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

2. What Is a Computer Network?
 Network
 is a collection of hardware components and
computers interconnected by
communication channels that allow sharing
of resources and information
 Collection of computers
 Communicate with one another over
transmission line
 Three basic types
 Local area network (LAN)
 Wide area network (WAN)
6-2  Internet

3. 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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4. WAN
 Connect computers in different
geographical areas
 Two or more cities
 Uses communication networks from
vendors
 Licensed by government
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5. Internet
• The Internet is a global system of
interconnected computer networks that use the
standard Internet protocol suite (TCP/IP) to
serve billions of users worldwide
• 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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6. LAN VS WAN
LAN WAN
Data Experiences more data
Experiences fewer data
transmission transmission errors as
transmission errors
Error: compared to LAN
WANs have a lower data
Data transfer LANs have a high data
transfer rate as compared to
rates: transfer rate
LANs
Computers connected to a
one LAN can be wide-area network are often
connected to other LANs connected through public
Connection: over any distance via networks, such as the
telephone lines and radio telephone system. They can
waves also be connected through
leased lines or satellites

7. LAN vs WAN
speed: high speed(1000mbps) less speed(150mbps)
Because it covers a Maintaining WAN is
relatively small difficult because of its
Maintenance
geographical area, LAN wider geographical
costs:
is easier to maintain at coverage and higher
relatively low costs. maintenance costs.
LANs tend to have less WANs tend to be less fault
problems associated tolerant. as it consists of a
Fault Tolerance: with them, as there are large amount of systems
a smaller amount of there is a lower amount of
systems to deal with. fault tolerance.
Network in an
Internet is the best
Example: organization can be a
example of a WAN
LAN

8. LAN vs WAN
Have a small geographical Have a large geographical range
Geographica range and do not need generally spreading across
l spread: any leased boundaries and need leased
telecommunication lines telecommunication lines
If there is a need to set-up In this case since networks in
a couple of extra devices remote areas have to be
Set-up costs:
on the network, it is not connected hence the set-up
very expensive to do that costs are higher
WANs (like the Internet) are not
Typically owned, owned by any one organization
controlled, and managed but rather exist under collective
Ownership:
by a single person or or distributed ownership and
organization management over long
distances

9. LAN vs WANs
LAN (Local Area WAN (Wide Area Network) is a
Network) is a computer computer network that covers a
network covering a small broad area (e.g., any network
Definition:
geographic area, like a whose communications links cross
home, office, schools, or metropolitan, regional, or national
group of buildings. boundaries over a long distance
layer 2 devices like Layers 3 devices Routers, Multi-
Compone switches, bridges. layer1 layer Switches and Technology
nts: devices like hubs , specific devices like ATM or Frame-
repeaters relay Switches etc

10. 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
6-10 the cable

11. Switches

12. 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
6-12

13. NIC card

14. 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(physical layer and data link layer)
 Personal computers usually support 10/100/1000
(bandwidth) Ethernet
6-14

15. 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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16. 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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17. 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
6-17

18. 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
6-18

19. 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
6-19

20. 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)
6-20

21. 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
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22. 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
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23. 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
6-23

24. Transmission Line Types, Uses, and
Speeds
Figure 6-11
6-24

25. 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
6-25

26. 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
6-26

27. 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
6-27

28. Criteria for Comparing WANs,
continued
 Performance
 Speed
 Latency (measure of time delay)
 Availability
 Loss rate
 Transparency
 Performance guarantees
 Growth potential
 Length of contract commitment
6-28

29. Security Guide: How Does
Encryption Work?
 Encryption
 Process of transforming clear text into coded text
 Used for secure storage or communication
 Uses algorithms
 Key
 Used to encrypt data
 Algorithm applies key to produce coded message
 Symmetric encryption
 Asymmetric encryption
6-29

30. 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
6-30

31. 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
6-31

32. 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
6-32

33. 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
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34. 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

35. 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