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21 Cards in this Set
- Front
- Back
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The delivery of frames across the local media requires the following Physical layer elements:
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* The physical media and associated connectors
* A representation of bits on the media * Encoding of data and control information * Transmitter and receiver circuitry on the network devices |
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The purpose of the Physical layer is to
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* create the signal that represents the bits in each frame, and back again
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There are three basic forms of network media on which data is represented:
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Copper cable
Fiber Wireless |
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The technologies defined by Physical layer standards:
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* Physical and electrical properties of the media
* Mechanical properties (materials, dimensions, pinouts) of the connectors * Bit representation by the signals (encoding) Definition of control information signals |
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The three fundamental functions of the Physical layer are:
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* The physical components
* Data encoding * Signaling |
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Bits are represented on the medium by changing one or more of the following characteristics of a signal:
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* Amplitude
* Frequency * Phase |
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What is NRZ signaling?
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Non-Return to Zero. Voltage pulses - high = 1, low = 0. Only good for slow data links.
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What is Manchester encoding?
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bit values are represented as voltage transitions. Low to high =1, high to low = 0
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What is the signaling method employed by 10BaseT Ethernet?
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Manchester encoding
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A code group is
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a sequence of code bits that represent data bit patterns
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Advantages using code groups include:
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* Reducing bit level error
* Limiting the effective energy transmitted into the media * Helping to distinguish data bits from control bits * Better media error detection |
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How do code groups reduce bit level error?
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the symbols force an ample number of bit transitions to occur on the media to synchronize transition timing (not too many 1s or 0s in a row)
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How do code groups limit the effective energy transmitted into the media?
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By ensuring 1s and 0s are evenly balanced
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How do code groups help distinguish control from data?
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Three code group symbols (data, control, invalid) that enable media to recognise.
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How does the code group 4b/5b work?
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For every four bits of data, a 5 bit code is sent. Enables faster data transmission despite more overhead.
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Data transfer can be measured in three ways
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* Bandwidth
* Throughput * Goodput |
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Bandwidth is
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the amount of information that can flow from one place to another in a given amount of time
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Throughput is
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the measure of the transfer of bits across the media over a given period of time
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Goodput is
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the measure of usable data transferred over a given period of time
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What is the wiring layout of a T568A cable?
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1,2 - Green
3,6 - Orange 4,5 - Blue 7,8 - Brown |
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What is the wiring layout of a T568B cable?
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1,2 - Orange
3,6 - Green 4,5 - Blue 7,8 - Brown |
