Download Using Management Information Systems

David Kroenke
Data Communications and
Internet Technology
Chapter 5
© 2007 Prentice Hall, Inc.
1




Know basic telecommunications
terminology.
Know the definition and characteristics of
LAN, WANs, and internets.
Understand the nature of processing in a
layered communications protocol.
Know the purpose of the five layers of the
TCP/IP-OSI protocol.
© 2007 Prentice Hall, Inc.
2



Understand Ethernet and wireless LANs.
Understand the characteristics of WANs
using personal computers with modems to
the Internet, networks of leased lines,
PSDNs and virtual private networks.
Know basic concepts involved in the
operation of the Internet.
© 2007 Prentice Hall, Inc.
3


A computer network is a collection of
computers that communicate with one another
over transmission lines.
Three basic types of networks are:
◦ Local area networks (LANs)–connects computers that
reside in a single geographic location on the
premises of the company that operates the LAN.
◦ Wide area networks (WANs)–connects computers at
different geographic sites.
◦ Internets–a network of networks
© 2007 Prentice Hall, Inc.
4


The networks that comprise an Internet use a
large variety of communication methods and
conventions, and data must flow seamlessly
across them.
To provide seamless flow, an elaborate
scheme called a layered protocol is used.
© 2007 Prentice Hall, Inc.
5
© 2007 Prentice Hall, Inc.
6
© 2007 Prentice Hall, Inc.
7
© 2007 Prentice Hall, Inc.
8




A protocol is a standard means for coordinating
an activity between two or more entities.
A communications protocol is a means for
coordinating activity between two or more
communicating computers.
Two machines must agree on the protocol to use,
and they must follow that protocol as they send
messages back and forth.
Communications protocols are broken into levels
of layers.
© 2007 Prentice Hall, Inc.
9



The International Organization for
Standardization (ISO) developed the Reference
Model for Open Systems Interconnection (OSI), an
architecture that has seven layers.
The Internet Engineering Task Force (IETP),
developed a four-layer scheme called the TCP/IP
(Transmission Control Program Internet Protocol)
architecture.
The most commonly used architecture today is a
five-layer blend of these two architectures called
the TCP/IP-OSI architecture.
© 2007 Prentice Hall, Inc.
10
© 2007 Prentice Hall, Inc.
11

Layer 5 generates and receives email (and
attachments like photos) according to one of the
standard email protocols generated for layer 5
◦ Most likely its Simple Mail Transfer (SMTP)
◦ Hypertext Transfer Protocol (HTTP) is used for the
processing of Web pages.

The Web and the Internet are not the same thing.
◦ The Web, which is a subset of the Internet, consists of
sites and users that process the HTTP protocol.
◦ The Internet is the communications structure that
supports all application-layer protocols, including
HTTP, SMTP, and other protocols.
© 2007 Prentice Hall, Inc.
12

FTP, or the File Transfer Protocol is another
application layer protocol.
◦ You can use FTP to copy files from one computer to
another.


An architecture is an arrangement of protocol
layers in which each layer is given specific tasks
to accomplish.
At each level of the architecture, there are one or
more protocols.
◦ Each protocol is a set of rules that accomplish the tasks
assigned to its layer.
© 2007 Prentice Hall, Inc.
13



A program is a specific computer product that
implements a protocol.
Programs that implement the HTTP protocol of
the TCP/IP-OSI architecture are called browsers.
Two common browsers are Netscape and
Microsoft Internet Explorer.
© 2007 Prentice Hall, Inc.
14
© 2007 Prentice Hall, Inc.
15



An email program (which uses SMTP) interacts
with another protocol called TCP, or
Transmission Control Program (TCP).
TCP operates at layer 4 of the TCP/IP-OSI
architecture.
The TCP program examines your data (files,
email, pictures, etc.) and breaks these lengthy
messages into pieces called segments.
© 2007 Prentice Hall, Inc.
16



TCP places identifying data in front of each
segment that are akin to the To and From
addresses that you would put on a letter for the
postal mail.
TCP programs also provide reliability.
If data is sent from a Dell computer to a
Macintosh computer, TCP program translates the
segments from Windows (Dell) to Macintosh
format, reassembles the segments into a
coherent whole, and makes that assembly
available to Macintosh computer.
© 2007 Prentice Hall, Inc.
17




TCP/IP interacts with protocols that operate at
Level 3, the next layer down.
For the TCP/IP architecture, the layer-3 protocol
is the Internet Protocol (IP).
The chief purpose of IP is to route messages
across an internet.
Routers are special-purpose computers that
implements the IP protocol.
© 2007 Prentice Hall, Inc.
18



Basic computer connectivity is accomplished
using Layers 1 and 2 of the TCP/IP-OSI
architecture.
Computing devices called switches facilitate data
communication.
A program implementing a Layer-2 protocol will
package each of your packets into frames, which
are the containers used at Layers 1 and 2
(Segments go into packets and packets go into
frames).
© 2007 Prentice Hall, Inc.
19


A local area network (LAN) is a group of
computers connected together on a single
company site.
Usually the computers are located within a half
mile or so of each other, although longer
distances are possible.
◦ The key distinction, however, is that all of the
computers are located on property controlled by the
company that operates the LAN.

Computers and printers are connected via a
switch, which is a special-purpose computer that
receives and transmits messages on the LAN.
© 2007 Prentice Hall, Inc.
20

Each device on a LAN (computer, printer, etc.)
has a hardware component called a network
interface card (NIC) that connects the device’s
circuitry to the cable.
◦ The NIC works with programs in each device to
implement Layer 1 and Layer 2 protocols.
◦ Each NIC has a unique identifier, which is called the
(MAC) media access control address.

The computers, printers, switches, and other
devices on a LAN are connected using one of two
media.
◦ Most connections are made using unshielded, twisted
pair (UTP) cable.
◦ A device called an RJ-45 connector is used to connect
the UTP cable into NIC devices on the LAN.
© 2007 Prentice Hall, Inc.
21

The connection between switches can use UTP
cable, but if they carry a lot of traffic or are far
apart UTP cable may be replaced by optical fiber
cables.
◦ The signals on such cables are light rays, and they are
reflected inside the glass core of the optical fiber cable.
◦ Optical fiber cable uses special connectors called ST
and SC connectors.
© 2007 Prentice Hall, Inc.
22
© 2007 Prentice Hall, Inc.
23
© 2007 Prentice Hall, Inc.
24
© 2007 Prentice Hall, Inc.
25
© 2007 Prentice Hall, Inc.
26

The committee that addresses LAN standards is
called the IEEE 802 Committee.
◦ Thus, IEEE LAN protocols always start with the number
802.

Today, the world’s most popular protocol for
LAN is the IEEE 802.3 protocol.
◦ This protocol standard, also called Ethernet, specifies
hardware characteristics such as which wire carries
which signals.
◦ It also describes how messages are to be packaged and
processed for transmission over the LAN.
◦ Ethernet operates at Layers 1 and 2 of the TCP/IP-OSI
architecture.
© 2007 Prentice Hall, Inc.
27

Most personal computers today are equipped
with an onboard NIC that supports what is called
10/100/1000 Ethernet.
◦ These products conform to the 802.3 specification and
allow for transmission at a rate of 10, 100, or 1,000
Mbps.
◦ Communications speeds are expressed in bits, whereas
memory sizes are expressed in bytes.
© 2007 Prentice Hall, Inc.
28


Wireless connections have become popular with
LANs.
The NIC for wireless devices have been replaced
by wireless NIC (WNIC).
◦ For laptop computers, such devices can be cards that
slide into the PCMA slot or they can be built-in,
onboard devices.

Several different wireless standard exist
◦ As of 2005, the most popular is IEEE 802.11g
◦ The current standard, 802.11g allows speeds of up to
54 Mbps.
◦ The WNICs operate according to the 802.11 protocol
and connect to an access point (AP).
© 2007 Prentice Hall, Inc.
29
© 2007 Prentice Hall, Inc.
30
© 2007 Prentice Hall, Inc.
31
© 2007 Prentice Hall, Inc.
32

A wide area network (WAN) connects computers
located at physically separated sites.
◦ A company with offices in Detroit and Atlanta must use
a WAN to connect the computers together.
◦ Because the sites are physically separated, the company
cannot string wire from one site to another.

An Internet service provider (ISP) has three
important functions:
◦ It provides you with a legitimate Internet address.
◦ It serves as your gateway to the Internet.
◦ It receives the communication from your computer and
passes them on to the Internet, and it receives
communication from the Internet and passes them on
to you.
© 2007 Prentice Hall, Inc.
33

Home computers and those of small businesses
are commonly connected to an ISP in one of
three ways:
◦ Using a regular telephone line
◦ Using a special telephone line called a DSL line
◦ Using cable TV line


All three ways require that the digital data in the
computer be converted to an analog, or wavy,
signal.
A device called a modem, or
modulator/demodulator performs this
© 2007 Prentice Hall, Inc.
34
© 2007 Prentice Hall, Inc.
35
© 2007 Prentice Hall, Inc.
36

A dial-up modem performs the conversion
between analog and digital in such a way that the
signal can be carried on a regular telephone line.
◦ You dial the number for your ISP and connect.
◦ The maximum transmission speed for a switch is 56
kbps.

The way messages are packaged and handled
between your modem and the ISP is governed by
a protocol known as Point-to-Point Protocol
(PPP).
◦ This Layer-2 protocol is used for networks that involve
just two computers.
© 2007 Prentice Hall, Inc.
37

A DSL modem is the second modem type.

DSL stands for digital subscriber line.

DSL modems operate on the same lines as voice
telephones and dial-up modems.
◦ They operate so that their signals do not interfere with
voice telephone service.
◦ They provide much faster data transmission speeds
than dial up modems.
◦ They always maintain a connection.
© 2007 Prentice Hall, Inc.
38




DSL data transmission and telephone
conversations can occur simultaneously.
DSL modems use their own Layer 1 and Layer 2
protocols for data transmission.
DSL lines that have different upload and
download speeds are called asymmetric digital
subscriber lines (ADSL).
Symmetrical digital subscriber lines (SDSL) offers
the same speed in both directions.
© 2007 Prentice Hall, Inc.
39





A cable modem is the third modem type.
Cable modems provide high-speed data
transmission using cable television lines.
At the maximum, users can download data up to
10 Mbps and can upload data at 256 kbps.
Narrowband lines typically have transmission
speeds less than 56 kbps.
Broadband lines have speeds in excess of 256
kbps.
© 2007 Prentice Hall, Inc.
40
© 2007 Prentice Hall, Inc.
41



A WAN connects computers located at
geographically distributed company sites.
The lines that connect these sites are leased from
telecommunication companies that are licensed
to provide them.
A variety of access devices connect each site to
the transmission.
◦ These devices are typically special-purposed
computers.
◦ The particular devices required depend on the line used
and other factors
◦ Sometimes switches and routers are employed.
© 2007 Prentice Hall, Inc.
42
© 2007 Prentice Hall, Inc.
43


Another WAN alternative is a public switched
network (PSDN), a network of computers and
leased lines that is developed and maintained by
a vendor that leases time on the network to other
organizations.
When using a PSDN, each site must lease a line to
connect to the PSDN network.
◦ The location at which this occurs is called a point of
presence (POP); it is the access point into the PSDN.
◦ Once a site has connected to the PSDN POP, the site
obtains access to all other sites connected to the PSDN.
© 2007 Prentice Hall, Inc.
44

PSDNs save the setup and maintenance activities
when using leased lines.
◦ They also save costs because a company does not have
to pay for the entire network.
◦ The company can just pay for the traffic that it sends.

Three Layer 1 and 2 protocols are used with
PSDNs:
◦ Frame Relay can process traffic in the range of 56 kbps
to 40 Mbps.
◦ Asynchronous transfer mode (ATM) can process speeds
from 1 to 156 Mbps (can handle both voice and data).
◦ Ethernet, the protocol developed for LANs
© 2007 Prentice Hall, Inc.
45
© 2007 Prentice Hall, Inc.
46




Virtual private network (VPN) is the fourth WAN
alternative.
A VPN uses the Internet or a private internet to
create the appearance of private point-to-point
connections.
A VPN uses the public Internet to create the
appearance of a private connection.
A connection called a tunnel, is a virtual pathway
over a public or shared network from the VPN
client to the VPN server.
© 2007 Prentice Hall, Inc.
47

VPN communications are secure.
◦ The VPN client software encrypts, or codes, the original
messages so that its contents are hidden.

Virtual private networks offer the benefit of
point-to-point leased lines, and they enable
remote access, both by employees and by any
others who have been registered with the VPN
server.
© 2007 Prentice Hall, Inc.
48
© 2007 Prentice Hall, Inc.
49
© 2007 Prentice Hall, Inc.
50
© 2007 Prentice Hall, Inc.
51


Many different computer networking alternatives
are available, each with different characteristics.
There are three types of costs that need to be
considered.
◦ Setup costs include the costs of acquiring transmission
lines and necessary equipment, such as switches,
routers, and access devices.
◦ Operational costs include lease fees for lines and
equipment, charges of the ISP, the cost of ongoing
training, etc.
◦ Maintenance costs include those for periodic
maintenance, problem diagnosis and repair, and
mandatory upgrades.
© 2007 Prentice Hall, Inc.
52

There are six considerations with regard to
performance:
◦
◦
◦
◦
◦
◦

Speed
Latency
Availability
Loss rate
Transparency
Performance guarantees
Other criteria to consider when comparing
network alternatives include the growth potential
(greater capacity) and the length of contract
commitment.
© 2007 Prentice Hall, Inc.
53
© 2007 Prentice Hall, Inc.
54

On most networks, and on every internet, two
address schemes identify computers and other
devices.
◦ Programs that implement Layer 2 protocols use physical
addresses, or MAC addresses.
◦ Programs that implement Layer 3, 4, and 5 protocols
use logical addresses, or IP addresses.
Physical Addresses (MAC Addresses)
◦ Each NIC is given an address at the factory that is the
device’s physical address or MAC address.
◦ By agreement among computer manufacturers, such
addresses are assigned in such a way that no two NIC
devices will ever have the same MAC address.
◦ Physical addresses are only known, shared, and used
within a particular network or network segment.
© 2007 Prentice Hall, Inc.
55
Logical Address (IP Addresses)
◦ Internets, including the Internet, and many private
networks use logical addresses, which are also called IP
addresses, for example, 192.168.2.28
Public Versus Private Addresses
◦ Public IP addresses are used on the Internet and
assigned to major institutions in blocks by the Internet
Corporation for Assigned Names and Numbers (ICANN).
◦ Each IP address is unique across all computers on the
Internet.
◦ Private IP addresses are used within private networks
and internets. They are controlled only by the company
that operates the private network or internet
© 2007 Prentice Hall, Inc.
56
Dynamic Host Configuration Protocol
◦ The DHCP server is a computer or router that hosts a
program called Dynamic Host Configuration Protocol
(DHCP).
◦ When the program finds such a device, your computer
will request a temporary IP address from the DNCP
server which is loaned to you while you are connected
to the LAN.
◦ When you disconnect, that IP address becomes
available, and the DHCP server will reuse it when
needed.
© 2007 Prentice Hall, Inc.
57
© 2007 Prentice Hall, Inc.
58

Switches work with frames at Layer 2.
◦ They send frames from switch to switch until they arrive
at their destination.
◦ They use MAC addresses.
◦ All switches have a table of data called a switch table.

Routers work with packets at Layer 3.
◦ They send packets from router to router until they
arrive at their destination.
◦ They use IP addresses.
© 2007 Prentice Hall, Inc.
59
© 2007 Prentice Hall, Inc.
60
Network Address Translation
◦ For Internet traffic, only public IP addresses can be
used.
 These addresses are assigned in blocks to large companies
and organizations like ISPs.
◦ All Internet traffic aimed at any computer within an
organization's LAN will be sent over the Internet using
the router’s IP public address for the given computer.
 The router will receive all packets for all computers for the
organization’s computers.
 When the router receives a packet, it determines the internal
IP address within the LAN for that computer.
 It then changes the address in the packet from the router’s IP
public address to the internal IP address of a computer in the
organization's LAN, the packet’s true destination.
© 2007 Prentice Hall, Inc.
61
Network Address Translation (continued)
◦ The process of changing public IP addresses into
private IP addresses, and the reverse, is called Network
Address Translation (NAT).
© 2007 Prentice Hall, Inc.
62
© 2007 Prentice Hall, Inc.
63




IP addresses are useful for computer-tocomputer communication, but they are not well
suited for human use.
The purpose of the domain name system (DNS) is
to convert user-friendly names into their IP
addresses.
Any registered, valid name is called a domain
name.
The process of changing a name into its IP
address is called resolving the domain name.
© 2007 Prentice Hall, Inc.
64


Every domain name must be unique, worldwide.
To ensure duplicate domain names do not occur,
an agency registers names and records the
corresponding IP addresses in a global directory.
© 2007 Prentice Hall, Inc.
65




ICANN is a nonprofit organization that is
responsible for administering the registration of
domain names.
ICANN 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.
The last letter in any domain name is referred to
as the top-level-domain (TLD).
◦ In the domain www.icann.org the
topHall,level
domain is
© 2007 Prentice
Inc.
66


A uniform resource locator (URL) is a document’s
address on the Web.
URLs begin with a domain and then are followed
by optional data that locates a document with
that domain.
◦ Thus, in the URL www.prenhall.com/kroenke , the
domain name is www.prenhall.com , and /kroenke is a
directory within that domain.
© 2007 Prentice Hall, Inc.
67




Domain name resolution is the process of
converting a domain name into a public IP
address.
The process starts from the TLD and works to
the left across the URL.
As of 2005, 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 each resolve each type of TLD.
© 2007 Prentice Hall, Inc.
68

Domain name resolution proceeds quickly
because there are thousands of computers called
domain name resolvers that store the
correspondence of domain names and IP
addresses
◦ These resolvers reside at ISPs, academic institutions,
large companies, government organizations, etc.
◦ For example, if a domain name solver is on your
campus and whenever anyone on your campus needs to
resolve a domain name, that resolver will store, or
cache, the domain name and IP address on a local file.
 When someone else on the campus needs to resolve the same
domain name, the resolver can supply the IP address from the
local file.
© 2007 Prentice Hall, Inc.
69
© 2007 Prentice Hall, Inc.
70

Two IP addressing schemes exist: IPv4 and IPv6.
IPv4
◦ IPv4 constructs addresses having 32 bits.
◦ These bits are divided into four groups of 8 bits, and a
decimal number represents each group.
◦ IPv4 addresses appear as 63.224.57.59.
◦ The largest decimal number that can appear between
the period are 255 (0 – 255).
IPv6
◦ Due to growth of the Internet IPv6 was developed.
◦ IPv6 construct addresses having 128 bits.
◦ Currently both IPv4 and IPv6 are used on the Internet.
© 2007 Prentice Hall, Inc.
71




A computer network is a collection of
computers that communicate with one
another over transmission lines.
Three types of computer networks are: LANs,
WANs, and Internets, including the Internet.
A protocol architecture divides
communications activities among several
layers.
Each layer has specific functions to perform.
© 2007 Prentice Hall, Inc.
72



A protocol is a set of rules for accomplishing
the functions of a particular layer.
LANS consist of computers at a single
organizational site that are connected via
UTP or optical fiber cables.
Each computer has a network interface card
(NIC), which is a special-purpose computer
that connects to the LAN’s cabling.
© 2007 Prentice Hall, Inc.
73



A switch is a special-purpose that receives
traffic from one computer and sends it to
another computer.
IEEE 802.3, or Ethernet, is the most popular
LAN standard.
The most popular wireless standard today is
IEEE 802.11g.
© 2007 Prentice Hall, Inc.
74



Networks of leased lines consist of highspeed lines that connect two points.
A public switched data network (PSDN) is a
network of computers and leased lines that is
developed and maintained by a vendor that
leases time on the network to other
organizations.
A virtual private network (VPN) uses the
Internet or other Internet to create the
appearance of private, point-to-point
connections.
© 2007 Prentice Hall, Inc.
75



Communicating devices have two addresses:
physical address (MAC) and an IP address
(logical address).
The process of converting IP addresses from
private to public and public to private is called
Network Address Translation (NAT).
The domain name system (DNS) resolves
domain names into IP addresses.
© 2007 Prentice Hall, Inc.
76
Access device
Access point
Analog signal
Architectures
Asymmetric digital
subscriber line (ADSL)
Asymmetric encryption
Asynchronous transfer
mode (ATM)
Broadband
Cable modem
Cache
Communications protocol
Device access router
Dial-up modem
Domain name
Domain name resolution
Domain name resolver
Domain name system (DSN)
DSL (digital subscriber line)
modem
Dynamic Host Configuration
Protocol (DHCP)
Encryption
Encryption algorithms
© 2007 Prentice Hall, Inc.
77
Ethernet
File Transfer Protocol (FTP)
Frame
Frame relay
HTTPs
Hypertext Transfer Protocol
(HTTP)
IEEE 802.3 protocol
International Organization
for Standardization (ISO)
Internet
Internet Corporation for
Assigned Names and
Numbers (ICANNN)
Internet Engineering Task
Force (IETF)
Internet Protocol (IP)
Internet service provider
(ISP)
IP address
IPv4
IPv6
Key
Layered protocols
Local area network (LAN)
Logical address
MAC address
Modem
© 2007 Prentice Hall, Inc.
78
Narrowband
Network
Network Address
Translation
(NAT)
Network interface card
(NIC)
Network of leased lines
Onboard NIC
Optical fiber cable
Physical address
Point-to-Point protocol
(PPP)
Point of presence (POP)
Private IP Address
Protocol
Public IP address
Public key/private key
Public switched data
network (PSDN)
Reference Model for Open
Systems Interconnection
Root server
Routing table
Secure Socket Layer (SSL)
Segment
Simple Mail Transfer
Protocol (SMTP)
© 2007 Prentice Hall, Inc.
79
SOHO (small office, home
office)
Switch
Switch table
Symmetric encryption
Symmetric digital subscriber
line (SDSL)
TCP/IP-OSI architecture
10/100/1000 Ethernet
Top-level domain (TLD)
Transmission Control
Program (TCP) Protocol
Transmission Control
Program/Internet Protocol
(TCP/IP) architecture
Tunnel
Uniform resource locator
(URL)
Unshielded twisted-pair
(UTP) cable
Virtual private network
Wide area network (WAN)
Wireless NIC (WNIC)
© 2007 Prentice Hall, Inc.
80
Nathan Myhrvold, the chief scientist at Microsoft
Corporation during the 1990s, once said that
humans are incapable of thinking exponentially.



Instead, when something changes exponentially, we
think of the fastest linear change we can imagine and
extrapolate from there.
His point was that no one could then imagine how much
growth there would be in magnetic storage and what we
would do with it.
We have all witnessed exponential growth in a number
of areas: Internet connection, Web pages, and the
amount of data accessible on the Internet.
© 2007 Prentice Hall, Inc.
81
Every business, every organization, needs to be
thinking about ubiquitous and cheap connectivity
that is growing exponentially.





What are the new opportunities?
What are the new threats?
How will our competition react?
How should we position ourselves?
How should we respond?
Understand that technology does not drive people
to do things they’re never done before, no matter
how much the technologists suggest it might.
© 2007 Prentice Hall, Inc.
82
We lost our independence with the introduction of
the DSL modem.



Up until then, you had to dial up, you had to take action,
to get connected.
The default mode was Off, and you had to do something
to get On.
Since DSL, the default mode has been On.
Today, perpetual connectivity is terrific: It is useful,
and it increases productivity.

Have we lost not only the ability to be off line, but also
the desire?
© 2007 Prentice Hall, Inc.
83
Today, we are choosing perpetual connectivity
because we want to. It’s voluntary:


We connect because we want the services, the
information, the instantaneous gratification.
But in the process, what do we lose?
© 2007 Prentice Hall, Inc.
84
Encryption is the process of transforming clear
text into coded, unintelligible text for secure storage
or communication.
Considerable research has gone into developing
encryption algorithms that are difficult to break.
A key is a number used to encrypt data.


The encryption algorithm applies the key to the original
message to produce the coded message.
Decoding (decrypting) a message is similar; a key is
applied to code the message to recover the original text.
© 2007 Prentice Hall, Inc.
85
In symmetric encryption, the same key is used to
encode and decode.
In asymmetric encryption, different keys are
used;

One key encodes the message, and the other key
decodes the message.
A special version of asymmetric encryption, public
key/private key, is popular on the Internet.

With this method, each site has a public key for encoding
messages and a private key for decoding them.
© 2007 Prentice Hall, Inc.
86
Most secure communication over the Internet uses
a protocol called HTTPS.
With HTTPS, data are encrypted using a protocol
called the Secure Socket Layer/Transport Layer
Security (SSL/TLS).

SSL uses a combination of public key/private key and
symmetric encryption.
The use of SSL/TLS makes it safe to send sensitive
data like credit card numbers and bank balances.

Just be certain that you see https//: in your browser and
not just http://.
© 2007 Prentice Hall, Inc.
87
You send a personal email to your friend at his job
that contains both text and a picture (6.2 megabytes
in size).
This email during its transmission from you to your
friend at his job, consumes his company’s entire
computing infrastructure.
Finally, if your friend reads his email during his
working hours, he will be consuming company
resources, his time and attention, which the
company has paid while he is at work.
© 2007 Prentice Hall, Inc.
88
The Hungarian writer, Frigyes Karinthy, came up
with the idea that everyone on earth is connected
to everyone else by five or six people.

Today, in fact with the Internet, the number may be
closer to three people than five or six.
Suppose you want to meet your university’s
president.



The president has a secretary who acts as a
gatekeeper.
If you walk up to that secretary and say, “I’d like a half
hour with President Jones,” you’re likely to be palmed
off to some other university administrator.
What else can you do?
© 2007 Prentice Hall, Inc.
89
The problem with the six-degree theory, is that
even though those six people do exist, we don’t
know who they are.

Even worse, we often don’t know who the person is with
whom we want to connect.
Most successful professionals consistently build
personal human networks.


They keep building them because they know that
somewhere there is someone whom they need to know
or will need to know.
They meet people at professional and social situations,
collect and pass out cards, and engage in pleasant
conversation (all part of a social protocol) to expand
their networks.
© 2007 Prentice Hall, Inc.
90