Chapter Extension 7
How the Internet Works
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Study Questions
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CE 7-2
How does e-mail travel?
What is a communications protocol?
What are the functions of the five TCP/IP OSI
layers?
How does the Internet work?
How does www.PrenHall.com become
192.52.0.34.65?
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
How Does E-mail Travel?
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Messages and attachments sent from first computer
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Routers determine the best way to move messages
through Internet
System employed to ensure all pieces are received
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CE 7-3
Broken down into pieces
Pieces called packets
Packets resent if necessary
Messages and attachments reassembled at
recipient’s computer
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
What Is a Communications
Protocol?
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Protocol
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Standardized means
Used for coordinating activities
Sequence of ordered steps
Communications protocol
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Means for coordinating activities between
communicating computers
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CE 7-4
Computers agree on protocol to use
Broken down into layers
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Layered Protocol Schemes
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Protocol architectures
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Reference Model for Open Systems
Interconnection (OSI)
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Transmission Control Program/Internet Protocol
(TCP/IP)
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CE 7-5
Developed by International Organization for
Standardization (ISO)
Developed by the Internet Engineering Task Force
(IETF)
TCP/IP-OSI architecture is blend
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
TCP/IP-OSI Architecture
Figure CE7-3
CE 7-6
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Terminology
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Architecture
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Arrangement of protocol layers
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Protocol
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Exist at each layer of architecture
Set of rules that accomplish tasks at that layer
Program
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CE 7-7
Each layer performs specific tasks
Specific computer product
Implements a protocol
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Layer 5
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Protocols
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Simple Mail Transfer Protocol (SMTP)
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Hypertext Transfer Protocol (HTTP)
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Processes Web pages
File Transfer Protocol (FTP)
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CE 7-8
Standard e-mail protocol
Used to copy files from one computer to another
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Layer 4
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Transmission Control program (TCP)
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Converts from one data representation to another
Breaks e-mail into segments
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Provides reliability
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CE 7-9
Adds identifying segments to beginning of pieces
Checks to see if all packets are received
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Layer 3
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Internet Protocol
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Interacts with TCP in Layer 4
Routers send messages across Internet
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Packages messages into packets
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CE 7-10
Works through IP
Special purpose computers
Places IP data in front of TCP data
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Layers 1 and 2
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Switches facilitate data communications
Layer 2 protocols
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CE 7-11
Program packages packets into frames
Basic computer connectivity accomplished at
layers 1 and 2
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Network Addresses: MAC and IP
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MAC addresses
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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
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Logical addresses
Written as series of dotted decimals
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Not permanently associated with hardware device
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CE 7-12
192.68.2.28
Can be reassigned as necessary
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
IP Addresses
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Two kinds of IP addresses:
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Public
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Private
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CE 7-13
Used on Internet
Assigned by ICANN
Each address is unique
Used within private networks
Controlled by company operating network
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Dynamic Host Configuration Protocol
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DHCP
Distributes temporary IP address to
computers
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CE 7-14
Address loaned while computer connected to LAN
When computer disconnected, IP address made
available to others
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Private IP addresses
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Assigned manually by network administrator
Usually given to:
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CE 7-15
Web servers
Shared devices
Most users are given addresses by DHCP
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Networks
Figure CE7-1
CE 7-16
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Using TCP/IP-OSI Protocols Within
the Hotel
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Hotel has private Web server
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Guest computer signs into Web server
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CE 7-17
IP address of server assigned by network administrator
Guest browser constructs request for server
Uses HTTP
TCP breaks request into segments, adds additional
data
TCP program hands segments to program that
implements IP
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Using TCP/IP-OSI Protocols Within
the Hotel (continued)
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IP program adds header into packet
Passes on to program that implements
Ethernet
Ethernet program translates IP address into
MAC address
Ethernet wraps packet into frame
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CE 7-18
Sends packet through switch
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Switches and Routers
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Switches
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Switch table
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Entries for every device on network
Work with frames in Layer 2
Use MAC addresses
Routers
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Routing tables
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CE 7-19
Table of data
Directs packet traffic on Internet
Work with packets in Layer 3
Use IP addresses
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Accessing Hotel Web Server
Figure CE7-6
CE 7-20
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Using TCP/IP-OSI Protocols Within
the Hotel (continued)
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Switch consults switch table
Directs frame to router
Ethernet unpacks frame, send packet to IP
Router consults routing table, sends packet one hop
down Internet
Ethernet determines MAC address needed
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CE 7-21
Ethernet packages packet into frame addressed to
appropriate MAC address
Sends frame to switch
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Using TCP/IP-OSI Protocols Within
the Hotel (continued)
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Switch sends frame to destination
Ethernet unpacks frame, send packet to IP program
IP program strips off header
Sends segment to program that implements TCP
TCP sends acknowledgement back to guest
computer indicating receipt
When both segments received, sent to Web server
program
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CE 7-22
Processes HTTP request
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Network Address Translation
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Internet traffic uses public IP addresses
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Routers may have two IP addresses
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Private one assigned by organization for local traffic
Public one assigned by ISP for Internet traffic
Network Address Translation
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CE 7-23
Assigned in blocks
Process of changing public IP addresses into private
addresses and reverse
Routers receive packets on Internet and redirects them to
individual computers on local network
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Your E-mail
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You enter e-mail address of recipient
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E-mail program works at application layer
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E-mail message sent to router
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Sends message to TCP
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Breaks into segments, placed in packets
Sent to router
Packets sent to Ethernet program
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CE 7-24
Implements SMTP to send email
Uses domain name system to get public IP address
Placed in frame
Sent to switch, sent to router
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Your E-mail (continued)
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Packets arrive at router
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CE 7-25
Implements NAT
Replaces private IP address with public IP address
Router consults table, sends to gateway router of
recipient
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
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
E-mail System
Figure CE7-7
CE 7-26
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Domain Name System
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DNS
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Converts user-friendly names into public IP
address
Resolves domain name
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Domain name
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Registered name
Uniform Resource Locator (URL)
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CE 7-27
ICANN manages resolution system
Document’s Web address
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Domain Name Resolution
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ICANN manages root servers
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Domain name resolvers
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CE 7-28
13 computers across the world
Maintain lists of IP addresses of servers
Cache name and IP address on local file
Used instead of going through entire resolution
process
© 2008 Prentice Hall, Experiencing MIS, David Kroenke
Active Review
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CE 7-29
How does e-mail travel?
What is a communications protocol?
What are the functions of the five TCP/IP OSI
layers?
How does the Internet work?
How does www.PrenHall.com become
192.52.0.34.65?
© 2008 Prentice Hall, Experiencing MIS, David Kroenke