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CS10001 Class Note: Chapter 8 Networking and Digital Communication
Objectives
 Describe the basic types of technology that make telecommunication possible
 Describe the nature and function of local area networks and wide area networks
 Discuss the uses and implications of email, instant messaging, blogging, teleconferencing,
and other forms of online communication
 Explain how wireless network technology is transforming the ways people work and
communicate
 Describe current and future trends in telecommunications and networking
Arthur C. Clarke’s Magical Prophecy
 Clarke’s laws
 If an elderly but distinguished scientist says that something is possible, he is almost
certainly right, but if he says that it is impossible he is very probably wrong.
 The only way to find the limits of the possible is to go beyond them into the impossible.
 Any sufficiently advanced technology is indistinguishable from magic.
Tomorrow’s Technology and You 9/e
 Arthur C. Clarke’s most famous work was the monumental 1968 film 2001: A Space
Odyssey, in which he collaborated with movie director Stanley Kubrick.
 Clarke’s most visionary work may be a paper published in 1945 in which he predicted the
use of geostationary communications satellites—satellites that match the Earth’s rotation so
they can hang in a stationary position relative to the spinning planet below, relaying wireless
transmissions between locations on the planet.
Basic Network Anatomy
 A computer network is any system of two or more computers that are linked together.
 How is networking important?
 People share computer hardware, thus reducing costs.
 People share data and software programs, thus increasing efficiency and production.
 People work together in ways that are otherwise difficult or impossible.
 Networks near and far
 In a LAN (local area network), computers are physically close to each other, usually in
the same building.
 Computers are linked within a building or cluster of buildings.
 Each computer and peripheral is an individual node on the network.
 Nodes are connected by cables, which may be either twisted pair (copper wires) or
coaxial cable.
 In a wireless network each node has a tiny radio (or less commonly, infrared) transmitter
connected to its network port.
 Computers send and receive data through the air rather than through cables.
 A MAN (metropolitan area network) links two or more LANs within a city.
 A WAN (wide area network) extends over a long distance.
 Each networked LAN
 site is a node on the WAN
 Data transmitted over common pathways called backbones
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 Communication frequently happens between LANs and WANs
 Routers: hardware devices or software programs that route messages as they travel
between networks
 Mesh networks: an alternative to today’s networks; rely on centralized routers
– Used to set up small, temporary communication systems
– Example: emergency personnel use at
fire scenes to coordinate actions
The importance of bandwidth
 Bandwidth refers to the quantity of data that can be transmitted through a communication
medium in a given amount of time.
 Typically measured in kilobits or megabits per second
 Bandwidth can be affected by:
– Physical media of the network
– Amount of traffic on the network
– Type of network connection
Specialized networks: from GPS to financial systems
 GPS (global positioning system)
 GPS is a specialized network developed by U.S. Department of Defense.
 It includes 24 satellites that circle the Earth.
 Each satellite contains a computer, an atomic
clock, and a radio.
 On the ground, a GPS receiver can use signals broadcast by three or four visible
satellites to determine its position.
 Networks that keep our global financial systems running:
 ATM (automated teller machine): a specialized terminal linked to a bank’s
main computer through a commercial banking network
 Choices for connecting their computer to a network
 Direct connection using cables
 Dial-up access to a remote system using phone lines to dial in directly
 Use the Internet to find the way to the computer they need to find
Direct connections
 A direct or dedicated connection is usually faster than other connection options
 Can transmit up to 100 Mbps (megabits per second)
 Common connections:
 T1–transmits voice, data, and video at about 1.5 Mbps
 T3–transmits data at about 45 Mbps
 Fiber optic–transmits data at more than 1 Gbps (gigabit per second)
Communication á la modem
 Called a dial-up connection
 Modem: a hardware device that connects a computer’s serial port to a telephone line (for
remote access)
 May be internal on the system board or external, sitting in a box linked to a serial port
 Modem transmission speed measured in bps (bits per second)
 Transmit at 28,000 bps to 56.6K bps
 Computers send digital signals.
 The modem (modulator/demodulator) converts the digital signals to analog so that the
message can be transmitted through telephone lines and then converts it back on the other
end.
 Internal modem is installed inside the computer’s chassis
 External modem is connected to the computer via a serial port or USB port
 Fax modem communicates with facsimile machines and computers
 Sometimes referred to as narrowband connections because of the low data transmission
speed
 Broadband connections
 Broadband connection is a connection with much greater bandwidth than modems have
 DSL uses standard phone lines and is provided by phone companies in many areas.
 Cable modems provide fast network connections through cable television networks in
many areas.
 High-speed wireless connections can connect computers to networks using radio
waves rather than wires.
 Satellite dishes can deliver fast computer network connections as well as television
programs.
 Wireless Network Technology
 A lightning-fast network connection when you’re away from your desk and when
bandwidth is less important than mobility and portability.
 The fastest growing wireless LAN technology is known as Wi-Fi .
 802.11b, 802.11g, and 802.11n are variations of IEEE 802.11 specifications for
wireless local area networks.
 Wi-Fi range is affected by
– Objects that may block signals
– Antenna placement
– Devices competing with other wireless networks for the same air space
 WiMAX is a new radio-based wireless standard where a single tower can provide
access to a 25-square-mile area.
 WEP (wired equivalent privacy) and firewalls are a way to help protect your
computer while using a wireless connection.
 Bluetooth: another type of wireless technology
 Named for a Danish king who overcame his country’s religious differences
 Overcomes differences between mobile phones, handheld computers, and PCs,
making it possible for all of these devices to communicate with each other regardless
of operating system
 With Bluetooth it’s possible to create a
PAN (personal area network)—a network that links a variety of personal electronic
devices so they can communicate with each other.
 Bluetooth technology is currently limited to simple device connectivity, but in the future
it will open up all kinds of possibilities:
 A pacemaker senses a heart attack and notifies the victim’s mobile phone to dial 911.
 A car radio communicates with parking-lot video cameras to find out where spaces
are available.
 More examples of Bluetooth possibilities:
 A pen scans business cards and sends the information to a PDA inside a briefcase.
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A medical wristband transmits an accident victim’s vital information to a doctor’s
handheld computer.
 A cell phone tells you about specials on clothes that are available in your size as you
walk past stores in a mall.
 Communication Software
 Protocol is a set of rules for the exchange of data between a terminal and a computer or
two computers.
 Communication software establishes a protocol that is followed by the computer’s
hardware.
 Communication software takes many forms:
 NOS (network operating system)
– System handles communications among many workstations.
 Client/server model
– One or more computers act as dedicated servers and all the remaining computers
act as clients.
 Peer-to-peer model
– Every computer on the network is both client and server.
 Many networks are hybrids, using features of the client/server and peer-to-peer
models.
 The Network Advantage
 Why do people use networks?
 Networks enable people to share computer hardware resources, reducing costs and
enabling people to take advantage of powerful computer equipment.
– Print servers that will organize print jobs from multiple users
 Networks enable people to share data and software programs, increasing efficiency
and productivity.
– Access to file servers, or storehouses for software and data, that users can share
 Networks enable people to work together or collaborate in ways that are difficult or
impossible without network technology.
– Groupware are programs designed to enable several networked users to work on
documents at the same time
Interpersonal Computing: From Communication to Communities
 The Many Faces of Email
 Email systems enable you to send and receive messages to others on the network.
 Web-based email systems and many older UNIX-based programs require that read and
unread messages are stored in post office boxes or folders on the remote mail servers.
 Many email messages are plain ASCII text.
 Even if their software can display HTML mail, not all email users want HTML emails:
 HTML encoding can slow down an email program
 An HTML email message can also carry a Web bug, an invisible piece of code that
reports information back to the sender
 Most email programs can send and receive formatted word processor documents, pictures,
and other multimedia files as attachments to messages.
 Email Issues
 Spam or junk email
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 Emails may contain links that trick users to enter phishing sites, which may capture
sensitive financial information.
Mailing Lists
 Mailing lists enable you to participate in email discussion groups on special-interest
topics.
 Subscribing to a busy list might mean receiving hundreds of messages each day.
 To avoid being overwhelmed by incoming mail, many list members sign up to receive
them in daily digest form.
 Some lists are moderated to ensure that the quality of the discussion remains high.
Newsgroups, Web Forums, and Blogs
 Newsgroup: a public discussion on a particular subject
 Notes are written to a central Internet site.
 Notes are redistributed through a worldwide newsgroup network called USENET.
 Listserv mail messages are delivered automatically to your mailbox, but you have to
seek out information in newsgroups.
 Mailing list messages are sent to a specific group of people, whereas newsgroup
messages are available for anyone to see.
 Moderated newsgroups contain only messages that have been filtered by designated
moderators.
 Blogs are an online journal that is updated frequently.
 Can have text, pictures, and other media
Rules of Thumb: Online Survival Tips
 Let your system do as much of the work as possible
 Store names and addresses in computer-accessible address book
 Don’t share your email address
 Don’t open suspicious attachments
 Protect your privacy
 Cross-check online information sources
 Be aware and awake
 Avoid information overload
Instant Messaging, Text Messaging, and Teleconferencing: Real-Time Communication
 Mailing lists and newsgroups are delayed or asynchronous communication.
 The sender and the recipients don’t have to be logged in at the same time.
 IM (instant messaging) has been possible since the days of text-only Internet access.
 Newer, easier to use messaging systems from AOL, Microsoft, Yahoo!, Apple, and
others have turned instant messaging into one of the most popular Internet activities.
 Online services also offer chat rooms—public or private virtual conference rooms where
people with similar interests or motivations can type messages to each other and receive
near instant responses.
 Several IM programs make it possible to carry on two-way video teleconferences.
 A video teleconference enables two or more people to communicate face to face over
long distances by combining video and computer technology.
Computer Telephony
 Voice mail is a messaging system with the ability to store, organize, and forward
messages.
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An example of a growing trend toward CTI (computer telephony integration) is the
linking of computers and telephones to gain productivity.
 It’s also possible to send voice signals through a LAN, a WAN, or the Internet, bypassing
the phone companies (and their charges) altogether.
 Handheld PDA computers use software to integrate the functions of a PDA, a phone, and
an Internet terminal.
 Internet telephony has become a legitimate competitor to traditional phone companies.
 VoIP (Voice-over IP) requires a broadband connection to carry your call over the
Internet.
 You can place a call using either a traditional phone with an adapter or an Internetconnected PC with a microphone headset and appropriate software.
 Advantages of VoIP
 Calls are less expensive if you already have a broadband connection.
 Calls are routed to you no matter where you are connected.
 VoIP phones integrate more easily with online address books, video conference
services, and other Internet services.
 Disadvantages of VoIP
 Communication is impossible during a power outage (most networks are unusable).
 There is no 911 or directory assistance service available.
 Quality is suspect because there is no guarantee of packets being delivered in a timely
manner.
Social Networking, Role Playing, and Virtual Communities
 Online communities such as MySpace and Facebook
 MMORPG (Massively multiplayer role playing games)
 SecondLife
Information Sharing: Social Bookmarking, Wikis, Media Sharing, and Crowdsourcing
 A wiki is a Web site designed to enable anyone who accesses it to contribute to it.
 A viral video is a video that spreads like a virus through email, blogs, or IMs
 YouTube has become a popular place to host the viral videos.
 Crowdsourcing is outsourcing of a task to a large community of people instead of
depending on a small group of contracted specialists.
Sharing Resources: Peer-to-Peer, Grid, and Cloud Computing
 Peer-to-peer file sharing allows users to share files, usually music, by making their hard
drives available to other users rather than posting them on a central server.
 Grid computing is about sharing processing power rather than sharing data.
 Cloud computing is a form of grid computing, but the resources come from the Internet
rather than a specific source.
Digital Communication in Perspective
 Many services we take for granted today—video rentals, cable TV, newspapers, and
magazines, for example—will be transformed or replaced by digital high-bandwidth
interactive delivery systems of the future.
 At the same time, entirely new forms of communication are likely to emerge.
 Telecommunications technology is rapidly changing our lives, and the changes will
accelerate as the technology improves.
Netiquette and Messaging Etiquette
 Netiquette is rules and guidelines for using the Internet.
 Rules of thumb:
 Say what you mean, and say it with care
 Keep it short
 Proofread your messages
 Don’t assume you’re anonymous
 Learn the “nonverbal” language of the Net
 Know your abbreviations
 Keep your cool
 Don’t be a source of spam
 Say no to spam
 Send no-frills mail
 Lurk before you leap
 Check your FAQs
 Know when to disconnect
 Give something back
Lesson Summary
 Networking is one of the most important trends in computing today.
 LANs are made up of computers that are close enough to be directly connected with cables or
wireless radio transmitters/receivers.
 Most LANs include shared printers and file servers.
 WANs are made up of computers separated by considerable distance.
 Many computer networks are connected together through the Internet so messages and data
can pass back and forth among them.
 Some specialized networks, including global positioning systems and financial systems serve
unique functions.
 Most computer networks today use the Ethernet architecture; an Ethernet port is a standard
feature on most modern PCs.
 Communication software takes care of the details of communication between machines—
details like protocols that determine how signals will be sent and received.
 Email, instant messaging, and teleconferencing are the most common forms of
communication between people on computer networks.
 It’s not clear how all of these emerging technologies will converge; what is clear is that the
wireless revolution is far from over.