Module 7 Part 1 Introduction To Networking. 2 Objectives Understand the history of data...
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Transcript of Module 7 Part 1 Introduction To Networking. 2 Objectives Understand the history of data...
2
ObjectivesObjectives
• Understand the history of data communications• Describe the basic components of a network• Explain the methods of data transmission,
including types of signals, modulation, and choices among transmission modes
• Differentiate among the various kinds of communications links and appreciate the need for protocols
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Data Communications SystemsData Communications Systems
• Computer systems that transmit data over communications lines such as telephone lines or cables
• History– Centralized data processing in early days– Distributed data processing began in late
1960s– Networks of personal computers began in
1980s
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Centralized Data ProcessingCentralized Data Processing
• Places all hardware, software, and processing in one location
• Very inconvenient and inefficient– Input data had to be physically transported to
computer– Processed material had to be delivered to
users
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Distributed Data ProcessingDistributed Data Processing
• Uses computers that are at a distance from central computer
• Local computers had access to central computers– Some processing done on local computers,
some on central computers
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NetworkNetwork
• A group of two or more computer system that are linked together to exchange data and share resources over communication lines
• Uses communications equipment to connect two or more computers and resources– Distributed data processing systems are
networks – Local area network (LAN) designed to share data
and resources among several users in office or building
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Putting Together a NetworkPutting Together a Network
• Basic Components– Sending device– Communications link– Receiving device
modems
routers
switches
(NIC) Network Interface Cards
computers
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Network FundamentalsNetwork Fundamentals
• Node – Any workstation or peripheral that is connected to
network server, computer, peripheral devices, such as printer
• Network Interface Card(NIC) – expansion boards that fit into a computer’s expansion
slot. – Provide electronic connection between a computer
and the network.
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• Routers – Can determine the best path to route data– If traffic is clogged on one path, the router will
determine an alternative path
• Switches– Perform same function as router– However, it is simpler and faster
mechanism than a router
Network FundamentalsNetwork Fundamentals
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Digital and Analog TransmissionDigital and Analog Transmission
• Digital transmission
• Analog transmission
• Modem
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Digital TransmissionDigital Transmission
• Sends data as distinct pulses, either on or off– Similar to how data travels through computer
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Analog TransmissionAnalog Transmission
• Continuous electrical signal in the form of a wave– Called carrier wave
• Many communications media already in place for analog (voice) transmission– Phone lines are most common
• Digital signal from computer must be converted to analog form to be transmitted over analog lines
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Converting Digital to AnalogConverting Digital to Analog
• Carrier wave can be altered– Amplitude (height) of wave– Frequency (number of times a wave repeats
during a cycle) of wave
• Conversion from digital to analog called modulation
• Conversion from analog to digital called demodulation
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Converting Digital to AnalogConverting Digital to Analog
analog signalContinuous electrical
wave
digital signalDistinct pulses that
represent bits grouped together into bytes
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ModemModem
• Short for modulator/demodulator
• Converts digital signal to analog and vice versa– Modulate convert from
digital to analog– Demodulate convert
from analog to digital– Speeds up to 56,000 bps
(56K)
Internal modem -resides on an expansion board that plugs into a computer
ADSL modem
PC Card modem
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Types of ModemsTypes of Modems
• External modem separate from computer
• Internal modem inserted into computer– Standard on most computers today
• PC Card modem slides into slot on laptop– Roughly credit card size
• Cable connects modem to standard phone jack
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Modem Data SpeedsModem Data Speeds
• Measured in bits per second (bps)– Early modems transmitted at 300 bps– Fastest current modems transmit at 56,000
bps
• Federal Communications Commission (FCC) restrictions prohibit actual speeds faster than 53,000 bps
• Actual speed depends on line conditions and other variables
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Other Communications DevicesOther Communications Devices
• ISDN
• DSL
• Cable modems
• Cellular modems
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Integrated Systems Digital Network (ISDN)
Integrated Systems Digital Network (ISDN)
• Special type of telephone circuit– Can move data at 128,000 bps– Includes two phone lines, so you can talk on
the phone while online
• Drawbacks– Expensive, especially at installation– Not available in all areas
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Digital Subscriber Line (DSL)Digital Subscriber Line (DSL)
Advantages of DSL: • Can leave your Internet connection open and
still use the phone line for voice calls. • The speed is much higher than a regular modem • DSL doesn't necessarily require new wiring; it
can use the phone line you already have. • The company that offers DSL will usually provide
the modem as part of the installation.
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Digital Subscriber Line (DSL)Digital Subscriber Line (DSL)
Drawbacks• A DSL connection works better when you are
closer to the provider's central office. • The connection is faster for receiving data than it
is for sending data over the Internet.
• The service is not available everywhere.
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Cable ModemsCable Modems
• Uses coaxial cable already in place for your TV– Very fast transmission speed, especially for
downloading– Always on: no need to dial a connection
• Drawbacks– All users share a cable segment’s capacity
• As more users in neighborhood go online, speed decreases
– No security for individual users or data• Purchase a firewall program for security
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Cellular ModemsCellular Modems
• Transmit data over the cellular telephone system– Roughly half the speed of a regular telephone
network
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Data TransmissionData Transmission
• Simplex sends data in one direction only– Example: television broadcasting
• Half-duplex sends data in both directions, but only one way at a time– Example: bank teller sends data about a deposit; after
data received, a confirmation returns
• Full-duplex allows transmission in both directions at same time– Example: a conversation– Typically used for high-speed data communication
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Communications MediaCommunications Media
• Physical means of data transmission• Bandwidth is measure of the capacity of the
communications link– Speed at which a line carries data and information– The faster the transfer rate, the faster you can send
and receive data and information– Usually expressed as a measure of bits per second
bits per second (bps)
kilobits per second (Kbps)
megabits per second (Mbps)
gigabits per second (Gbps)
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Types of Communications MediaTypes of Communications Media
• Wire pairs• Coaxial cables• Fiber optics• Microwave
transmission• Satellite
transmission• Wireless
transmission
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Wire PairsWire Pairs
• Also known as twisted pair– Two wires twisted around
each other to reduce electrical interference
• Inexpensive• Already in place (for
telephone systems)• Susceptible to electrical
interference and noise – Noise - anything that causes
signal distortion
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Coaxial CableCoaxial Cable
• A center conductor wire surrounded by layer of insulation and metallic sheath
• Commonly used to connect to cable TV• Higher bandwidth and less susceptibility to noise than
twisted pair
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Fiber OpticsFiber Optics
• Use light instead of electricity to send data• Much higher bandwidth than coaxial cable• Immune to electrical interference• Materials cheaper than coaxial, but installation costs
high
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Microwave TransmissionMicrowave Transmission
• Uses line-of-sight transmission of data signals– Sending microwave
must “see” receiver• Requires relay
stations approximately every 30 miles– Waves are straight,
earth is curved• Offers high speed
and cost-effectiveness
• Susceptible to weather conditions
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Satellite TransmissionSatellite Transmission
• A form of microwave transmission– Satellite acts as relay
station• Components
– Earth station sends and receives signal to satellite
– Transponder receives and amplifies signal, changes frequency, and retransmits data
• Useful when signal must travel thousands of miles
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Wireless TransmissionWireless Transmission
• Transmits data over relatively short distances without wires
• Examples– IrDA - uses infrared line-of-
sight– Bluetooth - uses radio waves
to connect mobile devices– 802.11 standards - govern
wireless transmission
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Setting StandardsSetting Standards
• Protocol - a set of rules for the exchange of data between a terminal and a computer or two computers– Agreement on how data is to be sent and
receipt acknowledged– Needed to allow computers from different
vendors to communicate– Transmission Control Protocol/Internet
Protocol (TCP/IP) permits any computer to communicate with the Internet