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Using MIS 2e
Chapter 6 Appendix
How the Internet Works
David Kroenke
10/02 – 4:00PM
© Pearson Prentice Hall 2009
6A-1
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.prenhall.com become 165.193.123.253?
© Pearson Prentice Hall 2009
6A-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.prenhall.com become 165.193.123.253?
© Pearson Prentice Hall 2009
6A-3
Q1 – How does email travel?
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There are many different network components involved in
sending an email message across the Internet.
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Different types of computers, like a PC or a MAC, are used.
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Different types of operating systems, such as Windows, MAC
OS, or Linux, are used.

Different types of email application programs, such as Outlook
or Mozilla Thunderbird, are used.

A combination of wired and wireless connections are used.
© Pearson Prentice Hall 2009
6A-4
Q1 – How does email travel?
We resolve these differences by using the following process for all
internet transmissions.

Messages are broken down first into segments using TCP, and
then into packets using IP, which routers send over an internet,
and finally into frames using the data link protocol, which the NIC
sends using the appropriate protocol for the transmission
media in use.

Once a message arrives at its intended destination, the data link and
TCP/IP protocols combine the frames into packets, the packets
into segments, and the segments into a message for the
receiving application program.

The key concept is to divide & conquer by using four layers of
software and one layer of firmware based on the protocol
layers.
© Pearson Prentice Hall 2009
6A-5
Q1 – How does email travel?
Application Layer
Document - 5
Document
TCP Layer
Segments - 4
Segments
Logical Address
IP Layer
Packets - 3
Packets
Packets
Physical Address
Data Link Layer
Firmware
Frames - 2
NIC
-1
Switch
Sending Computer
© Pearson Prentice Hall 2009
Frames
Router
Frames
NIC
Switch
Receiving Computer
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Segment, Packet, Frame Architecture

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
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All segments, packets, and frames have the same basic
architecture (see below).
A segment is broken into packets and a packet is broken into
frames.
The small frames can work their way through an internet, taking
various different paths based on congestion, with much greater
throughput then the large segments.
Plus, retransmitting a few frames takes much less time, in the
case of errors, then retransmitting segments.
Header
Addressing
© Pearson Prentice Hall 2009
Message Bits
Trailer
Reliability
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Q1 – How does email travel?

This figure shows how an email message uses various hardware
components to cross an internet. Transmissions go from computer to
switch to switch … to router to router … to switch to switch … to
computer. The protocol used to direct the transmission across a link (IP or
PPP) depends on the device receiving the transmission. IP is necessary
for routing across multiple devices and PPP is adequate for simple, point-topoint transmissions between adjacent devices.
Fig 6A-1 Sample Networks
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6A-8

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.prenhall.com become 165.193.123.253?
© Pearson Prentice Hall 2009
6A-9
Q2 – What is a communications protocol?

A protocol is a standardized means for coordinating an activity
between two or more entities.

The two communicating computers must agree on the protocol to be
used.
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The protocol specifies the format for the segments, packets, and
frames, and the interactions between computers, at the transport
and internet layers, to assure reliable transmissions.
© Pearson Prentice Hall 2009
6A-10
Q2 – What is a communications protocol?

Layers of communication protocols coordinate the activity
between two or more communicating computers and allow
messages to pass back and forth.

Each layer accomplishes a different function then passes the
message to the next layer in the protocol – up if the message is
incoming and down if the message is outgoing.

All messages are processed as a stream of bits, not bytes, by all
layers except for the application layer, the top layer.
© Pearson Prentice Hall 2009
6A-11

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.prenhall.com become 165.193.123.253?
© Pearson Prentice Hall 2009
6A-12
Q3 – What are the functions of the five TCP/IP—OSI layers?

The Internet uses layered protocols, also called protocol
architectures, which specify the format of a data transmission and
the processing rules implemented by the TCP/IP software at each
layer.
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The International Organization for Standardization (ISO)
developed a seven-layered Reference Model for Open Systems
Interconnection (OSI) architecture.
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The Internet Engineering Task Force (IETF) developed a fourlayered Transmission Control Program/Internet Protocol
(TCP/IP) architecture.
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Portions of these two architectures are combined to provide the
Internet with the TCP/IP—OSI architecture.
© Pearson Prentice Hall 2009
6A-13
Q3 – What are the functions of the five TCP/IP—OSI layers?

This chart gives
you the specific
and broad
functions of each
layer in the
TCP/IP-OSI
architecture.

All computers
using the Internet
use all five layers
of the TCP-OSI
architecture.
Fig 6A-3 TCP/IP-OSI Architecture
© Pearson Prentice Hall 2009
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Q3 – What are the functions of the five TCP/IP—OSI layers?


Throughout this appendix, and while you’re using the Internet, you’ll
hear these terms used frequently.
Remember, the architecture and the protocols are just concepts.
They do not actually exist in a physical form. The software and
hardware implement these concepts.

Architecture is the arrangement of protocol layers (application,
transport, internet, data link, physical) with each given specific tasks.

Protocols are sets of rules that accomplish tasks in each layer. These
rules specify the format of segments, packets, and frames, and the
interactions between the sending and receiving computers at the
transport (TCP) and internet (IP) layers to assure reliability.

Programs are specific software products that implement the rules and
interactions for reliability specified by the protocols at each layer.
© Pearson Prentice Hall 2009
6A-15
Q3 – What are the functions of the five TCP/IP—OSI layers?

Layer 5 is the application layer and uses protocols to govern how
applications work with each other. The following applications are
examples of programs which implement the TCP/IP protocols:

The Simple Mail Transfer Protocol (SMTP) is contained in
email application programs like Outlook and Mozilla Thunderbird.
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The Hypertext Transfer Protocol (HTTP) is contained in Web
browser programs like Internet Explorer and Mozilla Firefox.
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The File Transfer Protocol (FTP) is used to copy or move files
from one computer to another, generally within a Web browser
program.

The Web is a subset of the Internet. The Web consists of sites
and users that process the HTTP protocol using browsers mostly.
© Pearson Prentice Hall 2009
6A-16
Q3 – What are the functions of the five TCP/IP—OSI layers?

Layer 4, the transport layer, contains the Transmission Control
Program (TCP) protocols that convert the application data of
layer 5 into segments of bit streams with identifying headers and
trailers for addressing and message transmission reliability in
the sending computer. The reverse of this operation is performed
by the receiving computer.

Layer 3, the Internet layer, contains the Internet protocols (IP) that
route messages across an internet using a router computer. The
segments from layer 4 are broken into packets with identifying
headers and trailers for addressing and message transmission
reliability and are transmitted through multiple routers using
tables of router addresses at each router until they reach their
intended destination. The reverse of this operation is performed by
the receiving computer.
© Pearson Prentice Hall 2009
6A-17
Q3 – What are the functions of the five TCP/IP—OSI layers?

Layer 1, the physical layer, and layer 2, the data link layer,
provide basic computer connectivity using switches and NICs. The
packets from layer 3 are broken into frames in layer 2, and then
into electronic signals in layer 1 for the transmission media in use.
The reverse of this operation is performed by the receiving
computer.
© Pearson Prentice Hall 2009
6A-18
Q3 – What are the functions of the five TCP/IP—OSI layers?

This figure depicts the TCP/IP—OSI layers that an email message
travels through.
application
computers
routers
switches
NICs
transmission
media
Fig 6A-4 TCP/IP on Your Computer
© Pearson Prentice Hall 2009
6A-19

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.prenhall.com become 165.193.123.253?
© Pearson Prentice Hall 2009
6A-20
Q4 – How does the Internet work?

Each computer has two addresses, a physical and a logical address, that
networks and the Internet use to route messages to the correct location.

The physical address or MAC, media access control address, is
assigned to each NIC, network interface card, by the manufacturer. No
two are alike. This address is used by the protocols in layer 2 of the
TCP/IP—OSI architecture.

The logical address, or IP address, is used on internets, the Internet, and
private networks by the protocols in layer 3 of the TCP/IP—OSI
architecture. This address is written as numbers, like 192.168.2.28.
Hardware devices are not hard-coded with logical addresses but are
assigned as needed.

Physical addresses are only known, shared, and used within a particular
network, not an internet. Each MAC belongs to one and only one
hardware device.

Logical addresses are not permanently assigned to any hardware device,
are used within internets, and can be reassigned when necessary.
© Pearson Prentice Hall 2009
6A-21
Q4 – How does the Internet work?

There are two kinds of logical addresses:

Public IP addresses are used on the Internet and are unique across all
computers on the Internet. They are assigned by ICANN (Internet
Corporation for Assigned Names and Numbers)

Private IP addresses are used within private networks and internets
and are controlled by the company that operates the network.

Dynamic Host Configuration Protocol software is used on DHCP
servers. These programs loan temporary IP addresses to users when
they connect to a private network. Once the online session is completed,
the temporary IP address is returned to the DHCP server for re-use. Your
ISP uses DHCP to assign you a temporary IP address when you connect to
the Internet.

Each DHCP server is assigned a range of IP addresses to loan on its
network.
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Within a private network, administrators normally assign fixed, private IP
addresses permanently to servers so all computers on the network can
know immediately the addresses of all the servers for that network. The
end-user does not have to find the server address.
© Pearson Prentice Hall 2009
6A-22
Q4 – How does the Internet work?

This figure shows how a typical LAN transmits messages within the
network using a DHCP server.
Fig 6a-5 Hotel LAN in Hawaii
© Pearson Prentice Hall 2009
6A-23
Q4 – How does the Internet work?

Switches (special computers that receive and transmit messages
on a LAN) use MAC addresses on a specific network that tell them
where to send traffic. They work in layer 2 of the TCP/IP—OSI
architecture.

Similarly, routers use tables of router IP addresses on an internet
that tell them where to send traffic. They work in layer 3 of the
TCP/IP—OSI architecture.
© Pearson Prentice Hall 2009
6A-24
Q4 – How does the Internet work?

You can use the
figure on this slide
and the next one to
trace messages as
they pass through the
TCP/IP—OSI
protocols, switches,
and routers, using
private IP addresses.
Fig 6A-6 Accessing the (Private) Hotel Web Server – Part 1
© Pearson Prentice Hall 2009
6A-25
Q4 – How does the Internet work?
Fig 6A-6 Accessing the (Private) Hotel Web Server – Part 2
© Pearson Prentice Hall 2009
6A-26
Q4 – How does the Internet work?

This figure shows how TCP/IP—OSI protocols over the Internet use
Network Address Translation to change a public IP address into
a private IP address and vice versa.
Fig 6A-7 Hawaii Hotel to Ohio Company via Internet
© Pearson Prentice Hall 2009
6A-27

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.prenhall.com
become 165.193.123.253?
© Pearson Prentice Hall 2009
6A-28
Q5 – How does www.prenhall.com become 165.193.123.253?

It’s much easier for people to recognize alphabetical names rather
than a group of numbers. However, computers can only use
numbers. The domain name system (DNS) converts user-friendly,
domain names that people can use to IP addresses that
computers can use. The process is called resolving the domain
name. Just like you do when you find the telephone number for a
person’s name in a telephone directory.

Every domain name must be unique throughout the world and
recorded in a global directory, just like telephone numbers.
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ICANN administers how companies register domain names and it
manages the domain name resolution system.
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The term top-level domain (TLD) refers to the last letters in a
domain name. In the domain name www.prenhall.com – the last
three letters, com, is the TLD.
© Pearson Prentice Hall 2009
6A-29
Q5 – How does www.prenhall.com become 165.193.123.253?

Each Web address is called a Uniform Resource Locator (URL).
www.prenhall.com is the URL for Prentice Hall.

Converting a domain name into a public IP address is called Domain Name
Resolution: www.prenhall.com = 165.193.123.253

ICANN manages 13 root servers distributed around the world which
maintain lists of IP addresses of servers that resolve each type of TLD.
These root servers are augmented by thousands of domain name
resolvers around the world to provide quick domain name resolution.

Domain name resolvers (DNRs) are the bottom layer of servers which the
ISPs hit with a domain name to resolve. If the DNR server has a match for
the domain name in its IP address table cache, then the DNR server can
resolve the domain name into an IP address. If not, then the DNR server
hits the regional root server for the top-level domain name for the
domain name resolution. The DNR servers store the results of domain
name resolutions by the TLD root servers in a cache, and they periodically,
systematically audit their cache contents against appropriate TLD root
servers.
© Pearson Prentice Hall 2009
6A-30
VOIP and IPTV

The TCP/IP-OSI architecture can transmit anything represented by bits
which is formatted according to the TCP/IP protocols.
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Voice over IP (VoIP) uses the TCP/IP-OSI architecture to carry telephone
voice conversations.
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With VoIP, voice conversations are digitized by sampling, and are stored
as bits, packaged according to the TCP/IP protocol, and routed over the
Internet. You need to have appropriate application software and your
telephones connected to your computers to do this.

A problem occurs when a user connected to the Internet wants to contact
someone who has only telephone access, or the reverse situation.

This problem has been resolved by companies (Skype for example, who
offer their subscribers unrestricted telephone access using VoIP.

IPTV (Internet Protocol Television) uses TCP/IP-OSI to transmit television
and other video signals. A broadband connection is required. A set-top box
receives the signal and distributes it to multiple users within a site. This settop box can provide VoIP and text chat.
© Pearson Prentice Hall 2009
6A-31