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  1. 1. Networks Spring 2010
  2. 2. Types of Networks <ul><li>Types of Networks (based on coverage scope) </li></ul><ul><ul><li>LAN, MAN, WAN, etc. </li></ul></ul><ul><li>Components of Networks </li></ul><ul><ul><li>Connection systems(e.g. computers with NICs), Network OS, communication medium </li></ul></ul><ul><ul><li>Routers (direct messages between different networks)/Hubs/Switches/Bridges (connect similar networks)/Gateways (connect dissimilar networks) </li></ul></ul><ul><li>Types of LANs (based on computer roles) </li></ul><ul><ul><li>Client/Server, P2P </li></ul></ul><ul><li>Network Topologies </li></ul><ul><ul><li>Bus (susceptible to collisions) </li></ul></ul><ul><ul><li>Ring </li></ul></ul><ul><ul><li>Star (hub at the center, no collisions) </li></ul></ul>Bus Ring Star
  3. 3. Wired Communication Media <ul><li>Twisted-Pair Wire: Two strands of insulated copper wire, twisted around each other </li></ul><ul><ul><ul><li>Advantage: Relatively inexpensive and easy to change form </li></ul></ul></ul><ul><ul><ul><li>Disadvantages: relatively slow (1-128 Mbps), interference (what is it?) </li></ul></ul></ul><ul><li>What is Mbps? </li></ul><ul><li>Coaxial Cable: Insulated copper wire wrapped in a solid or braided metal shield, then an external cover </li></ul><ul><ul><li>Advantages: less interference, faster (~200 Mbps) </li></ul></ul><ul><li>Fiber-Optic Cable: Dozens or hundreds of thin strands of glass or plastic that transmit pulsing beams of light rather than electricity </li></ul><ul><ul><li>The light used is typically IR </li></ul></ul><ul><ul><li>Advantages: fast (~ 2Gbps), less interference, more reliable, lighter, cannot be easily wiretapped </li></ul></ul><ul><ul><li>Dispersion considerations, alleviated by repeaters and optical amplifiers (1987) </li></ul></ul>
  4. 4. Wireless Communication Media <ul><li>Infrared Transmission (IR): </li></ul><ul><ul><li>Transmission speeds of 1-4 Mbps, deprecated technology for wireless mice and keyboards </li></ul></ul><ul><li>Broadcast Radio: For long range communications ( ~ 2 Mbps) </li></ul><ul><li>Microwave Radio: Super-high frequency radio waves (~ 45 Mbps) </li></ul><ul><li>Communication Satellites: Microwave relay stations that orbit around the earth </li></ul><ul><ul><li>Eliminate the line-of -sight limitation of the above technologies </li></ul></ul><ul><ul><li>GEO (22K mi from earth): e.g. broadcast TV, weather, surveillance </li></ul></ul><ul><ul><li>MEO (5K-10K mi from earth): e.g. navigation and communication satellites such as U.S. NAVSTAR and GPS </li></ul></ul><ul><ul><li>LEO (200-1000 mi from earth): e.g. surveillance, imaging </li></ul></ul><ul><ul><li>Max. Coverage area? </li></ul></ul>GEO MEO LEO Different frequencies shown below. Which is lowest? Highest?
  5. 5. Wireless Communication Media <ul><li>Bluetooth: A wireless standard aimed at linking cell phones, PDAs, computers, and peripheral devices up to 30 ft, speeds < 1 Mbps </li></ul><ul><li>WiFi (Wireless Fidelity): A wireless standard aimed at helping portable computers and handheld devices to communicate at high speeds and share Internet connections at distances up to 300 ft </li></ul><ul><ul><li>Uses WAP, 10 x speed of Bluetooth </li></ul></ul><ul><ul><li>WiFi utilizes WEP, WPA & WPA2 </li></ul></ul><ul><ul><ul><li>WEP (Wired Equivalent Privacy) weakness </li></ul></ul></ul><ul><ul><ul><li>WPA (Wi-fi Protected Access) passphrase </li></ul></ul></ul><ul><ul><li>Rogue Access Point - either installed on a secure network without explicit authorization, or has been created to allow a cracker to conduct a man-in-the-middle attack. </li></ul></ul><ul><ul><li>Auto-connection concerns (should not be enabled… why?) </li></ul></ul>
  6. 6. Internet Connections <ul><li>Internet Service Provider (ISP) – a company that provides other companies or individuals with access to the Internet. </li></ul><ul><li>Three most popular ways to connect a home computer to the Internet </li></ul><ul><ul><li>Phone modem – converts computer data into analog audio signal for transfer over a telephone line. Transferred back upon arrival. (Easy to implement but slow data transfer rate about 64 Kb per second and dial-in is needed.) </li></ul></ul><ul><ul><li>Digital Subscriber Line (DSL) – uses phone lines but transfers only digital data to and from the phone company’s central office. (No need to dial in, maintains active Internet connection. Must be within a certain distance of a specific field office.) </li></ul></ul><ul><ul><li>Cable Modem – Data transferred on the same as your cable TV. (Becoming more popular. DSL and Cable are considered broadband connections and are the fastest way to surf the web.) </li></ul></ul>
  7. 7. Modems <ul><li>Modems are devices that convert signals between analog and digital formats to allow for proper transmission of data over different physical mediums </li></ul><ul><ul><li>Internal & External </li></ul></ul><ul><ul><li>Wireless </li></ul></ul><ul><ul><li>Cable </li></ul></ul><ul><ul><li>DSL </li></ul></ul><ul><ul><li>Power line </li></ul></ul>Audio coupled DSL modem Internal modem Cable modem
  8. 8. Networking Concepts <ul><li>Packet: A fixed-length block of data for transmission. Includes headers, src & dest addresses, and a payload. Data transmissions are broken up into packets. </li></ul><ul><li>Bandwidth: The range or band of frequencies that a transmission medium can carry in a given period of time. Can be expressed in Hz or bps. </li></ul><ul><ul><li>Baseband: Only one signal can travel at a time </li></ul></ul><ul><ul><li>Broadband: Several signals can be sent at once </li></ul></ul><ul><li>Download & Upload </li></ul><ul><li>Downlink & Uplink </li></ul>
  9. 9. The OSI Model <ul><li>The OSI Model: A seven-layer logical break-down of network interaction to facilitate communication standards </li></ul><ul><li>Consider the following real-life scenario </li></ul><ul><ul><li>John is planning to go to Los Angeles for a short summer vacation </li></ul></ul><ul><ul><li>John needs to decide on the following </li></ul></ul>Mode of Transportation Airline Date/Time Route etc … Airplane United July 20 th /5:00pm Columbia  Houston  LA More Specific Details
  10. 10. The OSI Model <ul><li>The layers of the OSI reference model </li></ul><ul><li>Number Layer </li></ul><ul><li>7 Application </li></ul><ul><li>6 Presentation </li></ul><ul><li>5 Session </li></ul><ul><li>4 Transport </li></ul><ul><li>3 Network </li></ul><ul><li>2 Data Link </li></ul><ul><li>1 Physical </li></ul><ul><li>Protocol: A set of conventions that govern the format of data transmitted electronically. They ensure that all data is exchanged in a consistent format. </li></ul><ul><li>TCP/IP: The protocols that enable all computers to interpret and use data transmitted over the Internet. </li></ul><ul><ul><li>TCP is a transport layer protocol and IP is a network layer protocol </li></ul></ul><ul><ul><li>TCP is reliable, in order, implements flow control </li></ul></ul>
  11. 11. IP Addresses <ul><li>IP Address: Used to uniquely identify computers on the Internet </li></ul><ul><ul><li>Can be dynamic (changes for each session) or static (fixed) </li></ul></ul><ul><ul><li>Syntax: four sets of numbers between 0 and 255 separated by decimals (for IPv4), e.g. </li></ul></ul><ul><ul><li>Dynamic IP addresses are assigned by DHCP servers </li></ul></ul><ul><ul><li>Dynamic addresses are suitable for clients, static addresses are suitable for persistent sites </li></ul></ul><ul><ul><li>What is the benefit of using dynamic IP addresses? </li></ul></ul>
  12. 12. Phone-Line Based Connections <ul><li>Dial-up: Cheap (< $20), slow (< 56 Kbps), widespread availability </li></ul><ul><ul><li>The “last mile” problem: replacing copper wire lines is a financial and technical challenge </li></ul></ul><ul><li>T-Carrier (T1/T2/T3): A traditional trunk line that carries multiple telephone circuits </li></ul><ul><ul><li>Speeds of up to 45 Mbps </li></ul></ul><ul><ul><li>Cost: > $1,000 </li></ul></ul><ul><li>Digital Subscriber Line (DSL): Principal competition to cable, always on </li></ul><ul><ul><li>Speeds of 1.5-9 Mbps for downloads and 64 Kbps-1.5Mbps for uploads </li></ul></ul><ul><ul><li>Availability limitations </li></ul></ul><ul><ul><li>Cost: ~ $40 </li></ul></ul>
  13. 13. Broadband Connections <ul><li>Cable: Connects PCs to cable TV systems utilizing unused portions of cable for data transfer, always on </li></ul><ul><ul><li>Speeds of 50 Mbps for downloads and 1.4 Mbps for uploads </li></ul></ul><ul><ul><li>Cost: ~ $40 </li></ul></ul><ul><ul><li>Availability? </li></ul></ul><ul><li>Satellite: Communications satellites transmit microwaves from earth-based stations, always on </li></ul><ul><ul><li>Speeds of 256-400 Kbps </li></ul></ul><ul><ul><li>Cost: ~ $100 </li></ul></ul><ul><li>Broadband over Power Lines (BPL): Uses existing electricity networks for data and voice transmission </li></ul><ul><ul><li>Has potential for interference with radio signals </li></ul></ul><ul><ul><li>Cost: ~ $30 </li></ul></ul><ul><li>WiFi </li></ul><ul><ul><li>Wi-Fi permits transmission speeds of 1-11 Mbps, 300 ft range </li></ul></ul><ul><ul><li>Is it legal and technically safe to use the unsecured wireless connection to which you do not subscribe? </li></ul></ul>
  14. 14. The Internet Hierarchy <ul><li>ISP (Internet Service Provider) </li></ul><ul><li>POP (Point Of Presence) </li></ul><ul><li>NAP (Network Access Point)/ PNAP (Private/Peer NAP) </li></ul><ul><li>Backbone </li></ul><ul><li>Internet 2 </li></ul><ul><ul><li>Cooperative university/business research project </li></ul></ul><ul><ul><li>New standards for large-scale higher-speed data transmission </li></ul></ul><ul><ul><li>Requires state-of-the-art infrastructure </li></ul></ul>
  15. 15. Wireless Technologies <ul><li>Cell Phones </li></ul><ul><ul><li>Analog (1G), Digital (2G), Broadband (3G) </li></ul></ul><ul><ul><li>2G: U.S. wireless standards (GSM, TDMA, CDMA, FDMA) </li></ul></ul><ul><ul><li>2.5G: GPRS, EDGE </li></ul></ul><ul><ul><li>3G: EV-DO, UMTS </li></ul></ul><ul><li>WiMAX </li></ul><ul><ul><li>Potential range: 30mi </li></ul></ul><ul><ul><li>Data transfer rates ranging from 15 Mbps to 40 Mbps </li></ul></ul><ul><li>Mobile Security Concerns </li></ul><ul><ul><li>SMS spoofing (some use legitimate software such as Clickatell, Verizon blocks about 50,000 spam SMS per day) </li></ul></ul><ul><ul><li>Malicious code attacks </li></ul></ul><ul><ul><ul><li>Spread through Bluetooth, required restarting phone after exposure and user opening malicious file </li></ul></ul></ul><ul><ul><ul><li>Actions: dialers, delete files, draining batteries </li></ul></ul></ul>