Data Communications and the Internet

1
Data Communications and the Internet

• Chapter 6

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Learning Objectives

• Know basic telecommunications terminology.
• Know the definition and characteristics of LAN,
  WANs, and internets.
• Understand the nature of processing in a layered
  communications protocol.
• Know the purpose of the five layers of the
  TCP/IP-OSI protocol.
• Understand Ethernet and wireless LANs.
• Understand the characteristics of WANs using
  personal computers with modems to the Internet,
  networks of leased lines, PSDNs and virtual
  private networks.
• Know basic concepts involved in the operation of
  the Internet.

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What Is Telecommunications?

• Telecommunications is any "...process that
  permits the passage from a sender to one or more
  receivers of information of any nature delivered
  in any usable form (printed copy, fixed or moving
  pictures, visible or audible signals, etc.) by
  means of any electromagnetic system (electrical
  transmission by wire, radio, optical
  transmission, guided waves, etc.)." Martin,
  James. Introduction to Teleprocessing. Englewood
  cliffs, NJPrentice-hall, 1972

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What Is Data Communications?

• Data communications "... can be defined as that
  part of telecommunications that relates to
  computer systems, or the electronic transmission
  of computer data. This definition excludes the
  transmission of data to local peripherals such as
  disk, tape, and printers."Stamper, David A.
  Business Data Communications. Redwood city, CA
  Benjamin/Cummings, 1989
• Data communications is sometimes called
  networking because it involves the transmission
  of data over a network.

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What are the Electromagnetic Waves?

• The motion of electrically charged particles
  produces electromagnetic waves. These waves are
  also called "electromagnetic radiation" because
  they radiate from the electrically charged
  particles.
• Radio waves, microwaves, visible light, and x
  rays are all examples of electromagnetic waves
  that differ from each other in wave length.
• Electromagnetic waves need no material medium for
  transmission. Light and radio waves can travel
  through interplanetary and interstellar space
  from the sun and stars to the earth. Regardless
  of their frequency and wavelength,
  electromagnetic waves travel at a speed of
  299,792 km (186,282 mi) per second in a vacuum.
  Berkeley National Lab

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What is the Electromagnetic Spectrum?

• The "electromagnetic spectrum" is a term used to
  describe the entire range of frequencies of
  electromagnetic radiation from zero to infinity.

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What is Electromagnetic Signal Frequency?

• Frequency refers to the number of times a current
  (electromagnetic wave) passes through a complete
  cycle. The measure of frequency is a Hertz (Hz),
  which represents one cycle per second.
• Frequencies are represented from a number from 0
  Hertz to 300 GHz (called the electromagnetic
  spectrum).
• KKilo1,000, MMega1,000,000,
  GGiga1,000,000,000

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What is a Communication Line Bandwidth?

• Communication line bandwidth is the difference
  between the minimum and maximum range of
  frequencies allowed by the communication line.
• Bandwidth higher frequency - lower frequency.
  For example A wire transmits in a frequency
  range from 100 Hz to 2,500 Hz. Its bandwidth is
  2,400 Hz.
• Bandwidth is important because it indicates how
  fast data can be transmitted over a specific
  channel. A wider bandwidth allows faster
  transmission speeds.

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Digital Versus Analog Data

• The world we live is an analog world. Light,
  voice, video are examples of analog data because
  the signal comes in a continuous form. A light
  bulb, for example, emits a steady stream of
  light.
• Analog data refers to physical quantities, which
  in data communications take the form of voltage
  and variations in the properties of waves
  Stamper
• Digital data is composed of items that are
  distinct from one another. That means that the
  items are discrete. Digital computers manipulate
  this type of data by converting it to binary data
  (1 or 0).

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Components of Communication Networks

• In order for communication to occur, there must
  be a source, a medium, a receiver and a message.
• The source (sender) is the device that sends the
  message (transmitter) and is any device that can
  be connected to the network like a PC or a
  telephone.
• The medium connects the source with the receiver
  and can be a copper cable, a fiber-optic cable,
  airwaves or another physical path.
• The receiver is the device that accepts the
  message.
• The message can be a file, a request, a response,
  a status message, a control message or
  correspondence. The message must be
  understandable.

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Communications Protocols

• A protocol is a standard means for coordinating
  an activity between two or more entities.
• A communications protocol is a means for
  coordinating activity between two or more
  communicating computers.
• Two machines must agree on the protocol to use,
  and they must follow that protocol as they send
  messages back and forth.
• Communications protocols are broken into levels
  of layers.

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Fundamental Networking Concepts

• A computer network is a collection of computers
  that communicate with one another over
  transmission lines.
• Three basic types of networks are
• Local area networks (LANs)connects computers
  that reside in a single geographic location on
  the premises of the company that operates the
  LAN.
• Wide area networks (WANs)connects computers at
  different geographic sites.
• Internetsa network of networks
• The networks that comprise an Internet use a
  large variety of communication methods and
  conventions, and data must flow seamlessly across
  them.
• To provide seamless flow, an elaborate scheme
  called a layered protocol is used.

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Local Area Networks

• A local area network (LAN) is a group of
  computers connected together on a single company
  site.
• Usually the computers are located within a half
  mile or so of each other, although longer
  distances are possible.
• The key distinction, however, is that all of the
  computers are located on property controlled by
  the company that operates the LAN.
• Computers and printers are connected via a
  switch, which is a special-purpose computer that
  receives and transmits messages on the LAN.

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NIC Interface Card

• Each device on a LAN (computer, printer, etc.)
  has a hardware component called a network
  interface card (NIC) that connects the devices
  circuitry to the cable.
• The NIC works with programs in each device to
  implement Layer 1 and Layer 2 protocols.
• Each NIC has a unique identifier, which is called
  the (MAC) media access control address.

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Contacted and Radiated Media

• A Communication network cannot exist without a
  medium to connect the source and receiver. If
  this medium can be seen physically, it is
  considered a contacted medium.
• Radiated media, or wireless media, do not use
  physical wires to transmit data. With radiated
  media, the signal is radiated through the air,
  water and vacuum of space.

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Communications Media

• The computers, printers, switches, and other
  devices on a LAN are connected using one of two
  media.
• Most connections are made using unshielded,
  twisted pair (UTP) cable.
• A device called an RJ-45 connector is used to
  connect the UTP cable into NIC devices on the
  LAN.
• The connection between switches can use UTP
  cable, but if they carry a lot of traffic or are
  far apart UTP cable may be replaced by optical
  fiber cables.
• The signals on such cables are light rays, and
  they are reflected inside the glass core of the
  optical fiber cable.

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LANs with Wireless Connections

• Wireless connections have become popular with
  LANs.
• The NIC for wireless devices have been replaced
  by wireless NIC (WNIC)
• For laptop computers, such devices can be cards
  that slide into the PCMA slot or they can be
  built-in, onboard devices.
• Several different wireless standard exist
• As of 2005, the most popular is IEEE 802.11g
• The current standard, 802.11g allows speeds of up
  to 54 Mbps.
• The WNICs operate according to the 802.11
  protocol and connect to an access point (AP).

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IEEE 802.3 or Ethernet Protocol

• The committee that addresses LAN standards is
  called the IEEE 802 Committee.
• Thus, IEEE LAN protocols always start with the
  number 802.
• Today, the worlds most popular protocol for LAN
  is the IEEE 802.3 protocol.
• This protocol standard, also called Ethernet,
  specifies hardware characteristics such as which
  wire carries which signals.
• It also describes how messages are to be packaged
  and processed for transmission over the LAN.
• Most personal computers today are equipped with
  an onboard NIC that supports what is called
  10/100/1000 Ethernet.
• These products conform to the 802.3 specification
  and allow for transmission at a rate of 10, 100,
  or 1,000 Mbps.
• Communications speeds are expressed in bits,
  whereas memory sizes are expressed in bytes.

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Wide Area Networks

• A wide area network (WAN) connects computers
  located at physically separated sites.
• A company with offices in Detroit and Atlanta
  must use a WAN to connect the computers together.
• Because the sites are physically separated, the
  company cannot string wire from one site to
  another.

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Networks of Leased Lines

• A WAN connects computers located at
  geographically distributed company sites.
• The lines that connect these sites are leased
  from telecommunication companies that are
  licensed to provide them.
• A variety of access devices connect each site to
  the transmission.
• These devices are typically special-purposed
  computers.
• The particular devices required depend on the
  line used and other factors
• Sometimes switches and routers are employed.

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Transmission Line Types, Uses, and Speeds
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What is the Internet

• The Internet is a collection of interconnected
  networks, all freely exchanging information.
• The Internet is the most famous computer network
  thats ever build. Its actually a network of
  networks tens of thousands of computers
  connected in a web, talking to one another
  through a common communications protocol."PC
  Magazine

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Connecting the Personal Computer to an ISP

• An Internet service provider (ISP) has three
  important functions
• It provides you with a legitimate Internet
  address.
• It serves as your gateway to the Internet.
• It receives the communication from your computer
  and passes them on to the Internet, and it
  receives communication from the Internet and
  passes them on to you.
• Home computers and those of small businesses are
  commonly connected to an ISP in one of three
  ways
• Using a regular telephone line
• Using a special telephone line called a DSL line
• Using cable TV line
• All three ways require that the digital data in
  the computer be converted to an analog, or wavy,
  signal.
• A device called a modem, or modulator/demodulator
  performs this conversion.

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Dial-Up Modems

• A dial-up modem performs the conversion between
  analog and digital in such a way that the signal
  can be carried on a regular telephone line.
• You dial the number for your ISP and connect.
• The maximum transmission speed for a switch is 56
  kbps.
• The way messages are packaged and handled between
  your modem and the ISP is governed by a protocol
  known as Point-to-Point Protocol (PPP).
• This protocol is used for networks that involve
  just two computers.

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DSL Modems

• A DSL modem is the second modem type.
• DSL stands for digital subscriber line.
• DSL modems operate on the same lines as voice
  telephones and dial-up modems.
• They operate so that their signals do not
  interfere with voice telephone service.
• They provide much faster data transmission speeds
  than dial up modems.
• They always maintain a connection.
• DSL data transmission and telephone conversations
  can occur simultaneously.
• DSL lines that have different upload and download
  speeds are called asymmetric digital subscriber
  lines (ADSL).
• Symmetrical digital subscriber lines (SDSL)
  offers the same speed in both directions.

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Cable Modems

• A cable modem is the third modem type.
• Cable modems provide high-speed data transmission
  using cable television lines.
• At the maximum, users can download data up to 10
  Mbps and can upload data at 256 kbps.
• Narrowband lines typically have transmission
  speeds less than 56 kbps.
• Broadband lines have speeds in excess of 256 kbps.

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IP Addressing Schemes

• Two IP addressing schemes exist IPv4 and IPv6.
• IPv4
• IPv4 constructs addresses having 32 bits.
• These bits are divided into four groups of 8
  bits, and a decimal number represents each group.
• IPv4 addresses appear as 63.224.57.59.
• The largest decimal number that can appear
  between the period are 255 (0 255).
• IPv6
• Due to growth of the Internet IPv6 was developed.
• IPv6 construct addresses having 128 bits.
• Currently both IPv4 and IPv6 are used on the
  Internet.

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Using TCP/IP-OSI Protocols over the Internet

• Network Address Translation
• For Internet traffic, only public IP addresses
  can be used.
• These addresses are assigned in blocks to large
  companies and organizations like ISPs.
• All Internet traffic aimed at any computer within
  an organization's LAN will be sent over the
  Internet using the routers IP public address for
  the given computer.
• The router will receive all packets for all
  computers for the organizations computers.
• When the router receives a packet, it determines
  the internal IP address within the LAN for that
  computer.
• It then changes the address in the packet from
  the routers IP public address to the internal IP
  address of a computer in the organization's LAN,
  the packets true destination.
• The process of changing public IP addresses into
  private IP addresses, and the reverse, is called
  Network Address Translation (NAT).

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Network Addresses MAC and IP

• On most networks, and on every internet, two
  address schemes identify computers and other
  devices.
• Programs that implement Layer 2 protocols use
  physical addresses, or MAC addresses.
• Programs that implement Layer 3, 4, and 5
  protocols use logical addresses, or IP addresses.
• Physical Addresses (MAC Addresses)
• Each NIC is given an address at the factory that
  is the devices physical address or MAC address.
• By agreement among computer manufacturers, such
  addresses are assigned in such a way that no two
  NIC devices will ever have the same MAC address.
• Physical addresses are only known, shared, and
  used within a particular network or network
  segment.
• Logical Address (IP Addresses)
• Internets, including the Internet, and many
  private networks use logical addresses, which are
  also called IP addresses, for example,
  192.168.2.28
• Public Versus Private Addresses
• Public IP addresses are used on the Internet and
  assigned to major institutions in blocks by the
  Internet Corporation for Assigned Names and
  Numbers (ICANN).
• Each IP address is unique across all computers on
  the Internet.
• Private IP addresses are used within private
  networks and internets. They are controlled only
  by the company that operates the private network
  or internet

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Dynamic Host Configuration Protocol

• The DHCP server is a computer or router that
  hosts a program called Dynamic Host Configuration
  Protocol (DHCP).
• When the program finds such a device, your
  computer will request a temporary IP address from
  the DNCP server which is loaned to you while you
  are connected to the LAN.
• When you disconnect, that IP address becomes
  available, and the DHCP server will reuse it when
  needed.

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The TCP/IP-OSI Architecture

• The International Organization for
  Standardization (ISO) developed the Reference
  Model for Open Systems Interconnection (OSI), an
  architecture that has seven layers.
• The Internet Engineering Task Force (IETP),
  developed a four-layer scheme called the TCP/IP
  (Transmission Control Program Internet Protocol)
  architecture.
• The most commonly used architecture today is a
  five-layer blend of these two architectures
  called the TCP/IP-OSI architecture.

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Layer 5

• Layer 5 generates and receives email (and
  attachments like photos) according to one of the
  standard email protocols generated for layer 5
• Most likely its Simple Mail Transfer (SMTP)
• Hypertext Transfer Protocol (HTTP) is used for
  the processing of Web pages.
• The Web and the Internet are not the same thing.
• The Web, which is a subset of the Internet,
  consists of sites and users that process the HTTP
  protocol.
• The Internet is the communications structure that
  supports all application-layer protocols,
  including HTTP, SMTP, and other protocols.
• FTP, or the File Transfer Protocol is another
  application layer protocol.
• You can use FTP to copy files from one computer
  to another.
• An architecture is an arrangement of protocol
  layers in which each layer is given specific
  tasks to accomplish.
• At each level of the architecture, there are one
  or more protocols.
• Each protocol is a set of rules that accomplish
  the tasks assigned to its layer.
• A program is a specific computer product that
  implements a protocol.
• Programs that implement the HTTP protocol of the
  TCP/IP-OSI architecture are called browsers.
• Two common browsers are Netscape and Microsoft
  Internet Explorer.

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Layer 4

• An email program (which uses SMTP) interacts with
  another protocol called TCP, or Transmission
  Control Program (TCP).
• TCP operates at layer 4 of the TCP/IP-OSI
  architecture.
• The TCP program examines your data (files, email,
  pictures, etc.) and breaks these lengthy messages
  into pieces called segments.
• TCP places identifying data in front of each
  segment that are akin to the To and From
  addresses that you would put on a letter for the
  postal mail.
• TCP programs also provide reliability.
• If data is sent from a Dell computer to a
  Macintosh computer, TCP program translates the
  segments from Windows (Dell) to Macintosh format,
  reassembles the segments into a coherent whole,
  and makes that assembly available to Macintosh
  computer.

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Layer 3

• TCP/IP interacts with protocols that operate at
  Level 3, the next layer down.
• For the TCP/IP architecture, the layer-3 protocol
  is the Internet Protocol (IP).
• The chief purpose of IP is to route messages
  across an internet.
• Routers are special-purpose computers that
  implements the IP protocol.

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Layers 1 and 2

• Basic computer connectivity is accomplished using
  Layers 1 and 2 of the TCP/IP-OSI architecture.
• Computing devices called switches facilitate data
  communication.
• A program implementing a Layer-2 protocol will
  package each of your packets into frames, which
  are the containers used at Layers 1 and 2
  (Segments go into packets and packets go into
  frames).

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Switches and Routers

• Switches work with frames at Layer 2.
• They send frames from switch to switch until they
  arrive at their destination.
• They use MAC addresses.
• All switches have a table of data called a switch
  table.
• Routers work with packets at Layer 3.
• They send packets from router to router until
  they arrive at their destination.
• They use IP addresses.

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Domain Name System

• IP addresses are useful for computer-to-computer
  communication, but they are not well suited for
  human use.
• The purpose of the domain name system (DNS) is to
  convert user-friendly names into their IP
  addresses.
• Any registered, valid name is called a domain
  name.
• The process of changing a name into its IP
  address is called resolving the domain name.
• Every domain name must be unique, worldwide.
• To ensure duplicate domain names do not occur, an
  agency registers names and records the
  corresponding IP addresses in a global directory.

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Domain Name Registration

• ICANN is a nonprofit organization that is
  responsible for administering the registration of
  domain names.
• ICANN does not register domain names itself
  instead it licenses other organizations to
  register names.
• ICANN is also responsible for managing the domain
  name resolution system.
• The last letter in any domain name is referred to
  as the top-level-domain (TLD).
• In the domain www.icann.org the top level domain
  is .org
• A uniform resource locator (URL) is a documents
  address on the Web.
• URLs begin with a domain and then are followed by
  optional data that locates a document with that
  domain.
• Thus, in the URL www.prenhall.com/kroenke , the
  domain name is www.prenhall.com , and /kroenke is
  a directory within that domain.

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Domain Name Resolution

• Domain name resolution is the process of
  converting a domain name into a public IP
  address.
• The process starts from the TLD and works to the
  left across the URL.
• As of 2005, ICANN manages 13 special computers
  called root servers that are distributed around
  the world.
• Each root server maintains a list of IP addresses
  of servers that each resolve each type of TLD.
• Domain name resolution proceeds quickly because
  there are thousands of computers called domain
  name resolvers that store the correspondence of
  domain names and IP addresses
• These resolvers reside at ISPs, academic
  institutions, large companies, government
  organizations, etc.
• For example, if a domain name solver is on your
  campus and whenever anyone on your campus needs
  to resolve a domain name, that resolver will
  store, or cache, the domain name and IP address
  on a local file.
• When someone else on the campus needs to resolve
  the same domain name, the resolver can supply the
  IP address from the local file.

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Top-Level Domains, 2005
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Virtual Private Network

• Virtual private network (VPN) is the fourth WAN
  alternative.
• A VPN uses the Internet or a private internet to
  create the appearance of private point-to-point
  connections.
• A VPN uses the public Internet to create the
  appearance of a private connection.
• A connection called a tunnel, is a virtual
  pathway over a public or shared network from the
  VPN client to the VPN server.
• VPN communications are secure.
• The VPN client software encrypts, or codes, the
  original messages so that its contents are
  hidden.
• Virtual private networks offer the benefit of
  point-to-point leased lines, and they enable
  remote access, both by employees and by any
  others who have been registered with the VPN
  server.

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Wide Area Network Using VPN
43
Criteria for Comparing Network Alternatives

• Many different computer networking alternatives
  are available, each with different
  characteristics.
• There are three types of costs that need to be
  considered.
• Setup costs include the costs of acquiring
  transmission lines and necessary equipment, such
  as switches, routers, and access devices.
• Operational costs include lease fees for lines
  and equipment, charges of the ISP, the cost of
  ongoing training, etc.
• Maintenance costs include those for periodic
  maintenance, problem diagnosis and repair, and
  mandatory upgrades.
• There are six considerations with regard to
  performance
• Speed
• Latency
• Availability
• Loss rate
• Transparency
• Performance guarantees
• Other criteria to consider when comparing network
  alternatives include the growth potential
  (greater capacity) and the length of contract
  commitment.

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Security GuideEncryption

• Encryption is the process of transforming clear
  text into coded, unintelligible text for secure
  storage or communication.
• Considerable research has gone into developing
  encryption algorithms that are difficult to
  break.
• A key is a number used to encrypt data.
• The encryption algorithm applies the key to the
  original message to produce the coded message.
• Decoding (decrypting) a message is similar a key
  is applied to code the message to recover the
  original text.
• In symmetric encryption, the same key is used to
  encode and decode.
• In asymmetric encryption, different keys are
  used
• One key encodes the message, and the other key
  decodes the message.
• A special version of asymmetric encryption,
  public key/private key, is popular on the
  Internet. With this method, each site has a
  public key for encoding messages and a private
  key for decoding them.
• Most secure communication over the Internet uses
  a protocol called HTTPS.
• With HTTPS, data are encrypted using a protocol
  called the Secure Socket Layer/Transport Layer
  Security (SSL/TLS). SSL uses a combination of
  public key/private key and symmetric encryption.
• The use of SSL/TLS makes it safe to send
  sensitive data like credit card numbers and bank
  balances. Just be certain that you see https//
  in your browser and not just http//.

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Ethics GuidePersonal Email at Work

• You send a personal email to your friend at his
  job that contains both text and a picture (6.2
  megabytes in size).
• This email during its transmission from you to
  your friend at his job, consumes his companys
  entire computing infrastructure.
• Finally, if your friend reads his email during
  his working hours, he will be consuming company
  resources, his time and attention, which the
  company has paid while he is at work.