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Data Transmission Topics of Chapter 3.0 3.1 Analog _ Digital

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					                                                  Topics of Chapter 3.0


             3.1 Analog & Digital Transmission

             3.2 Bandwidth

             3.3 Noise & Attenuation

             3.4 Transmission Media

             3.5 Data Communication Interface

             3.6 Operation & use of multiplexors
3.1




 Topic objectives:
3.1.1[List and differentiate between binary,analog & digital data]
3.1.2[Give examples of Analog data & Binary data]
3.1.3[Illustrate & explain the waveform of analog transmission & digital plotted over time]
3.1.4[Explain the change states of binary data into digital signal]
3.1.5[Define & explain baud rates for digital signals]
3.1.6[Illustrate the relationship between Data Rate and Bandwidth]
3.1.7[Explain what happens to data & signals]
3.1.8[Identify the reasons for the dominance of digital signaling & the difference between bits rates and baud rates]

Analog & Digital Transmission.



Signaling amounts to communicating information. The information being communicated can take
one of two forms—analog or digital:

         Analog information changes continuously and can take on many different values. An analog
          clock’s hands move constantly, displaying time on a continuous scale.
         Digital information is characterized by discrete states. A light bulb, for example, is on or off.
          A digital clock represents the time in one-minute intervals and doesn’t change its numbers
          again until the next minute. A digital clock can represent exact minutes but not the seconds
          that pass in between.

Frequently, information existing as one form must be converted to the other. This conversion often
involves the use of some encoding scheme that enables the original information to be recovered
from a signal after the signal has been received.
When an analog or a digital signal is altered so that it contains information, the process is called
modulation or encoding. AM radio, for example, transmits information by modulating the radio
signal, which increases or decreases the amplitude (signal strength) depending on the information
content. Many similar schemes are used to communicate information through different types of
signals.


3.1.1   Binary, Analog & Digital data.

Binary
Pertaining to a number system that has just two unique digits. For most purposes, we use the
decimal number system, which has ten unique digits, 0 through 9. All other numbers are then
formed by combining these ten digits. Computers are based on the binary numbering system, which
consists of just two unique numbers, 0 and 1. All operations that are possible in the decimal system
(addition, subtraction, multiplication, division) are equally possible in the binary system.

We use the decimal system in everyday life because it seems more natural (we have ten fingers
and ten toes). For the computer, the binary system is more natural because of its electrical nature
(charged versus uncharged).

In the decimal system, each digit position represents a value of 10 to the position's power. For
example, the number 345 means:

3 three 100s (10 to the 2nd power)

plus

4 four 10s (10 to the first power)

plus

5 five 1s (10 to the zeroth power)

In the binary system, each digit position represents a value of 2. For example, the binary number
1011 equals:

1 one 8 (2 to the 3rd power)

plus

0 zero 4s (2 to the 2nd power)

plus
1 one 2 (2 to the first power)

plus

1 one 1 (2 to the zeroth power)

So a binary 1011 equals a decimal 11.

Because computers use the binary number system, powers of 2 play an important role. This is why
everything in computers seems to come in 8s (2 to the 3rd power), 64s (2 to the 6th power), 128s (2
to the 7th power), and 256s (2 to the 8th power).

Programmers also use the octal (8 numbers) and hexadecimal (16 numbers) number systems
because they map nicely onto the binary system. Each octal digit represents exactly three binary
digits, and each hexadecimal digit represents four binary digits.



Analog data.
Also spelled analogue, describes a device or system that represents changing values as
continuously variable physical quantities. A typical analog device is a clock in which the hands move
continuously around the face. Such a clock is capable of indicating every possible time of day. In
contrast, a digital clock is capable of representing only a finite number of times (every tenth of a
second, for example). In general, humans experience the world analogically. Vision, for example, is
an analog experience because we perceive infinitely smooth gradations of shapes and colors.

When used in reference to data storage and transmission, analog format is that in which information
is transmitted by modulating a continuous transmission signal, such as amplifying a signal's
strength or varying its frequency to add or take away data. For example, telephones take sound
vibrations and turn them into electrical vibrations of the same shape before they are transmitted
over traditional telephone lines. Radio wave transmissions work in the same way. Computers, which
handle data in digital form, require modems to turn signals from digital to analog before transmitting
those signals over communication lines such as telephone lines that carry only analog signals. The
signals are turned back into digital form (demodulated) at the receiving end so that the computer
can process the data in its digital format.



Digital Data.
Describes any system based on discontinuous data or events. Computers are digital machines
because at their most basic level they can distinguish between just two values, 0 and 1, or off and
on. There is no simple way to represent all the values in between, such as 0.25. All data that a
computer processes must be encoded digitally, as a series of zeroes and ones.

The opposite of digital is analog. A typical analog device is a clock in which the hands move
continuously around the face. Such a clock is capable of indicating every possible time of day. In
contrast, a digital clock is capable of representing only a finite number of times (every tenth of a
second, for example).

In general, humans experience the world analogically. Vision, for example, is an analog experience
because we perceive infinitely smooth gradations of shapes and colors. Most analog events,
however, can be simulated digitally. Photographs in newspapers, for instance, consist of an array of
dots that are either black or white. From afar, the viewer does not see the dots (the digital form), but
only lines and shading, which appear to be continuous. Although digital representations are
approximations of analog events, they are useful because they are relatively easy to store and
manipulate electronically. The trick is in converting from analog to digital, and back again.


3.1.2 Example of Analog data & Binary data.

ANALOG DATA
For example, telephones take sound vibrations and turn them into electrical vibrations of the same
shape before they are transmitted over traditional telephone lines. Radio wave transmissions work
in the same way. Computers, which handle data in digital form, require modems to turn signals from
digital to analog before transmitting those signals over communication lines such as telephone lines
that carry only analog signals. The signals are turned back into digital form (demodulated) at the
receiving end so that the computer can process the data in its digital format.

DIGITAL DATA
This is the principle behind compact discs (CDs). The music itself exists in an analog form, as
waves in the air, but these sounds are then translated into a digital form that is encoded onto the
disk. When you play a compact disc, the CD player reads the digital data, translates it back into its
original analog form, and sends it to the amplifier and eventually the speakers.

Internally, computers are digital because they consist of discrete units called bits that are either on
or off. But by combining many bits in complex ways, computers simulate analog events. In one
sense, this is what computer science is all about.

Binary Data.
The binary or base-two numeral system is a system for representing numbers in which a radix of
two is used; that is, each digit in a binary numeral may have either of two different values. Typically,
the symbols 0 and 1 are used to represent binary numbers. Owing to its relatively straightforward
implementation in electronic circuitry, the binary system is used internally by virtually all modern
computers.
3.1.3 Waveform of analog & digital plotted overtime.

Signaling amounts to communicating information. The information being communicated can take
one of two forms—analog or digital:

      Analog information changes continuously and can take on many different values. An analog
       clock’s hands move constantly, displaying time on a continuous scale.
      Digital information is characterized by discrete states. A light bulb, for example, is on or off.
       A digital clock represents the time in one-minute intervals and doesn’t change its numbers
       again until the next minute. A digital clock can represent exact minutes but not the seconds
       that pass in between.

Frequently, information existing as one form must be converted to the other. This conversion often
involves the use of some encoding scheme that enables the original information to be recovered
from a signal after the signal has been received.

When an analog or a digital signal is altered so that it contains information, the process is called
modulation or encoding. AM radio, for example, transmits information by modulating the radio
signal, which increases or decreases the amplitude (signal strength) depending on the information
content. Many similar schemes are used to communicate information through different types of
signals.




A modem is the most common computer connectivity device that transmits an analog signal.
Modems transmit digital computer signals over telephone lines by converting them to analog form.
Modems are wonderfully handy for PC-to-PC communications or for accessing a LAN from a
remote location, but modems generally are too slow and too unreliable for the high-tech task of
linking busy LAN segments into a WAN. Because computer data is inherently digital, most WANs
use some form of digital signaling.
3.1.4   Change states of binary data into digital signal.

Digital Signals.
A digital signal is a signal that has been quantized from a discrete signal. By quantizing the signal,
the values of a discrete signal are no longer continuous but discrete.

In most applications, the digital signal's quantization is measured in bits. For example, compact disc
audio is signed 16-bit stereo audio sampled at 44.1 kHz, which means each second of CD audio
requires 16*2*44,100=1,411,200 bits.

Digital Signal Revolution.
Because of the Digital Revolution, the usage of digital signals has increased significantly. The entire
Internet is a network of digital signals and mobile phones have migrated from analog signals to
digital signals. Dial-up access to the Internet uses standard analog telephone lines which has
increasingly been replaced with broadband internet access, which use higher-bandwidth lines that
are used strictly in digital means (i.e., an ADSL line is never used for voice communications).

Digital Signal Processing
Digital signals are the basis of digital signal processing. Digital signal processors take digital signals
as input and output. Though, an input can be "attached" to an analog-to-digital converter or the
output can be "attached" to a digital-to-analog converter thus allowing a digital signal processor to
work in mixed-signal circuits.

The States of Binary.
In computing, a fixed-point number representation is a real data type for a number that has a fixed
number of digits after the decimal (or binary or hexadecimal) point. For example, a fixed-point
number with 4 digits after the decimal point could be used to store numbers such as 1.3467,
281243.3234 and 0.1000, but would round 1.0301789 to 1.0302 and 0.0000654 to 0.0001.

Fixed-point can exactly represent decimal fractions while still employing the base 2 arithmetic that is
efficient in most of today's computers. Most floating point representations in computers use base 2
values, which cannot exactly represent most fractions that are easily represented in base 10. For
example, one-tenth (.1) and one-hundredth (.01) can be represented only approximately by base-2
floating point representations, while they can be represented exactly in fixed-point representations
— one simply stores the data values multiplied by the appropriate power of 10.

As long as the numeric value uses only the number of digits specified after the decimal point, fixed-
point values can exactly represent all values up to its maximum value (determined by the number of
bits in its representation). This is in contrast to floating-point representations, which include an
automatically-managed exponent but cannot represent as many digits accurately (given the same
number of bits in its representation).
3.1.5    Baud rates for digital signals.

Baud Rate.
In telecommunication, data signaling rate (DSR) is the aggregate rate at which data pass a point in the transmission
path of a data transmission system.

Notes:

    1. The DSR is usually expressed in bits per second.
    2. The data signaling rate is given by where m is the number of parallel channels, ni is the number of significant
          conditions of the modulation in the I-th channel, and Ti is the unit interval, expressed in seconds, for the I-th
          channel.
    3.    For serial transmission in a single channel, the DSR reduces to (1/T)log2n; with a two-condition modulation, i. e.
          n =2, the DSR is 1/T.
    4.    For parallel transmission with equal unit intervals and equal numbers of significant conditions on each channel,
          the DSR is (m /T)log2 n; in the case of a two-condition modulation, this reduces to m /T.
    5.    The DSR may be expressed in bauds, in which case, the factor log2ni in the above summation formula should
          be deleted when calculating bauds.
    6.    In synchronous binary signaling, the DSR in bits per second may be numerically the same as the modulation
          rate expressed in bauds. Signal processors, such as four-phase modems, cannot change the DSR, but the
          modulation rate depends on the line modulation scheme, in accordance with Note 4. For example, in a 2400
          bit/s 4-phase sending modem, the signaling rate is 2400 bit/s on the serial input side, but the modulation rate is
          only 1200 bauds on the 4-phase output side.

Bit Rate.
In bit rate (sometimes written bitrate) is the frequency at which bits are passing a given (physical or metaphorical)
"point". It is quantified using the bit per second (bit/s) unit.

While often referred to as "speed", bit rate does not measure distance/time but number of bits/time, and thus should be
distinguished from the "propagation speed" (which depends on the transmission medium and has the usual physical
meaning).

The formal abbreviation for "bit per second" is "bit/s" (not bits/s). In less formal contexts the abbreviations b/s or bps are
often used, though this risks confusion with "bytes per second" (B/s). Even less formally, it is common to drop the "per
second", and simply refer to "a 128 kilobit audio stream" or "a 100 megabit network".

"Bit rate" is sometimes used interchangeably with "baud rate", which is only the same if each bit occurs in a unit interval.




For large bit rates, SI prefixes are used, not binary prefixes:

        1,000 bit/s = 1 Kbit/s (one kilobit or one thousand bits per second)
    1,000,000 bit/s = 1 Mbit/s (one megabit or one million bits per second)
1,000,000,000 bit/s = 1 Gbit/s (one gigabit or one billion bits per second)

There are typically eight bits in a byte (octet), but communications data rates are almost never expressed in bytes per
second, with the notable exceptions of disk and memory I/O transfer rates. To convert from byte/s to bit/s, simply
multiply by 8. Divide by 8 to go the other way.
Using binary prefixes, these rates take on different conversions (note that kibi-, mebi-, etc. are not typos):

        1,024 bit/s = 1 Kibit/s (one kibibit per second)
    1,048,576 bit/s = 1 Mibit/s (one mebibit per second)
1,073,741,824 bit/s = 1 Gibit/s (one gibibit per second)


Digital Signals
A digital signal is a signal that has been quantized from a discrete signal. By quantizing the signal, the values of a
discrete signal are no longer continuous but discrete.

In most applications, the digital signal's quantization is measured in bits. For example, compact disc audio is signed 16-
bit stereo audio sampled at 44.1 kHz, which means each second of CD audio requires 16*2*44,100=1,411,200 bits.



3.1.6   Relationship between Data Rate and Bandwidth.

Data Rate
data signaling rate (DSR) is the aggregate rate at which data pass a point in the transmission path
of a data transmission system.

Notes:

    1. The DSR is usually expressed in bits per second.
    2. The data signaling rate is given by where m is the number of parallel channels, ni is the
       number of significant conditions of the modulation in the I-th channel, and Ti is the unit
       interval, expressed in seconds, for the I-th channel.
    3. For serial transmission in a single channel, the DSR reduces to (1/T)log2n; with a two-
       condition modulation, i. e. n =2, the DSR is 1/T.
    4. For parallel transmission with equal unit intervals and equal numbers of significant conditions
       on each channel, the DSR is (m /T)log2 n; in the case of a two-condition modulation, this
       reduces to m /T.
    5. The DSR may be expressed in bauds, in which case, the factor log2ni in the above
       summation formula should be deleted when calculating bauds.
    6. In synchronous binary signaling, the DSR in bits per second may be numerically the same as
       the modulation rate expressed in bauds. Signal processors, such as four-phase modems,
       cannot change the DSR, but the modulation rate depends on the line modulation scheme, in
       accordance with Note 4. For example, in a 2400 bit/s 4-phase sending modem, the signaling
       rate is 2400 bit/s on the serial input side, but the modulation rate is only 1200 bauds on the 4-
       phase output side. Insert contents.
Bandwidth
Analog data signals related to bandwidth.
For analog signals, bandwidth is the width, usually measured in hertz, of a frequency band f 2 − f1. It
can also be used to describe a signal, in which case the meaning is the width of the smallest
frequency band within which the signal can fit.

It is usually notated B, W, or BW. The fact that real baseband systems have both negative and
positive frequencies can lead to confusion about bandwidth, since they are sometimes referred to
only by the positive half, and one will occasionally see expressions such as B = 2W, where B is the
total bandwidth, and W is the positive bandwidth. For instance, this signal would require a lowpass
filter with cutoff frequency of at least W to stay intact.

The bandwidth of an electronic filter is the part of the filter's frequency response that lies within 3
dB compared to the center frequency of its peak.




 In signal processing and control theory, the bandwidth is the frequency at which the closed-loop
                                    system gain drops to −3 dB.




In basic electric circuit theory when studying Band-pass and Band-reject filters the bandwidth
represents the distance between the two points in the frequency domain where the the signal is
1/Sqrt(2) of the maximum signal strength.
Digital data signals related to bandwidth.
For digital signals and by extension from the above, the word bandwidth is also used to mean the
amount of data that can be transferred through a digital connection in a given time period (i.e., the
connection's bit rate). In such cases, bandwidth is usually measured in bits or bytes per second.

In the physical world, a digital signal is usually represented in an analog form for actual
transmission. This can be a complex process. First the bit pattern must undergo a suitable form of
channel coding, appropriate to the expected noise level of the analog channel. Then it must be
transformed into an analog waveform using line coding, and modulated onto a carrier signal. The
latter two processes depend upon the actual nature of the transmission medium, whether it be
electrical, optical or electromagnetic.

Mathematically, the maximum digital bit rate for a given analog bandwidth and noise level is
determined by the Shannon-Hartley theorem. How closely this is approximated depends to a great
extent upon the choice of channel coding, which must introduce just enough redundancy to match
the noise level. Too little redundancy, and expensive retransmissions will reduce the useful bitrate.
Too much, and the error-correction overhead will reduce the bitrate left over for the signal. The
Shannon-Hartley limit is approached closely by Reed-Solomon codes used on optical media, and
even more closely by Turbo codes used in satellite communication.

In discrete time systems and digital signal processing, bandwidth is related to sampling rate
according to the Nyquist-Shannon sampling theorem.


3.1.7   Data signals.

When Modem is use to send binary data over ATL-Analog Line Transmission (ATL).
Modulation is the process of varying a carrier signal, typically a sinusoidal signal, in order to use
that signal to convey information. One of the three key characteristics of a signal are usually
modulated: its phase, frequency or amplitude. A device that performs modulation is known as a
modulator and a device that performs demodulation is known as a demodulator. A device that can
do both operations is a modem, a contraction of the two.

In digital modulation, the changes in the signal are chosen from a fixed list (the modulation
alphabet) each entry of which conveys a different possible piece of information (a symbol). The
alphabet is often conveniently represnted on a constellation diagram.

When a binary data is receive by a analog signal, it will be change to a from that can be understood
by the computer. This is called modulation and in otherwise called demodulation.

So device that is related and being used to change the data form is called MODEM.
Sending analog data over a digital line.
                                   send to a digital form. This procedure drives to a modulation to
Here we'll see a analog data will be
change the data in wave form to a digital or binary form using a modem as well to be manipulate by
devices such as computers. See below :




3.1. Dominance of digital signaling.

With the increasing use of computers the usage and need of digital signal processing has
increased. In order to use an analog signal on a computer it must be digitized with an analog to
digital converter (ADC). Sampling is usually carried out in two stages, discretization and
quantization. In the discretization stage, the space of signals is partioned into equivalence classes
and discretization is carried out by replacing the signal with representative signal of the
corresponding equivalence class. In the quantization stage the representative signal values are
approximated by values from a finite set.

In order to properly sample an analog signal the Nyquist-Shannon sampling theorem must be
satisfied. In short, the sampling frequency must be greater than twice the bandwidth of the signal
(provided it is filtered appropriately). A digital to analog converter (DAC) is used to convert the
digital signal back to analog. The use of a digital computer is a key ingredient into digital control
systems..

Accuracy of digital signaling.
Accuracy depends on the error in the conversion. If the ADC is not broken, this error has two
components: quantization error and (assuming the ADC is intended to be linear) non-linearity.
These errors are measured in a unit called the LSB, which is an abbreviation for least significant bit.
In the above example of an eight-bit ADC, an error of one LSB is 1/256 of the full signal range, or
about 0.4%.
Quantization error is due to the finite resolution of the ADC, and is an unavoidable imperfection in all
types of ADC. The magnitude of the quantization error at the sampling instant is between zero and
half of one LSB.

In the general case, the sampled signal is larger than one LSB, and the quantization error is not
correlated with the signal. Its RMS value is then 1/sqrt(12) LSB = 0.289 LSB. In the eight-bit ADC
example, this represents 0.113 % of the full signal range.

All ADCs suffer from non-linearity errors caused by their physical imperfections, causing their output
to deviate from a linear function (or some other function, in the case of a deliberately non-linear
ADC) of their input. These errors can sometimes be mitigated by calibration, or prevented by
testing.

Important parameters for linearity are integral non-linearity (INL) and differential non-linearity
(DNL).


3.2




Topic objectives:
3.2.1[Define the measurement,limitations & throughput of a bandwidth]

Bandwidth.

Bandwidth
bandwidth is the width, usually measured in hertz, of a frequency band f 2 − f1. It can also be used
to describe a signal, in which case the meaning is the width of the smallest frequency band within
which the signal can fit.

It is usually notated B, W, or BW. The fact that real baseband systems have both negative and
positive frequencies can lead to confusion about bandwidth, since they are sometimes referred to
only by the positive half, and one will occasionally see expressions such as B = 2W, where B is the
total bandwidth, and W is the positive bandwidth. For instance, this signal would require a lowpass
filter with cutoff frequency of at least W to stay intact.

The bandwidth of an electronic filter is the part of the filter's frequency response that lies within 3
dB compared to the center frequency of its peak.
3.2.1   Measurement, limitations & throughput of a bandwidth.

Limitation for device bandwidth.
Here is a list of connection bandwidths: the bandwidth of some computer devices employing
methods of data transport is listed by bit/s (in kilobit/s (kbit/s), megabit/s (Mbit/s), and gigabit/s
(Gbit/s) as appropriate) and also MB/s or megabytes per second. Listed in order from lowest
bandwidth to highest.

Whether to use bit/s or byte/s is a matter of debate. (See Talk) The most commonly cited
measurement is bolded. In general, parallel interfaces are quoted in byte/s, serial in bit/s.

Many of these figures are theoretical, and various real-world considerations may keep the actual
effective throughput much lower. See Measuring data throughput. The actual throughput achievable
on Ethernet networks, especially when heavily loaded, is the subject of hot debate.




        CONNECTION                        BITS          BYTES
        Modems

        (note: serial 1 start bit, 8 data bits, 1 stop bit)
        Modem 110 baud                    110 bit/s     13.75 B/s
        Modem 300 baud                    300 bit/s     30 B/s
        Modem 1200                        1.2 kbit/s    120 B/s
        Modem 2400                        2.4 kbit/s    240 B/s
        Modem 9600                        9.6 kbit/s    960 B/s
        Modem 14.4k                       14.4 kbit/s   1.44 kB/s
        Modem 28.8k                       28.8 kbit/s   2.88 kB/s
        Modem 36.6k                       36.6 kbit/s   3.36 kB/s
        Modem 56k*                        53.3 kbit/s   5.33 kB/s



        ISDN
        64k ISDN                          64.0 kbit/s 8 kB/s
                                          128.0
        128k dual-channel ISDN                        16 kB/s
                                          kbit/s
Computer interfaces
Serial RS-232 commonly      9.6 kbit/s    960 B/s
                            230.4
Serial RS-232 max                         23.0 kB/s
                            kbit/s
                            1536
USB Low Speed                             192 kB/s
                            kbit/s
Parallel (Centronics)       8.0 Mbit/s    1.0 MB/s
                            10.0
Serial RS-422 max                         1.25 MB/s
                            Mbit/s
                            12.0
USB Full Speed                            1.5 MB/s
                            Mbit/s
SCSI 1                      12.0 Mbit/s   1.5 MB/s
typical Hard disk average
                            80 Mbit/s     10 MB/s[1]
transfer rate
Fast SCSI 2                 80 Mbit/s     10 MB/s
Fast Wide SCSI 2            160 Mbit/s    20 MB/s
Ultra DMA ATA 33            264 Mbit/s    33 MB/s
Ultra Wide SCSI 40          320 Mbit/s    40 MB/s
FireWire (IEEE 1394) 50     400 Mbit/s    50 MB/s
USB Hi-Speed                480 Mbit/s    60 MB/s
Ultra DMA ATA 66            528 Mbit/s    66 MB/s
Ultra2 SCSI 80              640 Mbit/s    80 MB/s
FireWire (IEEE 1394b)       800 Mbit/s    100 MB/s
Ultra DMA ATA 100           800 Mbit/s    100 MB/s
                            1064
Ultra DMA ATA 133                         133 MB/s
                            Mbit/s
                            1064
PCI 32/33                                 133 MB/s
                            Mbit/s
                            1200
Serial ATA                                150 MB/s
                            Mbit/s
                            1280
Ultra 160 SCSI                            160 MB/s
                            Mbit/s
                            2128
AGP 1x                                    266 MB/s
                            Mbit/s
                            2400
Serial ATA (SATA300)                      300 MB/s
                            Mbit/s
                            2560
Ultra 320 SCSI                            320 MB/s
                            Mbit/s
PCI Express (x1 link)       4000          500 MB/s
                          Mbit/s
                          4256
AGP 2x                                532 MB/s
                          Mbit/s
                          4264
PCI 64/66                             533 MB/s
                          Mbit/s
                          5120
Ultra640 Scsi                         640 MB/s
                          Mbit/s
                          8512
AGP 4x                                1064 MB/s
                          Mbit/s
                          8528
PCI-X 133                             1066 MB/s
                          Mbit/s
                          10.00
InfiniBand                            1.25 GB/s
                          Gbit/s
                          16.00
PCI Express (x4 link)                 2 GB/s
                          Gbit/s
                          18.064
PCI-X DDR                             2.133 GB/s
                          Gbit/s
                          18.024
AGP 8x                                2.128 GB/s
                          Gbit/s
HyperTransport (800MHz,
                          51.2 Gbit/s 6.4 GB/s
16-pair)
PCI Express (x16 link)    64 Gbit/s   8 GB/s



Wireless
IrDA-Control              72 kbit/s   9 kB/s
                          1000
Bluetooth 1.1                         125 kB/s
                          kbit/s
                          2000
802.11 legacy 0.125                   250 kB/s
                          kbit/s
Bluetooth 2               3 Mbit/s    375 kB/s
802.11b DSSS 0.125        11 Mbit/s   1.375 MB/s
802.11b+ non-standard     44.0
                                      5.5 MB/s
DSSS 0.125                Mbit/s
                          54.00
802.11a 0.75                          6.75 MB/s
                          Mbit/s
                          54.00
802.11g DSSS 0.125                    6.75 MB/s
                          Mbit/s
Mobile telephone interfaces
                              2400 to
GSM CSD                       14400         300 to 1800 B/s
                              bit/s
HSCSD upstream                14.4 kbit/s   1800 B/s
HSCSD downstream              43.2 kbit/s   5.4 kB/s
GPRS upstream                 28.8 kbit/s   3.6 kB/s
GPRS downstream               57.6 kbit/s   7.2 kB/s
                              1920
UMTS downstream                             240 kB/s
                              kbit/s




Wide area network
DS0                           64 kbit/s 8 kB/s
                              64kbit/s to
Satellite Internet upstream               8 kB/s to 128 kB/s
                              1Mbit/s
                              128kbit/s
Satellite Internet downstream to          16kB/s to 2 MB/s
                              16Mbit/s
                              8 kbit/s to
Frame Relay                               1 kB/s to 5.625 MB/s
                              45 Mbit/s
                              2.3000
G.SHDSL                                   0.2875 MB/s
                              Mbit/s
                              64 kbit/s
SDSL                          to 4.608 8 kB/s to 0.576 MB/s
                              Mbit/s
                              64 kbit/s
ADSL upstream                 to 1024     8 kB/s to 128 kB/s
                              kbit/s
                              256 kbit/s
ADSL downstream                           32 kB/s to 1 MB/s
                              to 8 Mbit/s
                              1.540
DS1/T1                                    192.5 kB/s
                              Mbit/s
                              2.048
E1                                        256 kB/s
                              Mbit/s
                            8.448
E2                                     1.056 MB/s
                            Mbit/s
                            34.368
E3                                     4.296 MB/s
                            Mbit/s
                            44.7400
DS3/T3 ('45 Meg')                      5.5925 MB/s
                            Mbit/s
                            51.84
OC1                                    6.48 MB/s
                            Mbit/s
VDSL (upstream)             12 Mbit/s 1.5 MB/s
VDSL (downstream)           52 Mbit/s 6.5 MB/s
                            155.52
OC3                                    19.44 MB/s
                            Mbit/s
                            622.08
OC12                                   77.76 MB/s
                            Mbit/s
                            2.448
OC48                                   306 MB/s
                            Gbit/s
                            800 or
Fibre Channel               1600       100 or 200 MB/s
                            Mbit/s
                            10.24
10 Gigabit Ethernet                    1.28 GB/s
                            Gbit/s
                            10.000
OC192                                  1.250 GB/s
                            Gbit/s
                            13.21000
OC255                                  1.65125 GB/s
                            Gbit/s
                            40 Gbit/s
                            (something
OC768                                  5 GB/s
                            wrong
                            here!)



Local area network
                            230.4
LocalTalk                                28.8 kB/s
                            kbit/s
ARCNET (Standard)           2.5 Mbit/s   0.3125 MB/s
                            4.16
Token Ring (Original)                    0.52 MB/s
                            Mbit/s
Ethernet (10base-X)         10 Mbit/s    1.25 MB/s
Token Ring (Later)          16 Mbit/s    2.0 MB/s
Fast Ethernet (100base-X)   100 Mbit/s   12.5 MB/s
      FDDI                        100 Mbit/s 12.5 MB/s
      Gigabit Ethernet (1000base-
                                  1 Gbit/s   125 MB/s
      X)



      Memory Interconnect Buses / RAM
                               4264
      PC66 SDRAM                                 533 MB/s
                               Mbit/s
                               6400
      PC100 SDRAM                                800 MB/s
                               Mbit/s
                               8528
      PC133 SDRAM                                1066 MB/s
                               Mbit/s
      PC1600 DDR-SDRAM         12.8 Gbit/s       1.6 GB/s
      PC2100 DDR-SDRAM         16.8 Gbit/s       2.1 GB/s
      PC2700 DDR-SDRAM         21.6 Gbit/s       2.7 GB/s
      PC3200 DDR-SDRAM         25.6 Gbit/s       3.2 GB/s
      PC800 RDRAM (single-
                               12.8 Gbit/s       1.6 GB/s
      channel)
      PC800 RDRAM (dual-
                               25.6 Gbit/s       3.2 GB/s
      channel)
      PC1066 RDRAM (single-
                               16.8 Gbit/s       2.1 GB/s
      channel)
      PC1066 RDRAM (dual-
                               33.6 Gbit/s       4.2 GB/s
      channel)
      PC1200 RDRAM (single-
                               19.2 Gbit/s       2.4 GB/s
      channel)
      PC1200 RDRAM (dual-
                               38.4 Gbit/s       4.8 GB/s
      channel)

Notes

       56K modem capacity of 57.6 kbit/s was limited to 53.3 kbit/s over telephone lines; speed in
        practice typically 45 kbit/s.

       Actual Frame relay connections will vary in throughput from 8 kbit/s to 45 Mbit/s depending
        on configuration. Most commonly below 2 Mbit/s.

       ADSL connections will vary in throughput from 64 kbit/s to several Mbit/s depending on
        configuration. Most commonly below 2 Mbit/s. Some ADSL & SDSL connections have a
        higher bandwidth than T1 but their bandwidth is not guarranteed, and will drop when the
        system gets overloaded where as the T1 type connections are guarranteed & have no
           contention ratios.

          Satellite internet may have a high bandwidth but also has a high latency due to the distance
           between the modem, satellite & hub. One-way satellite connections exist where all the
           downstream traffic is handled by satellite and the upstream traffic by land-based connections
           such as 56K modems & ISDN.


3.3



Topic objectives:
3.3.1[Differentiate between noise and attenuation]
3.3.2[Identify how to handle attenuation problem]
3.3.3[Define Delay Distortion]
3.3.4[Identify the techniques in handling delay distortion]
3.3.5[Explain the four categories of Noise]



               Noise & Attenuation.


               In this chapter you will see some knowledge in noise and attenuation in
               computer networkings.

               Noise can be considered data without meaning; that is, data that is not being
               used to transmit a signal, but is simply produced as an unwanted by-product of
               other activities.


 3.3.1    Noise and attenuation.

Noise is fluctuations in and the addition of external factors to the stream of target information
(signal) being received at a detector. In communications, it may be deliberate as for instance
jamming of a radio or TV signal, but in most cases it is assumed to be merely undesired
interference with intended operations. Natural and deliberate noise sources can provide both or
either of random interference or patterned interference. Only the latter can be cancelled effectively
in analog systems; however, digital systems are usually constructed in such a way that their
quantized signals can be reconstructed perfectly, as long as the noise level remains below a
defined maximum, which varies from application to application.

More specifically, in physics, the term noise has the following meanings:

      1. An undesired disturbance within the frequency band of interest; the summation of unwanted
         or disturbing energy introduced into a communications system from man-made and natural
         sources.
      2. A disturbance that affects a signal and that may distort the information carried by the signal.
   3. Random variations of one or more characteristics of any entity such as voltage, current, or
      data.
   4. A random signal of known statistical properties of amplitude, distribution, and spectral
      density.
   5. Loosely, any disturbance tending to interfere with the normal operation of a device or system.

Noise and what can be done about it has long been studied. It was Shannon who established
information theory and in so doing clarified the essential nature of noise and the limits it places on
operation of our (or anyone's) equipment. Shannon's work was a breakthrough.

In some cases a little noise may be considered advantageous, allowing a dithered representation of
signals below the minimum strength, or between two quantization levels. This is especially true for
signals intended for human appreciation, since the brain seems to expect signals to contain a
degree of noise.


Attenuation
Attenuation is a measure of how much a signal weakens as it travels through a medium.

Attenuation is the decrease in intensity of a signal, beam, or wave as a result of absorption of
energy and of scattering out of the path to the detector, but not including the reduction due to
geometric spreading.

attenuation constant has the following meanings:

1. The real part of the propagation constant in any electromagnetic propagation medium.

The attenuation constant is usually expressed as a numerical value per unit length and may be
calculated or experimentally determined for each medium.

2. For a particular propagation mode in an optical fiber, the real part of the axial propagation
constant.


3.3.2 Identifying hoe to handle attenuation problem.


Attenuation is a measure of how much a signal weakens as it travels through a medium. This book
doesn’t discuss attenuation in formal terms, but it does address the impact of attenuation on
performance.

Attenuation is a contributing factor to why cable designs must specify limits in the lengths of
cable runs. When signal strength falls below certain limits, the electronic equipment that receives
the signal can experience difficulty isolating the original signal from the noise present in all
electronic transmissions. The effect is exactly like trying to tune in distant radio signals. Even if you
can lock on to the signal on your radio, the sound generally still contains more noise than the sound
for a local radio station.




3.3.3 Delay Distortion.

Distortion has the following meanings:

1.In a system or device, any departure of the output signal waveform from that which should result
from the input signal waveform's being operated on by the system's specified, i.e, ideal, transfer
function.

Distortion may result from many mechanisms. Examples include nonlinearities in the transfer
function of an active device, such as a vacuum tube, transistor, or operational amplifier. Distortion
may also be caused by a passive component such as a coaxial cable or optical fiber, or by
inhomogeneities, reflections, etc., in the propagation path.



2. In an optical fiber, the transit time required for optical power, traveling at a given mode's group
velocity, to travel a given distance.

Note: For optical fiber dispersion measurement purposes, the quantity of interest is group delay per
unit length, which is the reciprocal of the group velocity of a particular mode. The measured group
delay of a signal through an optical fiber exhibits a wavelength dependence due to the various
dispersion mechanisms present in the fiber.

Source: from Federal Standard 1037C

It is often desirable that group delay be constant across all frequencies; otherwise there is temporal
smearing of the signal. Because group delay is -d θ/d ω, as defined in (1), it therefore follows that a
constant group delay can be achieved if the transfer function of the device or medium has a linear
phase response (i.e., θ = θ0 + Kω where K is a constant).

Thresholds of audibility according to Blauert and Laws:

Frequency Threshold
500 Hz        3.2 ms
1 kHz         2 ms
2 kHz         1 ms
4 kHz         1.5 ms
8 kHz         2 ms
3.3.4   Techniques in handling delay distortion.

In this context, distortion refers to a clipping or compression of the wave form of an input. In
fuzzboxes and solid state distortions, the signal is boosted, and the tops of the waveform clipped
off.

In vacuum tube distortion, or tube modelling distortion, the top of the wave form is compressed, thus
giving a smoother distorted signal, that retains more of the data in the original waveform.

In telecommunications, either:

             1. In radar, the electronic delay of the start of the time base used to select a particular
                segment of the total.
             2. The amount of time by which an event is retarded.

So those things should be get in intention while detecting a delay distortion.


3.3.5   Categories of Noise.

Thermal noise
Johnson-Nyquist noise (sometimes thermal noise, Johnson noise or Nyquist noise) is the
noise generated by the equilibrium fluctuations of the electric current inside an electrical conductor,
which happens without any applied voltage, due to the random thermal motion of the charge
carriers (the electrons).

It is to be distinguished from shot noise, which consists of additional current fluctuations that occur
when a voltage is applied and a macroscopic current starts to flow. For the general case, the above
definition applies to charge carriers in any type of conducting medium (e.g. ions in an electrolyte).

The thermal noise power, P, in watts, is given by P = 4kBTΔf, where kB is Boltzmann's constant in
joules per kelvin, T is the conductor temperature in kelvins, and Δf is the bandwidth in hertz.
Thermal noise power, per hertz, is equal throughout the frequency spectrum, depending only on kB
and T. It is white noise, in other words.

In communications, noise power is often used. Thermal noise at room temperature can be
estimated in decibels as:

         P = − 174 + 10log(Δf)
Where P is measured in dBm (0 dBm = 1 mW) and Δf is bandwidth in Hz. For example:


Bandwidth      Power


1 Hz         -174 dBm


10 Hz        -164 dBm


1000 Hz      -144 dBm


5 kHz        -137 dBm


1 MHz        -114 dBm


6 MHz        -106 dBm


Intermodulation Noise/Interference
Intermodulation or intermod is the result of two radio signals of different frequencies being mixed
together, forming additional signals at frequencies that are not at harmonic frequencies (integer
multiples) of either. The largest intermodulation products appear at f1 + f2 or f1 − f2 (second-order
intermodulation), and less so at 2f1 − f2 or 2f2 − f1 (third order intermodulation).

The cause for intermodulation is the existence of non-linear characteristics of the according
equipment. The theoretical outcome of these nonlinearities can be calculated by conducting a
Volterra series of the characteristic, while the usual approximation of those nonlinearities is obtained
by conducting a Taylor series. According to the summands in those series, the above numbering of
orders is counted.

Intermodulation is rarely desirable in radio, as it essentially creates spurious emissions, which can
create minor to severe interference to other operations on the resulting frequency. It may be
desirable in audio if the intent is to create specific sound effects.

Intermodulation noise: Nonlinear distortion characterized by the appearance, in the output of a
device, of frequencies that are linear combinations of the fundamental frequencies and all
harmonics present in the input signals.

Note: Harmonic components themselves are not usually considered to characterize intermodulation
distortion. When the harmonics are included as part of the distortion, a statement to that effect
should be made.



Crosstalk
crosstalk (XT) has the following meanings:

1. Undesired capacitive, inductive, or conductive coupling from one circuit, part of a circuit, or
channel, to another.

2. Any phenomenon by which a signal transmitted on one circuit or channel of a transmission
system creates an undesired effect in another circuit or channel.

Note: In telephony, crosstalk is usually distinguishable as speech or signaling tones.


3.4



Topic objectives:
3.4.1[List 3 media commonly used for data transmission]
3.4.2[Define how transmission & reception are achieved in an unguided transmission media]
3.4.3[Identify the application & transmission characteristic of Terrestrial Microwave, Satelite]
3.4.4[Identify the applications of Infrared technology]

Transmission Media.

For the Networking Essentials exam, you need to know how to make decisions about network
transmission media based on some of the factors described in previous sections of this chapter.
The following sections discuss three types of network cabling media, as follows:

         Coaxial cable
         Twisted-pair cable
         Fiber-optic cable

Later in this chapter, you learn about some of the wireless communication forms.


 3.4.1 Data Transmission media

Twisted-pair cable has become the dominant cable type for all new network designs that employ
copper cable. Among the several reasons for the popularity of twisted-pair cable, the most
significant is its low cost. Twisted-pair cable is inexpensive to install and offers the lowest cost per
foot of any cable type.

A basic twisted-pair cable consists of two strands of copper wire twisted together (see below).




This twisting reduces the sensitivity of the cable to EMI and also reduces the tendency of the cable
to radiate radio frequency noise that interferes with nearby cables and electronic components. This
is because the radiated signals from the twisted wires tend to cancel each other out. (Antennas,
which are purposely designed to radiate radio frequency signals, consist of parallel, not twisted,
wires.)

Twisting also controls the tendency of the wires in the pair to cause EMI in each other. Whenever
two wires are in close proximity, the signals in each wire tend to produce noise, called crosstalk, in
the other. Twisting the wires in the pair reduces crosstalk in much the same way that twisting
reduces the tendency of the wires to radiate EMI.

Two types of twisted-pair cable are used in LANs: shielded and unshielded.



Shielded twisted-pair(STP)
Shielded twisted-pair cabling consists of one or more twisted pairs of cables enclosed in a foil wrap
and woven copper shielding. see below shows IBM Type 1 cabling:




the first cable type used with IBM Token Ring. Early LAN designers used shielded twisted-pair cable
because the shield further reduces the tendency of the cable to radiate EMI and thus reduces the
cable’s sensitivity to outside interference.

Coaxial and STP cables use shields for the same purpose. The shield is connected to the ground
portion of the electronic device to which the cable is connected. A ground is a portion of the device
that serves as an electrical reference point, and usually, it literally is connected to a metal stake
driven into the ground. A properly grounded shield prevents signals from getting into or out of the
cable.

As shown in above FIGURE, IBM Type 1 cable includes two twisted pairs of wire within a single
shield. Various types of STP cable exist, some that shield each pair individually and others that
shield several pairs. The engineers who design a network’s cabling system choose the exact
configuration. IBM designates several twisted-pair cable types to use with their Token Ring network
design, and each cable type is appropriate for a given kind of installation. A completely different
type of STP is the standard cable for Apple’s AppleTalk network.

Because so many different types of STP cable exist, stating precise characteristics is difficult. The
following sections, however, offer some general guidelines.


Unshielded Twisted-Pair (UTP) Cable.
Unshielded twisted-pair cable doesn’t incorporate a braided shield into its structure. However, the
characteristics of UTP are similar in many ways to STP, differing primarily in attenuation and EMI.
As shown below :




, several twisted-pairs can be bundled together in a single cable. These pairs typically are color
coded to distinguish them.

Telephone systems commonly use UTP cabling. Network engineers can sometimes use existing
UTP telephone cabling (if it is new enough and of a high enough quality to support network
communications) for network cabling.

UTP cable is a latecomer to high-performance LANs because engineers only recently solved the
problems of managing radiated noise and susceptibility to EMI. Now, however, a clear trend toward
UTP is in operation, and all new copper-based cabling schemes are based on UTP.

UTP cable is available in the following five grades, or categories:
      Categories 1 and 2. These voice-grade cables are suitable only for voice and for low data
       rates (below 4 Mbps). Cate-gory 1 was once the standard voice-grade cable for telephone
       systems. The growing need for data-ready cabling systems, however, has caused Categories
       1 and 2 cable to be supplanted by Category 3 for new installations.
      Category 3. As the lowest data-grade cable, this type of cable generally is suited for data
       rates up to 10 Mbps. Some innovative schemes, however, enable the cable to support data
       rates up to 100 Mbps. Category 3, which uses four twisted-pairs with three twists per foot, is
       now the standard cable used for most telephone installations.
      Category 4. This data-grade cable, which consists of four twisted-pairs, is suitable for data
       rates up to 16 Mbps.
      Category 5. This data-grade cable, which also consists of four twisted-pairs, is suitable for
       data rates up to 100 Mbps. Most new cabling systems for 100 Mbps data rates are designed
       around Category 5 cable.




In a UTP cabling system, the cable is only one component of the system. All connecting devices
also are graded, and the overall cabling system supports only the data rates permitted by the
lowest-grade component in the system. In other words, if you require a Category 5 cabling system,
all connectors and connecting devices must be designed for Category 5 operation.

Category 5 cable also requires more stringent installation procedures than the lower cable
categories. Installers of Cate-gory 5 cable require special training and skills to understand these
more rigorous requirements.

UTP cable offers an excellent balance of cost and performance characteristics, as discussed in the
following sections.


Coaxial cables
Coaxial cables were the first cable types used in LANs. As shown below:
coaxial cable gets its name because two conductors share a common axis; the cable is most
frequently referred to as a coax.

The components of a coaxial cable are as follows:

      A center conductor, although usually solid copper wire, sometimes is made of stranded wire.
      An outer conductor forms a tube surrounding the center conductor. This conductor can
       consist of braided wires, metallic foil, or both. The outer conductor, frequently called the
       shield, serves as a ground and also protects the inner conductor from EMI.
      An insulation layer keeps the outer conductor spaced evenly from the inner conductor.
      A plastic encasement (jacket) protects the cable from damage.




Thinnet is a light and flexible cabling medium that is inexpensive and easy to install.




Above illustrates some Thinnet classifications. Note that Thinnet falls under the RG-58 family, which
has a 50-Ohm impedance. Thinnet is approximately .25 inches (6 mm) in thickness.



Thicknet—big surprise—is thicker than Thinnet. Thicknet coaxial cable is approximately 0.5 inches
(13 mm) in diameter. Because it is thicker and does not bend as readily as Thinnet, Thicknet cable
is harder to work with. A thicker center core, however, means that Thicknet can carry more signals a
longer distance than Thinnet. Thicknet can transmit a signal approximately 500 meters (1650 feet).

Thicknet cable is sometimes called Standard Ethernet (although other cabling types described in
this chapter are used for Ethernet also). Thicknet can be used to connect two or more small Thinnet
LANs into a larger network.

Because of its greater size, Thicknet is also more expensive than Thinnet. Thicknet can be installed
safely outside, running from building to building.
Fiber-Optic Cable.
In almost every way, fiber-optic cable is the ideal cable for data transmission. Not only does this
type of cable accommodate extremely high bandwidths, but it also presents no problems with EMI
and supports durable cables and cable runs as long as several kilometers. The two disadvantages
of fiber-optic, however, are cost and installation difficulty.

The center conductor of a fiber-optic cable is a fiber that consists of highly refined glass or plastic
designed to transmit light signals with little loss. A glass core supports a longer cabling distance, but
a plastic core is typically easier to work with. The fiber is coated with a cladding that reflects signals
back into the fiber to reduce signal loss. A plastic sheath protects the fiber. See below:




A fiber-optic network cable consists of two strands separately enclosed in plastic sheaths—one
strand sends and the other receives. Two types of cable configurations are available: loose and
tight configurations. Loose configurations incorporate a space between the fiber sheath and the
outer plastic encasement; this space is filled with a gel or other material. Tight configurations
contain strength wires between the conductor and the outer plastic encasement. In both cases, the
plastic encasement must supply the strength of the cable, while the gel layer or strength wires
protect the delicate fiber from mechanical damage.

Optical fiber cables don’t transmit electrical signals. Instead, the data signals must be converted into
light signals. Light sources include lasers and light-emitting diodes (LEDs). LEDs are inexpensive
but produce a fairly poor quality of light suitable for less-stringent applications.




A laser is a light source that produces an especially pure light that is monochromatic (one color) and
coherent (all waves are parallel). The most commonly used source of laser light in LAN devices is
called an injection laser diode (ILD). The purity of laser light makes lasers ideally suited to data
transmissions because they can work with long distances and high bandwidths. Lasers, however,
are expensive light sources used only when their special characteristics are required.

The end of the cable that receives the light signal must convert the signal back to an electrical form.
Several types of solid-state components can perform this service.

One of the significant difficulties of installing fiber-optic cable arises when two cables must be
joined. The small cores of the two cables (some are as small as 8.3 microns) must be lined up with
extreme precision to prevent excessive signal loss.



3.4.2 How transmission are achieved in an unguided transmission media.


UTP
The data rates possible with UTP have pushed up from 1 Mbps, past 4 and 16 Mbps, to the point
where 100 Mbps data rates are now common.

STP
STP cable has a theoretical capacity of 500 Mbps, although few implementations exceed 155 Mbps
with 100-meter cable runs. The most common data rate for STP cable is 16 Mbps, which is the top
data rate for Token Ring networks.

Coaxial
LANs that employ coaxial cable typically have a bandwidth between 2.5 Mbps (ARCnet) and 10
Mbps (Ethernet). Thicker coaxial cables offer higher bandwidth, and the potential bandwidth of
coaxial is much higher than 10 Mbps. Current LAN technologies, however, don’t take advantage of
this potential.


Fiber-Optic
Fiber-optic cable can support high data rates (as high as 200,000 Mbps) even with long cable runs.
Although UTP cable runs are limited to less than 100 meters with 100 Mbps data rates, fiber-optic
cables can transmit 100 Mbps signals for several kilometers.
3.4.3 Terrestrial Microwave Satelite (application & transmission characteristic).


Microwaves are electromagnetic waves with wavelengths longer than those of infrared light, but
shorter than those radio waves.

Microwaves, also known as super-high frequency (SHF) signals, have wavelengths approximately
in the range of 30 cm (frequency = 1 GHz) to 1 mm (300 GHz). However, the boundaries between
far infrared light, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used
variously between different fields of study. The existence of electromagnetic waves, of which
microwaves are part of the higher frequency spectrum, was predicted by James Clerk Maxwell in
1864 from his famous Maxwell's equations. In 1888, Heinrich Hertz was the first to demonstrate the
existence of electromagnetic waves by building apparatus to produce radio waves.

Note: above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great
that the atmosphere is effectively opaque to higher frequencies of electromagnetic radiation, until
the atmosphere becomes transparent again in the so-called infrared and optical window frequency
ranges.

Microwaves can be generated by a variety of means, generally divided into two categories: solid
state devices and vacuum-tube based devices. Solid state microwave devices are based on
semiconductors such as silicon or gallium arsenide, and include field-effect transistors (FET's),
bipolar junction transistors (BJT's), Gunn diodes, and IMPATT diodes. Specialized versions of
standard transistors have been developed for higher speed which are commonly used in microwave
applications. Microwave variants of BJT's include the heterojunction bipolar transistor (HBT), and
microwave variants of FET's include the MESFET, the HEMT (also known as HFET), and LDMOS
transistor. Vacuum tube based devices operate on the ballistic motion of electrons in a vacuum
under the influence of controlling electric or magnetic fields, and include the magnetron, klystron,
travelling wave tube (TWT), and gyrotron.
Terrestrial microwave
Terrestrial microwave communication employs Earth-based transmitters and receivers. The
frequencies used are in the low-gigahertz range, which limits all communications to line-of-sight.
You probably have seen terrestrial microwave equipment in the form of telephone relay towers,
which are placed every few miles to relay telephone signals crosscountry.

Microwave transmissions typically use a parabolic antenna that produces a narrow, highly
directional signal. A similar antenna at the receiving site is sensitive to signals only within a narrow
focus. Because the transmitter and receiver are highly focused, they must be adjusted carefully so
that the transmitted signal is aligned with the receiver.

A microwave link frequently is used to transmit signals in instances in which it would be impractical
to run cables. If you need to connect two networks separated by a public road, for example, you
might find that regulations restrict you from running cables above or below the road. In such a case,
a microwave link is an ideal solution.

Some LANs operate at microwave frequencies at low power and use nondirectional transmitters
and receivers. Network hubs can be placed strategically throughout an organization, and
workstations can be mobile or fixed. This approach is one way to enable mobile workstations in an
office setting.

In many cases, terrestrial microwave uses licensed frequencies. A license must be obtained from
the FCC, and equipment must be installed and maintained by licensed technicians.

Terrestrial microwave systems operate in the low-gigahertz range, typically at 4-6 GHz and 21-23
GHz, and costs are highly variable depending on requirements. Long-distance microwave systems
can be quite expensive but might be less costly than alternatives. (A leased telephone circuit, for
example, represents a costly monthly expense.) When line-of-sight transmission is possible, a
microwave link is a one-time expense that can offer greater bandwidth than a leased circuit.

Costs are on the way down for low-power microwave systems for the office. Although these
systems don’t compete directly in cost with cabled networks, when equipment frequently must be
moved, microwave can be a cost-effective technology. Capacity can be extremely high, but most
data communication systems operate at data rates between 1 and 10 Mbps. Attenuation
characteristics are determined by transmitter power, frequency, and antenna size. Properly
designed systems are not affected by attenuation under normal operational conditions—rain and
fog, however, can cause attenuation of higher frequencies.

Microwave systems are highly susceptible to atmospheric interference and also can be vulnerable
to electronic eavesdropping. For this reason, signals transmitted through microwave are frequently
encrypted.




Satelite Microwave
Satellite microwave systems relay transmissions through communication satellites that operate in
geosynchronous orbits 22,300 miles above the earth. Satellites orbiting at this distance remain
located above a fixed point on earth.

Earth stations use parabolic antennas (satellite dishes) to communicate with satellites. These
satellites then can retransmit signals in broad or narrow beams, depending on the locations set to
receive the signals. When the destination is on the opposite side of the earth, for example, the first
satellite cannot transmit directly to the receiver and thus must relay the signal through another
satellite.

Because no cables are required, satellite microwave communication is possible with most remote
sites and with mobile devices, which enables transmission with ships at sea and motor vehicles.

The distances involved in satellite communication result in an interesting phenomenon: Because all
signals must travel 22,300 miles to the satellite and 22,300 miles when returning to a re-ceiver, the
time required to transmit a signal is independent of distance. It takes as long to transmit a signal to
a receiver in the same state as it does to a receiver a third of the way around the world. The time
required for a signal to arrive at its destination is called propagation delay. The delays encountered
with satellite transmissions range from 0.5 to 5 seconds.

Unfortunately, satellite communication is extremely expensive. Building and launching a satellite
can cost easily in excess of a billion dollars. In most cases, organizations share these costs or
purchase services from a commercial provider. AT&T, Hughes Network Services, and Scientific-
Atlanta are among the firms that sell satellite-based communication services.

Satellite links operate in the low-gigahertz range, typically at 11-14 GHz. Costs are extremely high
and usually are distributed across many users by selling communication services. Bandwidth is
related to cost, and firms can purchase almost any required bandwidth. Typical data rates are 1-10
Mbps. Attenuation characteristics depend on frequency, power, and atmospheric conditions.
Properly designed systems also take attenuation into account—rain and atmospheric conditions
might attenuate higher frequencies. Microwave signals also are sensitive to EMI and electronic
eavesdropping, so signals transmitted through microwave frequently are encrypted.

Earth stations can be installed by numerous commercial pro viders. Transmitters operate on
licensed frequencies and require an FCC license.


Microwave frequency bands

The microwave spectrum is usually defined as electromagnetic energy ranging from approximately
1 GHz to 1000 GHz in frequency, but older usage includes lower frequencies. Most common
applications are within the 1 to 40 GHz range. Microwave Frequency Bands are defined in the table
below:
                                        Microwave frequency bands
                                       Designation Frequency range
                                       L band     1 to 2 GHz
                                       S band     2 to 4 GHz
                                       C band     4 to 8 GHz
                                       X band     8 to 12 GHz
                                       Ku band    12 to 18 GHz
                                       K band     18 to 26 GHz
                                       Ka band    26 to 40 GHz
                                       Q band     30 to 50 GHz
                                       U band     40 to 60 GHz
                                       V band     50 to 75 GHz
                                       E band     60 to 90 GHz
                                       W band     75 to 110 GHz
                                       F band     90 to 140 GHz
                                       D band     110 to 170 GHz

The above table reflects Radio Society of Great Britain (RSGB) usage. The term P band is
sometimes used for UHF frequencies below L-band.


 3.4.4   Applications of Infrared Technology.

Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but
shorter than microwave radiation. The name means "below red" (from the Latin infra, "below"), red
being the color of visible light of longest wavelength. Infrared radiation spans three orders of
magnitude and has wavelengths between 700 nm and 1 mm.

Different regions in the infrared

IR is often subdivided into:

         near infrared NIR, IR-A DIN, 0.7–1.4 µm in wavelength, defined by the water absorption,
          and commonly used in fiber optic telecommunication because of low attenuation losses in
          the SiO2 glass (silica) medium.
         short wavelength IR SWIR, IR-B DIN, 1.4–3 µm, water absorption increases significantly at
          1450 nm
         mid wavelength IR MWIR, IR-C DIN, also intermediate-IR (IIR), 3–8 µm
         long wavelength IR LWIR, IR-C DIN, 8–15 µm)
      far infrared FIR, 15–1000 µm

However, these terms are not precise, and are used differently in various studies i.e. near (0.7–
5 µm) / mid (5–30 µm) / long (30–1000 µm). Especially at the telecom-wavelengths the spectrum is
further subdivided into individual bands, due to limitations of detectors, amplifiers and sources.
Infrared radiation is often linked to heat, since objects at room temperature or above will emit
radiation mostly concentrated in the mid-infrared band (see black body).

Plot of atmospheric transmittance in the infrared region.

The common nomenclature is justified by the different human response to this radiation (near
infrared = the red you just cannot see, far IR = thermal radiation), other definitions follow different
physical mechanisms (emission peaks, vs. bands, water absorption) and the newest follow
technical reasons (The common silicon detectors are sensitive to about 1050 nm, while InGaAs
sensitivity starts around 950 nm and ends between 1700 and 2200 nm, depending on the specific
configuration). Unfortunately the international standards for these specifications are not currently
available.

Telecommunication bands in the infrared

Optical telecommunication in the near infrared is technically often separated to different frequency
bands because of availability of light sources, transmitting /absorbing materials (fibers) and
detectors.

      O-band 1260–1360 nm
      E-band 1360–1460 nm
      S-band 1460–1530 nm
      C-band 1530–1565 nm
      L-band 1565–1625 nm
      U-band 1625–1675 nm


Application Of Infrared Technology.

Night Vision

Infrared is used in night-vision equipment, when there is insufficient visible light to see an object.
The radiation is detected and turned into an image on a screen, hotter objects showing up brighter,
enabling the police and military to acquire thermally significant targets, such as human beings and
automobiles.

Smoke is more transparent to infrared than to visible light, so fire fighters use infrared imaging
equipment when working in smoke-filled areas because it does not interfere with other devices in
adjoining rooms - this is especially important in areas of high population density (IR does not
penetrate walls).

Other Imaging

In infrared photography, infrared filters are used to capture only the infrared spectrum. Digital
cameras often use infrared blockers. Cheaper digital cameras and some camera phones which do
not have appropriate filters can "see" infrared, appearing as a bright white colour (try pointing a TV
remote at your digital camera). This is especially pronounced when taking pictures of subjects near
bright areas (such as near a lamp), where the resulting infrared interference can wash out the
image.

Thermography

Infrared radiation can be used to remotely determine the temperature of objects (if the emissivity is
known). This is termed thermography, or in the case of very hot objects in the NIR or visible it is
termed pyrometry. Thermography (thermal imaging) is mainly used in military and industrial
applications but the technology is reaching the public market in the form of infrared cameras on
cars due to the massively reduced production costs

Heating

Infrared radiation is used in Infrared saunas to heat the sauna's occupants and to remove ice from
the wings of aircraft (de-icing).

Communications

IR data transmission is also employed in short-range communication among computer peripherals
and personal digital assistants. These devices usually conform to standards published by IrDA, the
Infrared Data Association. Remote controls and IrDA devices use infrared light-emitting diodes
(LEDs) to emit infrared radiation which is focused by a plastic lens into a narrow beam. The beam
is modulated, i.e. switched on and off, to encode the data. The receiver uses a silicon photodiode
to convert the infrared radiation to an electric current. It responds only to the rapidly pulsing signal
created by the transmitter, and filters out slowly changing infrared radiation from ambient light.

Spectroscopy

Infrared radiation spectroscopy is the study of the composition of (usually) organic compounds,
finding out a compound's structure and composition based on the percent transmittance of IR
radiation through a sample. Different frequencies are absorbed by different stretches and bends in
the molecular bonds occurring inside the sample. Carbon dioxide, for example, has an absorption
band at 4.2µm.
3.5




Topic objectives:

3.5.1[Connect DTE & DCE system which employs either a serial printer,modem, or remote terminal]
3.5.2[Describe the principles of connecting a computer to a device using serial & parralel & the advantages of pararlel
trasmission]
3.5.3[Differentiate between Asynchronous Trasmission & Synchronous Transmission]
3.5.4[Differentiate between Full Duplex & Half Duplex Transmission]



Data Communication Interface.



A computer network is a system for communication among two or more computers. These
networks may be fixed (cabled, permanent) or temporary (as via modems).


 3.5.1 Connecting DTE & DCE system

DTE is an abbreviation for Data Terminal Equipment.

An end instrument that converts user information into signals for transmission or reconverts the
received signals into user information.

The functional unit of a data station that serves as a data source or a data sink and provides for
the data communication control function to be performed in accordance with link protocol.

The data terminal equipment (DTE) may be a single piece of equipment or an interconnected
subsystem of multiple pieces of equipment that perform all the required functions necessary to
permit users to communicate.

A user interacts with the DTE, or the DTE may be the user. The DTE interacts with the data circuit-
terminating equipment (DCE).

Usually, the DTE device is the terminal (or computer), and the DCE is a modem.
DCE-Data Circuit-Terminating Equipment
DCE is an abbreviation for Data Circuit-Terminating Equipment and its synonyms are Data
Communications Equipment and Data Carrier Equipment.

In a data station, the equipment that performs functions, such as signal conversion and coding, at
the network end of the line between the data terminal equipment (DTE) and the line, and that may
be a separate or an integral part of the DTE or of intermediate equipment.

The interfacing equipment that may be required to couple the data terminal equipment (DTE) into a
transmission circuit or channel and from a transmission circuit or channel into the DTE.

Data Communications Equipment (DCE) is a device that communicates with a Data Terminal
Equipment (DTE) device in RS-232C communications.

Usually, the DTE device is the terminal (or computer), and the DCE is a modem.

When two devices that are both DTE or both DCE that must be connected together without a
modem or a similar media translater between them, a NULL modem must be used


3.5.2 Serial & Pararrel Transmission


In telecommunication, serial transmission is the sequential transmission of the signal elements of
a group representing a character or other entity of data.

Note: The characters are transmitted in a sequence over a single line, rather than simultaneously
over two or more lines, as in parallel transmission. The sequential elements may be transmitted
with or without interruption. Synonym sequential transmission.
Parallel transmission is:

    1. The simultaneous transmission of the signal elements of a character or other data item.
    2. In digital communications, the simultaneous transmission of related signal elements over
       two or more separate paths.

Note: Protocols for parallel transmission, such as those used for computer ports, have been
standardized by ANSI

Serial Port.
A connector on a computer to which you can attach a serial line connected to peripherals which
communicate using a serial (bit-stream) protocol. The most common type of serial port is a 25-pin
D-type connector carrying EIA-232 signals. Smaller connectors (e.g. 9-pin D-type) carrying a
subset of EIA-232 are often used on personal computers. The serial port is usually connected to
an integrated circuit called a UART which handles the conversion between serial and parallel data.

In the days before bit-mapped displays, and today on multi-user systems, the serial port was used
to connect one or more terminals (teletypewriters or VDUs), printers, modems and other serial
peripherals. Two computers connected together via their serial ports, possibly via modems, can
communicate using a protocol such as UUCP or CU or SLIP.

Pararrel Port
An interface from a computer system where data is transferred in or out in parallel, that is, on more
than one wire. A parallel port carries one bit on each wire thus multiplying the transfer rate
obtainable over a single wire. There will usually be some control signals on the port as well to say
when data is ready to be sent or received.

The commonest kind of parallel port is a printer port, e.g. a Centronics port which transfers eight
bits at a time. Disks are also connected via special parallel ports

Advantages.
This type of port is most often used by a microprocessor to communicate with peripherals. The
most common kind of parallel port is a printer port, e.g. a Centronics port which transfers eight bits
at a time. Disks are also connected via special parallel ports, e.g. SCSI, ATA.

Before USB connections became widespread on mass-market computers, many external devices,
such as portable disk drives, for Windows systems used a rather awkward pass-through connector
so the device could share a parallel port with a printer. This was done because on mass-market
Windows boxes of the era lacked any equivalent of the SCSI connections then common on some
other platforms; the only convenient connection was usually the single printer port.

The parallel port of an IBM-PC compatible is the only standard computer peripheral that brings
standard computer logic voltages directly out to a set of pins. It is much beloved by experimenters
and engineers who often use it for inexpensive computer controlled projects. Standard logic
voltages are virtually harmless: five volts (roughly the same as two run-down flashlight batteries),
and ground (zero volts).
3.5.3 Asynchronous & Synchronous Transmission.


Synchronous and Asynchronous transmission are two different methods of transmission
sychronization. Synchronous transmissions are synchronized by an external clock, while
asynchronous transmissions are sychronized by special signals along the transmission medium.

The Need for Synchronization
Whenever an electronic device transmits digital (and sometimes analog) data to another electronic
device, there must be a certain rhythm established between the two devices, i.e., the receiving
device must have some way of knowing, within the context of the fluxuating signal that it's
receiving, where each unit of data begins and where it ends.

For example, a television transmitter produces a continuous stream of data in which each
horizontal line of image must be distinguishable from the preceding and suceeding lines, so that a
TV will be able to distinguish between them upon reception.

Or, a serial data signal between two PCs must have individual bits and bytes that the receiving PC
can distinguish. If it doesn't, then the receiving PC can't tell where one byte ends and the next one
begins. Or where one bit ends and begins.

So the signal must be synchronized in a way that the receiver can distinguish the bits and bytes as
the transmitter intends them to be distinguished.

Methods of Synchronization
There are two ways of synchronize the two ends of the communication.


Synchronous Transmission
In synchronous transmission, the stream of data to be transferred is encoded as fluctuating
voltages on one wire, and a periodic pulse of voltage is put on another wire that tells the receiver
"here's where one bit/byte ends and the next one begins".


Asynchronous Transmission
In asynchronous transmission, there is only one wire/signal carrying the transmission. the
transmitter sends a stream of data and periodically inserts a certain signal element into the stream
which can be "seen" and distinguished by the receiver as a synch signal.

Obviously, the term "asynchronous" is misleading in its literal interpretation and must be
understood as a term which is dictated by conventional usage.
 3.5.4 Full Duplex & Half Duplex.


Half-duplex
A half-duplex system allows communications in both directions, but only one direction at a time
(not simultaneously). Any radio system where you must use "Over" to indicate the end of
transmission, or any other procedure to ensure that only one party broadcasts at a time would be a
half-duplex system.

A good analogy for a half-duplex system would be a one lane road with traffic controllers at
each end. Traffic can flow in both directions, but only one direction at a time with this being
regulated by the controllers. Can be describe as a walkie-talkie system also.


Full-duplex
A full-duplex system allows communication in both directions, and unlike half-duplex allows this to
happen simultaneously. Most telephone networks are full duplex as they allow both callers to
speak at the same time.

A good analogy for a full-duplex system would be a two lane road with one lane for each
direction.


3.6



Topic objectives:
3.6.1[Explain the function & operation of a multiplexor]
3.6.2[Describe the practical benefits of multiplexors in a data communications environment]



Operation & Use of Multiplexer.


Multiplexer (often abbreviated to "mux" or "muldex") is a device for taking several separate digital
data streams and combining them together into one data stream of a higher data rate. This allows
multiple data streams to be carried from one place to another over one physical link, which saves
cost.

At the receiving end of the data link a complementary demultiplexer or "demux" is normally
required to break the high data rate stream back down into the original lower rate streams. In some
cases, the far end system may have more functionality than a simple demultiplexer and so, whilst
the demultiplexing still exists logically, it may never actually happen physically. This would be
typical where a multiplexer serves a number of IP network users and then feeds directly into a
router which immediately reads the content of the entire link into its routing processor and then
does the demultiplexing in memory from where it will be converted directly into IP packets.

It is usual to combine a multiplexer and a demultiplexer together into one piece of equipment and
simply refer to the whole thing as a "multiplexer". Both pieces of equipment are needed at both
ends of a transmission link because most communications systems transmit in both directions.

A real world example is the creation of telemetry for transmission from the
computer/instrumentation system of a satellite, space craft or other remote vehicle to a ground
system.


3.6.1   Function & Operation of a Multiplexor.

Multiplexing is a technique that enables broadband media to support multiple data channels.
Multiplexing makes sense under a number of circumstances:

        When media bandwidth is costly. A high-speed leased line, such as a T1 or T3, is expensive
         to lease. If the leased line has sufficient bandwidth, multiplexing can enable the same line to
         carry mainframe, LAN, voice, video conferencing, and various other data types.
        When bandwidth is idle. Many organizations have installed fiber-optic cable that is used only
         to partial capacity. With the proper equipment, a single fiber can support hundreds of
         megabits—or even a gigabit or more—of data.
        When large amounts of data must be transmitted through low-capacity channels.
         Multiplexing techniques can divide the original data stream into several lower-bandwidth
         channels, each of which can be transmitted through a lower-capacity medium. The signals
         then can be recombined at the receiving end.

Multiplexing refers to combining multiple data channels for transmission on a common medium.
Demultiplexing refers to recovering the original separate channels from a multiplexed signal.

Multiplexing and demultiplexing are performed by a multiplexor (also called a mux), which usually
has both capabilities.
3.6.2 Practical Benefits of multiplexors in data communications environment.


Time-Division Multiplexing



Time-division multiplexing (TDM) divides a channel into time slots that are allocated to the data
streams to be transmitted, as illustrated below :




If the sender and receiver agree on the time-slot assignments, the receiver can easily recover and
reconstruct the original data streams.

TDM transmits the multiplexed signal in baseband mode. Interestingly, this process makes it
possible to multiplex a TDM multiplexed signal as one of the data channels on an FDM system.

Conventional TDM equipment utilizes fixed-time divisions and allocates time to a channel,
regardless of that channel’s level of activity. If a channel isn’t busy, its time slot isn’t being
fully utilized. Because the time divisions are programmed into the configurations of the
multiplexors, this technique often is referred to as synchronous TDM.

If using the capacity of the data medium more efficiently is im-portant, a more sophisticated
technique, statistical time-division multiplexing (StatTDM), can be used. A stat-mux uses the time-
slot technique but allocates time slots based on the traffic demand on the individual channels, as
illustrated below:




Notice that Channel B is allocated more time slots than Channel A, and that Channel C is allocated
the fewest time slots. Channel D is idle, so no slots are allocated to it. To make this procedure
work, the data transmitted for each time slot includes a control field that identifies the channel to
which the data in the time slot should be assigned.
Frequency-Division Multiplexing




Above illustrates frequency-division multiplexing (FDM). This technique works by converting all
data channels to analog form. Each analog signal can be modulated by a separate frequency
(called a carrier frequency) that makes it possible to recover that signal during the demultiplexing
process. At the receiving end, the demultiplexor can select the desired carrier signal and use it to
extract the data signal for that channel.

FDM can be used in broadband LANs (a standard for Ethernet also exists). One advantage of
FDM is that it supports bidirec-tional signaling on the same cable.

				
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