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    Networks Networks Presentation Transcript

    • Networks Spring 2009
    • Wired Communication Media
      • Twisted-Pair Wire: Two strands of insulated copper wire, twisted around each other
        • Disadvantages: relatively slow (1-128 Mbps), interference
      • Coaxial Cable: Insulated copper wire wrapped in a solid or braided metal shield, then an external cover
        • Advantages: less interference, faster (~200 Mbps)
      • Fiber-Optic Cable: Dozens or hundreds of thin strands of glass or plastic that transmit pulsing beams of light rather than electricity
        • The light used is typically IR
        • Advantages: fast (~ 2Gbps), less interference, more reliable, lighter, cannot be easily wiretapped
        • Dispersion considerations, alleviated by repeaters and optical amplifiers (1987)
    • Wireless Communication Media
      • Infrared Transmission (IR):
        • Transmission speeds of 1-4 Mbps, deprecated technology for wireless mice and keyboards
      • Broadcast Radio: For long range communications ( ~ 2 Mbps)
      • Microwave Radio: Super-high frequency radio waves (~ 45 Mbps)
      • Communication Satellites: Microwave relay stations that orbit around the earth
        • Eliminate the line-of -sight limitation of the above technologies
        • GEO (22K mi from earth): e.g. broadcast TV, weather, surveillance
        • MEO (5K-10K mi from earth): e.g. navigation and communication satellites such as U.S. NAVSTAR and GPS
        • LEO (200-1000 mi from earth): e.g. surveillance, imaging
    • Wireless Communication Media
      • Bluetooth: A wireless standard aimed at linking cell phones, PDAs, computers, and peripheral devices up to 30 ft, speeds < 1 Mbps
      • 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
        • Uses WAP, 10 x speed of Bluetooth
        • WiFi utilizes WEP, WPA & WPA2
        • Auto-connection concerns
    • Modems
      • Modems are devices that convert signals between analog and digital formats to allow for proper transmission of data over different physical mediums
        • Internal & External
        • Wireless
        • Cable
        • DSL
        • Power line
      Audio coupled DSL modem Internal modem Cable modem
    • Networking Concepts
      • Packet: A fixed-length block of data for transmission. Includes headers, src & dest addresses, and a payload. Data transmissions are broken up into packets.
      • 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.
        • Baseband: Only one signal can travel at a time
        • Broadband: Several signals can be sent at once
      • Download & Upload
      • Downlink & Uplink
    • The OSI Model
      • The OSI Model: A seven-layer logical break-down of network interaction to facilitate communication standards
      • Consider the following real-life scenario
        • John is planning to go to Los Angeles for a short summer vacation
        • John needs to decide on the following
      Mode of Transportation Airline Date/Time Route etc … Airplane United July 20 th /5:00pm Columbia  Houston  LA More Specific Details
    • The OSI Model
      • The layers of the OSI reference model
      • Number Layer
      • 7 Application
      • 6 Presentation
      • 5 Session
      • 4 Transport
      • 3 Network
      • 2 Data Link
      • 1 Physical
      • Protocol: A set of conventions that govern the format of data transmitted electronically. They ensure that all data is exchanged in a consistent format.
      • TCP/IP: The protocols that enable all computers to interpret and use data transmitted over the Internet.
        • TCP is a transport layer protocol and IP is a network layer protocol
        • TCP is reliable, in order, implements flow control
    • IP Addresses
      • IP Address: Used to uniquely identify computers on the Internet
        • Can be dynamic (changes for each session) or static (fixed)
        • Syntax: four sets of numbers between 0 and 255 separated by decimals (for IPv4), e.g.
        • Dynamic IP addresses are assigned by DHCP servers
        • Dynamic addresses are suitable for clients, static addresses are suitable for persistent sites
        • What is the benefit of using dynamic IP addresses?
    • Phone-Line Based Connections
      • Dial-up: Cheap (< $20), slow (< 56 Kbps), widespread availability
        • The “last mile” problem: replacing copper wire lines is a financial and technical challenge
      • T-Carrier (T1/T2/T3): A traditional trunk line that carries multiple telephone circuits
        • Speeds of up to 45 Mbps
        • Cost: > $1,000
      • Digital Subscriber Line (DSL): Principal competition to cable, always on
        • Speeds of 1.5-9 Mbps for downloads and 64 Kbps-1.5Mbps for uploads
        • Availability limitations
        • Cost: ~ $40
    • Broadband Connections
      • Cable: Connects PCs to cable TV systems utilizing unused portions of cable for data transfer, always on
        • Speeds of 50 Mbps for downloads and 1.4 Mbps for uploads
        • Performance issues
        • Cost: ~ $40
      • Satellite: Communications satellites transmit microwaves from earth-based stations, always on
        • Speeds of 256-400 Kbps
        • Cost: ~ $100
      • Broadband over Power Lines (BPL): Uses existing electricity networks for data and voice transmission
        • Has potential for interference with radio signals
        • Cost: ~ $30
      • WiFi
        • Wi-Fi permits transmission speeds of 1-11 Mbps, 300 ft range
        • Is it legal and technically safe to use the unsecured wireless connection to which you do not subscribe?
    • The Internet Hierarchy
      • ISP (Internet Service Provider)
      • POP (Point Of Presence)
      • NAP (Network Access Point)/ PNAP (Private/Peer NAP)
      • Backbone
      • Internet 2
        • Cooperative university/business research project
        • New standards for large-scale higher-speed data transmission
        • Requires state-of-the-art infrastructure
    • Wireless Technologies
      • Cell Phones
        • Analog (1G), Digital (2G), Broadband (3G)
        • 2G: U.S. wireless standards (GSM, TDMA, CDMA, FDMA)
        • 2.5G: GPRS, EDGE
        • 3G: EV-DO, UMTS
      • WiMAX
        • Potential range: 30mi
        • Data transfer rates ranging from 15 Mbps to 40 Mbps
      • Mobile Security Concerns
        • SMS spoofing (some use legitimate software such as Clickatell, Verizon blocks about 50,000 spam SMS per day)
        • Malicious code attacks
          • Spread through Bluetooth, required restarting phone after exposure and user opening malicious file
          • Actions: dialers, delete files, draining batteries
    • Types of Networks
      • Components of Networks
        • Connection systems, computers with NICs, Network OS, Shared devices,
        • Routers (direct messages between different networks)/Hubs/Switches/Bridges (connect similar networks)/Gateways (connect dissimilar networks)
      • Types of Networks (based on coverage scope)
        • WAN, MAN, LAN, etc.
      • Types of LANs (based on computer roles)
        • Client/Server, P2P
      • Network Topologies
        • Bus (susceptible to collisions)
        • Ring
        • Star (hub at the center, no collisions)
      Bus Ring Star