Q2. What Are the Components of a LAN?
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Transcript 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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