REVIEW 5
CHAPTERS 14, 15, 16, & 17
1
CHAPTER 14
2
What Is Simulation?
Simulation
A model of a complex system and the experimental
manipulation of the model to observe the results
Systems that are best suited to being simulated are
dynamic, interactive, and complicated
Model
An abstraction of a real system
It is a representation of the objects within the system
and the rules that govern the interactions of the objects
3
Constructing Models
Continuous simulation
– Treats time as continuous
– Expresses changes in terms of a set of
differential equations that reflect the
relationships among the set of characteristics
– Meteorological models fall into this category
4
Constructing Models
Discrete event simulation
Made up of entities, attributes, and events
– Entity The representation of some object in
the real system that must be explicitly defined
– Attribute Some characteristic of a particular
entity
– Event An interaction between entities
5
Queuing Systems
Queuing system
A discrete-event model that uses random
numbers to represent the arrival and
duration of events
The system is made up of
– servers
– queues of objects to be served
6
Graphics
Graphics
Originally the language of communications for
engineers, designers, and architects
Computer-aided design (CAD)
A system that uses computers with advanced
graphics hardware and software to create
precision drawings or technical illustrations
7
Graphics
Illumination model
Simulation of light interaction at one point
on an object
Shading model (shading)
Process of using an illumination model
to determine the appearance of an
entire object
Rendering
The process of creating an entire image
8
CHAPTER 15
9
Networking
Computer network
A collection of computing devices connected in
order to communicate and share resources
Connections between computing devices can be
physical using wires or cables or wireless using
radio waves or infrared signals
10
Networking
Node (host)
Any device on a network
Data transfer rate (bandwidth)
The speed with which data is moved from
one place to another on a network
11
Networking
Computer networks have opened up an
entire frontier in the world of computing
called the client/server model
Figure 15.1 Client/Server interaction
12
Networking
Protocol
A set of rules that defines how data is formatted and
processed on a network; i.e., rules that allow client/server
interaction
File server
A computer that stores and manages files for multiple
users on a network
Web server
A computer dedicated to responding to requests (from the
browser client) for web pages
13
Types of Networks
Local-area network (LAN)
A network that connects a relatively small number
of machines in a relatively close geographical area
Ring topology connects all nodes in a closed loop on
which messages travel in one direction
Star topology centers around one node to which all
others are connected and through which all messages
are sent
Bus topology nodes are connected to a single
communication line that carries messages in both
directions
14
Types of Networks
Ethernet
Figure 15.2 Various network topologies
The industry standard bus technology for
local-area networks
Types of Networks
Wide-area network (WAN)
A network that connects local-area networks over
a potentially large geographic distance
Metropolitan-area network (MAN)
The communication infrastructures that have been
developed in and around large cities
Gateway
One particular set up to handle all communication
going between that LAN and other networks
16
Packet Switching
Packet
A unit of data sent across a network
Router
A network device that directs a packet between networks
toward its final destination
Packet switching
Messages are divided into fixed-sized, numbered packets;
packets are individually routed to their destination, then
reassembled
Packet Switching
Figure 15.4
Messages
sent by
packet
switching
Take a message, break it into three packets, and
simulate this process
18
Network Protocols
Network protocols are layered such that
each one relies on the protocols that
underlie it
Sometimes referred to as a protocol stack
Figure 15.6 Layering of key network protocols
19
TCP/IP
Transmission Control Protocol (TCP)
Software that breaks messages into packets,
hands them off to the IP software for delivery, and
then orders and reassembles the packets at their
destination
Internet Protocol (IP)
Software that deals with the routing of packets
through the maze of interconnected networks to
their final destination
20
High-Level Protocols
Other protocols build on TCP/IP protocol suite
Simple Mail Transfer Protocol (SMTP) used to specify
transfer of electronic mail
File Transfer Protocol (FTP) allows a user to transfer
files to and from another computer
Telnet used to log onto one computer from another
Hyper Text Transfer Protocol (http) allows exchange
of Web documents
21
Firewalls
Firewall
A gateway machine and its software that protects
a network by filtering the traffic it allows
Access control policy
A set of rules established by an organization that
specifies what types of network communication
are permitted and denied
22
Network Addresses
Hostname
A name made up of words separated by dots that
uniquely identifies a computer on the Internet
IP address
An address made up of four one-byte numeric
values separated by dots that uniquely identifies a
computer on the Internet
23
Network Addresses
Figure 15.9
An IP address
is stored in
four bytes
24
Domain Name System
Domain name system (DNS)
A distributed system for managing hostname
resolution
Domain name server
A computer that attempts to translate a hostname
into an IP address
25
Domain Name System
Host number
The part of the IP address that specifies a
particular host (machine) on the network Yes, but
what is it?
Domain name
The part of a hostname that specifies a specific
organization or group
Top-level domain (TLD)
The last section of a domain name that specifies
the type of organization or its country of origin
26
CHAPTER 16
27
The World Wide Web
The Web
An infrastructure of information combined and the
network software used to access it
Web page
A document that contains or references various
kinds of data
Links A connection between one web page and
another
28
The World Wide Web
Website
A collection of related web pages
Web browser
A software tool that retrieves and displays eb
pages
Web server
A computer set up to respond to requests for web
pages
29
The World Wide Web
Uniform Resource Locator (URL)
A standard way of specifying the location of a Web
page, containing the hostname, "/", and a file
What is the relationship between the
Internet and the Web?
30
Cookies
Cookie
A small text file that a web server stores on your
local computer’s hard disk
– A cookie contains information about your visit to the
site
– Cookies can be used
• to determine number of unique visitors to the site
• to customize the site for future visits
• to implement shopping carts that can be maintained from visit
to visit
– Cookies are not dangerous
31
HTML
Hypertext Markup Language (HTML)
The language used to create or build a Web page
Markup language
A language that uses tags to annotate the
information in a document
Tags
The syntactic element in a markup language that
indicates how information should be displayed
32
Java Applets
Java applet
A Java program designed to be embedded
into an HTML document, transferred over
the Web, and executed in a browser
<P><APPLET code = "FactByte.class"
width=250 height=150></APPLET></P>
33
XML
Extensible Markup Language (XML)
A language that allows the user to describe the
content of a document
– HTML describes how a document should look
– XML describes a document's meaning
Metalanguage
A language for talking about, or defining, other
languages
XML is a metalanguage
34
CHAPTER 17
35
Information Security
Information security
The techniques and policies used to ensure
proper access to data
Confidentiality
Ensuring that data is protected from
unauthorized access
36
CIA Triad of Information
Security
Ensuring
that data
can be
modified
only by
appropriate
mechanisms
The degree to which authorized
users can access information for
legitimate purposes
37
Ensuring that data is
protected from
unauthorized access
Preventing Unauthorized Access
Authentication credentials
Information users provide to identify
themselves for computer access
• User knowledge Name, password, PIN
• Smart card A card with an embedded
memory chip used for identification
• Biometrics Human characteristics such
as fingerprints, retina or voice patterns
38
Preventing Unauthorized Access
CAPTCHA
Software that verifies that the user is not
another computer
You have to look at a weird set of
characters and key them back in.
Why does this work?
39
© reCAPTCHA
Computer Security
Malicious Code
A computer program that attempts to bypass
appropriate authorization and/or perform unauthorized
functions
Worm stands alone, targets network resources
Trojan horse disguised as benevolent resource
Virus self-replicating
Logic bomb set up to execute at system event
40
Antivirus Software
Software installed to detect and remove
malicious code
Signature detection recognizes known
malware and removes
Heuristics are strategies used to identify
general patterns
41
Computer Security
Security Attacks
An attack on the computer system itself
Password guessing Obvious
Phishing Trick users into revealing
security information
Spoofing Malicious user masquerades as
authorized user
Back door Unauthorized access to anyone
who knows it exists
42
Computer Security
Buffer overflow Defect that could cause a system
to crash and leave the user with heightened
privileges
Denial-of-service Attach that prevents authorized
user from accessing the system
Man-in-the-middle Network communication is
intercepted in an attempt to obtain key data
43
Cryptography
Cryptography
The field of study related to encoded information
(comes from Greek word for "secret writing")
Encryption
The process of converting plaintext into ciphertext
Decryption
The process of converting ciphertext into plaintext
44
Cryptography
Cipher
An algorithm used to encrypt and decrypt text
Key
The set of parameters that guide a cipher
Neither is any good without the other
45
Cryptography
Substitution cipher
A cipher that substitutes one character with another
Caesar cipher
A substitution cipher that shifts characters a certain
number of positions in the alphabet
Transposition ciphers
A cipher that rearranges the order of existing characters
in a message in a certain way (e.g., a route cipher)
46
Cryptanalysis
Cryptanalysis
The process of decrypting a message
without knowing the cipher or the key used
to encrypt it
Substitution and transposition ciphers are
easy for modern computers to break
To protect information more sophisticated
schemes are needed
47
Public/Private Keys
Public-key cryptography
An approach in which each user has two
related keys, one public and one private
One's public key is distributed freely
A person encrypts an outgoing message,
using the receiver's public key.
Only the receiver's private key can decrypt
the message
48
Public/Private Keys
Digital signature
Data that is appended to a message, made from
the message itself and the sender's private key, to
ensure the authenticity of the message
Digital certificate
A representation of a sender's authenticated
public key used to minimize malicious forgeries
49