Transmission Media - PowerPoint PPT Presentation


Title: Transmission Media


1
Transmission Media
2
Transmission of Information
  • From physics
  • Energy
  • Electromagnetic wave propagation
  • From mathematics
  • Coding theory

3
Transmission Media
  • Copper wire
  • Need two wires
  • Possibilities
  • Twisted pair
  • Coaxial Cable
  • Optical Fiber
  • Flexible
  • Light stay in
  • Air/space
  • Used for electromagnetic transmission

4
Twisted pair wiring
5
Coaxial Cable
6
Type of Satellite
  • Geosynchronous Satellite
  • Low Earth Orbit
  • Low Earth Orbit Satellite Arrays

7
Satellite
8
Two important Physical Limits of a Transmission
System
  • Propagation Delay
  • Time required for signal to travel across media
  • Example electromagnetic radiation travels
    through space at the speed of light (3 108
    meters per second)
  • Bandwidth
  • Maximum times per second the signal can change

9
Transmission of Data
  • Network hardware encodes information for
    transmission
  • Two types of encoding
  • Analog (amount of energy proportional to the
    value of item sent)
  • Digital (two forms of energy to encode 0 and 1)
  • Computer networks use the latter

10
Example Digital Encoding
  • Medium
  • Copper wire
  • Energy form
  • Electric current
  • Encoding
  • Negative voltage encodes 1
  • Positive voltage encodes 0

11
Illustration of Digital Encoding
  • Known as waveform diagram
  • X-axis corresponds to time
  • Y-axis corresponds to voltage

12
Encoding Details
  • All details specified by a standard
  • ASCII standard
  • Several organizations produce networking
    standards
  • IEEE
  • Institute for Electrical and Electronic Engineers
  • ITU
  • International Telecommunications Union
  • EIA
  • Electronic Industries Association
  • Standard RS-232-C
  • Hardware that adheres to standard interoperable

13
Standard RS-232-C
  • Example use
  • Connection to keyboard/mouse
  • Serial port on PC
  • Voltage 15 or -15
  • Cable limit to lt 50 feet
  • Uses asynchronous communication
  • When the transmitter has nothing to send, it
    leaves the wire with a negative voltage that
    corresponds to bit value 1

14
Asynchronous Communication
  • Sender and receiver must agree on
  • Number of bits per character
  • Duration of each bit
  • Receiver
  • Does not know when a character will arrive
  • May wait forever
  • To ensure meaningful exchange
  • Start bit before character
  • One or more stop bits after character

15
Illustration of RS-232
  • Start bit
  • Same as 0
  • Not part of data
  • Stop bit
  • Same as 1
  • Follows data

16
Duration of a bit in RS-232C
  • Determined by baud rate
  • Example baud rate 9.6Kbaud, 28.8Kbaud, 33.6Kbaud
  • Duration of bit is 1/baud_rate
  • Sender and receiver must agree a priori
  • Received samples signal
  • Disagreement results in framing error

17
Two Way Communication
  • Desirable in practice
  • Requires each side to have transmitter and
    receiver
  • Called full duplex
  • Distinguished from half duplex transmission
    (simplex transmission)

18
Illustration of Full-Duplex Communication
  • Transmitter on one side connected to receiver on
    other side
  • Separate wires needed to carry current in each
    direction
  • Common ground wire
  • DB-9, DB-15, or DB-25 connector used
  • Pin 2 is transmit
  • Pin 3 is receive
  • A computer transmits on pin 2 and receives on pin
    3
  • A modem transmits on pin 3 and receives on pin 2

19
Electrical Transmission
  • Its is an ugly world
  • Electrical energy dissipates as it travels along
  • Wires have resistance, capacitance, and
    inductance which distort signals
  • Magnetic or electrical interference distort
    signals
  • Distortion can result in loss or
    misinterpretation

20
Illustration of Distorted Signal For a Single Bit
  • In practice
  • Distortion can be much worse than illustrated

21
Consequences
  • RS-232 hardware must handle minor distortions
  • Take multiple samples per bit
  • Tolerate less than full voltage
  • Cannot use electrical current for long-distance
    transmission

22
Nyquist Intersymbol Interference Theorem
  • Nyquists theorem states that the maximum data
    rate in bits per second that can be achieved over
    a transmission system of bandwidth B is 2B
  • If the transmission system uses K possible values
    of voltage instead of two, D denotes the maximum
    data rate in bits per second, then D 2Blog2K

23
Shannons Theorem
  • Noise Background interference
  • C Blog2(1S/N)
  • C effective limit on the channel capacity in
    bits per second
  • B hardware bandwidth
  • S average signal power
  • N average noise power
  • Example Voice telephone system
  • S/N 1000, B 3000Hz
  • C 30,000bps

24
The Bottom Line
  • Nyquists theorem means finding a way to encode
    more bits per cycle improves the data rate
  • Shannons theorem means that no amount of clever
    engineering can overcome the fundamental physical
    limits of a real transmission system
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Transmission Media

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Transcript and Presenter's Notes

Title: Transmission Media


1
Transmission Media
2
Transmission of Information
  • From physics
  • Energy
  • Electromagnetic wave propagation
  • From mathematics
  • Coding theory

3
Transmission Media
  • Copper wire
  • Need two wires
  • Possibilities
  • Twisted pair
  • Coaxial Cable
  • Optical Fiber
  • Flexible
  • Light stay in
  • Air/space
  • Used for electromagnetic transmission

4
Twisted pair wiring
5
Coaxial Cable
6
Type of Satellite
  • Geosynchronous Satellite
  • Low Earth Orbit
  • Low Earth Orbit Satellite Arrays

7
Satellite
8
Two important Physical Limits of a Transmission
System
  • Propagation Delay
  • Time required for signal to travel across media
  • Example electromagnetic radiation travels
    through space at the speed of light (3 108
    meters per second)
  • Bandwidth
  • Maximum times per second the signal can change

9
Transmission of Data
  • Network hardware encodes information for
    transmission
  • Two types of encoding
  • Analog (amount of energy proportional to the
    value of item sent)
  • Digital (two forms of energy to encode 0 and 1)
  • Computer networks use the latter

10
Example Digital Encoding
  • Medium
  • Copper wire
  • Energy form
  • Electric current
  • Encoding
  • Negative voltage encodes 1
  • Positive voltage encodes 0

11
Illustration of Digital Encoding
  • Known as waveform diagram
  • X-axis corresponds to time
  • Y-axis corresponds to voltage

12
Encoding Details
  • All details specified by a standard
  • ASCII standard
  • Several organizations produce networking
    standards
  • IEEE
  • Institute for Electrical and Electronic Engineers
  • ITU
  • International Telecommunications Union
  • EIA
  • Electronic Industries Association
  • Standard RS-232-C
  • Hardware that adheres to standard interoperable

13
Standard RS-232-C
  • Example use
  • Connection to keyboard/mouse
  • Serial port on PC
  • Voltage 15 or -15
  • Cable limit to lt 50 feet
  • Uses asynchronous communication
  • When the transmitter has nothing to send, it
    leaves the wire with a negative voltage that
    corresponds to bit value 1

14
Asynchronous Communication
  • Sender and receiver must agree on
  • Number of bits per character
  • Duration of each bit
  • Receiver
  • Does not know when a character will arrive
  • May wait forever
  • To ensure meaningful exchange
  • Start bit before character
  • One or more stop bits after character

15
Illustration of RS-232
  • Start bit
  • Same as 0
  • Not part of data
  • Stop bit
  • Same as 1
  • Follows data

16
Duration of a bit in RS-232C
  • Determined by baud rate
  • Example baud rate 9.6Kbaud, 28.8Kbaud, 33.6Kbaud
  • Duration of bit is 1/baud_rate
  • Sender and receiver must agree a priori
  • Received samples signal
  • Disagreement results in framing error

17
Two Way Communication
  • Desirable in practice
  • Requires each side to have transmitter and
    receiver
  • Called full duplex
  • Distinguished from half duplex transmission
    (simplex transmission)

18
Illustration of Full-Duplex Communication
  • Transmitter on one side connected to receiver on
    other side
  • Separate wires needed to carry current in each
    direction
  • Common ground wire
  • DB-9, DB-15, or DB-25 connector used
  • Pin 2 is transmit
  • Pin 3 is receive
  • A computer transmits on pin 2 and receives on pin
    3
  • A modem transmits on pin 3 and receives on pin 2

19
Electrical Transmission
  • Its is an ugly world
  • Electrical energy dissipates as it travels along
  • Wires have resistance, capacitance, and
    inductance which distort signals
  • Magnetic or electrical interference distort
    signals
  • Distortion can result in loss or
    misinterpretation

20
Illustration of Distorted Signal For a Single Bit
  • In practice
  • Distortion can be much worse than illustrated

21
Consequences
  • RS-232 hardware must handle minor distortions
  • Take multiple samples per bit
  • Tolerate less than full voltage
  • Cannot use electrical current for long-distance
    transmission

22
Nyquist Intersymbol Interference Theorem
  • Nyquists theorem states that the maximum data
    rate in bits per second that can be achieved over
    a transmission system of bandwidth B is 2B
  • If the transmission system uses K possible values
    of voltage instead of two, D denotes the maximum
    data rate in bits per second, then D 2Blog2K

23
Shannons Theorem
  • Noise Background interference
  • C Blog2(1S/N)
  • C effective limit on the channel capacity in
    bits per second
  • B hardware bandwidth
  • S average signal power
  • N average noise power
  • Example Voice telephone system
  • S/N 1000, B 3000Hz
  • C 30,000bps

24
The Bottom Line
  • Nyquists theorem means finding a way to encode
    more bits per cycle improves the data rate
  • Shannons theorem means that no amount of clever
    engineering can overcome the fundamental physical
    limits of a real transmission system
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