1 SYST5030/4030 FUNDAMENTAL CONCEPTS Analog versus Digital Bandwidth (or channel capacity) Switched vs. leased lines Transmission Media Transmission mode (parallel/serial, synchronous/asynchronous Transmission method (simplex, half-duplex, full- duplex)
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SYST5030/4030 1 FUNDAMENTAL CONCEPTS UAnalog versus Digital UBandwidth (or channel capacity) USwitched vs. leased lines UTransmission Media UTransmission.
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FUNDAMENTAL CONCEPTS
Analog versus Digital Bandwidth (or channel capacity) Switched vs. leased lines Transmission Media Transmission mode (parallel/serial, synchronous/asynchronous Transmission method (simplex, half-duplex, full-duplex)
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Digital or analog channel. . . .
Recall there are 2 types of signals:
digital and analog.
Similarly, there are two types of channels...
Digital Channels
- designed to carry digital signals, i.e. 0's and 1's- signal becomes weak every few miles- need BIT REPEATERS to strengthen it
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Analog Channels- designed to carry analog signals, like speech
- signal again becomes weak every few miles
- need AMPLIFIERS (instead of BIT REPEATERS)
Digital versus Analog
•Digital channels are better.
•Increasingly the phone network is becoming digital.
•More than 90% lines in the US telephone network are digital now (e.g., Sprint is 100% digital).
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Bandwidth of channel
Digital Channel
B.W. (or channel capacity) is defined in Bits/sec. that canflow through it. (Also called DATA RATE.)
Analog Channel
B.W. defined in terms of cycles/sec. (or Hertz) e.g. B.W. oftelephone line to carry speech is approx. 3000 Hz.
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Note:
1) Highest frequency component in speech is about 4000 Hz.
2) Bandwidth required to transmit an analog signal acrossan analog channel is determined by the highestfrequency component in the signal.
3) Rapid changes in signal level correspond tohigh frequency.
gradual changes in signal level correspondto low frequency.
•Frequency (pitch) is measured in cycles per second
•Phase corresponds to the wave’s relative position
•Bandwidth is the difference between the lowest and highest
frequency (measured in cycles per second or Hz.)
• In general, voice contains many different frequencies.
Properties of Analog Signals
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Switched versus leased. . . .
A channel is switched if it is shared among several users.
It is leased if it is reserved exclusively for a single user.Hence, no switching is necessary.
Your home phone line is a switched channel.
Large companies have leased lines between their variousoffices around the US and the world if the volume oftraffic between these offices is large.
Kai Larsen:
When does switching make sense?
When does leasing make sense?
Kai Larsen:
When does switching make sense?
When does leasing make sense?
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Transmission Media - Copper wire
- Pairs of wire from home to local telephone company office- Limited bandwidth- Deteriorates at high frequency- Ubiquitous on the local loop.- Wires are twisted together in helical pattern to minimize noise and interference.
Two Norwegians who started skiing towards the North Pole, 255 km into their 1,741 km long journey… relying only on their Iridium satellite telephone receives the final call… Iridium was going down…
Motorola, however, decided to provided mission critical service…June 3rd 2000 they reached the pole. Ever since, the pole has been without telephone coverage…
Kai Larsen:
Two Norwegians who started skiing towards the North Pole, 255 km into their 1,741 km long journey… relying only on their Iridium satellite telephone receives the final call… Iridium was going down…
Motorola, however, decided to provided mission critical service…June 3rd 2000 they reached the pole. Ever since, the pole has been without telephone coverage…
The Iridium story:Rune Gjeldnes and Torry Larsen attempting to be the first explorers to reach the North Pole completely un-supported. Start weight of sledges: 175 kilos, each… 1741 km long journey…Nine expeditions had tried before…all failed…
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- Transmit signal to satellite 22,230 miles in space (GEOs)- 0.5 - 0.6 sec. delay in transmission.- Various bands between 1 and 40 GHz are used for satellite
transmission.- 600 MHz band at 12 GHz => 200,000 telephone
channels or 100 TV channels.
Other types of satellites: LEO, MEO, HALE.
Transmission media - Wireless Satellite
Kai Larsen:Did you know that:
GEO -> Geo-stationary orbitMEO -> Medium Earth OrbitLEO -> Low Earth OrbitHALE -> High Altitude Long Endurance
Kai Larsen:Did you know that:
GEO -> Geo-stationary orbitMEO -> Medium Earth OrbitLEO -> Low Earth OrbitHALE -> High Altitude Long Endurance
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Transmission media - Microwave
No physical medium - i.e., wireless. Based on radio waves above 100 MHz. Signal is beamed from transmission tower. Microwaves travel in straight lines Usually place 100m towers 50 miles apart. Used for long distance telephone Subject to weather interference (e.g., rain)
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Phone Coder Light Source
Regenerator Decoder Phone
- Latest technology, current speeds > 10 Gbps- Hair thin strands of glass, called optical fibers- Light pulses travel through high quality glass.- Need repeaters every 20 km.- Single fiber-optic cable carries several 100,000 calls.