1. An Introduction to Networking
Chapter 1
Updated January 2007
Panko’s
Business Data Networks and Telecommunications, 6th edition
Copyright 2007 Prentice-Hall May only be used by adopters of the book
Copyright 2005 Prentice-Hall

2. Builds
Slides with the “mouse click” icon in the upper right hand corner are “build” slides
Not everything on the slide will appear at once
Each time the mouse click icon is clicked, more information on the slide will appear.
<This is a note primarily for you. However, students should understand builds it if they are working from copies of slides; otherwise, they may be confused when everything doesn’t appear at once.>
<Read the slide.>
Copyright 2005 Prentice-Hall

3. Part I: Basic Networks Concepts
Concepts we will see throughout the book
Copyright 2005 Prentice-Hall

4. Figure 1-1: Basic Networking Concepts
What Is a Network?
A network is a transmission system that connects two or more applications running on different computers.
Network
Copyright 2005 Prentice-Hall

5. Part II: The Nine Elements of a Network
Although the idea of “network” is simple, you must understand the nine elements found in most networks
Copyright 2005 Prentice-Hall

6. Figure 1-3: Elements of a Network
Client Application
Server Application
Message (Frame)
Switch 2
Access
Line 1.
Networks connect
applications on different computers.
Client
Computer
Server
Computer
Switch 1
Switch 3
Networks connect computers:
2. Clients (fixed and mobile) and
3. Servers
Trunk
Line
Mobile
Client
Outside
World
Wireless
Access Point
Router
Copyright 2005 Prentice-Hall

7. Figure 1-3: Elements of a Network
Client Application
Server Application
Message (Frame)
Client
Computer
Server
Computer 4.
Computers (and routers)
usually communicate
by sending messages
called frames
Switch 1
Switch 3
Trunk
Line
Mobile
Client
Outside
World
Wireless
Access Point
Router
Copyright 2005 Prentice-Hall

8. Figure 1-3: Elements of a Network
Client Application
Server Application
Message (Frame)
Client
Sends
Frame
to Sw1
Sw2 Sends
Frame
To Sw3
Sw1 Sends
Frame
to Sw2
Switch 2
Client
Computer
Server
Computer
Sw3 Sends
Frame to
Server
Switch 1
Switch 3
Trunk
Line
Mobile
Client 5.
Switches Forward
Frames Sequentially
Switch 4
Outside
World
Wireless
Access Point
Router
Copyright 2005 Prentice-Hall

9. Figure 1-5: Ethernet Switch Operation
C3- is out Port 15
D C4-B6-F9
Switching Table
Port Host
10 A1-44-D5-1F-AA-4C
13 B2-CD-13-5B-E4-65
15 C3-2D-55-3B-A9-4F
16 D C4-B6-F9
Switch 2
Port 15 3
Frame to C3…
Frame to C3… 1
C3-2D-55-3B-A9-4F
A1-44-D5-1F-AA-4C
B2-CD-13-5B-E4-65
Switch sends frame to C3-
A1- sends a frame to C3-
Copyright 2005 Prentice-Hall

10. Figure 1-3: Elements of a Network
Client Application
Server Application
Message (Frame)
Switch 2
Access
Line
Client
Computer
Server
Computer 6.
Wireless Access
Points Connect
Wireless Stations
to Switches
Switch 1
Switch 3
Trunk
Line
Mobile
Client
Switch 4
Outside
World
Wireless
Access Point
Router
Copyright 2005 Prentice-Hall

11. Figure 1-3: Elements of a Network
Client Application
Server Application
Message (Frame)
Switch 2
Access
Line
Client
Computer
Server
Computer 7.
Routers connect networks
to the outside world;
Treated just like computers
in single networks
Switch 1
Switch 3
Trunk
Line
Mobile
Client
Switch 4
Outside
World
Yes, single networks can
contain routers
Wireless
Access Point
Router
Copyright 2005 Prentice-Hall

12. Figure 1-3: Elements of a Network
Client Application
8. Access Lines
Connect Computers
to Switches
Server Application
Message (Frame)
Access
Line
Switch 2
Client
Computer
Server
Computer
Switch 1
Switch 3
Trunk
Line
Mobile
Client
9. Trunk Lines Connect
Switches to Switches and
Switches to Routers
Switch 4
Outside
World
Wireless
Access Point
Router
Copyright 2005 Prentice-Hall

13. Figure 1-4: Packet Switching and Multiplexing
Breaking Communications into
Small Messages is Called
Packet Switching, even if the
Messages are Frames AC AC
Client
Computer A AC
Server
Computer C AC AC BD AC
Trunk Line
Multiplexed Packets
Share Trunk Lines
So Packet Switching
Reduces the Cost of Trunk Lines BD
Access
Line BD BD
Router D
Mobile Client
Computer B
Copyright 2005 Prentice-Hall

14. Network Elements: Recap
Name the 9 Elements of Single networks.
Without looking back through your handout
Never talk about an
innovation “reducing cost,” “increasing speed,” etc.
without specifying
which element is cheaper or faster.
For example, multiplexing
only reduces the cost of
trunk lines; other
costs are not decreased
Copyright 2005 Prentice-Hall

15. Part III: Transmission Speed
Copyright 2005 Prentice-Hall

16. Figure 1-6: Transmission Speed
Measuring Transmission Speed
Measured in bits per second (bps)
In metric notation:
Increasing factors of 1,000 …
Not factors of 1,024
Kilobits per second (kbps)-note the lowercase k
Megabits per second (Mbps)
Gigabits per second (Gbps)
Terabits per second (Tbps)
Copyright 2005 Prentice-Hall

17. Figure 1-6: Transmission Speed
Measuring Transmission Speed
What is 23,000 bps in metric notation?
What is 3,000,000,000 in metric notation?
What is 15,100,000 bps in metric notation?
Occasionally measured in bytes per second
If so, written as Bps
Usually seen in file download speeds
Copyright 2005 Prentice-Hall

18. Figure 1-6: Transmission Speed
Writing Transmission Speeds in Proper Form
The rule for writing speeds (and metric numbers in general) in proper form is that there should be 1 to 3 places before the decimal point
23.72 Mbps is correct (2 places before the decimal point).
2,300 Mbps has four places before the decimal point, so it should be rewritten as 2.3 Gbps (1 place).
0.5 Mbps has zero places to the left of the decimal point. It should be written as 500 kbps (3 places).
Copyright 2005 Prentice-Hall

19. Figure 1-6: Transmission Speed
Writing Transmission Speeds in Proper Form
How to convert 1,200 Mbps to proper form
Divide the number 1,200 by 1000
Move decimal point three places to the left: 1.200
Multiply the metric suffix Mbps by 1,000
Gbps
Result:
1.2 Gbps
Copyright 2005 Prentice-Hall

20. Figure 1-6: Transmission Speed
Writing Transmission Speeds in Proper Form
How to convert Mbps to proper form
Multiply the number by 1000
Move decimal point three places to the right: 36
Divide the metric suffix Mbps by 1,000
kbps
Result:
36 kbps
Copyright 2005 Prentice-Hall

21. Figure 1-6: Transmission Speed
Writing Transmission Speeds in Proper Form
How should you write the following in proper form?
kbps
0.47 Gbps
11,200 Mbps
.0021 Gbps
Copyright 2005 Prentice-Hall

22. Figure 1-6: Transmission Speed
Rated Speed
The speed in bits per second that you should get (advertised or specified in the standard).
Throughput
The speed you actually get
Almost always lower than the rated speed
On Shared Transmission Lines
Aggregate throughput—total throughput for all users
Individual throughput—what individual users get
Copyright 2005 Prentice-Hall

23. Part IV: LANs and WANs
Copyright 2005 Prentice-Hall

24. Figure 1-8: LANs Versus WANs
Characteristics
Scope
LANs
WANs
For transmission within
a site. Campus,
building, and SOHO
(Small Office or Home
Office) LANs
For transmission
between sites
Campus
LAN
Building
LAN
Wide Area
Network
Home
LAN
Copyright 2005 Prentice-Hall

25. Figure 1-8: LANs Versus WANs
Characteristics
LANs
WANs
Cost per bit Transmitted
Low
High
Typical Speed
Unshared 100 Mbps
to a gigabit per
second to each
desktop. Even faster
trunk line speeds.
Shared 128 kbps to
several megabits per
second trunk line
speeds
It’s simple economics. If the cost per unit is higher, the number of units demanded will be lower.
Corporations cannot afford high-speed for most of their WAN transmission
Copyright 2005 Prentice-Hall

26. Figure 1-9: Local Area Network (LAN) in a Large Building
Wall Jack
Workgroup Switch 2
Client
Server
Workgroup Switch 1
Wall Jack To
WAN
Core Switch
Router
Frames from the client to the server go through Workgroup Switch 2, through the Core Switch, through Workgroup Switch 1, and then to the server
Copyright 2005 Prentice-Hall

27. Part V: Internets
Copyright 2005 Prentice-Hall

28. Figure 1-11: Internets Single LANs Versus Internets
In single networks (LANs and WANs), all devices connect to one another by switches—our focus so far.
In contrast, an internet is a group of networks connected by routers so that any application on any host on any single network can communicate with any application on any other host on any other network in the internet.
Application
Application
WAN
LAN
LAN
Router
Copyright 2005 Prentice-Hall

29. Host Figure 1-11: Internets Internet Components
All computers in an internet are called hosts
Clients as well as servers
Client PC
(Host)
Cellphone
VoIP Phone
PDA
Server
Internet
Cat
(Ignores
Internet)
Copyright 2005 Prentice-Hall

30. Figure 1-11: Internets Hosts Have Two Addresses IP Address
This is the host’s official address on its internet
32 bits long
Expressed for people in dotted decimal notation (e.g., )
Single-Network Addresses
This is the host’s address on its single network
Ethernet addresses, for instance, are 48 bits long
Expressed in hexadecimal notation (e.g., AF-23-9B-E )
Copyright 2005 Prentice-Hall

31. Figure 1-11: Internets
Networks are connected by devices called routers
Switches provide connections within networks, while routers provide connections between networks in an internet.
Frames and Packets
In single networks, message are called frames
In internets, messages are called packets
Copyright 2005 Prentice-Hall

32. Figure 1-11: Internets Packets are carried within frames
One packet is transmitted from the source host to the destination host across the internet
Its IP destination address is that of the destination host
WAN
LAN
LAN
Router
Copyright 2005 Prentice-Hall

33. Figure 1-11: Internets Packets are carried within frames
In each network, the packet is carried in (encapsulated in) a frame
If there are N networks between the source and destination hosts, there will be one packet and N networks between the source and destination hosts, there will be one packet and N frames for a transmission
WAN
LAN
LAN
Router
Copyright 2005 Prentice-Hall

34. Figure 1-12: Internet with Three Networks
Host A R1
Packet
Network X
A packet goes all the
way across the internet;
It’s path is its route
Network Y
Route A-B
Network Z R2
Host B
Copyright 2005 Prentice-Hall

35. Figure 1-12: Internet with Three Networks
In Network X, the Packet is Placed in Frame X
Frame X
Details in
Network X
Packet
Switch
Host A
AB-23-D1-A8-34-DD
Switch
Server
Host
Data link
A-R1
A data Link is a
frame’s path through
its single network
Switch X1
A route is a packet’s
path through the internet
Mobile Client
Host
Switch X2
Router R1
D6-EE-92-5F-C1-56
Route A-B
Network X
Copyright 2005 Prentice-Hall

36. Figure 1-12: Internet with Three Networks
Details in
Network Y To
Network X
Route
A-B
Router R1
Frame Y
Data Link
R1-R2
Packet To
Network Z
Router R2
AF-3B-E B5
Network Y
Copyright 2005 Prentice-Hall

37. Figure 1-12: Internet with Three Networks
Network Z
Details in
Network Z
Frame Z
Packet
Data Link
R2-B
Switch Z1
Host B
55-6B-CC-D4-A7-56
Switch
Router R2
Switch Z2
Switch
Router
Mobile Client Host
Mobile Client
Computer
Copyright 2005 Prentice-Hall

38. Figure 1-12: Internet with Three Networks
In this internet with three networks, in a transmission,
There is one packet
There are three frames (one in each network)
If a packet in an internet must pass through 10 networks,
How many packets will be sent?
How many frames must carry the packet?
Copyright 2005 Prentice-Hall

39. Figure 1-13: Converting IP Addresses into Dotted Decimal Notation
IP Address (32 bits long)
Divided into 4 bytes. These
are segments.
Convert each byte to
decimal (result will be
between 0 and 255)*
128
171 17 13
Dotted decimal notation
(4 segments separated by
dots)
*The conversion process is described in the Hands On section
at the end of the chapter.
Copyright 2005 Prentice-Hall

40. Figure 1-17: The Internet 1. Webserver Host Computer 1. User PC Host3.
Internet Backbone
(Multiple ISP Carriers)
Access
Line
Access
Line
Router
NAP
NAP
ISP
ISP
ISP
NAP
ISP 2.
User PC’s
Internet Service
Provider 2.
Webserver’s
Internet Service
Provider 4.
NAPs = Network Access Points
Connect ISPs
Copyright 2005 Prentice-Hall

41. Figure 1-14: The Internet, internets, Intranets, and Extranets
Lower-case internet
Any internet
Upper-case Internet
The global Internet
Intranet
An internet restricted to users within a single company
Extranet
A group of resources that can be accessed by authorized people in a group of companies
Copyright 2005 Prentice-Hall

42. Figure 1-20: IP Address Management
Every Host Must Have a Unique IP address
Server hosts are given static IP addresses (unchanging)
Clients get dynamic (temporary) IP addresses that may be different each time they use an internet
Dynamic Host Configuration Protocol (DHCP) (Figure 1-21)
Clients get these dynamic IP addresses from Dynamic Host Configuration Protocol (DHCP) servers (Figure 1- 21)
Copyright 2005 Prentice-Hall

43. Figure 1-21: Dynamic Host Configuration Protocol (DHCP)
1. DHCP Request Message:
“My 48-bit Ethernet address is A3-4E-CD F”.
Please give me a 32-bit IP address.”
2. Pool of
IP Addresses
Client PC
A3-4E-CD F
DHCP
Server
3. DHCP Response Message:
“Computer at A3-4E-CD F,
your 32-bit IP address is ”.
(Usually other configuration parameters as well.)
Copyright 2005 Prentice-Hall

44. Figure 1-20: IP Address Management
Domain Name System (DNS) (Figure 1-22)
IP addresses are official addresses on the Internet and other internets
Hosts can also have host names (e.g., cnn.com)
Not official—like nicknames
If you only know the host name of a host that you want to reach, your computer must learn its IP address
DNS servers tell our computer the IP address of a target host whose name you know. (Figure 1-22)
Copyright 2005 Prentice-Hall

45. Figure 1-22: The Domain Name System (DNS)1.
Client Host
wishes to reach
Voyager.cba.hawaii.edu;
Needs to know
its IP Address
DNS Table
Host Name IP Address
… …
Voyager.cba.hawaii.edu
2. Sends DNS Request Message
“The host name is Voyager.cba.hawaii.edu”
Local
DNS
Host
Voyager.cba.hawaii.edu
Copyright 2005 Prentice-Hall

46. Figure 1-22: The Domain Name System (DNS)
DNS Table 3.
DNS Host
looks up the
target host’s
IP address
Host Name IP Address
… …
Voyager.cba.hawaii.edu
DNS
Host
4. DNS Response Message
“The IP address is ” 5.
Client sends packets to
Voyager.cba.hawaii.edu
Copyright 2005 Prentice-Hall

47. Figure 1-22: The Domain Name System (DNS)
The local DNS host
sends back the response;
the user is unaware that
other DNS hosts were involved
DNS Table
Host Name IP Address
… …
Voyager.cba.hawaii.edu
Client Host
Local
DNS
Host
1. DNS Request Message
3. DNS Response Message 2.
Request &
Response
If local DNS host does not
have the target host’s IP address,
it contacts other DNS hosts
to get the IP address
Anther DNS Host
Copyright 2005 Prentice-Hall

48. Part VI: Security
Copyright 2005 Prentice-Hall

49. Figure 1-23: Firewall and Hardened Hosts
Allowed Legitimate Packet
Border
Firewall
Attacker
The
Internet
Hardened
Server
Border firewall
should pass
legitimate packets
Legitimate
Packet
Hardened
Client PC
Legitimate
Host
Internal
Corporate
Network
Log File
Copyright 2005 Prentice-Hall

50. Figure 1-23: Firewall and Hardened Hosts
Server
Border firewall
should deny (drop)
and log
attack packets
Attack
Packet
Border
Firewall
Attacker
The
Internet
Hardened
Client PC
Denied
Attack
Packet
Legitimate
Host
Internal
Corporate
Network
Log File
Copyright 2005 Prentice-Hall

51. Figure 1-23: Firewall and Hardened Hosts
Server
Attack
Packet
Attack
Packet
Border
Firewall
Attacker
The
Internet
Hosts should
be hardened
against attack packets
that get through
Attack
Packet
Denied
Attack
Packet
Hardened
Client PC
Legitimate
Host
Internal
Corporate
Network
Log File
Copyright 2005 Prentice-Hall

52. Figure 1-24: Cryptographic Protections
Cryptography
The use of mathematical operations to thwart attacks on message dialogues between pairs of communicating parties (people, programs, or devices)
Initial Authentication
Determine the other party’s identity to thwart impostors
Copyright 2005 Prentice-Hall

53. Figure 1-24: Cryptographic Protections
Message-by-Message Protections
Encryption to provide confidentiality so that an eavesdropper cannot reach intercepted messages
Electronic signatures provide message-by-message authentication to prevent the insertion of messages by an impostor after initial authentication
Electronic signatures usually also provide message integrity; this tells the receiver whether anyone has changed the message en route
Copyright 2005 Prentice-Hall

54. Topics Covered
Copyright 2005 Prentice-Hall

55. Network Elements: Recap
Applications (the only element that users care about)
Computers
Clients
Servers
Switches and Routers
Transmission Lines
Trunk lines
Access Lines
Messages (Frames)
Wireless Access Points
Never talk about an
innovation “reducing cost,” “increasing speed,” etc.
without specifying
which element is cheaper or faster.
For example, multiplexing
only reduces the cost of
trunk lines; other
costs are not decreased
Copyright 2005 Prentice-Hall

56. Recap: LANs and WANs LANs transmit data within corporate sites
WANs transmit data between corporate sites
Each LAN or WAN is a single network
LAN costs are low and speeds are high
WAN costs are high and speeds are lower
WAN
Copyright 2005 Prentice-Hall

57. Recap: Internets Most firms have multiple LANs and WANs.
They must create internets
An internet is a collection of networks connected by routers so that any application on any host on any single network can communicate with any application on any other host on any other network in the internet.
Application
Application
WAN
LAN
LAN
Router
Router
Copyright 2005 Prentice-Hall

58. Recap: Internets Elements of an Internet
Computers connected to the internet are called hosts
Both servers and client PCs are hosts
Routers connect the networks of the internet together
In contrast, switches forward frames within individual networks
Router
Router
WAN
LAN
LAN
Client PC Host
Server Host
Copyright 2005 Prentice-Hall

59. Recap: Internets Hosts Have Two Addresses IP Address
This is the host’s official address on its internet
32 bits long
Expressed for people in dotted decimal notation (e.g., 128, 171, 17.13)
Single Network Addresses
This is the host’s address on its single network
Ethernet addresses, for instance, are 48 bits long
Expressed in hexadecimal notation, e.g., AF-23-9B-E
Copyright 2005 Prentice-Hall

60. Recap: Internets Switches versus Routers Messages
Switches move frames through a single network (LAN or WAN)
Routers move packets through internets
Messages
Messages in single networks are called frames
Messages in internets are called packets
Packets are encapsulated within (carried inside) frames
Copyright 2005 Prentice-Hall

61. Recap: Security Security Firewalls Hardened Hosts
Cryptographic security for sensitive dialogues
Initial authentication
Encryption for confidentiality
Electronic signatures for authentication and message integrity
Copyright 2005 Prentice-Hall