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Networks and the
Internet
Unit E
1
Objectives
Introduce Networks
Classify Networks
Understand Network Topology
Explore Network Hardware
Explore Communications Channels
Transport Data
Explore LAN Standards
Explore Wireless
2
Objectives
Understand Internet connections
Introduce IP Addresses and Domain
Names
Connect to the Internet using Dial-up
Connect to the Internet using
Broadband
Connect to the Internet using Cable
Connect to the Internet without Wires
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Communications Network
The combination of hardware,
software and connecting links that
transport data
Data is encoded, sent to its
destination then decoded
Noise
Encoded
Data
Source
Signal
Communications
Channel
Transmitter
Decoded
Data
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Receiver
Destination
Shared Resources
Networks share hardware,
software, and data
Sharing reduces costs
– Peripheral devices, site licenses
Provides access to Internet
Share data
– Groupware, e-mail, IM, online
conferencing
5
Shared Resources (cont.)
Networks are vulnerable
– Unauthorized access
– Malicious code
• Viruses, Trojan horses, worms
Networks are becoming more
standardized
Most benefits outweigh risks
– Computers can be protected
6
Network Classifications by
Geographic Coverage
PAN: Personal Area Network
(PDAs)
WAN: Wide Area Network
(Internet is one)
MAN: Metropolitan Area Network
(50 miles)
LAN: Local Area Network (single
building)
7
Network Classifications by
Organizational Structure
Client/Server:
– One or more computers configured as
servers and other computers configures
as clients
– Server is central repository for data
Peer-to-Peer (P2):
– Treats every computer as an equal
– Workstations transfer data to each other
without going through server
– File-sharing networks
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Network Classifications by
Organizational Structure
9
Network Software Licenses
Single-user
Multiple-user
– Priced per user
Concurrent-user
– Certain number of copies at a time
Site
– Any and all computers at a location
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Network Classifications
CATEGORY DESCRIPTION
EXAMPLES
Geographical
Area where network devices PAN, LAN, WAN, MAN
are located
Organizational
Hierarchy of devices
Client/Server, P2P
Physical
Layout and relationship
between devices
Star, bus, ring, mesh,
tree
Network
Technologies for cables and
signals that carry data
Twisted-pair, coaxial,
or fiber-optic cable;
RF; microwaves;
Infrared; power or
phone line
Bandwidth
Capacity of network
Broadband,
narrowband
Communications
protocols
Standards for orderly & safe
data transfer
TCP/IP, SPX/IPX,
NetBEUI/NetBIOS,
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AppleTalk
Network Topology
Physical arrangement of devices,
cables, and wires
5 common topologies named for
their shapes
– Star (central connection point)
– Ring (connects devices in a circle)
– Bus (common backbone)
– Mesh (each device connected to others)
– Tree (blend of star and bus)
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Network Topology
Star
Bus
Ring
13
Network Topology (cont.)
Each connection point on a
network is a Node:
– Server
– Workstation
– Network peripheral
– Network device
14
Interconnecting Networks
Two similar networks can be
connected by a bridge
– Transfers data without regard to format
Gateway
– A device or software used to join dissimilar
networks by making data compatible
Router
– Electronic device that connects 2 or more
networks
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Network Hardware Overview
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Network Hardware
Server (also called host computer)
– Distribute resources to network users
– Contains network management software
and files
Workstation (also called client)
– PC on a LAN
– Client is software that lets it talk to server
17
Network Hardware
Network Interface Card (NIC)
– Example: Ethernet card
Connection Devices
– Modem: converts PC digital signals
– Hub: connects nodes on a LAN
– Router: decides best way to route data
on network
– Gateway: entrance to another network
– Repeater: amplifies and regenerates
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signals
Network Addresses
Physical address:
– Every node has one
– Built into circuitry of
network device
Logical address:
– Used if physical address
is incompatible with
particular network
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Wired Communication
Channels
Twisted-pair cables (phones)
– STP: shielded twisted pair
– UTP: unshielded twisted pair for small
networks
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Wired Communication
Channels
Coaxial cable (television)
– High capacity
21
Wired Communication
Channels
Fiber-optic cable
– Pulses of light in thin glass tubes
– Essential to Internet backbone
22
Wireless Communication
Channels
RF: radio frequency signals
– Send and receive by a transceiver with
antenna
Microwaves
– More capacity than radio waves
– Need clear path between transmitter
and receiver
– Cannot penetrate metal objects
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Wireless Communication
Channels
Satellites
– Signal relayed from ground station
to satellite
– Transponder on satellite receives,
amplifies and retransmits signal
back to earth
– Key technology for Internet
backbone
24
Wireless Communication
Channels
Infrared light
– Short distance with clear line of site
– Example: connect notebook with printer
Laser light
– Larger distance with clear line of site
– Example: between buildings in future
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Bandwidths
The transmission capacity of a
communications channel measured
in bps (bits per second)
Low-bandwidth carries less data than
high bandwidth
– Telephone
– Narrowband
High-bandwidth
– Coaxial cable
– DSL lines
– Called broadband
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Transporting Data
Depends On:
Network Topology:
configuration
Packet Switching
Technology: determines how
data is broken up
Protocols: rules for
successful and accurate
data transmission
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Packet Switching Technology
Packet is a parcel of data on network
or a file broken into small, equal size
pieces
Contains
–
–
–
–
Sender address
Destination address
Sequence number
Data
Packet switching: packets sent
independently of each other
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Circuit Switching
Establishes a dedicated, private
link between phone lines during
a call
Inefficient because it reserves a
circuit even if data is not being
transmitted
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Communications Protocol
Allows two devices to negotiate
and agree on how data will be
transmitted
TCP/IP
– Transport Control Protocol/Internet
Protocol
– Most common
– TCP: breaks data into packets
– IP: addresses packets
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Controlling Direction
of Data Flow
Simplex: one direction (TV)
Half duplex: can send and
receive data, but not at same
time (CB radio)
Full Duplex: can send and
receive data at same time on
same channel (Telephone)
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Protocol Characteristics
Handshaking: negotiating
transmission speed
Synchronous Protocol: sender and
receiver synchronize signal with a
fixed clock rate
Asynchronous Protocol: requires a
start and stop bit (most common)
Parity bits: used for error checking
32
Communications Protocols
PROTOCOL
MAIN USE
TCP/IP
Internet
NetBIOS/NETBEUI
Microsoft
networks
Macintosh
networks
Novell networks
AppleTalk
IPX/SPX
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LAN Standards
Institute of Electrical and
Electronics Engineers (IEEE)
IEEE designation numbers
identify compatible network
technologies
– ARCnet: old, simple, inexpensive
– Token Ring: ring topology
– FDDI: fiber-optic cables
– Ethernet: simultaneous broadcast of
data packets
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Ethernet
Packets accepted only by device
to which it is addressed
CSMA/CD protocol
Refers to a family of LAN
technologies
– Various transmission rates
– Fiber-optic and twisted-pair cables
– Bus or star topology
Connect many workstations
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Ethernet
36
Home Ethernet Equipment
Ethernet card in each
workstation and peripheral
device
Link between network nodes
such as cable
Central connection point (hub)
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Wireless Standards
Wi-Fi (Wireless Fidelity)
– Set of wireless networking technologies
– Defined by IEEE 802.11 standards
– Compatible with Ethernet
Popular because of absence of
cables
Desirable for notebook and tablet
computers
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Wi-Fi Disadvantages
Speed
– Radio waves
Distance
– 25-150 feet
Security
– War driving/LAN-jacking
– Wired Equivalent Privacy: encryption
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Wi-Fi (cont.)
Wi-Fi cards required
– Include transceiver and antenna
– Can be added to notebooks, PCs, and Tablets
– Wireless access point is same as hub or router
in Ethernet
Bluetooth makes short-range
wireless connections between
devices such as a mouse, keyboard,
printer
40
Internet Connections
The Internet isn’t owned or
operated by corporations or
governments
Traffic exceeds 100 trillion bytes
(terabytes) each week
Backbone provides high-speed
routes for data traffic
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Internet Connections
Users connect to Internet Service
Provider (ISP) or through LAN
ISP provides e-mail and access
to Web
Networks use TCP/IP as
standard
42
Internet Connections
Ping software: Packet Internet Groper
– Checks internet pathways to be sure they are
open
Traceroute software: traces data paths
SMTP
POP
FTP
SSL
HTTP
TELNET
IMAP
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IP Addresses
ISP gives unique IP address to
subscriber
Series of numbers in 4 parts
– 204.127.129.001
Static IP address: permanent, usually
servers
Dynamic IP address: temporary, for
one session
Look at your Internet configuration
settings to find your IP address
44
Domain Names
Translates directly into IP address
Examples: course.com, rutgers.edu
Top-level domain: indicated by
extension
ICANN handles domain name
registration and control
edu
com
info
gov
org
mil
int
net
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Dial-up Internet Connections
Plain old telephone
service (POTS)
Dial-up connection
via modem
Circuit switching
technology gives
continuous private
link
46
Dial-up Internet Connections
Modem: Modulate/demodulate;
digital to analog
– Speed: 56 Kbps
– Upstream actually 33 Kbps
– Downstream actually 44 Kbps
VIOP (Voice Over IP): can talk on
computer at same time as
running other programs on-line
47
Broadband Internet
Connections
High-speed digital
communications links for voice
and data
DSL: Digital Subscriber Line
(always-on)
– Uses standard copper phone cables
– Fastest and most affordable to
individuals
– Variations are ADSL, SDSL, HDSL AND
DSL lite
– DSL modems give 1.5 Mbps
downstream
48
Broadband Internet
Connections
ISDN: Integrated Services Digital
Network
– 64 or 128 Kbps
– Mostly used for business LANs
– Need ISDN terminal adapter
–1.544 Mbps
–24 channels
–43 Mbps
T1
–Used by business
and ISPs on
dedicated leased
lines
–672 channels
T3
–Also called DS3
(Digital Service-3)
49
Security When Always-On
Same IP address when
on – hackers can use
High-speed access
desirable for hackers
Turn machine off often
50
Cable Internet Connections
You need
– Ethernet card
– Cable modem: usual ISP
provides
– Splitter to connect both
modem and TB if necessary
Could slow down as
more neighbors use
service
51
Cable Security
DOCSIS-compliant cable
modems
– Security technology filters packets to
certain ports
– Secures your computer from your
neighbors
– Doesn’t close up all security holes
associated with always-on connections
52
Wireless Internet Connections
DSS: Direct Satellite Service
– Some allow only downstreaming
Two-way Satellite Service
– Downstream 500 Kbps vs. 40-60 Kbps
upstream
Cellular telephone infrastructure
is slowest at 14.4 Kbps
53
Wireless Internet Connections
Mobile Internet Connections
Public Wi-Fi
– Range of coverage: hotspot
WWAN (wireless WAN)
– Cell phone networks
– Cell-ready modem or subscription
WAP (wireless access protocol)
54
TechTalk: Installing a LAN
Install Ethernet NIC
– On motherboard or with PC card; both have
port for network cable
Attach cable to NIC port and hub port
Turn on PCs
Windows should automatically detect
and establish connection
Can activate file sharing and drive
mapping by using Windows Network
Neighborhood
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Context: Education
CBT (computer-based training)
CAL (computer-aided learning)
CAI (computer-aided instruction)
Simulations
99% of American public schools
have computers
– Not all students have daily access
though
56
Context: Education
Some colleges require incoming
students to have a computer
DE/DL (Distance
Education/Learning)
Life-long learning
57
Issue: Free Wi-Fi?
58
Networks and the
Internet
End
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