Chapter 6 Data Communications © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke.

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


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?


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


LAN

Connects computers residing in single location– 2 to several hundred computers– One geographic area– Communication lines can be placed where the

organization wants


WAN

Connect computers in different geographical areas– Two or more cities

Uses communication networks from vendors– Licensed by government


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


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


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


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


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


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


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


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


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


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)


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


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


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


Transmission Line Types, Uses, and Speeds

Figure 6-11


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?


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


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


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


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


Criteria for Comparing WANs, continued

Performance– Speed– Latency– Availability– Loss rate– Transparency– Performance guarantees

Growth potential Length of contract commitment


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


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


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


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


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


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


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


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


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?

Chapter 6 Data Communications © 2008 Pearson Prentice Hall, Experiencing MIS, David Kroenke.

Documents

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