CMSC 100
Networks, the Internet, and Social Networking
Professor Marie desJardins
Tuesday, October 9, 2012
Some material adapted from instructor slides for Schneider & Gerstung
Networks
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Introduction
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Computer networks have had a revolutionary impact on society and
technology
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Electronic commerce
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Worldwide communications
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Spread of information and data
We take for granted:
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access to information on any subject
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immediate contact with people around the world
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streaming audio and video
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wired or wireless access from every device
Networks
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Basic Networking
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Computer network: made up of computing devices, nodes, and
interconnections
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Networks may be wired or wireless; communication links use various
technologies
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Wired:
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Dial-up
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Broadband
Wireless:
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WLAN
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WWAN
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Dialin Phone Connections
Switched, dial-up telephone lines
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Analog lines
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Transmit digital data
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Modem modulates carrier wave
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Bandwidth = capacity
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Speeds up to 56k bps
Can make a voice call or transmit data
– not both!
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Broadband Connectivity
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Broadband: transmission rate > 256k bps
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Home users:
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Networks
Digital subscriber line (DSL)
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Uses phone lines, but sends digital signal on different frequencies than
voice (can transmit voice and digital signal simultaneously)
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Down: 5-15 Mbps, Up: 1-2 Mbps
Cable modem
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Uses cable TV lines
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Down: 10-20 Mbps, Up: 1-3Mbps
Asymmetric download/upload times
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Dedicated Network
Connections
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Commercial/institutional users:
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Networks
Ethernet (1970s)
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Dedicated coaxial cable
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Operates at 10 Mbps
Fast Ethernet (early 1990s)
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Dedicated lines (coaxial, fiber-optic, or twisted-pair)
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Operates at 100 Mbps
Gigabit Ethernet Standard (late 1990s)
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From gigabit networking research project
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IEEE standard
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Operates at 1000 Mbps
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Wireless Connectivity
Wireless data communication
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Radio, microwave, infrared signals to mobile computers
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Laptops, tablet computers, smartphones, etc.
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Mobile computing: deliver data regardless of location
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Bluetooth:
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Networks
Low-power, close range (30-50 feet), connect devices like wireless mice,
cameras, video games, phone headsets
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Wireless Networks
Wireless local area network (WLAN)
 Computers transmit wirelessly to local base station with wired
connection
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Range of 150-300 feet
Wi-Fi (Wireless Fidelity)
Wireless wide area network (WWAN)
 Computers transmit wirelessly to remote base station with wired
connection
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Networks
Cellular technology: antennas on towers miles apart
Example: 4G: voice and data, transmits at 5-20 Mbps
Security: wireless signals easy to intercept
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Local Area Networks
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Wired connection
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Computers, printers, and servers in close proximity
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Examples: same room, office building, campus
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Privately owned and operated
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Topology: how computers connected, affects how they communicate
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Network Topologies
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Bus topology
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Shared lines
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Take turns using line
Ring topology
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Messages circulate until
destination is reached
Star topology
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Networks
All send to central node,
which routes to destination
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Ethernet
Ethernet LAN with shared cable
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Bus topology
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Single cable over short distances
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Multiple cables over longer
distances
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Repeater amplifies signal
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Bridge routes messages only
when necessary
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Wide Area Network
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Wired connection
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Computers located at great distances
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Examples: across state or country
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Dedicated point-to-point lines
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Computers connect to other computers on individual lines
Store-and-forward, packet-switched
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Networks
Packets go from node to node until they reach their destination
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Routing
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Routing algorithms are used to move packets efficiently and balance
load across the network
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Routing of packets determined dynamically (and locally)
A-B-C-D or A-B-F-D or A-E-F-D or A-E-F-B-C-D
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Redundant paths, fault
tolerance, responsiveness to
traffic load
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Networks
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Internet
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Combination of LANs and WANs
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Connected by routers that direct message traffic
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Internet service provider (ISP) provides access to the Internet for
private individuals and organizations
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ISPs exist at multiple levels: local, regional, national, international
(tier-1 (“T1”) network or Internet backbone)
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Basic Networking
Concepts (continued)
Internet growth has been astonishing:
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Communication Protocols
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Protocol: a standard set of rules for communicating
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Standards evolve over time
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International agreements make Internet possible
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Internet Society makes standards and promotes research:
www.isoc.org
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Protocol hierarchy/protocol stack, TCP/IP
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layers of protocols
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physical transmission to end application rules and standards
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HTTP
Hypertext Transfer Protocol (HTTP)
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Web page/service identified by unique URL (Uniform Resource
Locator)
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protocol://host name/page
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Multiple protocols: http, mailto, news, ftp
Web browser uses TCP to send formatted messages to Web server,
and vice versa
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Networks
TCP uses network layer (IP), data link layer, and physical layer
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HTTP (cont.)
Process: http://hostname/page
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Browser reads protocol, extracts host name (and requests IP address
from DNS server)
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Sends a connect message to port 80 on that machine
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After connection established, sends “Get” message with page
information
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Server responds with message containing page contents, size, and
indicates connection closes at end of message
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Network Services and
Benefits
Interpersonal Communications
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Electronic mail (e-mail)
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Send message to be read at recipient’s convenience
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Fast, multimedia, broadcast medium
Bulletin board system (BBS)
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Public forum for shared communications
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Evolved into Internet forums, chat rooms
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Instant messaging and texting
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Social networking
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Networks
Online social groups designed for rich interaction
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Social Networking
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How do you social network?
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Privacy
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Security
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Socialization
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Changes in society
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Network Services and
Benefits (continued)
Resource sharing
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Print server serves all computers on a LAN
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File server provides storage to all users
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Client/server computing
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Distributed databases and data warehouses
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Some nodes provide services, other nodes use those services
Massive data stored in various sites online
Groupware or wiki
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Networks
Support collaborative knowledge/data construction
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Network Services and
Benefits (continued)
Electronic commerce (e-commerce)
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Early applications
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Automatic paycheck deposit
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ATMs
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Checkout scanners and inventory systems
Current applications
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Online stores for everything
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Electronic bill payment
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Online payment systems (Paypal)
Future?
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Summary
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Computing devices can communicate through various wired and
wireless media
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Computer networks vary in size and form, including LANs, WANs,
WLANs, and WWANs
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LANs are configured differently from WANs, and use different
communication methods
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The Internet is a WAN of WANs
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Protocols are necessary to standardize communications across
different media and among different computers
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The Internet has permitted new kinds of connections among people:
e-mail, e-commerce, resource sharing
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