1. CS105 Introduction to Computer Concepts Computer networks 101
Instructor: Cuong (Charlie) Pham

2. 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
Q: What are the devices in a computer network?
Repeaters, Hubs, Switches, and Routers
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3. 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
Wireless N and G
The best way to answer your question is to state the purpose of a router. A router is designed to connect two different networks together. In your case the LAN, or your local network of computers and the WAN, or the Internet. The wireless speed of your router is the LAN speed. The LAN consists of all the computers and devices connected to your router in your house. Connections will always default to the slowest device. For example if you have a wireless N router (300 Mbps) connected to a wireless G laptop (54 Mbps), then the laptop can communicate with the router at 54 Mbps. If you wanted to copy a file from your laptop to a desktop connected to your router via a Ethernet cable (100 Mbps) connection, then you could do that at the laptop's wireless G speed of 54 Mbps. Now for the DSL speed. The Internet is the other network connected to your router via your DSL modem. The Internet is a Wide Area Network or WAN. Your DSL modem can communicate with your Internet provider at a maximum of around 6 Mbps. This connection bandwidth is shared by your entire LAN via your router. If one user is utilizing 4 Mbps of the bandwidth that only leaves 2 Mbps for the rest of the users on the LAN. Being that your (WAN) Internet connection is less than 6 Mbps and a wireless G router is many times faster at 54 Mbps, there is no advantage in Internet speed by choosing a wireless N router. The only advantage would be in transferring files around between computers on your local LAN. Wireless N also has a larger range, meaning you can get a wireless signal at a larger distance from the router. However, remember to get either the speed or range improvements of wireless N, both devices have to be N. A wireless N router hooked to a wireless G adapter on a laptop computer will have the range and speed of wireless G. I'm not saying not to buy a wireless N router, I use one myself. Just don't expect any improvement in Internet speed. People that recommend N to improve Internet speed don't understand the concept, or they're lucky enough to live in a area and have the money to afford using ungodly fast and expensive Internet connections such as Comcast Cable's Extreme 105 Mbps. Direct CAT5 Ethernet connections are 100 Mbps, there is also a newer Gigabit Ethernet (1000 Mbps) which uses special CAT6 cabling and Gigabit devices and network adapters. As with the wireless devices it will always default to the slowest standard.
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4. 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 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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5. Cabling Top: Unshielded Twisted Pair and Shielded Twisted Pair Cable
Bottom: Coaxial and Optical Fiber Cable
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6. Network Types LAN (Local Area Network) WAN (Wide …)
MAN (Metropolitan …)
PAN (…)
Internet
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7. 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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8. 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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9. 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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10. WLAN (Wireless LAN) Wi-Fi (Wireless Fidelity) Access Point (AP)
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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11. WLAN (Wireless LAN) Standard Security 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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12. 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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13. Gateway
One particular set up to handle all communication going between that LAN and other networks
Figure Local-area networks connected across a distance to create a wide-area network
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14. 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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15. 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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16. Dial-up Services ISDN Integrated Services Digital Network
2 data channel (56K each)
1 voice channel
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17. Broadband Services xDSL (Digital Subscriber Line) Speed
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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18. Broadband Services Cable Need a cable modem
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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19. Broadband Services Satellite Need a satellite dish
A technology that provide digital data transmission over satellites
Speed
Downlink
500Kbps - 1Mbps
Uplink
50Kbps - 100Kbps
Need a satellite dish
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20. Home Network (single machine)
Wall Jack
DSL/Cable Modem
USB/Ethernet Cable
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21. Home Network (multiple machines)
Wall Jack
DSL/Cable Modem
Hub/Switch/Router
USB/Ethernet Cable
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22. Home Network (multiple machines)
Wall Jack
Ethernet Cable
DSL/Cable Modem
Hub/Switch/Router
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23. Home Wireless Network Wall Jack Ethernet Cable DSL/Cable Modem
Hub/Switch/Router
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24. Network Security
Firewall A gateway machine and its software that protects a network by filtering the traffic it allows
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25. Network Addresses Hostname
A name made up of words separated by dots that uniquely identifies a computer on the Internet
IP address
An address made up of four one-byte numeric values separated by dots that uniquely identifies a computer on the Internet
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26. Where does the host number
Network Addresses
Figure An IP address is stored in four bytes
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
Where does the host number
come from?
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27. Domain Name System Host number
The part of the IP address that specifies a particular host (machine) on the network Yes, but what is it?
Domain name
The part of a hostname that specifies a specific organization or group
Top-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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28. Domain Name System matisse.csc.villanova.edu Domain name TLD Computer
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29. Domain Name System
Figure Top-level domains, including some relatively new ones
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30. 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
Do you
someone
in another
country?
Figure Some of the top-level domain names based on country codes
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31. Domain Name System Domain name system (DNS)
A distributed system for managing hostname resolution
Domain name server
A computer that attempts to translate a hostname into an IP address
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32. References Computer Science Illuminated Ch 15 Slides Modem Cabling
DSL
Cabling
nToNetworking.ppt
Basic Computer Network by Weesan Lee
_network.ppt
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33. References (cont) Domain Names
faq.htm
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