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CS105 INTRODUCTION TO COMPUTER CONCEPTS
COMPUTER NETWORKS 101
Instructor: Cuong (Charlie) Pham
CS105 Section 2 - Lecture 10
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Computer Network
A collection of computing devices connected in order to communicate and share resources
Connections between computing devices can be physical using wires or cables or wireless using radio waves or infrared signals
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CS105 Section 2 - Lecture 10
Network Devices
To connect multiple segments of networks into a larger one Hub: A multiport
repeater to enhance signal within the same network
Switch: Like hub but with intelligent Better performance
Router: Forward packets from one network to another
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Cabling Coaxial Cable
Thinnet looks like regular TV cable. It is about 1/4 inch in diameter and is very flexible and easy to work with.
Thicknet is about 1/2 inch in diameter and not very flexible. Thicknet is older and not very common anymore except as a backbone within and between buildings. Coax transmits at 10 Mbps..
Twisted Pair. Twisted pair looks like telephone wire and consists of insulated strands of copper wire twisted together. There are two versions of twisted pair cable: Shielded Twisted Pair (STP). STP is commonly used in Token Ring
networks Unshielded Twisted Pair (UTP). UTP is used in Ethernet
networks. Transmission rates vary between 10-100-1000-10000 Mbps. Fiber-Optic Cable. Fiber-optic cable consists of a thin
cylinder of glass surrounded by glass cladding, encased in protective outer sheath. Fiber-optic cable is very fast (over 1Gbps). It can transmit over long distances (2 km +) but is expensive.
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Cabling
Top: Unshielded Twisted Pair and Shielded Twisted Pair Cable
Bottom: Coaxial and Optical Fiber Cable
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Network Types
LAN (Local Area Network) WAN (Wide …) MAN (Metropolitan …) PAN (…) Internet
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LAN
A network that connects a relatively small number of machines in a relatively close geographical area
E.g., office buildings
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LAN Topologies
Ring topology connects all nodes in a closed loop on which messages travel in one direction
Star topology centers around one node to which all others are connected and through which all messages are sent
Bus topology nodes are connected to a single communication line that carries messages in both directions
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Ethernet
The industry standard bus (star) technology for LAN 10BaseT
10Mbps (Mega bits per second)
100BaseT 100Mbps
1000BaseT 1000Mbps or 1Gbps
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CS105 Section 2 - Lecture 10
WLAN (Wireless LAN)
Wi-Fi (Wireless Fidelity) A wireless technology that
connects computers without cables
Access Point (AP) A device (base station) that
connects wireless devices together
Usually connected to a wired-network
SSID (Service Set ID) A “name” for the AP, eg.
mobilenet Hotspot
The area covered by wireless access points
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WLAN (Wireless LAN)
Standard 802.11b - 11Mbps 802.11g - 54Mbps 802.11a - 54Mbps
Security WEP (Wired Equivalent Privacy) WPA (Wi-Fi Protected Access) To prevent wardriving
2.4G
5G
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WAN/MAN
Wide-area network (WAN) A network that connects local-area networks over a potentially large geographic distance Metropolitan-area
network (MAN) The communication infrastructures that have been developed in and around large cities
Internet A wide area network that spans the planet
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Gateway
Figure 15.1 Local-area networks connected across a distance to create a wide-area network
One particular set up to handle all communication going between that LAN and other networks
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Internet Connections
Internet backbone A set of high-speed networks that carry Internet traffic, provided by companies such as AT&T, Verizon, GTE, British Telecom, and IBM
Internet service provider (ISP) A company that provides other companies or individuals with access to the Internet
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Dial-up Services
Modem Modulator/demodulator A device that converts analog signal to
digital (modulation) and vice versa (demodulation)
Speed 1200/2400/9600 bps 14.4/28.8/33.6 Kbps 56 Kbps
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Dial-up Services
ISDN Integrated Services Digital Network 2 data channel (56K each) 1 voice channel
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Broadband Services
xDSL (Digital Subscriber Line) A technology that provides digital data transmission
over unused frequencies on traditional telephone lines For example, ADSL (Asymmetric DSL) Speed
Downlink 128Kbps - 4Mbps
Uplink 64Kbps - 800Kbps
Need a DSL modem Splitters are needed to separate the voice and
data signal
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Broadband Services
Cable A technology that provides digital data transmission
over cable TV infrastructure Speed
Downlink 128Kbps - 3~5Mbps
Uplink 64Kbps - 128Kbps~1Mbps
Need a cable modem
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Broadband Services
Satellite A technology that provide digital data transmission
over satellites Speed
Downlink 500Kbps - 1Mbps
Uplink 50Kbps - 100Kbps
Need a satellite dish
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Home Network (single machine)
USB/Ethernet Cable
DSL/Cable Modem
Wall Jack
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Home Network (multiple machines)
USB/Ethernet Cable
DSL/Cable Modem
Wall Jack
Hub/Switch/Router
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Home Network (multiple machines)
Ethernet Cable
DSL/Cable Modem
Wall Jack
Hub/Switch/Router
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Home Wireless Network
Ethernet Cable
DSL/Cable Modem
Wall Jack
Hub/Switch/Router
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Network Security
Firewall A gateway machine and its software that protects a network by filtering the traffic it allows
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Network Addresses
Hostname A name made up of words separated by dots that uniquely identifies a computer on the InternetIP addressAn address made up of four one-byte numeric values separated by dots that uniquely identifies a computer on the Internet
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Network Addresses
Class A: first byte for network address and three remaining bytes for host number
Class B: first two bytes for network address and the last two bytes for host number
Class C: first three bytes for network address and the last byte for host number
Figure 15.9
An IP address is stored in four bytes
Where does the host number come from?
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Domain Name System
Host numberThe part of the IP address that specifies a particular host (machine) on the network Yes, but what is it?Domain nameThe part of a hostname that specifies a specific organization or groupTop-level domain (TLD)The last section of a domain name that specifies the type of organization or its country of origin
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Domain Name System
matisse.csc.villanova.edu
Computer
name Domain nameTLD
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Domain Name System
Figure 15.10 Top-level domains, including some relatively new ones
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Domain Name System
Organizations based in countries other than the United States use a top-level domain that corresponds to their two-letter country codes
Figure 15.11Some of the top-level domain names based on country codes
Do you email
someonein anothercountry?
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Domain Name System
Domain name system (DNS) A distributed system for managing hostname resolutionDomain name serverA computer that attempts to translate a hostname into an IP address
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References
Computer Science Illuminated Ch 15 Slides Modem
http://en.wikipedia.org/wiki/Modem DSL
http://en.wikipedia.org/wiki/Digital_subscriber_line
Cabling http://ww2.it.nuigalway.ie/.../ct101/
CT101_IntroductionToNetworking.ppt Basic Computer Network by Weesan Lee
http://www.cs.ucr.edu/~weesan/cs6/03_basic_computer_network.ppt
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References (cont)
Domain Names http://www.icann.org/topics/new-gtld-strate
gy-faq.htm http://www.iana.org/root-whois/index.html