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DATA COMMUNICATION. Data Communication. Data communication refers to the exchange of data between a source and a receiver via form of transmission media such as a wire cable.
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Data Communication • Data communication refers to the exchange of data between a source and a receiver via form of transmission media such as a wire cable. • Data communications (DC) is the process of using computing and communication technologies to transfer data from one place to another, and vice versa.
Components • Message • Sender • Receiver • Medium/ communication channel • Encoder and decoder
Data Flow Network • In computers, the path of data from source document to data entry to processing to final reports. Data changes format and sequence (within a file) as it moves from program to program.
Network Criteria • Performance- Performance is the defined as the rate of transferring error free data. It is measured by the Response Time. • Consistency- Consistency is the predictability of response time and accuracy of data. • Reliability- Reliability is the measure of how often a network is useable. • Recovery- Recovery is the Network's ability to return to a prescribed level of operation after a network failure. • Security- Security is the protection of Hardware, Software and Data from unauthorized access. Restricted physical access to computers, password protection, limiting user privileges and data encryption are common security methods.
Network Category • Local Area Network (LAN)- LANs connect groups of computers and low-voltage devices together across short distances (within a building or between a group of two or three buildings in close proximity to each other) to share information and resources. • Metropolitan Area Network (MAN)- These types of networks are larger than LANs but smaller than WANs – and incorporate elements from both types of networks. MANs span an entire geographic area (typically a town or city, but sometimes a campus). • Wide Area Network (WAN)- A WAN connects computers together across longer physical distances.
Data Signals And Periods • Analog Data- Analog data is data that is represented in a physical way. Where digital data is a set of individual symbols, analog data is stored in physical media, whether that's the surface grooves on a vinyl record, the magnetic tape of a VCR cassette, or other non-digital media. • Digital Data- Digital data is data that represents other forms of data using specific machine language systems that can be interpreted by various technologies. The most fundamental of these systems is a binary system, which simply stores complex audio, video or text information in a series of binary characters, traditionally ones and zeros, or "on" and "off" values.
Analog Signal Transmission- Transmission of data in analog form is done in the form of continuous waveforms. An analog signal resembles the one shown in Figure. • Digital Signal Transmission- Digital data transmission is the transmission of discrete data using two distinct electric states. A '1' for "on" and '0' for "off" represents these two states. • Analog Signal- An analog signal is a continuous signal that contains time-varying quantities. • Digital Signal- A digital signal refers to an electrical signal that is converted into a pattern of bits.
Bitrate-Bitrate, as the name implies, describes the rate at which bits are transferred from one location to another. In other words, it measures how much data is transmitted in a given amount of time. • Bit-length-Bit-length is the number of binary digits, called bits, necessary to represent an integer[1] in the binary number system. • Attenuation- Attenuation is a general term that refers to any reduction in the strength of a signal. Attenuation occurs with any type of signal, whether digital or analog. • Distortion-Distortion is the alteration of the original shape (or other characteristic) of something.
Bandwidth-Bandwidth is defined as a range within a band of frequencies or wavelengths. Bandwidth is also the amount of data that can be transmitted in a fixed amount of time. • Throughput-Throughput is a measure of how many units of information a system can process in a given amount of time. It is applied broadly to systems ranging from various aspects of computer and network systems to organizations. • Latency-Network latency describes a delay that takes place during communication over a network (including the Internet). For example, a slow router may cause a delay of a few milliseconds when one system on a LAN tries to connect to another through the router. • Jitter-Jitter is any deviation in, or displacement of, the signal pulses in a high-frequency digitalsignal. The deviation can be in terms of amplitude, phase timing or the width of the signal pulse.
Digital And Analog Transimission Periods • Digital-to-analog conversion (DAC) Digital-to-analog conversion is a process in which signals having a few (usually two) defined levels or states (digital) are converted into signals having a theoretically infinite number of states (analog). A common example is the processing, by a modem,of computer data into audio-frequency (AF) tones that can be transmitted over a twisted pair telephone line. The circuit that performs this function is a digital-to-analog converter (DAC). Amplitude-shift keying (ASK) is a form of amplitude modulation that represents digitaldata as variations in the amplitude of a carrier wave.
Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). The modulation is accomplished by varying the sine and cosine inputs at a precise time. It is widely used for wireless LANs, RFID and Bluetooth communication. • Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier signal.[1] The technology is used for communication systems such as amateur radio, caller ID and emergency broadcasts
Analog to Analog Conversion • Analog-to-analog conversion, or modulation, is the representation of analog information by an analogsignal. It is a process by virtue of which a characteristic of carrier wave is varied according to the instantaneous amplitude of the modulating signal. • Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting information via a radiocarrier wave.
Phase modulation (PM) is a modulation pattern for conditioning communication signals for transmission. It encodes a message signal as variations in the instantaneous phase of a carrier wave. Phase modulation is one of the two principal forms of angle modulation, together with frequency modulation. • In telecommunications and signal processing, frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. • In analog frequency modulation, such as FM radio broadcasting of an audio signal representing voice or music, the instantaneous frequency deviation, the difference between the frequency of the carrier and its center frequency, is proportional to the modulating signal.
Digital to Digital Conversion • This section explains how to convert digital data into digital signals. It can be done in two ways, line coding and block coding. For all communications, line coding is necessary whereas block coding is optional. • Line Coding -The process for converting digital data into digital signal is said to be Line Coding. Digital data is found in binary format.It is represented (stored) internally as series of 1s and 0s.
Analog to Digital Conversion • Analog to Digital Converter samples the analogsignal on each falling or rising edge of sample clock. In each cycle, the ADC gets of the analog signal, measures and converts it into a digital value. The ADC converts the output data into a series of digitalvalues by approximates the signal with fixed precision. • Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the amplitude of the analog signal is sampled regularly at uniform intervals, and each sample is quantized to the nearest value within a range of digital steps.
A delta modulation(DM or Δ-modulation) is an analog-to-digital and digital-to-analog signal conversion technique used for transmission of voice information where quality is not of primary importance. DM is the simplest form of differential pulse-code modulation (DPCM) where the difference between successive samples are encoded into n-bit data streams.
Transmission Modes • Serial Transmission-In serial transmission, bits are sent sequentially on the same channel (wire) which reduces costs for wire but also slows the speed of transmission. Also, for serial transmission, some overhead time is needed since bits must be assembled and sent as a unit and then disassembled at the receiver. • Parallel Transmission-In parallel transmission, multiple bits (usually 8 bits or a byte/character) are sent simultaneously on different channels (wires, frequency channels) within the same cable, or radio path, and synchronized to a clock. Parallel devices have a wider data bus than serial devices and can therefore transfer data in words of one or more bytes at a time.
