c): Hierarchy of Internet Service Providers Hon Wai Leong, NUS (UIT 2201, Networks) Page 36 Copyright © 2007 by Leong Hon Wai

Overall Structure of the Internet (cont…) q Internet Service Provider (ISP) v A wide-area network v Provides a pathway from a specific network to other networks, or from an individual’s computer to other networks q ISPs are hierarchical v Interconnect to each other in multiple layers to provide greater geographical coverage Hon Wai Leong, NUS (UIT 2201, Networks) Page 37 Copyright © 2007 by Leong Hon Wai

Overall Structure of the Internet q Internet v A huge interconnected “network of networks” v Includes nodes, LANs, WANs, bridges, routers, and multiple levels of ISPs v Early 2003 u 170 million nodes (hosts) u. Hundreds of thousands of separate networks located in over 225 countries Hon Wai Leong, NUS (UIT 2201, Networks) Page 38 Copyright © 2007 by Leong Hon Wai

Communication Protocols q A protocol v A mutually agreed upon set of rules, conventions, and agreements for the efficient and orderly exchange of information q TCP/IP v The Internet protocol hierarchy v Governs the operation of the Internet v Five layers Hon Wai Leong, NUS (UIT 2201, Networks) Page 39 Copyright © 2007 by Leong Hon Wai

Figure 7. 10 The Five-Layer TCP/IP Internet Protocol Hierarchy Hon Wai Leong, NUS (UIT 2201, Networks) Page 40 Copyright © 2007 by Leong Hon Wai

Physical Layer q Protocols govern the exchange of binary digits across a physical communication channel q Goal: Create a bit pipe between two computers Hon Wai Leong, NUS (UIT 2201, Networks) Page 41 Copyright © 2007 by Leong Hon Wai

Data Link Layer q Protocols carry out v Error handling v Framing q Creates an error-free message pipe q Composed of two services v Layer 2 a: Medium access control v Layer 2 b: Logical link control Hon Wai Leong, NUS (UIT 2201, Networks) Page 42 Copyright © 2007 by Leong Hon Wai

Data Link Layer (continued) q Medium access control protocols v Determine how to arbitrate ownership of a shared line when multiple nodes want to send at the same time q Logical link control protocols v Ensure that a message traveling across a channel from source to destination arrives correctly Hon Wai Leong, NUS (UIT 2201, Networks) Page 43 Copyright © 2007 by Leong Hon Wai

Network Layer q Delivers a message from the site where it was created to its ultimate destination q Critical responsibilities v Create a universal addressing scheme for all network nodes v Deliver messages between any two nodes in the network Hon Wai Leong, NUS (UIT 2201, Networks) Page 44 Copyright © 2007 by Leong Hon Wai

Network Layer (continued) q Provides a true network delivery service v Messages are delivered between any two nodes in the network, regardless of where they are located q IP (Internet Protocol) layer v Network layer in the Internet Hon Wai Leong, NUS (UIT 2201, Networks) Page 45 Copyright © 2007 by Leong Hon Wai

Transport Layer q Provides a high-quality, error-free, order- preserving, end-to-end delivery service q TCP (Transport Control Protocol) v Primary transport protocol on the Internet v Requires the source and destination programs to initially establish a connection Hon Wai Leong, NUS (UIT 2201, Networks) Page 46 Copyright © 2007 by Leong Hon Wai

Figure 7. 15: Logical View of a TCP Connection Hon Wai Leong, NUS (UIT 2201, Networks) Page 47 Copyright © 2007 by Leong Hon Wai

Application Layer q Implements the end-user services provided by a network q There are many application protocols v HTTP v SMTP v POP 3 v IMAP v FTP Hon Wai Leong, NUS (UIT 2201, Networks) Page 48 Copyright © 2007 by Leong Hon Wai

Figure 7. 16: Some Popular Application Protocols on the Internet Hon Wai Leong, NUS (UIT 2201, Networks) Page 49 Copyright © 2007 by Leong Hon Wai

Application Layer (continued) q Uniform Resource Locator (URL) v A symbolic string that identifies a Web page v Form protocol: //host address/page v The most common Web page format is hypertext information u. Accessed using the HTTP protocol Hon Wai Leong, NUS (UIT 2201, Networks) Page 50 Copyright © 2007 by Leong Hon Wai

Network Services and Benefits q Services offered by computer networks v Electronic mail (email) v Bulletin boards v News groups v Chat rooms v Resource sharing u. Physical resources u. Logical resources Hon Wai Leong, NUS (UIT 2201, Networks) Page 51 Copyright © 2007 by Leong Hon Wai

Network Services and Benefits … q Services offered by computer networks v Client-server computing v Information sharing v Information utility v Electronic commerce (e-commerce) Hon Wai Leong, NUS (UIT 2201, Networks) Page 52 Copyright © 2007 by Leong Hon Wai

WWW and Hypertext documents Figure 7. 21 Hypertext Documents Hon Wai Leong, NUS (UIT 2201, Networks) Page 53 Copyright © 2007 by Leong Hon Wai

WWW – web-pages q Web-pages are documents v similar to any other document, but v written in special “web-languages” uhtml (hypertext markup language) uxml (extensible markup language) v Allows text, pictures, formatting, etc q More sophisticated web-pages v Dynamic pages (dhtml) v Allows “programming” u. Pages with forms, questionnaires, etc u. Languages: cgi, perl, jsp, asp, etc… Hon Wai Leong, NUS (UIT 2201, Networks) Page 54 Copyright © 2007 by Leong Hon Wai

WWW – continued… q Tools for Creating Web-Pages v Back to basics (eg: UIT 2201 pages) v Frontpage, Dreamweaver, etc q Web-Sites v Individual Servers v Web-Hosting Servers q Web Applications v Forms, registration, etc v ASP (Application Service Providers) Hon Wai Leong, NUS (UIT 2201, Networks) Page 55 Copyright © 2007 by Leong Hon Wai

Summary q Computer network: A set of independent computer systems connected by telecommunication links q Options for transmitting data on a network: Dial-up telephone lines, DSL, cable modem, Ethernet, Fast Ethernet q Types of networks: Local area network (LAN) and wide area network (WAN) Hon Wai Leong, NUS (UIT 2201, Networks) Page 56 Copyright © 2007 by Leong Hon Wai

Summary (continued) q The Internet is a huge interconnected "network of networks" q TCP/IP is the Internet protocol hierarchy, composed of five layers: physical, data link, network, transport, and application q The World Wide Web is an information system based on the concept of hypertext Hon Wai Leong, NUS (UIT 2201, Networks) Page 57 Copyright © 2007 by Leong Hon Wai

Thank you. Hon Wai Leong, NUS (UIT 2201, Networks) Page 58 Copyright © 2007 by Leong Hon Wai