Data Communications PDF

ECEN100 Communications 4: Data Communications LECTURE 1: INTRODUCTION TO DATA COMMUNICATIONS Definition and Importance of Data Communications Just like humans communicate in a variety of ways – by speaking, texting, and emailing – data similarly transfers from one place to another using differ...

ECEN100 Communications 4: Data Communications LECTURE 1: INTRODUCTION TO DATA COMMUNICATIONS Definition and Importance of Data Communications Just like humans communicate in a variety of ways – by speaking, texting, and emailing – data similarly transfers from one place to another using different mediums. The process of moving electronic and digital data is called data communication. Data communication is the process of transferring data from one place to another or between two locations. Data communication refers to the process of transmitting and receiving data between two or more devices over a communication channel. It involves the conversion of data into signals that can be transmitted and then decoding those signals at the receiving end. Basic Components of Data Communication Systems A communication system is made up of the following components: 1. Message: Piece of information that is to be transmitted from one person to another. It could be a text file, an audio file, a video file, etc. 2. Sender: It is simply a device that sends data messages. 3. Receiver: It is a device that receives messages. 4. Transmission Medium or Communication Channels: Communication channels are the medium that connect two or more workstations. 5. Set of rules (Protocol): When someone sends the data (sender), it should be understandable to the receiver also otherwise it is meaningless. It defines how data is transmitted and communicated. Therefore, there are some of rules (protocols) that is followed by every computer connected to the internet and they are: 1. TCP(Transmission Control Protocol): It is responsible for dividing messages into packets on the source computer and reassembling the received packet at the destination or recipient computer. It also makes sure that the packets have the information about the source of the message data, the destination of the message data, the sequence in which the message data should be re-assembled, and checks if the message has been sent correctly to the specific destination. 2. IP(Internet Protocol): It is responsible for handling the address of the destination computer so that each packet is sent to its proper destination. Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications Data Communications Models TCP/IP Model The Transmission Control Protocol/Internet Protocol (TCP/IP) model came before the Open Systems Interconnection (OSI) model, and it has four layers. Example of TCP/IP model at host. Application layer where data originates on the sender’s side and used to create data. A web browser is example to generate data that gets sent through the rest of the layers, assisted by the Domain Name System (DNS), which associates web domain names with their Internet Protocol (IP) addresses. In transport layer, the data gets encoded so it can transported through the internet using either the User Datagram Protocol (UDP) or Transmission Control Protocol (TCP) In the network access layer, the data gets the header and a trailer, and these tell the data where to go. This information is then conveyed to the network interface layer. At the network interface or data link layer, the packet of data gets formatted and prepared to be transported and routed through the network. OSI Model The OSI model is another way of transmitting data over the internet. The biggest difference between the OSI and TCP/IP models is the OSI model has seven layers instead of four. Both provide data communication services, enabling users to send and receive information from their IP address using the services made available by their internet service provider (ISP). Example of OSI model at target. In physical layer, this consists of data connection between a device generating data and the network. In datalink layer, it is the point-to-point connection that transmits the data to the network layer. In the network layer, the data gets its address and routing instructions in preparation journey across the network. In transport layer, the data hops between different points on the network on its way to its destination. In session layer, it has a connection that manages the sessions between applications. In the presentation layer, data gets encrypted Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications and decrypted and converted into a form that is accessible by the application layer. In application layer, an application, such as internet browser, gets the data and a user can interact with it. Types of Data Transmission Serial and Parallel Serial Communication. In serial communication, data transmission occurs bit by bit on a single communication line or channel. This process means that data bits are sent one after the other in a sequence or series, with the receiving device collecting and reassembling these bits into a complete message. How serial data is transmitted? The device is sending data, called the transmitter, send a start bit to the device receiving the data, known as receiver. The start bit is like a heads up, signaling, to notify that transmitter about to send some data. Next, the transmitter sends the data by bit in a specific order. When all the data bits have been sent, the transmitter sends a stop bit. Start Bit – 0, 8 Data Bits, Stop Bit - 1 The telegraph was one of the first devices for long-distance serial communication, using a single wire to transmit data. Serial communication protocols and standards began to develop in the 1960s. These protocols, such as RS-232, SPI, I2C, RS485, USB, and MIPI, are widely used in electronic circuits, LCDs, OLEDs, computer systems, embedded systems, and telecommunications. Parallel Communication. Parallel communication is a method of transmitting data in which multiple bits are sent simultaneously over multiple channels or cables. These bits are generally sent in data groups of 8 bits, known as bytes, in a single clock pulse. This means each bit is transmitted over a dedicated cable. This technique is like a multi-lane highway, with each 'bit' having its own lane, allowing for simultaneous data transmission. How parallel data is transmitted? The transmitter signals the receiver about data transmission readiness. The data is divided into multiple bit groups, and the transmitter sends all the bits simultaneously over separate communication lines or cables. The receiver gets all the data streams and arranges them in the correct order to reconstruct the original data. Once all parallel bits are received, and data is reconstructed, the communication is complete. Parallel communication is typically faster than serial communication, as it can transmit more data in the same amount of time. However, it is also more complex and requires more hardware. Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications Parallel communication is often used in applications where high data rates are required, such as in printers, scanners, and external hard drives. It is also used in some internal computer buses, such as the PCI bus. Analog and Digital Analog-to-Analog Transmission. For example, radio broadcasting where audio signals are modulated onto a carrier frequency and transmitted over the air. Digital-to-Digital Transmission. For example, data communication over a computer network where binary data is transmitted between devices. Analog-to-Digital Transmission. For example, voice communication over VoIP (Voice over Internet Protocol) where analog voice signals are converted to digital data. The analog signal (e.g., voice) is sampled at regular intervals. The sampled values are Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications quantized into discrete levels. The quantized values are encoded into a digital format (e.g., PCM). The digital data is transmitted over the network. The receiving device decodes the digital data and converts it back to an analog signal (if needed). Digital-to-Analog Transmission. For example, modem communication where digital data from a computer is converted to analog signals for transmission over telephone lines. Digital data is modulated onto an analog carrier signal (e.g., FSK, QAM). The modulated analog signal is transmitted over the medium (e.g., telephone lines). The receiving modem demodulates the signal to recover the original digital data. 4-QAM Constellation Diagram 8-QAM Constellation Diagram Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications Communication Channels and Media Wired (Guided) Media a. Twisted Pair Cable. It consists of pair of insulated copper wires twisted together b. Fiber Optic Cable. It uses light signals to transmit data through thin strands of glass or plastic. c. Coaxial Cable. It has a central core conductor of a solid copper wire enclosed in an insulating sheet and the middle core conductor is made up of copper mesh and lastly an outer metallic wrap that helps in noise cancellation. Commonly used in cable television, broadband internet, CCTV, and ethernet connection setup. Wireless (Unguided) Media a. Radio. Channel for electromagnetic waves with frequencies ranging from 3 kHz to 300 GHz. Commonly used for Wi-Fi, Bluetooth, AM/FM radio, and mobile phone communications. b. Microwaves. Channel for electromagnetic waves with frequencies ranging from 300 MHz to 300 GHz. Commonly used for long-distance communication, satellite links, and point-to- point communication. c. Infrared. Channel for electromagnetic waves with frequencies just below visible light, ranging from 300 GHz to 400 THz. Commonly used for short-range communication such as remote controls and some wireless peripherals. d. Satellite. It operates over wide range of frequencies. L-Band (1-2GHz) for GPS, mobile satellite services, mobile application S-Band (2-4 GHz) for weather radar, satellite telemetry, atmospheric penetration C-Band (4-8 GHz) for satellite television broadcasts X-Band (8-12 GHz) for military application and radar applications Ku-Band (12-18 GHz) for VSAT (Very Small Aperture Terminal) Systems Ka-Band (26.5-40 GHz) for high-throughput satellite services, broadband internet services Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications LECTURE 2: NETWORK TOPOLOGY AND TRANSMISSION MODES Network Topologies Network topology refers to the arrangement of different elements like nodes, links, and devices in a computer network. It defines how these components are connected and interact with each other. Point to Point Topology Point-to-point networks contains exactly two hosts such as computer, switches or routers, servers connected back to back using a single piece of cable. Often, the receiving end of one host is connected to sending end of the other and vice-versa. - Bus Topology All devices share single communication line or cable. Bus topology may have problem while multiple hosts sending data at the same time. Therefore, Bus topology either uses CSMA/CD technology or recognizes one host as Bus Master to solve the issue. It is one of the simple forms of networking where a failure of a device does not affect the other devices. But failure of the shared communication line can make all other devices stop functioning. The cable which is used to connect devices is known as coaxial cable or RJ- 45 cable. Both ends of the shared channel have line terminator. The data is sent in only one direction and as soon as it reaches the extreme end, the terminator removes the data from the line. Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications Star Topology All hosts in Star topology are connected to a central device, known as hub device, using a point- to-point connection. The hub device can be any of the following such as Layer-1 device (hub or repeater), Layer-2 device (switch or bridge), or Layer-3 device (router or gateway). As in bus topology, hub acts as single point of failure. If hub fails, connectivity of all hosts to all other hosts fails. Every communication between hosts, takes place through only the hub. Star topology is not expensive as to connect one more host, only one cable is required and configuration is simple. Ring Topology In ring topology, each host machine connects to exactly two other machines, creating a circular network structure. When one host tries to communicate or send message to a host which is not adjacent to it, the data travels through all intermediate hosts. To connect one more host in the existing structure, the administrator may need only one more extra cable. Failure of any host results in failure of the whole ring. Thus, every connection in the ring is a point of failure. Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications Mesh Topology In this type of topology, a host is connected to one or multiple hosts. This topology has hosts in point-to-point connection with every other host or may also have hosts which are in point-to-point connection to few hosts only. Hosts in Mesh topology also work as relay for other hosts which do not have direct point-to- point links. Mesh technology comes into two types: a. Full Mesh. All hosts have a point-to-point connection to every other hosts in the network. Thus, for every new host n(n-1)/2 connections are required. It provides the most reliable network structure among all network topologies. b. Partially Mesh. Not all hosts have point-to-point connection to every other host. Hosts connect to each other in some arbitrarily fashion. This topology exists where we need to provide reliability to some hosts out of all. Tree Topology Also known as Hierarchical Topology, this is the most common form of network topology in use presently. This topology imitates as extended Star topology and inherits properties of bus topology. Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications This topology divides the network in to multiple levels/layers of network. Mainly in LANs, a network is bifurcated into three types of network devices. The lowermost is access- layer where computers are attached. The middle layer is known as distribution layer, which works as mediator between upper layer and lower layer. The highest layer is known as core layer, and is central point of the network, i. e. root of the tree from which all nodes fork. All neighboring hosts have point- to-point connection between them. Similar to the Bus topology, if the root goes down, then the entire network suffers even though it is not the single point of failure. Every connection serves as point of failure, failing of which divides the network into unreachable segment. Daisy Chain This topology connects all the hosts in a linear fashion. Similar to Ring topology, all hosts are connected to two hosts only, except the end hosts. Means, if the end hosts in daisy chain are connected then it represents Ring topology. Each link in daisy chain topology represents single point of failure. Every link failure splits the network into two segments. Every intermediate host works as relay for its immediate hosts. Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications Hybrid Topology A network structure whose design contains more than one topology is said to be hybrid topology. Hybrid topology inherits merits and demerits of all the incorporating topologies. The figure represents an arbitrarily hybrid topology. The combining topologies may contain attributes of Star, Ring, Bus, and Daisy-chain topologies. Most WANs are connected by means of Dual-Ring topology and networks connected to them are mostly Star topology networks. Internet is the best example of largest Hybrid topology Transmission Modes in Computer Network Transmission modes also known as communication modes, are methods of transferring data between devices on buses and networks designed to facilitate communication. They are classified into three types: Simplex Mode, Half-Duplex Mode, and Full-Duplex Mode. Parameters Simplex Half Duplex Full Duplex Direction of Unidirectional Two-way directional Two-way directional Communicatio communication communication but one at communication n a time simultaneously Sender and Sender can send the Sender can send the data Sender can send the Receiver data but that receiver and also can receive the data and also can can’t receive the data data but one at a time receive the data simultaneously Channel Usage Usage of one channel Usage of one channel for Usage of two channels for the transmission of the transmission of data for the transmission of data data Performance Less performance than Less performance than Better performance half duplex and full full duplex than simplex and half duplex duplex Bandwidth 𝐶 = 𝐵𝑊 𝐶 = 𝐵𝑊 ∗ 𝑡𝑝 𝐶 = 2 ∗ 𝐵𝑊 ∗ 𝑡𝑝 Utilization Maximum utilization of Lesser utilization of Doubles the utilization 𝑪 = 𝑪𝒂𝒑𝒂𝒄𝒊𝒕𝒚 single bandwidth 𝑩𝑾 = 𝑩𝒂𝒏𝒅𝒘𝒊𝒅𝒕𝒉 single bandwidth at the of transmission 𝒕𝒑 : 𝒑𝒓𝒐𝒑𝒂𝒈𝒂𝒕𝒊𝒐𝒏 𝒅𝒆𝒍𝒂𝒚 time of transmission bandwidth Suitable For Transmission when Requirement of both Requirement of sending there is requirement of sending data, but not at and receiving data full bandwidth of the same time simultaneously in both delivering data directions Examples Keyboard and monitor Two-way Radio System Telephone Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications Mode Advantages Easiest and most Bidirectional, most Simultaneous reliable, cost-effective, efficient than simplex, bidirectional feedback or response is less expensive than full communication, ideal for not required such as duplex real-time applications broadcasting or such as video surveillance conferencing or gaming most efficient mode, high reliability Disadvantages One-way only, no way Less reliable than full Most expensive mode, to verify if the duplex, delay between more complex, requires transmitted data has transmission and high level of bandwidth been received correctly reception and may not be necessary for some types of communication Performance Metrics in Networks Bandwidth Bandwidth refers to the maximum amount of data that can be transmitted and received within a specific period of time, usually measured in bits per second (bps). For instance, if a network has high bandwidth, it means that a larger volume of data can be transmitted and received. Using the analogy of water flowing through a pipe, bandwidth is like the width of the pipe— the wider the pipe, the more water (or data) can flow through at once. Bandwidth represents the potential capacity, but it doesn’t guarantee that water will flow efficiently or quickly. Throughput Throughput is the measure of how much data is successfully transmitted and received over a network in a specific time period, typically measured in bits per second (bps). It reflects the average rate at which data packets reach their destination. High throughput indicates good network performance, while low throughput may result to packet loss and potential issues. Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications Using a water analogy, throughput can be compared to the flow of water through a pipe. High throughput is like a wide pipe that allows large volume of water to flow through per second. Latency Latency measures delay. Delay is simply the time taken for a data packet to reach its destination after being sent. We measure network latency as round trips, although it may sometimes be measured in one-way trips. However, round-trip measurements are more common, because devices usually wait for an acknowledgment from the destination machine to be returned before transmitting the complete set of data. This acknowledgment verifies the connection to the destination device. If your network is experiencing high levels of latency, this signals poor or slow network performance. In short, the higher your network delay and latency, the longer it will take for a data packet to reach the appropriate destination. The result of latency is often choppy and lagging services. Using water analogy, if the pipe is narrow or has obstacles, the water flow is slow, and it takes longer for water to get from point A to point B. This is similar to high network latency, where data packets experience delays due to network congestion, long distances, or inefficient routing. Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications LECTURE 3: WIRE CIRCUITS AND SYNCHRONIZATION Introduction to Wire Circuits Types of Wire Circuits Two-wire Circuits. It uses a single pair of wires to carry signals, one wire for signals, and one wire for ground. In this type of circuit, data transmission occurs in one direction at a time, which is known as half-duplex communication. The same pair of wires is used for both sending and receiving signals, but not simultaneously. Ground is explicitly included to provide common reference and complete the circuit for signal. Four-wire Circuits It uses two pairs of wires—one pair for transmitting and another pair for receiving signals. An additional ground wire is optional but often included. The separation of sending and receiving paths helps reduce interference and allows for higher data transfer rates. In 4-wire circuits, ground may not be explicitly required because the differential pairs already handle signal integrity and noise rejection. The following wires are: a. Transmit Data Positive (TD+). Carries positive side of the differential signal for transmitting. b. Transmit Data Negative (TD-). Carries the negative side of the differential signal for transmitting. c. Receive Data Positive (RD+). Carries the positive side of the differential signal for receiving. d. Receive Data Negative (RD-). Carries the negative side of the differential signal for receiving. Methods of Switching Circuit Switching. It establishes a dedicated communication path between two devices for the duration of the communication session. Data is transmitted along the established path with a consistent bandwidth and latency. Traditional telephone networks are a prime example of circuit-switched systems. Packet Switching. Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications Packet switching divides data into small packets, which are sent independently through the network and reassembled at the destination. If a path fails, packets can be rerouted through alternate paths, providing greater reliability. Modern data networks, including the Internet, predominantly use packet switching. Data Encoding Techniques Techniques used for different types of transmission a. Analog to Analog signal – Amplitude Modulation, Frequency Modulation, Phase Modulation b. Analog to Digital signal – Pulse Code Modulation, Delta Modulation c. Digital to Analog signal – Amplitude Shift Keying, Frequency Shift Keying, Phase Shift Keying d. Digital to Digital signal – Non Return to Zero, Return to Zero, Manchester, Differential Manchester, Bipolar Encoding Encoding is the process of using various patterns of voltage or current levels to represent 1s and 0s of the digital signals on the transmission link. The common types of line encoding are Unipolar, Polar, Bipolar, and Manchester. The data encoding technique is divided into the following types, depending upon the type of data conversion. Unipolar Scheme All signals are either above or below the axis. a. NRZ (Non Return to Zero) - positive voltage defines bit 1 and the zero voltage defines bit 0. Signal does not return to zero at the middle of the bit thus it is called NRZ. Polar Scheme Voltages are on both sides of the axis. a. NRZ-L (NRZ-Level) - the level of the voltage determines the value of the bit, typically binary 1 map to logic-level high, and binary 0 maps to logic-level low. Some systems use the opposite convention depending on the assumption of level. b. NRZ-I (NRZ-Invert) - two-level signal has a transition at a boundary if the next bit that we are going to transmit is a logical 1, and does not have a transition if the next bit that we are going to transmit is a logical 0 c. RZ (Return to Zero) - uses three values positive, negative, and zero and in this scheme signal goes to 0 in the middle of each bit, for bit 1 half of the signal is represented by +V and half by zero and for bit 0 half of the signal is represented by -V and half by zero voltage. d. Manchester - for bit 1 there is transition form - V to +V volts in the middle of the bit and for bit Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications 0 there is transition from +V to -V volts in the middle of the bit. e. Differential Manchester - there is always a transition at the middle of the bit but the bit values are determined at the beginning of the bit. If the next bit is 0, there is a transition, if the next bit is 1, there is no transition Bipolar Schemes In this scheme there are three voltage levels positive, negative, and zero. The voltage level for one data element is at zero, while the voltage level for the other element alternates between positive and negative. a. Alternative Mark Inversion (AMI) - neutral zero voltage represents binary 0. Binary 1’s are represented by alternating positive and negative voltages b. Pseudoternary - bit 1 is encoded as a zero voltage and the bit 0 is encoded as alternating positive and negative voltages Synchronization Methods Synchronous Transmission Asynchronous Transmission Data is sent in form of blocks or frames Data is sent in form of bytes or characters Transmission is fast Transmission is slow Transmission is costly Transmission is economical Time interval of transmission is constant Time interval of transmission is not constant, it is random Users have to wait till the transmission is Users do not have to wait for the completion of complete before getting a response back from transmission in order to get a response from the the server server No gap present between data Gap present between data Efficient use of transmission lines is done Transmission line remains empty during a gap in character transmission Start and stop bits are not used in transmitting Start and stop bits are used in transmitting data data that imposes extra overhead Needs precisely synchronized clocks for the Does not need synchronized clocks as parity bit information of new bytes is used in this transmission for information of new bytes Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications Errors are detected and corrected in real time Errors are detected and corrected when the data is received Low latency due to real-time communication High latency due to processing time and waiting for data to become available Examples: Telephonic conversations, Video Examples: Email, File transfer,Online forms conferencing, Online gaming Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering