How the Internet Works
David Kroenke
Using MIS 3e
Chapter 6A
Appendix
• 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.
Chapter Appendix Preview
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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.combecome 165.193.123.253?
Study Questions
• 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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How Email Travels
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.combecome 165.193.123.253?
Study Questions
Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall 6A-7
• 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
What Is a Communications
Protocol?
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.combecome 165.193.123.253?
Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall 6A-9
1.
Reference Model for Open Systems Interconnection
(
OSI
)
•
Seven layers
•
Developed by International Organization for
Standardization (ISO)
2.
Transmission Control Program/Internet Protocol (
TCP/IP
)
(
video
)
•
Four layers
•
Developed by the Internet Engineering Task Force
(IETF)
3.
TCP/IP-OSI
architecture is a five-layer blend of OSI and
TCP/IP.
What Are the Functions of the Five
TCP/IP-OSI Layers?
TCP/IP-OSI Architecture
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•
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)
Layer 5: Protocols
CE10-11
• 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
Layer 4: Transmission Control
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TCP/IP-OSI on Your Computer
• 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.
Layer 3: Internet Protocol (IP)
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• 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
Layers 1 and 2
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.combecome 165.193.123.253?
Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall 6A-17
• 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
How Does the Internet Work?
• 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 necessaryNetwork Addresses: MAC and IP
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• 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
Public vs. Private IP Addresses
•
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
Dynamic Host Configuration
Protocol
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• 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
Using TCP/IP-OSI Protocols
Within the Hotel
Private IP Addresses at the
Hawaii Hotel
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• 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
Using TCP/IP-OSI Protocols
Within the Hotel
• 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
Communications Processing
on the Switches
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• 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)
Communications Processing
on the Router
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.
Communications Processing
on the Web Server
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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
Using TCP/IP-OSI Protocols
over the Internet
• 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
Your Email!: How Does It Get to
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Accessing the (Private)
Hotel Web Server
• 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.
Your Email!: How Does It Get to
[email protected]?
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• 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.
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
Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall 6A-33
Hawaii Hotel to OhioCompany
LAN via Internet
Figure CE7-7
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?
Study Questions
Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall 6A-35
• 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
How Does
www.pearsonhighered.com
Become 165.193.123.253?
•
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
Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall 6A-37
U.S. Top-Level Domains
• 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 resolutionis 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 serversthat are distributed around the world. Each root server maintains a list of IP addresses of servers that resolve each type of TLD.
Domain Name Resolution
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• Domain name resolution proceeds more quickly because there are thousands of computers called domain name resolversthat 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
Domain Name Resolution
• 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.
Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall 6A-41
• 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.
VoIP and IPTV
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?
Active Review
Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall 6A-43
• 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.
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.
Case Study 6A: A SOHO Network
Administration
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• 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.
Case Study 6A: A SOHO Network
Administration
A SOHO Network
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Structure of a SOHO Network
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