Management Information SystemsManagement Information Systems

Data Communications

Chapter 6

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This Could Happen to You

Dee needs to decide where she will run the blogIt 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 networkProtected 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?

NetworkCollection of computers

Communicate with one another over transmission line

Three basic typesLocal 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 location2 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 areasTwo or more cities

Uses communication networks from vendorsLicensed 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 conventionsSeamless flow of data provided by layered protocol

Set of rules that communicating devices follow

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Local area networkComputers connected on single company siteUsually located within half mile areaProperty controlled by company operating network

Company can run cabling as necessary

ComponentsSwitch

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

Q2. What Are the Components of a LAN?

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區域網路（ LAN ）

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NIC Devices

MAC addressUnique identifier

Media connectionsUnshielded 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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圖 6-3 網路卡

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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 standardSpecifies 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 operationNICs 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 sitesNo 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 analogModem 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 supportCustomers had problems

Customers needed to add more devices

Coupled installation with support packageExtra 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 varyAsymmetric digital subscriber lines (ADSL)

Symmetrical digital subscriber lines (SDSL)

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Cable Modems (1)

Provide high-speed data transmission

Use cable television linesHigh-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

SpeedsNarrowband

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 transmissionSwitch

Router

Alternative is leasing linesT1, 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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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 exponentiallyWhat are the threats and opportunities?

Problem Solving Guide: Thinking Exponentially Is Not Possible, but…

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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 itPeople 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 linesDeveloped and maintained by vendor

Time leased on network

Utility that supplies network for other companies to leaseEach 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 relayProcess traffic at 56 kbps to 40 Mbps

Simplest and easiest to support

Asynchronous transfer mode (ATM)Process speeds from 1 to 156 Mbps

EthernetOperates 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)

CostsSetup 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)

PerformanceSpeed

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)

EncryptionProcess of transforming clear text into coded text

Used for secure storage or communication

Uses algorithms DES, 3DES, AES

KeyUsed 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 keyPublic key used to encrypt messagesPublic key sent to other party to encode messages to be sent backDecoded with private keyComplex and slow

HTTPSSecure 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 firewallsPerimeter 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 networkUses 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 separationOften unaware of those in the chain

Build personal human networks for successSomeone, 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 computersDee creates blog entries on Web pages using Moveable Type

Salespeople use pages served by Moveable Type

Client computers contain VPN client softwareInteracts 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 fashionWill not allow outside person to do setup

Would then have access to system

Consultant can create server on unprotected test serverCan 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 departmentThreatens 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