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Using MIS 3e
Chapter 6A
Appendix
How the Internet Works
David Kroenke
Chapter Appendix Preview
•
•
The chapter appendix discusses the third type of network, internets, and
explains in particular how one such network—the Internet—works.
Using the example of email from a hotel in Hawaii to a company in Ohio,
the appendix explains the nature of layered protocols and describes
how the Internet uses the TCP/IP—OSI protocol architecture. The
appendix also explains how the Internet transforms URLs such as
pearsonhighered.com into globally unique logical addresses.
You may be tempted to skip the appendix, and, if time is short, you may
need to. However, the Internet is the foundation of 21st-century
commerce, and knowing Internet components and their interactions is
part of a business professional’s literacy. Just as you need to know
terms like LIFO and FIFO and understand what it means when marginal
revenue equals marginal cost, so, too, you need to know what TCP/IP
and related protocols are and how they are used.
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6A-2
Study Questions
Q1: How does email travel?
Q2:
What is a communications protocol?
Q3:
What are the functions of the five TCP/IP-OSI layers?
Q4:
How does the Internet work?
Q5:
How does www.pearsonhighered.com become
165.193.123.253?
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6A-3
How Does Email Travel?
• Messages and attachments sent from your computer
 Broken down into pieces called packets
 Packets sent to LAN switch
• Routers determine the best way to move messages
through Internet to destination
• Software at destination email server ensures all
packets are received
 Requests missing packets to be resent
• Messages and attachments reassembled at
recipient’s email server and readied to be opened by
recipient
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6A-4
How Email Travels
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6A-5
Study Questions
Q1:
How does email travel?
Q2: What is a communications protocol?
Q3:
What are the functions of the five TCP/IP-OSI layers?
Q4:
How does the Internet work?
Q5:
How does www.pearsonhighered.com become
165.193.123.253?
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6A-6
What Is a Communications
Protocol?
• Protocol
 Standardized means for coordinating activity
between two or more entities
 Follows a sequence of ordered steps
• Communications protocol
 Means for coordinating activities between
communicating computers
• Computers agree on protocol to use
 Broken down into layers based on category of task
performed
• Divide and conquer concept
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6A-7
Study Questions
Q1:
How does email travel?
Q2:
What is a communications protocol?
Q3: What are the functions of the five TCP/IP-OSI
layers?
Q4:
How does the Internet work?
Q5:
How does www.pearsonhighered.com become
165.193.123.253?
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6A-8
What Are the Functions of the Five
TCP/IP-OSI Layers?
1.
2.
3.
Reference Model for Open Systems Interconnection
(OSI)
• Seven layers
• Developed by International Organization for
Standardization (ISO)
Transmission Control Program/Internet Protocol (TCP/IP)
(video)
• Four layers
• Developed by the Internet Engineering Task Force
(IETF)
TCP/IP-OSI architecture is a five-layer blend of OSI and
TCP/IP.
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TCP/IP-OSI Architecture
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Layer 5: Protocols
•
•
•
•
SMTP—Simple Mail Transfer Protocol
HTTP—Hypertext Transfer Protocol
FTP—File Transfer Protocol
Three important terms
1. Architecture—arrangement of protocol layers in
which each layer is given specific tasks to
accomplish
2. Protocol—a set of rules that accomplish tasks
assigned to its layer
3. Program—a specific computer product that
implements a protocol (Example: browser)
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CE10-11
Layer 4: Transmission Control
Program (TCP)
• Email program (SMTP) interacts with TCP
• TCP operates at Layer 4
• TCP
 Breaks email message and attachments into
segments
 Attaches To/From addresses to each segment
 Ensures reliability that all segments are received
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TCP/IP-OSI on Your Computer
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Layer 3: Internet Protocol (IP)
• TCP interacts with Layer 3 protocols
• Purpose of IP:
 Route messages across an Internet
 Packages each segment into a packet
 Places IP data in front of TCP data on each packet
• Routers use IP data to decide where to send
packets.
• Dozens of Internet routers involved in getting
email message from Hawaii to Cincinnati.
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Layers 1 and 2
• Handles basic computer connectivity
• Packages packets into frames
• Frames transmitted between programs,
switches (SW1, SW3), internal routers (RH)
shown in Figure CE10-1
• Switches facilitate communication
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6A-15
Study Questions
Q1:
How does email travel?
Q2:
What is a communications protocol?
Q3:
What are the functions of the five TCP/IP-OSI layers?
Q4: How does the Internet work?
Q5:
How does www.pearsonhighered.com become
165.193.123.253?
Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall
6A-16
How Does the Internet Work?
• Each computer and device has two
addresses: (1) physical address; (2) logical
address.
• Layer 2 protocol programs use physical
addresses or MAC addresses
• Layer 3 and 4 programs use logical addresses
or IP addresses
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Network Addresses: MAC and IP
• MAC addresses
 Physical addresses
 Implemented by programs that use Layer 2
protocols
 Each NIC card given an address by manufacturer
 Address only shared within network or segment
• IP addresses
 Logical addresses
 Written as series of dotted decimals
• 192.68.2.28
 Not permanently associated with hardware device
• Can be reassigned as necessary
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Public vs. Private IP Addresses
• Public IP address
 Used on Internet
 Assigned by ICANN (Internet Corporation for
Assigned Names and Numbers)
 Each address is unique
• Private IP address
 Used within private networks
 Controlled by company operating network
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6A-19
Dynamic Host Configuration
Protocol
• DHCP server—computer or router that hosts
DHCP program
• Program distributes temporary IP address to
computers and devices on connecting to
network
 Address loaned while computer connected to LAN
 When computer disconnected, IP address made
available to others
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Using TCP/IP-OSI Protocols
Within the Hotel
• Hotel has private Web server
 IP address of hotel server (HS with address IP8) assigned
by network administrator
 Router (RH with IP address IP9) is a DHCP server
• Guest computer signs into Web server
 Guest browser sends service request to hotel server
 TCP program breaks request into segments and adds data
to each segment
 TCP programs hands segments to IP program for routing
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Private IP Addresses at the
Hawaii Hotel
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Using TCP/IP-OSI Protocols
Within the Hotel
• IP program adds IP9 header and passed
wrapped packet to an Ethernet program
• Ethernet program translates IP address into MAC
address of device IP9 (Hotel router)
• Ethernet wraps packet into frame addressed
to hotel router (RH)
• Sends packet through switch
• Since Ethernet program on your computer connected
to switch S3 when you signed on, frame is relayed
accordingly
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Communications Processing
on the Switches
•
•
•
•
Switch consults switch table
Directs frame to router
Ethernet unpacks frame, sends packet to IP
Router consults routing table, sends packet
one hop down network
• Ethernet determines MAC address needed
 Ethernet packages packet into frame addressed to
appropriate MAC address
 Sends frame to switch S1
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Communications Processing
on the Router
• Routers
 Routing tables
• Contain data where to send packets
• Directs packet traffic on LAN and Internet
 Ethernet unpacks frames addressed to router RH as they
arrive
 Sends packets to IP program on router
 IP changes packet destination to IP8
 Ethernet matches IP8 to MAC address HS (hotel server),
puts packets in frame with HS MAC address
 Sends frame to switch S1
 Switches relay frame to hotel server (HS)
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Communications Processing
on the Web Server
At Web server HS:
• Ethernet unpacks frame, sends packet to IP program.
• IP program strips off IP header, sends packet to TCP
program.
• TCP sees packet is one of two.
• TCP sends receipt acknowledgement back to email
sender.
• TCP waits for second packet.
• When packet two arrives, TCP sends complete
request (contained in both packets) to Web server for
HTTP protocol processing.
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Using TCP/IP-OSI Protocols
over the Internet
Network Address Translation
• LAN use private IP addresses
• Internet traffic uses public IP addresses
 Hotel’s ISP assigns public IP address to hotel router (IPx)
• Router RH has two IP addresses
 Private one assigned by organization for local traffic
 Public one assigned by ISP for Internet traffic
• Network Address Translation (NAT)
 Process of changing public IP addresses into private
addresses and reverse
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Your Email!: How Does It Get to
[email protected]?
• You enter email address of recipient
 Email program works at application layer
• Implements SMTP to send email
• Uses domain name system to get public IP address
• Email message sent to router
 Sends message to TCP
• Breaks into segments, placed in packets
• Sent to router RH
• Packets sent to Ethernet program
 Placed in frame
 Sent to switch S3, then S1, and sent to router
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Accessing the (Private)
Hotel Web Server
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Your Email!: How Does It Get to
[email protected]?
• Packets of email and picture arrive at router.
 Implements NAT
 Replaces private IP address with public IP address
• Router consults table, sends packets to router R2 (San
Francisco).
• Packets travel router to router until they reach
OhioCompany router.
• Segments unpacked from packets, sent to TCP program.
• Program waits for all segments, then sends to program
that implements SMTP.
• Program operates at Layer 5, puts message in mailbox of
CarterK.
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Domain Name Resolution
• Uniform Resource Locator (URL)
 User-friendly document Web address
 For example: www.pearsonhighered.com/kroenke
• Domain name resolution
 Process of converting a domain name into a public IP
address
 Starts from the TLD and works to the left across URL
• ICANN manages 13 special computers called root
servers distributed around the world.
 Each root server maintains a list of IP addresses of servers
that resolve each type of TLD.
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Domain Name Resolution
• Domain name resolvers
 Thousands of computers at academic institutions,
large companies, government organizations
 Cache domain names and IP addresses locally
 Save time by not needing to go through entire
resolution process somewhere else
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Hawaii Hotel to OhioCompany
LAN via Internet
Figure CE7-7
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6A-33
Study Questions
Q1:
How does email travel?
Q2:
What is a communications protocol?
Q3:
What are the functions of the five TCP/IP-OSI layers?
Q4:
How does the Internet work?
Q5: How does www.pearsonhighered.com become
165.193.123.253?
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6A-34
How Does www.pearsonhighered.com
Become 165.193.123.253?
• Domain name system (DNS)




Converts user-friendly names into their IP address
Domain name—a registered, valid name
Every DNS is unique in world
Resolving the domain name
• Process of changing a domain name into its IP address (Layer 5
application)
• Top-level domain (TLD)
 Examples—.com; .org; .edu; .gov
 Non-United States—www.somewhere.uk
 Industry—.aero
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Domain Name Registration
• ICANN—International Corporation for Assigned
Names and Numbers
 A nonprofit organization responsible for administering the
registration of domain names.
 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.
• DNS (Domain Name System )
 Converts user-friendly names into public IP address
 Resolves domain names
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U.S. Top-Level Domains
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Domain Name Resolution
• Uniform resource locator (URL) (pronounced “U-R-L” or “Earl”)
is a document’s address on the Web.
• URLs begin with a domain name and followed by optional data
that locates a document within that domain. Thus, in the URL
 www.pearsonhighered.com/kroenke, the domain name is
www.pearsonhighered.com, and /kroenke is a directory within
that domain.
• Domain name resolution is the process of converting a domain
name into a public IP address.
 Process starts from the TLD and works to left across the URL
 As of 2009, 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 resolve each type of
TLD.
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Domain Name Resolution
• Domain name resolution proceeds more quickly because there
are thousands of computers called domain name resolvers that
store domain names and IP addresses.
• These resolvers reside at ISPs, academic institutions, large
companies, governmental organizations, and so forth.
• Resolvers convert a domain name into an IP address.
•
 Resolver stores, or caches, a domain name and IP address on a
local file when someone on campus uses a domain name.
 Then, when someone else on campus uses same domain name,
there is no need for the resolver to go through entire resolution
process. Instead, resolver can supply the IP address from the local
file.
Curious to know your current IP address, go to
http://www.whatis/MyIPAddress.com
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6A-39
VoIP and IPTV
• Voice over IP (VoIP, pronounced “voyp”) uses the TCP/IP-OSI
architecture to carry telephone voice conversations.
• With VoIP, voice conversations are stored as bits, broken into IP
packets, and routed over the Internet. No separate telephone line
is required; same connection that routes email, HTTP, and other
data also carries voice conversations.
• A problem occurs when a user who is connected to the Internet
wants to dial someone who has only regular telephone access,
or, equivalently, when someone who has a regular telephone
wants to call someone who has a VoIP connection.
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VoIP and IPTV
• Companies, such as Skype, have solved this problem and offer
subscribers unrestricted telephone access using VoIP.
•
•
•
 Skype is particularly economical for those who make frequent
international calls. Some users complain quality of transmission is
not as high as for regular telephone, but they use Skype anyway
because cost savings are worth it.
Internet Protocol Television (IPTV ) uses TCP/IP-OSI to transmit
television and other video signals.
Broadband connection is required.
Device called a set-top box receives the IPTV signal and distributes it
to multiple televisions or home entertainment centers.
 Some set-top devices provide VoIP, text chat, and other services as
well (for example, Tornado M10 Media Center).
• Expect to see increased use of both VoIP and IPTV in years to
come.
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6A-41
Active Review
Q1:
How does email travel?
Q2:
What is a communications protocol?
Q3:
What are the functions of the five TCP/IP-OSI
layers?
Q4:
How does the Internet work?
Q5:
How does www.pearsonhighered.com become
165.193.123.253?
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6A-42
Case Study 6A: A SOHO Network
Administration
• Small, flat, black box is a DSL modem that is
connected to a telephone line.
• DSL modem also connects to the silver, upright box
with the small dark gray antenna.
• Silver box is a Microsoft wireless base station.
Wireless base station, a marketing term Microsoft
uses to soften the complexity of what’s actually in
gray box.
• Box contains an ethernet LAN switch, an 802.11g
wireless access point, and a router.
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6A-43
Case Study 6A: A SOHO Network
Administration
• Notice several UTP cables that connect the wireless base station
to computers and other devices on the LAN.
• A generic term for Microsoft’s Wireless Base Station is device
access router, the term you should use when you go shopping
for one.
• Wireless Base Station also contains a small special-purpose
computer that has firmware programs installed.
 These programs provide DHCP service as well as NAT.
 Programs for administration and for setting up wireless
security.
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Case Study 6A: A SOHO Network
Administration
• Notice the printer (behind the tape dispenser).
• Printer has a small black box with a gray UTP
cable and a small black power line going into
it.
• Black box is an NIC that connects the printer
to the LAN. This NIC is called a printer server,
and it, too, has a special-purpose computer
with firmware that allows for setting up and
administering the printer server and printer.
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6A-45
A SOHO Network
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6A-46
Structure of a SOHO Network
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6A-47
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Copyright © 2011 Pearson Education, Inc.
Publishing as Prentice Hall
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6A-48