Fundamentals of Data Communication in Advanced Computer Networking, Slides of Computer Science

Download Fundamentals of Data Communication in Advanced Computer Networking and more Slides Computer Science in PDF only on Docsity! Advanced Computer Networking Sep 2021 Data Chapter One Basics Components of Data communication “* There are five basic components of data communication. 1. Message 2. Sender 3. Receiver 4. Medium 5. Protocol Protocol Protocol Le —|_mesese [> Le Cont'd... 1. Message: it is the information (data) to be communicated. Popular forms of information include text, pictures, audio, video etc. 2. Sender: it is the device which sends the data messages. It can be a computer, workstation, telephone handset, video camera, etc. 3. Receiver: it is the device which receives the data messages. It can be a computer, workstation, telephone handset, television etc 4. Transmission Medium: it is the physical path by which a message travels from sender to receiver. Some examples include twisted-pair wire, coaxial cable, fiber-optic cable, radio waves etc. 5. Protocol: it is a set of rules that governs the data communication. It represents an agreement between the communication device. Data Representation Techniques # Information today comes in different forms such as text, numbers, images, audio, and video. ? Text * In data communications, text is represented as a bit pattern, a sequence of bits (Os or 1s). ¢ Different sets of bit patterns have been designed to represent text symbols. Each set is called a code, and the process of representing symbols is called coding. ¢ Today, the prevalent coding system is called Unicode, which uses 32 bits to represent a symbol or character used in any language in the world. The American Standard Code for Information Interchange (ASCII), developed some decades ago in the United States, now constitutes the first 127 characters in Unicode and is also referred to as Basic Latin. Data Transmission #Signal is electric or electromagnetic representations of data, physically propagates along medium #Transmission is the communication of data by the propagation and processing of signals. Data transmission occurs between transmitter and receiver over some transmission medium. #The successful transmission of data depends principally on two factors: the quality of the signal being transmitted and the characteristics of the transmission medium. #Transmission media may be classified as guided or unguided. In both cases, communication is in the form of electromagnetic waves. Guided media: the waves are guided along a physical path; "Eg. twisted pair, coaxial cable, and optical fiber. Unguided media (Wireless): provide a means for transmitting electromagnetic waves but do not guide them; "Eg. propagation through air, vacuum, and seawater. » Analog and Digital Data The terms analog and digital correspond, roughly, to continuous and discrete, respectively. # Analog data take on continuous values in some interval. For example, voice and video are continuously varying patterns of intensity. Most data collected by sensors, such as temperature and pressure, are continuous valued. eo Digital data take on discrete values; examples are text and integers. The most familiar examples of analog data are audio and video. A familiar example of digital data is text or character strings. 11 Analog and Digital Signals In a communications system, data are propagated from one L y propag point to another by means of electromagnetic signals. An analog signal is a continuously varying electromagnetic wave that may be propagated over a variety of media, depending on spectrum. Or digital signal is a sequence of voltage pulses that may be transmitted over a wire medium; for example, a constant positive voltage level may represent binary O and a constant negative voltage level may represent binary 1. 12 Analog and Digital Signaling of Analog and Digital Data eo Digital data can be represented by analog signals, with a different voltage level for each of the two binary digits. Analog Signals: Represent data with continuously varying electromagnetic wave nto Oe OO" Analog Data ——<—@§$i—g“§98§ ——@£ << Analog Signal (voice sound waves) Telephone oigital Date Cu Lr 1 Sa F $$ ———— Analog Signal (binary voltage pulses) (modulated on Modem carrier frequency) Cont’ oo # Analog data can be represented by digital signals. The device that performs this function for voice data is a codec (coder-decoder). Digital Signals: Represent data with sequence of voltage pulses Analog Signa™™———> = —M —_ Digital Signal Codec Digital Data ———____—_—_——————_—_> — . rCDigital Signal Digital Transceiver Analog and Digital Transmission #Analog transmission is a means of transmitting analog signals without regard to their content; the signals may represent analog data (e.g., voice) or digital data (e.g., binary data that pass through a modem). @in either case, the analog signal will become weaker (attenuate) after a certain distance. To achieve longer distances, the analog transmission system includes amplifiers that boost the energy in the signal. AUnfortunately, the amplifier also boosts the noise components. With amplifiers cascaded to achieve long distances, the signal becomes more and more distorted. Aor analog data, such as voice, quite a bit of distortion can be tolerated and the data remain intelligible. However, for digital data, cascaded amplifiers will introduce errors. 17 Transmission Impairments Signals travel through transmission media, which are not perfect. The imperfection causes signal impairment. This means that the signal at the beginning of the medium is not the same as the signal at the end of the medium. ® most significant impairments are * attenuation * distortion * noise 20 Attenuation Attenuation means a loss of energy. When a signal, simple or composite, travels through a medium, it loses some of its energy in overcoming the resistance. Some of the electrical energy in the signal is converted to heat. To compensate for this loss, amplifiers are used to amplify the signal. 21 Original Point | Attenuated Transmission medium Point 2 Amplified Point 3 22 Noise (? Additional signals inserted between transmitter and receiver Several types of noise, such as thermal noise, induced noise, crosstalk, and impulse noise, may corrupt the signal. ® Thermal noise: the random motion of electrons in a wire, which creates an extra signal not originally sent by the transmitter. Induced noise: comes from sources such as motors and appliances. Crosstalk: is the effect of one wire on the other. Impulse noise: is a spike that comes from power lines, lightning, and so on. Transmitted Noise | Received Point | Transmission medium Point 2 26 Mode of Data Transmission Communication between two devices can be simplex, half-duplex, or full-duplex. ( Simplex Mode * In simplex mode, the communication is unidirectional, as on a one-way Street. * Only one of the two devices on a link can transmit; the other can only receive ¢ The simplex mode can use the entire capacity of the channel to send data in one direction. § Direction of data oa Mainframe Monitor 27 Cont'd... Full-Duplex * In full-duplex mode (also called duplex), both stations can transmit and receive simultaneously. ¢ The full-duplex mode is like a two-way street with traffic flowing in both directions at the same time. ¢In full-duplex mode, signals going in one direction share the capacity of the link with signals going in the other direction. This sharing can occur in two ways: Either the link must contain two physically separate transmission paths, one for sending and the other for receiving; or the capacity of the channel is divided between signals traveling in both directions. Cont'd... *One common example of full-duplex communication is the telephone network. ¢ When two people are communicating by a telephone line, both can talk and listen at the same time. ¢ The full-duplex mode is used when communication in both directions is required all the time. The capacity of the channel, however, must be divided between the two directions. 3 Direction of data all the time 2 ie - \ ee = a - Multiplexing Multiplexing deals with the division of the resources to create multiple channels. Multiplexing describes how several users can share a medium with minimum or no interference. Multiplexing allows several transmission sources to share a larger transmission capacity. The two common forms of multiplexing are frequency division multiplexing (FDM) and time division multiplexing (TDM). Time Division Multiplexing # Basically two types of TDM. 1. Synchronous time division multiplexing 2. Statistical time division multiplexing red a a a a = o 35 Synchronous time division multiplexing can be used with digital signals or analog signals carrying digital data. @ In this form of multiplexing, data from various sources are Carried in repetitive frames. Each frame consists of a set of time slots, and each source is assigned one or more time slots per frame. The effect is to interleave bits of data from the various Sources. 36 Statistical time division multiplexing Provides a generally more efficient service than synchronous TDM for the support of terminals. With statistical TDM, time slots are not pre-assigned to particular data sources. User data are buffered and transmitted as rapidly as possible using available time slots. 37