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 andcomputers interconnected bycommunication
channels that allow sharingof resources and information Collection
of computers Communicate with one another overtransmission 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 placedwhere the organization wants6-3 4.
WAN Connect computers in differentgeographical areas Two or more
cities Uses communication networks fromvendors Licensed by
government6-4 5. Internet The Internet is a global system
ofinterconnected computer networks that use thestandard Internet
protocol suite (TCP/IP) toserve billions of users worldwide Network
of networks Connect LANs, WANs, and other internets Private
networks of networks Use a variety of communication methods
andconventions Seamless flow of data provided by layered protocol
Set of rules that communicating devices follow6-5 6. LAN VS WANLAN
WANDataExperiences more dataExperiences fewer
datatransmissiontransmission errors astransmission
errorsError:compared to LANWANs have a lower dataData transfer LANs
have a high datatransfer rate as compared torates:transfer
rateLANsComputers connected to aone LAN can bewide-area network are
oftenconnected to other LANs connected through publicConnection:
over any distance via networks, such as thetelephone lines and
radio telephone system. They canwaves also be connected
throughleased lines or satellites 7. LAN vs WANspeed: high
speed(1000mbps) less speed(150mbps) Because it covers aMaintaining
WAN is relatively small difficult because of itsMaintenance
geographical area, LAN wider geographicalcosts: 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
associatedtolerant. as it consists of aFault Tolerance: with them,
as there arelarge amount of systems a smaller amount ofthere is a
lower amount of systems to deal with.fault tolerance. Network in
anInternet is the bestExample: organization can be aexample of a
WAN LAN 8. LAN vs WANHave a small geographical Have a large
geographical rangeGeographica range and do not need generally
spreading acrossl spread: any leasedboundaries and need
leasedtelecommunication lines telecommunication linesIf there is a
need to set-up In this case since networks ina couple of extra
devices remote areas have to beSet-up costs:on the network, it is
not connected hence the set-upvery 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
collectiveOwnership: by a single person or or distributed ownership
and organizationmanagement over long distances 9. LAN vs WANsLAN
(Local Area WAN (Wide Area Network) is aNetwork) is a computer
computer network that covers anetwork covering a small broad area
(e.g., any networkDefinition:geographic area, like a whose
communications links crosshome, office, schools, or metropolitan,
regional, or nationalgroup of buildings. boundaries over a long
distancelayer 2 devices like Layers 3 devices Routers,
Multi-Compone switches, bridges. layer1layer Switches and
Technologynts:devices like hubs ,specific devices like ATM or
Frame-repeatersrelay Switches etc 10. What Are the Components of a
LAN? Local area network Computers connected on single companysite
Usually located within half mile area Property controlled by
company operatingnetwork Company can run cabling as necessary
Components Switch Special purpose computer that receives and
transmits messages Network interface card (NIC) Hardware that
connects each devices circuitry to6-10 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 connectors6-12 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) Ethernet6-14 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 standards6-15 16. What Are the
Alternatives for a WAN? WANs connect computers at separate sites No
cabling between sites Cable connections made through
licensedcommunications companies Internet service provider (ISP)
Provides legitimate Internet address Serves as gateway to Internet
Pay for Internet6-16 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
conversion6-17 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 andtear6-18 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
handling6-19 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 connected6-21 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 kbps6-22 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
transmitted6-23 24. Transmission Line Types, Uses, and SpeedsFigure
6-116-24 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
companiesto lease Each site leases line to connect to PSDN network
ataccess point Point of presence (POP) Saves setup and maintenance
activities6-25 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 Gpbs6-26 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,
upgrades6-27 28. Criteria for Comparing WANs, continued Performance
Speed Latency (measure of time delay) Availability Loss rate
Transparency Performance guarantees Growth potential Length of
contract commitment6-28 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 encryption6-29 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 sites public key,
decoded withprivate key6-30 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 prohibited6-31 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 communications6-32 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
VPN6-33 34. How Does the Knowledge in This Chapter Help Dee?,
continued IT department cannot schedule resources to setupblog
server in timely fashion Will not allow outside person to do setup
Would then have access to system Consultant can create server on
unprotected testserver 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 server6-34 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 departments work Her
proposal is the lesser of two evils6-35
