Hon Wai Leong, NUS (UIT2201, Networks) Page 1 Copyright © 2007 by Leong Hon Wai Networks, Internet & WWW  Reading Materials:  Ch 7 of [SG3]  Additional Notes: (from web-site)  Contents:  Motivation for Networks  Types of Networks and Their Structure  Communication Protocols – routing info  Network Services / Applications  Internet and WWW

Hon Wai Leong, NUS (UIT2201, Networks) Page 2 Copyright © 2007 by Leong Hon Wai Networks, Internet, WWW  Context so far…  Use algorithm to solve problem  Database used to organize massive data  Algorithms implemented using hardware Educational Goals for this Chapter:  The computer as a tool for  Communication and Collaboration  Information Sharing  Resource Sharing  Shared Services

Hon Wai Leong, NUS (UIT2201, Networks) Page 3 Copyright © 2007 by Leong Hon Wai Introduction to Computer Network  What is a Computer Network  Computers connected together  Why: Share information and resources  What kind of information u data files (pictures, videos, audio), programs u movies, tv and radio signals  What kind of services u a shared printer u a shared software application

Hon Wai Leong, NUS (UIT2201, Networks) Page 4 Copyright © 2007 by Leong Hon Wai Basic Networking Concepts  A Computer Network  A set of independent computer systems u connected by telecommunication links  Purpose: u sharing information and resources  Nodes, hosts, or end systems u individual computers on a network

The Ever-changing Internet Different colors based on IP address

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

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

Hon Wai Leong, NUS (UIT2201, Networks) Page 10 Copyright © 2007 by Leong Hon Wai A Brief History of the Internet and the World Wide Web: The Internet  August 1962: First proposal for building a computer network  Made by J. C. R. Licklider of MIT  ARPANET  Built by the Advanced Research Projects Agency (ARPA) in the 1960s  Grew quickly during the early 1970s

Hon Wai Leong, NUS (UIT2201, Networks) Page 11 Copyright © 2007 by Leong Hon Wai The Internet (continued)  NSFNet: A national network built by the National Science Foundation (NSF)  October 24, 1995: Formal acceptance of the term Internet  Internet service providers start offering Internet access once provided by the ARPANET and NSFNet

ARPANET,

Hon Wai Leong, NUS (UIT2201, Networks) Page 13 Copyright © 2007 by Leong Hon Wai Figure 7.20 State of Networking in the Late 1980s

Hon Wai Leong, NUS (UIT2201, Networks) Page 14 Copyright © 2007 by Leong Hon Wai The World Wide Web  Development completed in May 1991  Designed and built by Tim Berners-Lee  Components  Hypertext u A collection of documents interconnected by pointers called links  URL (Uniform Resource Locator) u The worldwide identification of a Web page located on a specific host computer

History of the Internet Tim Berners-Lee at CERN in 1989 Tim Berners-Lee at CERN in 1989 Proposal for WWW in 1990 Proposal for WWW in 1990 First web page on November 13, 1990 First web page on November 13, 1990 Hypertext - Text that contains links to other text. Hypertext - Text that contains links to other text. Ted Nelson’s Xanadu Ted Nelson’s Xanadu Vannevar Bush’s Memex Vannevar Bush’s Memex( W3C W3C Get more info at:

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

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

Hon Wai Leong, NUS (UIT2201, Networks) Page 18 Copyright © 2007 by Leong Hon Wai The Basic Communication Link  Dial-up telephone line,  A circuit is temporarily established ubetween caller and callee  Analog medium (analog signals)  Requires modem at both ends to transmit information produced by a computer uComputer produces digital information

Hon Wai Leong, NUS (UIT2201, Networks) Page 19 Copyright © 2007 by Leong Hon Wai Figure 7.1 Two Forms of Information Representation Analog vs Digital Signals

Hon Wai Leong, NUS (UIT2201, Networks) Page 20 Copyright © 2007 by Leong Hon Wai Figure 7.2: Modulation of a Carrier to Encode Binary Information Analog  Digital Conversion

Hon Wai Leong, NUS (UIT2201, Networks) Page 21 Copyright © 2007 by Leong Hon Wai The Communication Link (cont…)  Dial-up phone links  Transmission rate: 56 Kbps  Broadband  Transmission rate: > 256 Kbps Home Use: * DSL * Cable modem Office & Commercial Use: * Ethernet * Fast Ethernet * Gigabit Ethernet

Hon Wai Leong, NUS (UIT2201, Networks) Page 22 Copyright © 2007 by Leong Hon Wai Figure 7.3: Transmission Time of an Image at Different Transmission Speeds Comparison of Transmission Speed

Hon Wai Leong, NUS (UIT2201, Networks) Page 23 Copyright © 2007 by Leong Hon Wai Communication Links (continued)  Wireless Data Communication  Uses radio-wave, microwave, infrared  Enables “mobile computing”  Two types: u Wireless Local Access Network u Wireless Wide-area Access Network

Hon Wai Leong, NUS (UIT2201, Networks) Page 24 Copyright © 2007 by Leong Hon Wai Local Area Networks  Local Area Networks (LAN)  Used to connects computers in a small area (say, in a building)  Common LAN topologies

Hon Wai Leong, NUS (UIT2201, Networks) Page 25 Copyright © 2007 by Leong Hon Wai Local Area Networks (cont…)  Most commonly wired by Ethernet  Using bus topology  Two ways to wire-up an Ethernet LAN Hub Shared Cable

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

Ethernet

Ethernet Variations

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

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

Hon Wai Leong, NUS (UIT2201, Networks) Page 31 Copyright © 2007 by Leong Hon Wai Wide Area Networks  To connect across town, country, ocean  Dedicated point-to-point lines  Expensive.  By major service providers (SP)  Users buy services from SP  Uses different protocol:  Store-and-forward, packet-switched tech.

Hon Wai Leong, NUS (UIT2201, Networks) Page 32 Copyright © 2007 by Leong Hon Wai Wide Area Networks  To connect across town, country, ocean Figure 7.7: Typical Structure of a Wide Area Network

Hon Wai Leong, NUS (UIT2201, Networks) Page 33 Copyright © 2007 by Leong Hon Wai Overall Structure of the Internet  All real-world networks, including the Internet, are a mix of LANs and WANs  Example: A company or a college u One or more LANs connecting its local computers uIndividual LANs interconnected into a wide- area company network

Hon Wai Leong, NUS (UIT2201, Networks) Page 34 Copyright © 2007 by Leong Hon Wai Structure of Large Network  Large networks contains hybrid… Figure 7.8(a): Structure of a Typical Company Network

Hon Wai Leong, NUS (UIT2201, Networks) Page 35 Copyright © 2007 by Leong Hon Wai Figure 7.8(b): Structure of a Network Using an ISP

Hon Wai Leong, NUS (UIT2201, Networks) Page 36 Copyright © 2007 by Leong Hon Wai Figure 7.8(c): Hierarchy of Internet Service Providers

Hon Wai Leong, NUS (UIT2201, Networks) Page 37 Copyright © 2007 by Leong Hon Wai Overall Structure of the Internet (cont…)  Internet Service Provider (ISP)  A wide-area network  Provides a pathway from a specific network to other networks, or from an individual’s computer to other networks  ISPs are hierarchical  Interconnect to each other in multiple layers to provide greater geographical coverage

Hon Wai Leong, NUS (UIT2201, Networks) Page 38 Copyright © 2007 by Leong Hon Wai Overall Structure of the Internet  Internet  A huge interconnected “network of networks”  Includes nodes, LANs, WANs, bridges, routers, and multiple levels of ISPs  Early 2003 u170 million nodes (hosts) uHundreds of thousands of separate networks located in over 225 countries

Hon Wai Leong, NUS (UIT2201, Networks) Page 39 Copyright © 2007 by Leong Hon Wai Communication Protocols  A protocol  A mutually agreed upon set of rules, conventions, and agreements for the efficient and orderly exchange of information  TCP/IP  The Internet protocol hierarchy  Governs the operation of the Internet  Five layers

Hon Wai Leong, NUS (UIT2201, Networks) Page 40 Copyright © 2007 by Leong Hon Wai Figure 7.10 The Five-Layer TCP/IP Internet Protocol Hierarchy

Hon Wai Leong, NUS (UIT2201, Networks) Page 41 Copyright © 2007 by Leong Hon Wai Physical Layer  Protocols govern the exchange of binary digits across a physical communication channel  Goal: Create a bit pipe between two computers

Hon Wai Leong, NUS (UIT2201, Networks) Page 42 Copyright © 2007 by Leong Hon Wai Data Link Layer  Protocols carry out  Error handling  Framing  Creates an error-free message pipe  Composed of two services  Layer 2a: Medium access control  Layer 2b: Logical link control

Hon Wai Leong, NUS (UIT2201, Networks) Page 43 Copyright © 2007 by Leong Hon Wai Data Link Layer (continued)  Medium access control protocols  Determine how to arbitrate ownership of a shared line when multiple nodes want to send at the same time  Logical link control protocols  Ensure that a message traveling across a channel from source to destination arrives correctly

Hon Wai Leong, NUS (UIT2201, Networks) Page 44 Copyright © 2007 by Leong Hon Wai Network Layer  Delivers a message from the site where it was created to its ultimate destination  Critical responsibilities  Create a universal addressing scheme for all network nodes  Deliver messages between any two nodes in the network

Hon Wai Leong, NUS (UIT2201, Networks) Page 45 Copyright © 2007 by Leong Hon Wai Network Layer (continued)  Provides a true network delivery service  Messages are delivered between any two nodes in the network, regardless of where they are located  IP (Internet Protocol) layer  Network layer in the Internet

Hon Wai Leong, NUS (UIT2201, Networks) Page 46 Copyright © 2007 by Leong Hon Wai Transport Layer  Provides a high-quality, error-free, order- preserving, end-to-end delivery service  TCP (Transport Control Protocol)  Primary transport protocol on the Internet  Requires the source and destination programs to initially establish a connection

Hon Wai Leong, NUS (UIT2201, Networks) Page 47 Copyright © 2007 by Leong Hon Wai Figure 7.15: Logical View of a TCP Connection

Hon Wai Leong, NUS (UIT2201, Networks) Page 48 Copyright © 2007 by Leong Hon Wai Application Layer  Implements the end-user services provided by a network  There are many application protocols  HTTP  SMTP  POP3  IMAP  FTP

Hon Wai Leong, NUS (UIT2201, Networks) Page 49 Copyright © 2007 by Leong Hon Wai Figure 7.16: Some Popular Application Protocols on the Internet

Hon Wai Leong, NUS (UIT2201, Networks) Page 50 Copyright © 2007 by Leong Hon Wai Application Layer (continued)  Uniform Resource Locator (URL)  A symbolic string that identifies a Web page  Form protocol://host address/page  The most common Web page format is hypertext information uAccessed using the HTTP protocol

Hon Wai Leong, NUS (UIT2201, Networks) Page 51 Copyright © 2007 by Leong Hon Wai Network Services and Benefits  Services offered by computer networks  Electronic mail ( )  Bulletin boards  News groups  Chat rooms  Resource sharing uPhysical resources uLogical resources

Hon Wai Leong, NUS (UIT2201, Networks) Page 52 Copyright © 2007 by Leong Hon Wai Network Services and Benefits …  Services offered by computer networks  Client-server computing  Information sharing  Information utility  Electronic commerce (e-commerce)

Hon Wai Leong, NUS (UIT2201, Networks) Page 53 Copyright © 2007 by Leong Hon Wai Figure 7.21 Hypertext Documents WWW and Hypertext documents

Hon Wai Leong, NUS (UIT2201, Networks) Page 54 Copyright © 2007 by Leong Hon Wai WWW – web-pages  Web-pages are documents  similar to any other document, but  written in special “web-languages” uhtml (hypertext markup language) uxml (extensible markup language)  Allows text, pictures, formatting, etc  More sophisticated web-pages  Dynamic pages (dhtml)  Allows “programming” uPages with forms, questionnaires, etc uLanguages: cgi, perl, jsp, asp, etc…

Hon Wai Leong, NUS (UIT2201, Networks) Page 55 Copyright © 2007 by Leong Hon Wai WWW – continued…  Tools for Creating Web-Pages  Back to basics (eg: UIT2201 pages)  Frontpage, Dreamweaver, etc, etc  Web-Sites  Individual Servers  Web-Hosting Servers  Web Applications  Forms, registration, etc  ASP (Application Service Providers)

Hon Wai Leong, NUS (UIT2201, Networks) Page 56 Copyright © 2007 by Leong Hon Wai Summary  Computer network: A set of independent computer systems connected by telecommunication links  Options for transmitting data on a network: Dial-up telephone lines, DSL, cable modem, Ethernet, Fast Ethernet  Types of networks: Local area network (LAN) and wide area network (WAN)

Hon Wai Leong, NUS (UIT2201, Networks) Page 57 Copyright © 2007 by Leong Hon Wai Summary (continued)  The Internet is a huge interconnected "network of networks"  TCP/IP is the Internet protocol hierarchy, composed of five layers: physical, data link, network, transport, and application  The World Wide Web is an information system based on the concept of hypertext

Hon Wai Leong, NUS (UIT2201, Networks) Page 58 Copyright © 2007 by Leong Hon Wai Thank you.