Download Q2. What Are the Components of a LAN?

Management Information Systems
Chapter 6
Data Communications
This Could Happen to You
Dee needs to decide where she will run the blog
It needs to be private to maintain a competitive advantage
Sales people need to have easy access
Passwords may be needed to restrict access
Emerson has a private network
Protected by firewall
Employees access through VPN (Virtual Private Network)
 Can be protected from unauthorized access
 Sales people can access with same password they already use
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Study Questions
Q1. What is a computer network?
Q2. What are the components of a LAN?
Q3. What are the alternatives for a WAN?
Q4. How does encryption work?
Q5. What is the purpose of a firewall?
Q6. What is a VPN and why is it important?
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Q1. What Is a Computer Network?
Network
Collection of computers
Communicate with one another over transmission line
Three basic types
Local area network (LAN)
Wide area network (WAN)
Internet
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主要的網路類型
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LAN
Connects computers residing in single location
2 to several hundred computers
One geographic area
Communication lines can be placed where the
organization wants
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WAN
Connect computers in different geographical areas
Two or more cities
Uses communication networks from vendors
Licensed by government
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Internet
Network of networks
Connect LANs, WANs, and other internets
Private networks of networks
Use a variety of communication methods and
conventions
Seamless flow of data provided by layered protocol
 Set of rules that communicating devices follow
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Q2. What Are the Components of a LAN?
Local area network
Computers connected on single company site
Usually located within half mile area
Property controlled by company operating network
 Company can run cabling as necessary
Components
Switch
 Special purpose computer that receives and transmits messages
Network Interface Card (NIC)
 Hardware that connects each device’s circuitry to the cable
 Onboard NIC or card that fits into an expansion slot
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區域網路（LAN）
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NIC Devices
MAC address
Unique identifier
Media connections
Unshielded twisted pair (UTP) cable
 RJ-45 connector
Optical fiber cables
 Light rays reflected inside glass core surrounded by cladding
 Uses ST and SC connectors
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網路卡
圖6-3
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無遮蔽式雙絞線電纜
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光纖電纜
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IEEE 802.3 Protocol
Ethernet protocol standard
Specifies hardware characteristics
Describes how messages are packages
Determines how messages are processed
Operates at Layers 1 and 2 of TCP/IP-OSI architecture
Personal computers usually support 10/100/1000
Ethernet
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LANs with Wireless Connections
Wireless NIC (WNIC)
LAN operation
NICs operate on 802.3 protocol
WNICs operate on 802.11 protocol
WNICS connect to Access Point (AP)
 AP processes both standards
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無線區域網路
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LAN 和
WAN
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Q3. What Are the Alternatives for a WAN?
WANs connect computers at separate sites
No cabling between sites
Cable connections made through licensed
communications companies
Internet service provider (ISP)
Provides legitimate Internet address
Serves as gateway to Internet
Pay for Internet
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Connecting to the ISP
Connections made through:
Regular telephone lines
Use of DSL line
Cable TV lines
All require digital data to be converted to analog
Modem makes conversion
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類比與數位訊號
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個人電腦的網際網路管道
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MIS In Use: Larry Jones (Student) Network
Services
Larry set up LAN networks
Realized that he had to offer support
Customers had problems
Customers needed to add more devices
Coupled installation with support package
Extra charges for support beyond normal wear and tear
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Dial-Up Modems
Handles conversion between analog and digital
Connection made by dialing ISP
Maximum transmission speed of 56 kbps
Modulation governed by V.34, V.90. or V.92
standards
PPP (Point-to-Point Protocol) controls message
packaging and handling
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DSL Modems
Operates over telephone lines
Do not interfere with voice telephone service
Faster data transmission than dial-up
Connection always maintained
Use their own Layer 1 and 2 protocols
Download and upload speeds vary
Asymmetric digital subscriber lines (ADSL)
Symmetrical digital subscriber lines (SDSL)
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Cable Modems (1)
Provide high-speed data transmission
Use cable television lines
High-capacity optical fiber cable run to neighborhood
distribution center
Television cables connect at distribution center and runs
to subscribers
Does not interfere with television transmission
Up to 500 subscribers connected at each center
 Performance varies based on number connected
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Cable Modems (2)
Download speed up to 10Mbps, upload up to 256
kbps
Operate with Layer 1 and 2 protocols
Speeds
Narrowband
 Transmission speeds less then 56 kbps
Broadband
 Transmission speeds in excess of 256 kbps
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Networks of Leased Lines
WAN connects computers located at geographically
distributed sites
Access devices connect sites to transmission
Switch
Router
Alternative is leasing lines
T1, T3
Set up as a point-to-point line
Only predefined sites can use leased lines
Provide low cost per bit transmitted
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使用租用線路的 WAN
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Transmission Line Types, Uses and
Speeds
Figure 6-11
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Problem Solving Guide: Thinking
Exponentially Is Not Possible, but…
Nathan Myhrvoid claimed that:
Humans cannot think exponentially
Think of fastest linear change and extrapolate from there
Was writing about growth of magnetic storage
Also applies to growth of computer network phenomena
Ubiquitous and cheap connectivity is growing exponentially
What are the threats and opportunities?
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Exponential Phenomena Brings Changes
Technology doesn’t drive people to do new things
Social progress occurs in small, evolutionary, adaptive
steps
Technology may enable a capability, but people may not
want it
People want to do what they are doing more easily
They want to solve existing problems
Respond by hedging your bets
The more time involved, the more potential for error
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Public Switched Data Network (PSDN)
Network of computers and leased lines
Developed and maintained by vendor
Time leased on network
Utility that supplies network for other companies to
lease
Each site leases line to connect to PSDN network at
access point
 Point of presence (POP)
 Saves setup and maintenance activities
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PSDN Protocols
Frame relay
Process traffic at 56 kbps to 40 Mbps
Simplest and easiest to support
Asynchronous transfer mode (ATM)
Process speeds from 1 to 156 Mbps
Ethernet
Operates at speeds of 10 to 40 Gpbs
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使用 PSDN 的廣域網路
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Criteria for Comparing WANs (1)
Costs
Setup costs
 Examples: costs of acquiring lines and equipment
Operational costs
 Examples: lease fees, ISP charges, training
Maintenance costs
 Examples: periodic maintenance, repair, upgrades
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Criteria for Comparing WANs (2)
Performance
Speed
Latency
Availability
Loss rate
Transparency
Performance guarantees
Growth potential
Length of contract commitment
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比
較
網
路
的
考
量
點
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Q4. Security Guide: How Does Encryption
Work? (1)
Encryption
Process of transforming clear text into coded text
Used for secure storage or communication
Uses algorithms
 DES, 3DES, AES
Key
Used to encrypt data
Algorithm applies key to produce coded message
 Symmetric encryption
 Asymmetric encryption
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Security Guide: How Does Encryption
Work? (2)
Public key / Private key
Public key used to encrypt messages
Public key sent to other party to encode messages to be sent back
Decoded with private key
Complex and slow
HTTPS
Secure communication over Internet
 Encrypted using SSL (Secure Socket Layer) / TLS (Transport Layer

Security) protocol
Encodes messages using Web site’s public key, decoded with
private key
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Q5. What Is the Purpose of a Firewall?
Computer device that prevents unauthorized network access
May be special-purpose computer or program
Organizations may have multiple firewalls
Perimeter firewalls sit outside organizational network
Internal firewalls are inside network
Packet-filtering firewalls examine source address, destination address, and
other data before allowing message to pass
May filter both incoming and outgoing messages
Access control list (ACL) encodes rules stating what packets are
allowed or prohibited
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多重防火牆的使用
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Q6. What Is a VPN and Why Are VPNs
Important?
Virtual private network
Uses Internet or private network to create appearance
of point-to-point connections
Uses public Internet to create appearance of private
network
Client and server have point-to-point connection called
tunnel
 Private pathway over shared network
Secure, encrypted communications
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以 VPN 做遠距連結：實際、實體連結
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以 VPN 做遠距連結：表面上的連結
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使用 VPN 的廣域網路
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Ethics Guide: Human Networks Matter
More
Six degrees of separation
Often unaware of those in the chain
Build personal human networks for success
Someone, somewhere that you need to know or will need to know
Meet people at professional and social situations
 Pass out and collect cards
 Converse to expand network
 Look for new channels
Social network theory
 Weak and strong ties
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How Does the Knowledge in This Chapter
Help Dee? (1)
Dee and salespeople use thin client computers
Dee creates blog entries on Web pages using Moveable Type
Salespeople use pages served by Moveable Type
Client computers contain VPN client software
Interacts with VPN server via Internet
Secure, private connections
Firewalls stop traffic not addressed to VPN server
Salespeople know how to use VPN
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How Does the Knowledge in This Chapter
Help Dee? (2)
IT department cannot schedule resources to setup blog
server in timely fashion
Will not allow outside person to do setup
 Would then have access to system
Consultant can create server on unprotected test server
Can be copied onto network server after acceptance
Requires some internal IT labor
Consultant could include Trojan horse virus or malware
 Install only software from known sources
 Code should not reside on production server
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How Does the Knowledge in This Chapter
Help Dee? (3)
Dee negotiates with IT department
Threatens to set up own system of user Ids and
passwords
Says she will set up blog on public server
Would cause confusion that would add to IT
department’s work
Her proposal is the lesser of two evils
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在網誌使用防火牆和 VPN
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