CS105 Introduction to Computer Concepts Computer networks 101

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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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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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 SecurityFirewall A gateway machine and its software that protects a network by filtering the traffic it allows


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Network AddressesHostname 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 SystemHost 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 Systemmatisse.csc.villanova.edu

Computername Domain name

TLD


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Domain Name System

Figure 15.10 Top-level domains, including some relatively new ones


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Domain Name SystemOrganizations 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 SystemDomain 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

http://en.wikipedia.org/wiki/Modem




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References (cont) Domain Names

http://www.icann.org/topics/new-gtld-strategy-faq.htm

http://www.iana.org/root-whois/index.html



http://www.iana.org/root-whois/index.html

CS105 Introduction to Computer Concepts Computer networks 101

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