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Chapter 6
Data Communications
© 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
6-2 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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
Can be protected from unauthorized access Sales people can access with same password they already
use
6-3 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
Study Questions
What is a computer network? What are the components of a LAN? What are the alternatives for a WAN? How does encryption work? What is the purpose of a firewall? What is a VPN and why is it important? How does the knowledge in this chapter help
Dee?
6-4 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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
6-5 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
LAN
Connects computers residing in single location– 2 to several hundred computers– One geographic area– Communication lines can be placed where the
organization wants
6-6 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
WAN
Connect computers in different geographical areas– Two or more cities
Uses communication networks from vendors– Licensed by government
6-7 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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
6-8 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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
6-9 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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
6-10 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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
6-11 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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
6-12 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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
6-13 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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
6-14 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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
6-15 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
Dial-Up Modems
Handles conversion between analog and digital
Connection made by dialing ISP Maximum transmission speed of 56kbps Modulation governed by V.34, V.90. or V.92
standards PPP controls message packaging and
handling
6-16 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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)
6-17 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
Cable Modems
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
6-18 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
Cable Modems, continued
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
6-19 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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
6-20 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
Transmission Line Types, Uses, and Speeds
Figure 6-11
6-21 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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?
6-22 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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
6-23 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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
6-24 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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
6-25 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
Criteria for Comparing WANs
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
6-26 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
Criteria for Comparing WANs, continued
Performance– Speed– Latency– Availability– Loss rate– Transparency– Performance guarantees
Growth potential Length of contract commitment
6-27 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
Security Guide: How Does Encryption Work?
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
6-28 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
Security Guide: How Does Encryption Work?, continued
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/TLS protocol Encodes messages using Web site’s public key, decoded with
private key
6-29 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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
6-30 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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
6-31 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
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
6-32 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
How Does the Knowledge in This Chapter Help Dee?
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
6-33 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
How Does the Knowledge in This Chapter Help Dee?, continued
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
6-34 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
How Does the Knowledge in This Chapter Help Dee?, continued
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
6-35 © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke
Active Review
What is a computer network? What are the components of a LAN? What are the alternatives for a WAN? How does encryption work? What is the purpose of a firewall? What is a VPN and why is it important? How does the knowledge in this chapter help
Dee?
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