Chapter 2Making the Connection:The Basics of Networking
Copyright 2006 Pearson Addison-Wesley. All rights reserved.
Networked Computers Change Our LivesThe Connected/Networked Information Age has brought profound changesNowhere is remote (True?)People are interconnected (Everyone?)Social relationships are changing (How?)English may be becoming a universal languageFreedom of speech and assembly have expandedOther Issues? Security, Privacy, Oversight?
Nowhere Is RemoteInternet is a complete information resource (almost) no matter where you areSome differences remain because older sources are not yet all onlineNorth Korea? China? Mt. Everest?Homes are not remote from workInformation workers can telecommute and live long distances from their officesWorking longer hours? 24/7?
People Are More InterconnectedFamily and friends can stay in closer, more frequent contact via Internet than via telephone or "snail mail"Network effect People and ComputersWWW lets us meet people passivelyPeople with similar interests find each other through search engines, social media, etc.Associations can form rapidlyFacebook. Twitter. Quality? Privacy? Other Issues?
Social Interactions Are ChangingTime spent online displaces other in-person social activities (displacement effect)The effects are complicated. Pros? Cons?The Internet is changing social interactions, but we don't (yet) fully understand how
Is English Becoming a Universal Language?Influence of American pop culture since World War IIDominance of science and technology in English-speaking countries (Even countries such as China and India use English widely in technical fields)Much software is available only in EnglishMost web pages are in English. Changing?Universal or Common? Thoughts?
Freedom of Speech and of Assembly Have ExpandedInternet use is unmediated (True or False?)No editorial oversight or significant restrictionsAllows for political and artistic expressionBlogs record personal, political, artistic thoughts for public viewing (Sourced vs. Social content)Like-minded people can communicate, even on private topicsRepercussions? Google a potential date or employee/employer? Professor?
Communication TypesGeneral CommunicationSynchronous: sender and receiver are active at the same time (telephone call, IM)Asynchronous: sending and receiving occur at different times (email, podcast)Broadcast communication (all) or Multicast (group): single sender and many receivers (Email, Twitter, Feeds, etc.)Point-to-point communication: single sender and single receiver (Letter, cell call, etc.)
Internet's Communication PropertiesInternet provides a universal communication medium" linking all computers connected to itCan be applied in many ways:Point-to-point asynchronousEmail is alternative to standard mailPoint-to-point synchronous (virtual)IM, Skype is alternative to telephoneMulticasting (and conferencing)Chat rooms are alternatives to magazinesBroadcastingWeb pages are alternatives to radio and television, newspapers and books.
The Client/Server Interaction ProtocolServer is the computer that stores information (web page, files, images, email, etc.) or provides servicesClient computer & software accesses the informationWhen you click link, your computer enters the client/server relationship with web serverOnce the page is sent to you, the client/server relationship ends. (Stateless communication)Server can form many brief relationships so it can serve many clients at the same timeClients may access one or many servers over time, depending on individual needs. May also serve.
Computer IP AddressesEach computer connected to the Internet is given a unique numerical address. four numbers (0-255, or 00-FF hexadecimal - one byte each) separated by dotsExample: 22.214.171.124 Memorizing?Billions, but still running out (IPv4 vs. IPv6)Hostnames: Human-readable symbolic names, based on domain hierarchyEasier to read and rememberExample: www.iona.edu
DNS ServersThe Domain Name System translates the human-readable names into IP addressesInternet host knows the IP address of its nearest DNS name server, a computer that keeps a list of domain names and corresponding IP addressesWhen you use a hostname to send information, your computer asks the DNS server to look up the IP address (client-server!)If the DNS server doesn't know the IP address, it asks a authoritative name server (aka Root name server), which keeps the master list of name-to-address relationships
Top-level DomainsDomain is a related group of networked computersTop-level domains appear in the last part of domain name:.edueducational institutions.orgorganizations.netnetworks.milmilitary.govgovernment agenciesMnemonic two-letter country designators such as .ca (Canada)Long List in book and at:http://en.wikipedia.org/wiki/Internet_country_codes
Example: spiff.cs.washington.eduThe name of the computer is spiffWhich is part of the Computer Science and Engineering Department domain (cs)Which is part of the University of Washington domain (washington)Which is part of the educational domain (edu)Hierarchy of Domain Names
Following Protocol - TCPProtocol is how the information is actually sentTCP/IP (Transmission Control Protocol/ Internet Protocol)Information is broken into a sequence of small fixed-size units called IP packetsEach packet has space for the unit of data, the destination IP address, and a sequence numberThe packets are sent over the Internet one at a time using whatever route is availableBecause each packet can take a different route, congestion and service interruptions do not delay transmissions
Moving Packets: Wires and MoreInternet uses electrical, electronic, and fiber optical communication meansTelephone lines, dedicated fiber optic lines, etc.The technology used to move the packet is independent from the protocol; transmission of a single file may use multiple technologies
Far and Near: WAN and LANInternet is a collection of Wide Area Networks (WAN), designed to send information between widely separated locationsLocal Area Networks (LAN) connect computers usually close enough to be linked by a single cable or wire pair. Can also be bridged (Iona-Rockland)Ethernet is the main technology for LAN Often used to connect all the computers in a lab or buildingWireless is also a major LAN technology
EthernetChannel (wire, wire pair, or optical fiber) that winds past a set of computersEach computer is connected to the channel, allowing it to send a signal that can be detected by all computers connected to the channelDecentralized scheme: Each computer listens to the channel. If it's quiet, it's free. The computer transmits unless another starts at the same time. In that case, both stop for a random time and then try again.
Connecting a Computer to the InternetBy ISP (for home users, small busines):Internet Service Providers (ISP) sell connections to the Internet (like Comcast and Earthlink)User plugs into telephone system or dedicated connection (DSL, Cable Modem) to ISP Home computer talks to ISP's computerModems convert the bits a computer outputs into a form that is compatible with the carrierISP's computer is connected to Internet, and relays information for its customers
Connecting a Computer to the InternetBy Enterprise Network Connections (LAN):Large networked organizations such as schools, businesses, or governmental unitsThe organization creates a LAN or intranetThe intranet connects to the Internet by a gatewayInformation from a Web computer is sent across Internet, through gateway, across LAN to user's computer
Wireless Networks Protocol 802.11A variation on the LAN connectionA computer (called the hub or router) is physically connected to the InternetThe hub broadcasts and receives radio frequency (rf) signalsMobile computers also send and receive signalsThe hub relays Internet requests for the networked computers
The World Wide Web (WWW)Web servers: Computers programmed to send files (web pages, images, audio, video, etc.) to browsers running on other computers connected to the InternetWeb servers and their files make up the World Wide Web. (Structure + Information)The World Wide Web is a subset of the Internet, one service out of many.The Internet is the road, the Web is one form of traffic on the road
Requesting a Web PageWeb request creates a client/server interactionUniform Resource Locator (URL) has 3 main parts:http://www.widgets.com/hardware/support/faq.htmlProtocol: http://ftp://Hypertext Transfer ProtocolFile Transfer ProtocolTells the computer how to handle the fileServer computer's name:Server's IP address translated by the domain hierarchy (DNS Domain Name System)Page's pathname:Tells the server which file (page) is requested and where to find it.
The Internet, the Web & Domain NamesWWW is just a name; web sites do not have to use itFor DNS to work, user must give the exact domain name. (Server or Browser may insert the "www)To help users reach them, organizations can do :Redirection: Supply the probable addressRegister multiple domain namesExample: Museum of Modern Art has registered both "moma.org" and "www.moma.org" to the same IP address
Describing a Web PagePages are stored as a description of how they should appear on the screen (markup)Web browser creates and presents the image from the description file (source file)Browser can adapt the displayed page more easily this way. Most files are smaller.Menu: View --> Source or Page Source in a browser to see the HTML or other codeNote that code is NOT WYSIWYG!
Hypertext WWWs Common LanguageHypertext Markup Language (HTML and XHT