3: Chapter Making the Connection: The Basics of Networking
Fluency with Information Technology Third Edition
by Lawrence Snyder
Networked Computers Change Our Lives
The Information Age has brought profound changes
Nowhere is remote People are interconnected Social relationships are changing English is becoming a universal language Freedom of speech and assembly have expanded
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Nowhere Is Remote
Internet is a complete information resource no matter where you are
Some differences remain because older sources are not yet all online
People Are More Interconnected
Family and friends stay in closer, more frequent contact via Internet than via telephone or "snail mail" WWW lets us meet people passively
People with similar interests find each other through search engines Associations can form rapidly
Homes are not remote from work
Information workers can telecommute and live long distances from their offices
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Social Interactions Are Changing
Time spent online displaces other inperson social activities (displacement effect) The effects are complicated (pros/cons) The Internet is changing social interactions, but we don't fully understand how
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English Is Becoming a Universal Language
Influence of American pop culture since World War II Dominance of science and technology in English-speaking countries Much software is available only in English Most web pages are in English
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Freedom of Speech and of Assembly Have Expanded
Internet use is unmediated
No editorial oversight or significant restrictions Wikis
Communication Types
General Communication
Synchronous: sender and receiver are active at the same time
e.g., telephone call, instant messaging (IM)
Allows for political and artistic expression Blogs record personal thoughts for public viewing Like-minded people can communicate, even on private topics
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Asynchronous: sending and receiving occur at different times
e.g., e-mail
Broadcast communication (or multicast): single sender and many receivers Point-to-point communication: single sender and single receiver
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The Internet's Communication Properties
Internet provides a general communication "fabric" linking all computers connected to it
Can be applied in many ways:
Point-to-point asynchronous
E-mail is alternative to standard mail
Point-to-point synchronous
IM is alternative to telephone
Multicasting
Chat rooms are alternatives to magazines
Broadcasting
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Web pages are alternatives to radio and television
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The Client/Server Structure
Server is the computer that stores the web page
Web server, file server, mail server
Client is the computer that accesses the web page When you click link, your computer enters client/server relationship with web server Once the page is sent to you, the client/server relationship ends Server can form many brief relationships so it can serve many clients at the same time
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The Medium of the Message
The Name Game of Computer Addresses
IP addresses: Each computer connected to the Internet is given a unique numerical address
For example: 128.95.1.207
Hostnames: Human-readable symbolic names, based on domain hierarchy
Easier to read and remember For example: spiff.cs.washington.edu
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DNS Servers
The Domain Name System (DNS) translates the humanreadable hostnames into IP addresses Internet host knows the IP address of its nearest DNS server, a computer that keeps a list of host/domain names and corresponding IP addresses When you use a hostname to send information, your computer asks the DNS server to look up the IP address If the DNS server doesn't know the IP address, it asks a Root name server, which keeps the master list of nameto-address relationships
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Top-level Domains
Domain is a related group of networked computers Top-level domains appear in the last part of domain name:
.edu educational institutions .org organizations .net networks .mil military .gov government agencies Mnemonic two-letter country designators such as .ca (Canada)
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Following Protocol
A protocol describes how the information is actually sent TCP/IP (Transmission Control Protocol/Internet Protocol)
Information is broken into a sequence of small fixed-size units called IP packets Each packet has space for the unit of data, the source and destination IP addresses, and a sequence number The packets are sent over the Internet one at a time using whatever route is available Because each packet can take a different route, congestion and service interruptions do not delay transmissions
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Moving Packets: Wires and More
Internet uses electrical, electronic, and optical communication means Telephone 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 LAN
Internet is a collection of Wide Area Networks designed (WAN), to send information between widely separated locations
Multiple hops
ping, traceroute
Local Area Networks (LAN) connect computers close enough to be linked by a single cable or wire pair
Ethernet is the main technology for LAN
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Ethernet
Channel (wire, wire pair, or optical fiber) that winds past a set of computers Each computer is connected to the channel, allowing it to send a signal that can be detected by all computers connected to the channel Decentralized scheme: Each computer listens to the channel, and 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.
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Connecting a Computer to the Internet
By ISP:
Internet Service Providers sell connections to Internet (like AOL and Earthlink) User plugs into telephone system or dedicated connection to ISP (DSL, cable) Home computer talks to ISP's computer ISP's computer is connected to Internet, and relays information for its customers
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Connecting a Computer to the Internet (cont'd)
By Enterprise Network Connections (LAN):
Large networked organizations such as schools, businesses, or governmental units The organization creates a LAN or intranet The intranet connects to the Internet by a gateway Information from a Web computer is sent across Internet, through gateway, across LAN to user's computer
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Wireless Networks
A variation on the LAN connection A computer (called the access point or hub) is physically connected to the Internet (wired)
The hub broadcasts and receives radio frequency (rf) signals (wireless) Mobile computers also send and receive signals (wireless) Access point hands out temporary IP addresses via DHCP (Dynamic Host Configuration Protocol)
The World Wide Web
Web servers: Computers programmed to send files to browsers running on other computers connected to the Internet Web servers and their files make up the World Wide Web The World Wide Web is a subset of the Internet
The hub relays Internet requests for the connected wireless computers
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Requesting a Web Page
Web request creates a client/server interaction Uniform Resource Locator (URL) has three main parts
http://www.widgets.com/hardware/support/faq.html
Describing a Web Page
Pages are stored as a description of how they should appear on the screen Web browser created the image from the description file
Browser can adapt the source image more easily
1. Protocol:
http:// ftp:// Hypertext Transfer Protocol File Transfer Protocol Tells the computer how to handle the file
2. Server computer's name:
Server's IP address given by the domain hierarchy
3. Page's pathname:
Tells the server which file (page) is requested and where to find it.
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Hypertext
Hypertext Markup Language (HTML) Markup languages describe the layout of a document
Margin width Font Text style Image placement Etc.
The Internet and the Web
When is the "www" required and when is it optional? WWW is just a name; web servers do not have to use it In order for DNS to work, user must give the exact hostname To help users reach them, organizations do two things:
1. Redirection: server inserts the &...