ICT (A/L) Unit 6 - Data Communication and Computer Networking PDF

ICT (A/L) Unit:6 - Data Communication and Computer Networking Competency Level 6.1: signals and their properties 1) Data communication Data communication is the process of transmitting data between two or more communicating devices over some transmission media. 2) A Communication Model Sourc...

ICT (A/L) Unit:6 - Data Communication and Computer Networking Competency Level 6.1: signals and their properties 1) Data communication Data communication is the process of transmitting data between two or more communicating devices over some transmission media. 2) A Communication Model Source (Sender) - Generates and prepares data to be transmitted Transmission System - Responsible for transmitting data towards destination Destination (Receiver) - Receives data from the transmission system and hands over it to the application 3) Computer Network: A computer network consists of two or more computers that are linked together using a communication medium in order to share resources. 4) Signals: A signal is an electronic voltage or current, which varies with time. It is used to transfer data from one end to another. Analog signal: Analog signals are in continuous wave form in nature and represented by continuous electromagnetic waves. Examples of such signals are sound, light and temperature etc. Digital signal: Digital stands for discrete values and hence it means that they use specific values to represent any information. In digital signal, only two values are used to represent something i-e: 1 and 0 (binary values). Properties of signals Amplitude : The height of the wave measured in meters Frequency : The number of complete waves that pass a point in one second, measured in Hertz (Hz) Wavelength : The distance between adjacent crests, measured in meters Phase : phase is a position of a point in time (instant) on a waveform cycle. Propagation speed in a media The speed at which a wave propagates through a given medium.The propagation speed also varies from medium to medium depending on the properties of the medium. Characteristics of Analog and Digital Signals 1. Adaptability: Analog signals are less adjustable for a range of use, whereas digital signals are more adjustable for a range of use. 2. Continuity: Analog signals use a continuous variety of amplitude values whereas digital signal takes a limited set of distinct values at consistently spaced spots in the time. 3. Type of Data: Analog signals are continuous in nature, whereas digital signals are discrete. 4. Type of Waves: Analog signal wave type is sinusoidal, whereas a digital signal is a square wave. 5. Medium of Transmission: Analog signal medium of transmission is wire or wireless, whereas a digital signal is a wire. 6. Type of Values: Analog signal value type if positive as well as negative, whereas a digital signal is positive.  7. Security: The security of an analog signal is not encrypted, whereas a digital signal is encrypted. 8. Bandwidth: The analog signal bandwidth is low, whereas the digital signal is high. 9. Hardware: Analog signal hardware is not elastic, whereas digital is elastic in execution 10. Data Storage: The data storage of an analog signal is in the wave signal form, whereas digital signal stores the data in the binary bit form. 11. Portability: Analog signals are portable similar to the thermometer and low cost, whereas digital signals are portable similar to computers and expensive. 12. Data transmission: In analog, the signal can be deterioration due to noise throughout transmission, whereas digital signal can be noise resistant throughout transmission devoid of any deterioration. 13. Power Consumption: Analog devices use more power, whereas digital devices use less power. 14. Data Transmission Rate: The data transmission rate in the analog signal is slow, whereas in the digital signal it is faster. Examples The best examples of the analog signal are video, human voice in the air, radio transmission waves or TV transmission waves. Analog signals can be utilized in analog devices exclusively, thermometer, whereas digital signals are appropriate for digital electronic devices like computers, PDA, cell phones. Advantages of Digital Signal Over Analog Signal There are several advantages using digital signal over an analog signal. Digital signals are more secure, and they do not get damaged by noise. These signals use high bandwidth They allow the signals transmitted over a lengthy distance. Digital signal has a higher rate transmission By using these signals, we can translate the messages, audio, video into device language. Digital signals enable the transmission of multidirectional concurrently. Competency Level 6.2 – Signal Transmission Media  1. Guided Media: It is also referred to as Wired or Bounded transmission media. Signals being transmitted are directed and confined in a narrow pathway by using physical links. Features: High Speed Secure Used for comparatively shorter distances There are 3 major types of Guided Media: (i) Twisted Pair Cable – It consists of 2 separately insulated conductor wires wound about each other. Generally, several such pairs are bundled together in a protective sheath. They are the most widely used Transmission Media. Twisted Pair is of two types: Unshielded Twisted Pair (UTP): This type of cable has the ability to block interference and does not depend on a physical shield for this purpose. It is used for telephonic applications. Advantages: Least expensive Easy to install High speed capacity Disadvantages: Susceptible to external interference Lower capacity and performance in comparison to STP Short distance transmission due to attenuation Shielded Twisted Pair (STP): This type of cable consists of a special jacket to block external interference. It is used in fast-data-rate Ethernet and in voice and data channels of telephone lines. Advantages: Better performance at a higher data rate in comparison to UTP Eliminates crosstalk Comparatively faster Disadvantages: Comparatively difficult to install and manufacture More expensive Bulky (ii) Coaxial Cable – It has an outer plastic covering containing 2 parallel conductors each having a separate insulated protection cover. Coaxial cable transmits information in two modes: Baseband mode(dedicated cable bandwidth) and Broadband mode(cable bandwidth is split into separate ranges). Cable TVs and analog television networks widely use Coaxial cable. Advantages: High Bandwidth Better noise Immunity Easy to install and expand Inexpensive Disadvantages: Single cable failure can disrupt the entire network (iii) Optical Fiber Cable – It uses the concept of reflection of light through a core made up of glass or plastic. The core is surrounded by a less dense glass or plastic covering called the cladding. It is used for transmission of large volumes of data. Advantages: Increased capacity and bandwidth Light weight Less signal attenuation Immunity to electromagnetic interference Resistance to corrosive materials Disadvantages: Difficult to install and maintain High cost Fragile unidirectional, ie, will need another fiber, if we need bidirectional communication 2. Unguided Media: It is also referred to as Wireless or Unbounded transmission media. No physical medium is required for the transmission of electromagnetic signals. Features: Signal is broadcasted through air Less Secure Used for larger distances There are 3 major types of Unguided Media: (i) Radiowaves – These are easy to generate and can penetrate through buildings. The sending and receiving antennas need not be aligned. Frequency Range:3KHz – 1GHz. AM and FM radios and cordless phones use Radiowaves for transmission. Further Categorized as (i) Terrestrial and (ii) Satellite. (ii) Microwaves – It is a line of sight transmission i.e. the sending and receiving antennas need to be properly aligned with each other. The distance covered by the signal is directly proportional to the height of the antenna. Frequency Range:1GHz – 300GHz. These are majorly used for mobile phone communication and television distribution. (iii) Infrared – Infrared waves are used for very short distance communication. They cannot penetrate through obstacles. This prevents interference between systems. Frequency Range:300GHz – 400THz. It is used in TV remotes, wireless mouse, keyboard, printer, etc. Signal Properties 1) Latency: Network Latency is an expression of how much time it takes for a unit of data to travel from one point to another. Latency is usually measured in milliseconds. 2) Bandwidth: Bandwidth is a range of frequencies and measured in Hertz. 3) Noise: Noise is a received signal that makes no sense. 4) Attenuation: attenuation is the reduction of the signal energy as it travels through the given medium. 5) Distortion: Distortion is alteration (distort) of properties of a transferred signal caused by the capacitance and inductance of the communication medium. Simple topology: point-to-point connection: A Point-to-point topology connects two networking devices such as computers, switches, routers, or servers connected back to back using a single piece of cable. Advantages: Highest Bandwidth because there is only two nodes having entire bandwidth of a link, Very fast compared to other network topologies because it can access only two nodes, Very simple connectivity, It provides low Latency. Disadvantages: This topology is only used for small areas where nodes are closely located. The entire network depends on the common channel in case of link broken entire network will become dead. Competency Level 6.3 - How digital data is encoded using signal elements Modulations: Modulation is the technique used to send information by modifying the basic characteristics such as frequency, amplitude and phase, of an electromagnetic signal (modulating signal) by attaching it to a higher frequency signal (carrier signal), producing a modulated signal. Analog data to Analog signals Conversion 1) Amplitude Modulation (AM) Amplitude of carrier signal varies according to the amplitude of modulating signal. The frequency or phase of the carrier signal remains unchanged. 2) Frequency Modulation (FM) The carrier signal frequency changes according to the frequency of the Modulating signal. 3) Phase Modulation (PM) The phase of a carrier signal is modulated in order to reflect the changes in voltage (amplitude) of an analog data signal Digital data-to-Analog signal Conversion If the modulating signal is a digital signal, then three modulation schemes can be used: 1) Amplitude Shift Keying (ASK) In this conversion technique, the amplitude of an analog carrier signal is modified to reflect binary data. When binary data represents digit 1, the amplitude is held at 1, otherwise it is set to 0. Both frequency and phase remain same as in the original carrier signal 2) Frequency Shift Keying (FSK) In this conversion technique, the frequency of the analog carrier signal is modified to reflect binary data. 3) Phase Shift Keying (PSK) In this conversion scheme, the phase of the original carrier signal is altered to reflect the binary data. Synchronization: synchronization is used to ensure that the data streams are received and transmitted correctly between two devices. Usually a clock signal is transmitted in sequence with a data stream to maintain proper signal timing.  Digital data to Digital signals Signal Encoding Schemes: 1) Non-return to Zero Level (NRZ-L): is an encoding scheme in which two different voltages for 0 and 1 bits are used to represent data and remain constant during a bit interval. 2) Non-return to Zero Inverted (NRZ-I): in this encoding scheme, in which a “1" is represented by a transition of the physical level, while a "0" has no transition. 3) Manchester encoding: in Manchester encoding voltage changes from low to high or high to low in the middle of the signal. Bi-phase Manchester In this type of coding, the transition is done at the middle of the bit-interval. The transition for the resultant pulse is from High to Low in the middle of the interval, for the input bit 1. While the transition is from Low to High for the input bit 0. Differential Manchester In this type of coding, there always occurs a transition in the middle of the bit interval. If there occurs a transition at the beginning of the bit interval, then the input bit is 0. If no transition occurs at the beginning of the bit interval, then the input bit is 1.  Analog data to Digital signals – A signal is pulse code modulated to convert its analog information into a binary sequence, i.e., 1s and 0s. The output of a PCM will resemble a binary sequence. The following figure shows an example of PCM output with respect to instantaneous values of a given sine wave. Instead of a pulse train, PCM produces a series of numbers or digits, and hence this process is called as digital. Each one of these digits, though in binary code, represent the approximate amplitude of the signal sample at that instant. In Pulse Code Modulation, the message signal is represented by a sequence of coded pulses. This message signal is achieved by representing the signal in discrete form in both time and amplitude. The most commonly used method is the Pulse Code Modulation (PCM)- Error Control: Error is a condition when the output information does not match with the input information. During transmission, digital signals suffer from noise that can introduce errors in the binary bits travelling from one system to other. That means a 0 bit may change to 1 or a 1 bit may change to 0. During data transmission, sometimes data bits may get flipped due to various reasons. In such situations the data bit received is in error. Error detection is the process of identifying that the data bit has been altered during transmission. Error correction and recovery mechanisms are used to correct the data bits received in error and to recover the actual data bits. Parity Check: is one simple error detection mechanism where an extra bit of data is added and sent along with the original data bits to make number of 1s in the data as either even in the case of even parity, or odd in the case of odd parity Example: 1 Example 2 Competency Level 6.4 - Public Switched Telephone Network (PSTN) to connect two remote devices Public Switched Telephone network (PSTN) 1) PSTN – Dial Up Connections: Requires a modem and a phone line to dial into a service provider’s node, in order to get the connection The public switched telephone network (PSTN) refers to the international telephone system that uses copper wires to carry analog voice data. It consists of a collection of individual telephones that are hardwired to a public exchange. The public switched telephone network was formerly known simply as the public telephone network. PSTN Advantages It is a tried and tested technology. It is easily maintainable. Setup can be done without any hassles. Usage is simple PSTN Disadvantages It requires a dedicated line for making and completing a call. Scalability is limited. You cannot use bandwidth optimally with this technology. You need to pay maintenance fees every month. Call charges are higher than VOIP. Note: VoIP is short for Voice over Internet Protocol. Voice over Internet Protocol is a category of hardware and software that enables people to use the Internet as the transmission medium for telephone calls by sending voice data in packets using IP rather than by traditional circuit transmissions of the PSTN. VOIP Advantages VOIP is the newest technology for telephony. It transmits data by a packet switching method. This increases the affectivity of data transmission. You can transmit data, video and voice at the same time. It is scalable to a large extent. Bandwidth is well utilized since the data is transmitted in a compressed form. Not too much of hardware is needed since the internet is at the core of this form of communication. There is a huge reduction in call costs by properly using bandwidth. This means that making calls via VOIP is cheap and easy. You get free value added services. 2) Modulation, Demodulation and Modems: Modems are the devices used to modulate the digital signal in to analog signal (called modulation) and then send the modulated signal over the telephone lines. At the receiver, the modems are then used again to convert the analog signal to digital signal (Demodulation) therefore the receiving device can receive the data correctly. Different modulation schemes are used to modulate data and Pulse Code Modulation (PCM) is one method in which the samples of an analog signal are taken (called a pulse amplitude modulated signal) and then are shown that the original signal can be constructed at the receive end using these samples. Competency Level 6.5 - Connecting multiple devices into a network 1. Network Topology Network topology is the pattern of connection in designing computer network. 1. Star topology: This is a commonly used design and built by centralizing a switch/hub and computers. A star topology is designed with each node is (file server, workstations, and peripherals) connected directly to a central network hub or switch. Advantages: Easy to install and wire. No disruptions to the network when connecting or removing devices. Easy to detect faults and to remove parts. Disadvantages: Requires more cable length than a linear topology. If the hub, switch, or concentrator fails, nodes attached are disabled. More expensive than linear bus topologies because of the cost of the hubs, etc. Switches and hubs: Hubs and switches are common network devices that function as a common connection point for network devices that make up a network. A switch receives data in one of its incoming connections and forwards the data only on the outgoing connection which connects to the destination device. A hub receives data in one of its incoming connections and then shall forward the data to all of its outgoing connection. In this way a switch is a more intelligent device than a hub. Switch/hub- A connection between two or more computers. A guided/wired transmission media is used. ❖ Note: the differences between the hub and switch ✓ Transmission speed (hub