Unbelievable Facts About Data Communication.

Data Communication:



 Since the purpose of Computers, data communications and networks is to process data into information. Data are stored inside a computer and transmitted on a communications system in the form of binary digits, or bits. The digits are either 1's or O's and are coded in
accordance with the binary (base 2) number system.
The binary bits inside a computer are represented by the level of a polarity of electrical signals. A high-level signal within a storage element in the computer could represent a 1; low-Level signal a 0. These elements are strung together to form numbers and characters, such as the number 6 or the letter A, in accordance with established codes.
Data are transmitted along the communications path (often the telephone network) between computer-oriented devices using electrical signals and bit sequence to represent numbers and characters. In some instances, the data representation may be by light signals, as in optic fibers. The bit representations depict user data and control data. The control data are used to manage the communications network and the flow of the user data.
depicts how the data move from a sending computing device, through the communications medium, and into a receiving computer device. The order should be aware that the binary data code is converted to base 10 for human consumption when it is displayed on terminals and printouts.
The term bps refer to the number of binary bits per second that are transferred through a communication path or component. If a 2,400 bit/s line uses an 8-bit code to represent a number of character, then the character per second rate is 300 (2,400/8 =300). The majority of communications speeds are quoted in bit/s rates.
It should be emphasized that a bit traveling down a communications path, as in is actually a representation of the electrical/electromagnetic or optical state of the line for a certain period of time. The bit 1 may be depicted by placing a negative voltage on the line for a few fractions of a second arid a 0 could be represented by a low-level signal positive voltage for the same period of time.


Transmission Characteristics  A general knowledge of the characteristics of electrical transmission is essential if the reader is to gain an understanding of data communIcations, Line capacity error Control techniques, communications software, and many other network components are all analyzed and designed around the capabilities and limitations of electricity.the data are transmitted on a communications channel by the alteration of an electrical signal to represent 1's and O's. The electrical signal state manifests itself by either the signal level or some other property of the complex electrical signal. The movement of the signal over its transmission path is referred to as signal propagator. On a wire path, signal propagation is a flow of electrical current. Radio transmission between computer sites without the use of wires is accomplished by emitting an electrical signal that propagates as an electromagnetic wave.
 The term baud is another commonly used in data communications. This term describes the rate of change of the signal on the line, that is, how many times (per second) the signal changes its pattern. As a simple example, the sending device assembles the bits into groups of two and then modifies the oscillating waveform (that is. changes the signal state) to one of four amplitudes to represent any combination of 2 bits (00, 01, 10, II). In this example, the bit transfer rate across the Communications path is twice the baud(or rate of signal change). Most modems today use up to 8 bits per baud to achieve greater signal transfer capacity.
The process is called modulation. This term means that the data stream changes or modulates the signal on the communications path (channel or link).
The signal is also distinguished by its frequency or number of complete oscillations of the waveform in a given time. Frequency is measured in oscillation per second. The electrical industry has defined the unit of I hertz (Hz) to mean one Oscillation per second.
The other term used to describe frequency is cycles per second( ) frequency of the wave has no relation to the amplitude. Signals can have many different combinations of the two. The amplitude indicates the signal level and the amount of negative or positive voltage, while the frequency indicates the rate (in Hertz) of the signal oscillation. The phase of the signal describes the point to which the signal has advanced In its cycle. the phases of the signal are identified as the beginning of the cycle. 1/4 of the cycle,1/2 of the cycle,3/4 of the cycle, and the completion of the cycle. The wave can also be labeled with degree markings like that of a sine wave or a 36O circle. The sine wave is so named because the wave varies in the same manner as the trigonometric sine function. The sine wave is derived from circular motion. The amplitude of the wave increases to a maximum at 90degrees, in the same manner, that the sine of an angle of rotation increases to a maximum of 90°. Since a complete cycle represents a 360° rotation around the circle. 1/4 of a cycle point represents a phase value of 90 degrees.
 The wave depicts the signal at its maximum strength at two points in the cycle. One-half of the cycle is represented by a positive voltage and the other one-half by a negative voltage. The changing voltage state results in electrical charges changing their direction of flow down the wire circuit. The voltage continuously varies its amplitude and periodically reverses its polarity. The nature of the charge is the only difference. The strength, either positive or negative. is the same at the two peaks in the cycle.
Transmission capacity, speed, and delay :
The transmission capacity, stated in bits per second (bit/s), of a communications system, is quite important because response time and throughput for the user applications running on a computer depend on the capacity of the system. For example, a 4,800-bit/s line will provide twice the capacity of a 2,400-bit/s line and result in increased throughput and better response time.
The telephone network is designed to carry voice, which is a low-bandwidth signal. Adequate voice fidelity requires a frequency spectrum of about 3 kHz. The frequency spectrum for voice-grade circuits does not allow for a high rate of bits per second to be transmitted.
The limiting factors on transmission capacity are the bandwidth, signal power, and noise on the conductor. An increased signal power can indeed increase the line capacity and also provide for greater distance for the propagation of the signal. However, excessive power may destroy components in the system and/or may not be economically feasible.
The noise on a line is a problem that is inherent to the line itself and cannot be eliminated. Noise (called thermal, Gaussian, white, or background noise) results from the constant, random movement of electrons on the conductor and provides a limit to the channel capacity. The hiss you hear on a telephone line is such a noise. Any electrical conductor is a source of a noise. The power of the noise is proportional to the bandwidth, so in lncre*aod b.ndwIdtb will also contain additional noise. An electronic technique known— filtering Is used to reduce the added noise



 Since the purpose of Computers, data communications and networks is to process data into information. Data are stored inside a computer and transmitted on a communications system in the form of binary digits, or bits. The digits are either 1's or O's and are coded in
accordance with the binary (base 2) number system.
The binary bits inside a computer are represented by the level of a polarity of electrical signals. A high-level signal within a storage element in the computer could represent a 1; low level signal a 0. These elements are strung together to form numbers and characters, such as the number 6 or the letter A, in accordance with established codes.
Data are transmitted along the communications path (often the telephone network) between computer-oriented devices using electrical signals and bit sequence to represent numbers and characters. In some instances, the data representation may be by light signals, as in optic fibers. The bit representations depict user data and control data. The control data are used to manage the communications network and the flow of the user data.
depicts how the data move from a sending computing device, through the communications medium, and into a receiving computer device. The order should be aware that the binary data code is converted to base 10 for human consumption when it is displayed on terminals and printouts.
The term bps refer to the number of binary bits per second that are transferred through a communication path or component. If a 2,400 bit/s line uses an 8-bit code to represent a number of character, then the character per second rate is 300 (2,400/8 =300). The majority of communications speeds are quoted in bit/s rates.
It should be emphasized that a bit traveling down a communications path, as in is actually a representation of the electrical/electromagnetic or optical state of the line for a certain period of time. The bit 1 may be depicted by placing a negative voltage on the line for a few fractions of a second arid a 0 could be represented by a low-level signal positive voltage for the same period of time.


Transmission Characteristics  A general knowledge of the characteristics of electrical transmission is essential if the reader is to gain an understanding of data communIcations, Line capacity error Control techniques, communications software, and many other network components are all analyzed and designed around the capabilities and limitations of electricity.the data are transmitted on a communications channel by the alteration of an electrical signal to represent 1's and O's. The electrical signal state manifests itself by either the signal level or some other property of the complex electrical signal. The movement of the signal over its transmission path is referred to as signal propagator. On a wire path, signal propagation is a flow of electrical current. Radio transmission between computer sites without the use of wires is accomplished by emitting an electrical signal that propagates as an electromagnetic wave.
 The term baud is another commonly used in data communications. This term describes the rate of change of the signal on the line, that is, how many times (per second) the signal changes its pattern. As a simple example, the sending device assembles the bits into groups of two and then modifies the oscillating waveform (that is. changes the signal state) to one of four amplitudes to represent any combination of 2 bits (00, 01, 10, II). In this example, the bit transfer rate across the Communications path is twice the baud(or rate of signal change). Most modems today use up to 8 bits per baud to achieve greater signal transfer capacity.
The process is called modulation. This term means that the data stream changes or modulates the signal on the communications path (channel or link).
The signal is also distinguished by its frequency or number of complete oscillations of the waveform in a given time. Frequency is measured in oscillation per second. The electrical industry has defined the unit of I hertz (Hz) to mean one Oscillation per second.
The other term used to describe frequency is cycles per second( ) frequency of the wave has no relation to the amplitude. Signals can have many different combinations of the two. The amplitude indicates the signal level and the amount of negative or positive voltage, while the frequency indicates the rate (in Hertz) of the signal oscillation. The phase of the signal describes the point to which the signal has advanced In its cycle. the phases of the signal are identified as the beginning of the cycle. 1/4 of the cycle,1/2 of the cycle,3/4 of the cycle, and the completion of the cycle. The wave can also be labeled with degree markings like that of a sine wave or a 36O circle. The sine wave is so named because the wave varies in the same manner as the trigonometric sine function. The sine wave is derived from circular motion. The amplitude of the wave increases to a maximum at 90degrees, in the same manner, that the sine of an angle of rotation increases to a maximum of 90°. Since a complete cycle represents a 360° rotation around the circle. 1/4 of a cycle point represents a phase value of 90 degrees.
 The wave depicts the signal at its maximum strength at two points in the cycle. One-half of the cycle is represented by a positive voltage and the other one-half by a negative voltage. The changing voltage state results in electrical charges changing their direction of flow down the wire circuit. The voltage continuously varies its amplitude and periodically reverses its polarity. The nature of the charge is the only difference. The strength, either positive or negative. is the same at the two peaks in the cycle.
Transmission capacity, speed, and delay :
The transmission capacity, stated in bits per second (bit/s), of a communications system, is quite important because response time and throughput for the user applications running on a computer depend on the capacity of the system. For example, a 4,800-bit/s line will provide twice the capacity of a 2,400-bit/s line and result in increased throughput and better response time.
The telephone network is designed to carry voice, which is a low-bandwidth signal. Adequate voice fidelity requires a frequency spectrum of about 3 kHz. The frequency spectrum for voice-grade circuits does not allow for a high rate of bits per second to be transmitted.
The limiting factors on transmission capacity are the bandwidth, signal power, and noise on the conductor. An increased signal power can indeed increase the line capacity and also provide for greater distance for the propagation of the signal. However, excessive power may destroy components in the system and/or may not be economically feasible.
The noise on a line is a problem that is inherent to the line itself and cannot be eliminated. Noise (called thermal, Gaussian, white, or background noise) results from the constant, random movement of electrons on the conductor and provides a limit to the channel capacity. The hiss you hear on a telephone line is such a noise. Any electrical conductor is a source of a noise. The power of the noise is proportional to the bandwidth, so in lncre*aod b.ndwIdtb will also contain additional noise. An electronic technique known— filtering Is used to reduce the added noise



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