BCA III SEM com nw.pdf

BCA III SEM Data Communication and Computer Networks Unit 1 What is Computer Networking? A network set up by connecting two or more computers and other supporting hardware devices through communication channels is called a computer netwo...

BCA III SEM Data Communication and Computer Networks Unit 1 What is Computer Networking? A network set up by connecting two or more computers and other supporting hardware devices through communication channels is called a computer network. It enables computers to communicate with each other and to share commands, data, etc., including the hardware and software resources. Each computing device in a network is called a node or station. The nodes can be routers, personal computers, and servers. Data transformation is done via the network using rules known as protocols. The protocols are the set of rules which every node of the network should follow for transferring information over the wired or wireless network. Working of a Computer Network The nodes (like computers, switches, and modems) are the sources of generating and transmitting data. Then the link (a transmission media) is used to bond among the nodes. By following the protocols, the nodes will transfer and receive data via connections. computer network architecture defines the design associated among these physical and logical components. It provides the definitions for the network's physical components, functional organization, protocols, and procedures. Goals of Networks Computer Network means an interconnection of autonomous (standalone) computers for information exchange. The connecting media could be a copper wire, optical fiber, microwave, or satellite. Goals of computer network Goals of computer network are as follow : To provide sharing of resources such as information, devices or processors To provide inter-process communication among user and processors. It provides the network user with maximum performance at minimum cost It provides centralized control for a geographically distributed system. It provides compatibility of dissimilar equipment and software. It provides centralized management and allocation of network resources. It provides distributed processing functions. Networking Elements – The computer network includes the following networking elements: 1. At least two computers 2. Transmission medium either wired or wireless 3. Protocols or rules that govern the communication 4. Network software such as Network Operating System Network Criteria: The criteria that have to be met by a computer network are: 1. Performance – It is measured in terms of transit time and response time. Transit time is the time for a message to travel from one device to another Response time is the elapsed time between an inquiry and a response. Performance is dependent on the following factors: The number of users Type of transmission medium Capability of connected network Efficiency of software Bandwidth Network topology Network protocols Distance Network congestion Network hardware 2. Reliability – It is measured in terms of Frequency of failure Recovery from failures 1  Robustness during catastrophe Quality of service (QoS) Reducing single points of failure Capacity planning Network architecture 3. Security – It means protecting data from unauthorized access. 4. Network topology- it is another crucial factor to consider when designing a computer network. It refers to the way in which computers, devices, and links are arranged in a network. Common topologies include bus, star, ring, mesh, and hybrid, each with its own advantages and disadvantages in terms of cost, scalability, reliability, and performance. The choice of topology depends on the specific needs and constraints of the network. Other important criteria that must be met by a computer network include performance, reliability, and security. Goals of Computer Networks: The following are some important goals of computer networks: 1. Resource Sharing – Many organization has a substantial number of computers in operations, which are located apart. Ex. A group of office workers can share a common printer, fax, modem, scanner, etc. 2. High Reliability – If there are alternate sources of supply, all files could be replicated on two or more machines. If one of them is not available, due to hardware failure, the other copies could be used. 3. Inter-process Communication – Network users, located geographically apart, may converse in an interactive session through the network. In order to permit this, the network must provide almost error-free communications. 4. Flexible access – Files can be accessed from any computer in the network. The project can be begun on one computer and finished on another. 5. Security– Computer networks must be secure to protect against unauthorized access, data breaches, and other security threats. This includes implementing measures such as firewalls, antivirus software, and encryption to ensure the confidentiality, integrity, and availability of data. 6. Performance– Computer networks must provide high performance and low latency to ensure that applications and services are responsive and available when needed. This requires optimizing network infrastructure, bandwidth utilization, and traffic management. 7. Scalability- Computer networks must be designed to scale up or down as needed to accommodate changes in the number of users, devices, and data traffic. This requires careful planning and management to ensure the network can meet current and future needs. Other goals include Distribution of processing functions, Centralized management, and allocation of network resources, Compatibility of dissimilar equipment and software, Good network performance, Scalability, Saving money, Access to remote information, Person to person communication, etc. Advantages: Resource sharing: Networks enable the sharing of resources such as printers, scanners, storage devices, and software applications, which can reduce costs and increase efficiency. Communication and collaboration: Networks provide a platform for communication and collaboration among users, allowing for easy sharing of information and ideas. Centralized management: Networks allow for centralized management of devices, users, and resources, making it easier to control and monitor the network. Scalability: Networks can be scaled up or down to accommodate changes in the number of users, devices, or data volume. Accessibility: Networks can provide remote access to resources, enabling users to work from anywhere and improving accessibility to information and resources. Disadvantages: Security vulnerabilities: Networks can be vulnerable to security threats such as hacking, viruses, and malware, which can compromise sensitive data and disrupt network operations. Complexity: Networks can be complex to set up, configure, and maintain, requiring specialized knowledge and expertise. 2 Dependence on infrastructure: Networks depend on the underlying infrastructure such as cables, routers, switches, and servers, which can be prone to failures or downtime, disrupting network operations. Cost: Networks can be expensive to set up and maintain, requiring investments in hardware, software, and personnel. Performance limitations: Networks have performance limitations such as bandwidth constraints, latency, and congestion, which can affect the speed and reliability of network operations. Computer Network Architecture Computer Network Architecture is defined as the physical and logical design of the software, hardware, protocols, and media of the transmission of data. Simply we can say that how computers are organized and how tasks are allocated to the computer. The two types of network architectures are used: o Peer-To-Peer network o Client/Server network Peer-To-Peer network o Peer-To-Peer network is a network in which all the computers are linked together with equal privilege and responsibilities for processing the data. o Peer-To-Peer network is useful for small environments, usually up to 10 computers. o Peer-To-Peer network has no dedicated server. o Special permissions are assigned to each computer for sharing the resources, but this can lead to a problem if the computer with the resource is down. Advantages Of Peer-To-Peer Network: o It is less costly as it does not contain any dedicated server. o If one computer stops working but, other computers will not stop working. o It is easy to set up and maintain as each computer manages itself. Disadvantages Of Peer-To-Peer Network: o In the case of Peer-To-Peer network, it does not contain the centralized system. Therefore, it cannot back up the data as the data is different in different locations. o It has a security issue as the device is managed itself. Client/Server Network o Client/Server network is a network model designed for the end users called clients, to access the resources such as songs, video, etc. from a central computer known as Server. o The central controller is known as a server while all other computers in the network are called clients. 3  o A server performs all the major operations such as security and network management. o A server is responsible for managing all the resources such as files, directories, printer, etc. o All the clients communicate with each other through a server. For example, if client1 wants to send some data to client 2, then it first sends the request to the server for the permission. The server sends the response to the client 1 to initiate its communication with the client 2. Advantages Of Client/Server network: o A Client/Server network contains the centralized system. Therefore we can back up the data easily. o A Client/Server network has a dedicated server that improves the overall performance of the whole system. o Security is better in Client/Server network as a single server administers the shared resources. o It also increases the speed of the sharing resources. Disadvantages Of Client/Server network: o Client/Server network is expensive as it requires the server with large memory. o A server has a Network Operating System(NOS) to provide the resources to the clients, but the cost of NOS is very high. o It requires a dedicated network administrator to manage all the resources. Network Services? o Network services are applications at the network application layer that connect users working in offices, branches, or remote locations to applications and data in a network. These services typically run on servers. What are some types of network services? Here are examples of types of network services: Internet and cloud connectivity Branch office and campus connectivity Private data center services Secure cloud-connectivity services Virtual network services In computer networking, a network service is an application running at the network application layer and above, that provides data storage, manipulation, presentation, communication or other capability which is often implemented using a client–server or peer-to-peer architecture based on application layer network protocols. Each service is usually provided by a server component running on one or more computers (often a dedicated server computer offering multiple services) and accessed via a network by client components running on other devices. However, the client and server components can both be run on the same machine. Clients and servers will often have a user interface, and sometimes other hardware associated with it. Examples are the Domain Name System (DNS) which translates domain names to Internet Protocol (IP) addresses and the Dynamic Host Configuration Protocol (DHCP) to assign networking configuration information to network hosts. Authentication servers identify and authenticate users, provide user account profiles, and may log usage statistics. E-mail, printing and distributed (network) file system services are common services on local area networks. They require users to have permissions to access the shared resources. 4  Other network services include: Directory services e-Mail File sharing Instant messaging Online game Printing File server Voice over IP Video on demand Video telephony World Wide Web Simple Network Management Protocol Time service Wireless sensor network Network examples 1. The World Wide Web. This is a directed network in which nodes represent Web pages and edges are the hyperlinks between pages. More precisely, there exists an edge from page p to page q if page p contains at least one hyperlink pointing to page q. Usually, the actual number of hyperlinks from p page q is not important and hence the network modelling the Web is unweighted. 2. The Internet. This is a collection of routers linked by various physical lines. The Internet is a growing network with no central control authority. When adding a new node to the Internet, two factors mainly determine the router node to connect to: distance and bandwidth. While distance puts obvious constraints, bandwidth, a measure of connection speed of the router, is typically the dominant factor. This explains the emergence of hubs in the Internet. 3. Powerline and airline networks. These are human-made networks that might be involved in random failures as well as targeted attacks. Failures may have cascading effects: the failure of one node may recursively provoke the failure of connected nodes. Clearly, such events on these networks might have catastrophic consequences. The topology of the network directly influences the magnitude and reach of such events. 4. Citation networks. An article citation network links scholarly papers through bibliographic references contained in the bibliography of the papers. This network is directed and follows the temporal ordering of papers: we cite the past, not the future 5. Language networks. In these networks the nodes are words and the links represent relationships among words like significant co-occurrence in texts. 6. Food webs. These are networks created by nature. In food webs, species are connected by links telling which species feeds on which other species. The links of these networks seldom go both ways, and hence food webs are also an example of directed networks. Studying food webs is important to understand the ecosystem dynamics. 7. Economic networks. Market can be viewed as a huge directed multi-relational network. Companies, firms, financial institutions, governments play the role of nodes. Links symbolize different interactions between them, for instance purchases and sales or financial loaning, and the weight of the links captures the value of the transaction. Viewing the economy as a network of interacting actors is useful to make sense of global financial meltdowns, which are provoked by a sequence of failures cascading over the highly connected and interdependent network economy. 8. Metabolic and protein networks. The nodes of metabolic networks are simple molecules like water or ATP. The links are the biochemical reactions that take place between these molecules. Moreover, proteins can be viewed as nodes of a complex network in which two proteins are connected if they can physically interact. 9. Social networks. Social networks link people according to various social relationships, like acquaintance, friendship, collaboration, and sexual relation. They are of paramount importance to understand and anticipate the spread of ideas, innovations, fads, as well as biological and computer viruses 5 Network Standardization Many network vendors and suppliers exist, each with their own ideas of how things should be done. Without coordination, there would be complete chaos, and users would be able to get nothing done. The only way out is to agree upon some network standards. Not only do standards allow different computers to communicate, they also increase the market for products adhering to the standard, which leads to mass production, economies of scale in manufacturing, and other benefits that decrease price and further increase acceptance. We will take a quick look at the subject of international standardization. Standards fall into two categories: 1. de facto, and 2. de jure. De facto (Latin for "from the fact") standards are those that have just happened, without any formal plan. The IBM PC and its successors are defacto standards for small office computers because dozens of manufacturers have chosen to copy IBM's machines very closely. UNIX is the de facto standard for operating systems in university computer science departments. De jure (Latin for "by law") standards, in contrast, are formal, legal standards adopted by some authorized standardization body. nternational standardization authorities are generally divided into two classes: 1. Those established by treaty among national governments, and 2. Voluntary, non-treaty organizations. In the area of computer network standards, there are several organizations of each type. Networking models are frameworks that represent how devices and systems communicate and interact within a network. They help organize the flow of data, ensure efficient communication, and share resources. What are Centralized Systems? Centralized systems are a type of computing architecture where all or most of the processing and data storage is done on a single central server or a group of closely connected servers. This central server manages all operations, resources, and data, acting as the hub through which all client requests are processed. The clients, or nodes, connected to the central server typically have minimal processing power and rely on the server for most computational tasks. Centralized Systems Key Characteristics of Centralized Systems 1. Single Point of Control: All data processing and management tasks are handled by the central server. Easier to manage and maintain since there is one primary location for administration. 2. Simplicity: Simplified architecture with a clear structure where all operations are routed through the central node. Easy to deploy and manage due to centralized nature. 6  3. Efficiency: Efficient use of resources as the central server can be optimized for performance. Easier to implement security measures and updates centrally. 4. Scalability Issues: Limited scalability as the central server can become a bottleneck if the load increases significantly. Adding more clients can strain the server’s resources, leading to performance degradation. 5. Single Point of Failure: If the central server fails, the entire system can become inoperative. High availability and redundancy measures are essential to mitigate this risk. What are Decentralized Systems? Decentralized systems are computing architectures where multiple nodes, often spread across different locations, share control and processing power without a single central authority. Each node in a decentralized system operates independently but collaborates with others to achieve common goals. This structure enhances fault tolerance, scalability, and resilience compared to centralized systems. Decentralized System Key Characteristics of Decentralized Systems: 1. Distributed Control: No single point of control or failure. Each node operates independently, contributing to the overall system’s functionality. 2. Fault Tolerance: If one node fails, the system can continue to function with the remaining nodes. Enhanced resilience against failures and attacks. 3. Scalability: Easier to scale by adding more nodes without overwhelming a central point. Load distribution across multiple nodes improves performance and resource utilization. 4. Coordination and Communication: Nodes must communicate and coordinate to maintain system integrity and consistency. Complex algorithms and protocols often manage this coordination. 5. Autonomy and Redundancy: Each node can operate autonomously, contributing to redundancy and reducing single points of failure. Data and services are often replicated across multiple nodes for reliability. What are Distributed Systems? Distributed systems are computing architectures where multiple independent nodes or computers work together to achieve a common goal. These nodes communicate and coordinate with each other over a network, appearing as a single coherent system to the end user. Distributed systems aim to improve performance, reliability, scalability, and resource sharing by leveraging the collective power of interconnected devices. 7 Distributed Systems Key Characteristics of Distributed Systems 1. Geographical Distribution: Nodes are spread across different physical locations. They communicate via a network, such as a local area network (LAN) or the internet. 2. Resource Sharing: Nodes share resources such as processing power, storage, and data. This enables more efficient utilization of resources. 3. Concurrency: Multiple nodes operate concurrently, performing tasks simultaneously. This parallelism enhances the system’s overall performance and throughput. 4. Scalability: Easy to scale by adding more nodes to the system. System capacity and performance improve with the addition of resources. 5. Fault Tolerance: Designed to handle failures gracefully. Redundancy and replication ensure the system remains operational even if some nodes fail. 6. Transparency: The complexity of the distributed system is hidden from users. Users interact with the system as if it were a single entity. Differences between Centralized, Decentralized and Distributed Systems Aspect Centralized Systems Decentralized Systems Distributed Systems Single central server Multiple nodes with Multiple interconnected nodes controls and manages independent control, no working together as a single Definition all operations. central authority. system. Centralized control Distributed control, each Shared control, nodes with a single point of node operates collaborate to achieve common Control management. independently. goals. 8 Aspect Centralized Systems Decentralized Systems Distributed Systems High risk; if the Reduced risk; failure of Reduced risk; designed for fault Single Point of central server fails, the one node does not impact tolerance and redundancy. Failure whole system fails. the entire system. Limited scalability, More scalable, can add Highly scalable, can add more can become a nodes independently. nodes to distribute the load. Scalability bottleneck. Central server Resources are spread Efficient resource sharing across Resource resources are heavily across multiple nodes. nodes. Utilization utilized. Can be high initially Generally good, High performance due to parallel but may degrade with performance improves processing and resource sharing. Performance increased load. with more nodes. More complex, requires Easier to manage Complex, requires coordination managing multiple centrally. and management of many nodes. Management nodes. Lower latency, as Can vary, depends on the Potentially higher latency due to operations are distance between nodes. network communication Latency managed centrally. Network Topology Topology: It refers to the physical arrangement and representation of all the nodes and components of the network. In general terms, Topology defines the structure of the entire network. The network topology is divided into five types. They are bus topology, star topology, ring topology, mesh topology, and tree topology. 1) Bus Topology: In this arrangement, the nodes (computers) are connected through interface connectors to a single communication line (central cable) that carries the message in both the directions. The central cable to which all the nodes are connected is the backbone of the network. It is called a bus. The signal in this arrangement travels in both directions to all the machines until it finds the recipient machine. It is easy to set up than other topologies as it uses only a single central cable to establish the network. Advantages: o Configuration of the network is easy. o Less costly because a single cable is used to connect all nodes. 9  o The Bus topology supports a maximum of 10 Mbps speed by using the network's coaxial or twisted pair cables. Disadvantages o Due to the multipoint communication model, it is difficult to identify and isolate the faulty terminals. o The reconfiguration will affect the network and slows down the performance. o Signal interference is another drawback of the bus topology; if two or more nodes transmit the messages simultaneously, their signals will collide. o A single node failure also causes the breakdown of the whole network. 2) Ring Topology: As the name suggests, in a ring topology, the computers are connected in a circular and closed loop. The message in this topology moves only in one direction around the ring from one node to another node and is checked by each node for a matching destination address. So, the data keeps moving until it reaches its destination. All nodes are equal; a client-server relationship does not exist between them. As the nodes are in the form of a ring, if one node fails to transmit the data, the flow of communication is severed. Advantages: o The data transfer and Communication are easy due to easy packet movement. o The installation of the network and reconfiguration is easy. o The presence of errors in links and faulty nodes can be easily identified and isolated. o The reliability of the ring topology is more. Disadvantages: o As the data transmission is unidirectional, the packet will travel all the nodes to reach the destination. o One node failure incurs damage to the entire network. o Reconfiguration (adding new nodes) is easy but gets down the performance of the network. o The delay is more in data transmission when the network contains more stations. 3) Star Topology: In this topology, all the computers are separately connected to a central node or connection point, which can be a server, a hub, a router, or a switch. This topology offers an advantage that if a cable does not work, only the respective node will suffer, the rest of the nodes will work smoothly. All data or messages that one node sends to another passes through the central hub. This topology is easy to design and implement as well as it is easy to add additional nodes to the central node. The major drawback of this topology is that it is prone to bottleneck or failure at the central connection point, i.e., failure at the central node will affect the entire communication. Advantages: o Easy installation and reconfiguration. o Less expensive as compared to mess Topology because the star requires less wiring. 10  o Easy to identify and isolate the faulty networks and links. o When we add a new node, there is no interruption to other nodes in the network as the node is directly connected to the hub. o Using star topology, we can achieve a high speed of data transfers. Disadvantages o If the hub fails, the whole network will not work. o The star topology is more expensive than the bus topology because of the hub. o We use more wire than that of the bus and ring topology. o Every node completely depends on the hub for making decisions to transmit and process the data packets. 4) Mesh Topology In a mesh topology, every device is connected to another device in a network using a point-to-point connection. The connection is generally known as a dedicated connection, as the link transports data between two devices. The number of links in a mesh topology is calculated using the formula below. Military organizations use mesh topology to avoid breaks down in communications. Many connections = n * (n - 1) /2. Here, "n" represents the number of nodes in a network. Advantages: o Easy to transmit data. o We can send data from many devices simultaneously. Mesh topology will handle much traffic as compared to other topologies. o If one link is broken or remains faulty, data transfer can occur between nodes using other links. Hence data transmission is uninterrupted and reliable. o The physical margins will not allow other persons to enter and access the messages. o Fault detection and isolation are easy. Disadvantages: o The cabling used to construct the network is more. o The installation cost is high compared to other topologies due to more wiring. o The installation and reconfiguration are tough because of the presence of many links. 5) Tree Topology Tree topology is the combination of star and bus topologies. The nodes are connected to a hub as in star topology, and all the star-connected nodes are placed in a bus topology. The tree topology is a hybrid connection. Advantages: o Network extension is easy. 11  o The network is broken into smaller star-connected topology units. The nodes connected in a tree topology are easier to maintain. o Fault detection and correction are easy. o If one of the stars connected unit of nodes goes faulty, the other segments will not be affected and network can be runed with remaining nodes. Disadvantages: o The main disadvantage is that if the bus cable is damaged, the entire topology will not work. o The management of Topology becomes easier when the number of nodes and star-connected topologies is increased in large numbers. o The reconfiguration becomes difficult when new nodes are added. Transmission modes o The way in which data is transmitted from one device to another device is known as transmission mode. o The transmission mode is also known as the communication mode. o Each communication channel has a direction associated with it, and transmission media provide the direction. Therefore, the transmission mode is also known as a directional mode. o The transmission mode is defined in the physical layer. The Transmission mode is divided into three categories: o Simplex mode o Half-duplex mode o Full-duplex mode Simplex mode o In Simplex mode, the communication is unidirectional, i.e., the data flow in one direction. o A device can only send the data but cannot receive it or it can receive the data but cannot send the data. o This transmission mode is not very popular as mainly communications require the two-way exchange of data. The simplex mode is used in the business field as in sales that do not require any corresponding reply. o The radio station is a simplex channel as it transmits the signal to the listeners but never allows them to transmit back. o Keyboard and Monitor are the examples of the simplex mode as a keyboard can only accept the data from the user and monitor can only be used to display the data on the screen. o The main advantage of the simplex mode is that the full capacity of the communication channel can be utilized during transmission. Advantage of Simplex mode: o In simplex mode, the station can utilize the entire bandwidth of the communication channel, so that more data can be transmitted at a time. Disadvantage of Simplex mode: o Communication is unidirectional, so it has no inter-communication between devices. Half-Duplex mode 12  o In a Half-duplex channel, direction can be reversed, i.e., the station can transmit and receive the data as well. o Messages flow in both the directions, but not at the same time. o The entire bandwidth of the communication channel is utilized in one direction at a time. o In half-duplex mode, it is possible to perform the error detection, and if any error occurs, then the receiver requests the sender to retransmit the data. o A Walkie-talkie is an example of the Half-duplex mode. In Walkie-talkie, one party speaks, and another party listens. After a pause, the other speaks and first party listens. Speaking simultaneously will create the distorted sound which cannot be understood. Advantage of Half-duplex mode: o In half-duplex mode, both the devices can send and receive the data and also can utilize the entire bandwidth of the communication channel during the transmission of data. Disadvantage of Half-Duplex mode: o In half-duplex mode, when one device is sending the data, then another has to wait, this causes the delay in sending the data at the right time. Full-duplex mode o In Full duplex mode, the communication is bi-directional, i.e., the data flow in both the directions. o Both the stations can send and receive the message simultaneously. o Full-duplex mode has two simplex channels. One channel has traffic moving in one direction, and another channel has traffic flowing in the opposite direction. o The Full-duplex mode is the fastest mode of communication between devices. o The most common example of the full-duplex mode is a telephone network. When two people are communicating with each other by a telephone line, both can talk and listen at the same time. Advantage of Full-duplex mode: o Both the stations can send and receive the data at the same time. Disadvantage of Full-duplex mode: o If there is no dedicated path exists between the devices, then the capacity of the communication channel is divided into two parts. Differences b/w Simplex, Half-duplex and Full-duplex mode Basis for Simplex mode Half-duplex mode Full-duplex mode comparison Direction of In simplex mode, the In half-duplex mode, In full-duplex mode, the communication communication communication is the communication is is bidirectional. unidirectional. bidirectional, but one at a time. Send/Receive A device can only Both the devices can Both the devices can send and receive the send the data but send and receive the data simultaneously. cannot receive it or it data, but one at a time. can only receive the 13  data but cannot send it. Performance The performance of The performance of The Full-duplex mode has better half-duplex mode is full-duplex mode is performance among simplex and half- better than the better than the half- duplex mode as it doubles the utilization simplex mode. duplex mode. of the capacity of the communication channel. Example Examples of Example of half- Example of the Full-duplex mode is a Simplex mode are duplex is Walkie- telephone network. radio, keyboard, and Talkies. monitor. Unit 2- Data Communication – Transferring data over a transmission medium between two or more devices, systems, or places is known as data communication. Nowadays, computing and telecommunications depend heavily on this data transmission, which makes a variety of applications conceivable, including email, video chatting, the Internet, and many more things. In this article, we will learn about Data communication, Definition, Components, Types, and Channels. Components of Data Communication A communication system is made up of the following components: 1. Message: A message is a 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. It can be a computer, mobile, telephone, laptop, video camera, or workstation, etc. 3. Receiver: It is a device that receives messages. It can be a computer, telephone mobile, workstation, etc. 4. Transmission Medium / Communication Channels: Communication channels are the medium that connect two or more workstations. Workstations can be connected by either wired media or wireless media. 5. Set of rules (Protocol): When someone sends the data (The sender), it should be understandable to the receiver also otherwise it is meaningless. For example, Sonali sends a message to Chetan. If Sonali writes in Hindi and Chetan cannot understand Hindi, it is a meaningless conversation. What is Transmission media? o Transmission media is a communication channel that carries the information from the sender to the receiver. Data is transmitted through the electromagnetic signals. o The main functionality of the transmission media is to carry the information in the form of bits through LAN(Local Area Network). o It is a physical path between transmitter and receiver in data communication. o In a copper-based network, the bits in the form of electrical signals. o In a fibre based network, the bits in the form of light pulses. 14  o In OSI(Open System Interconnection) phase, transmission media supports the Layer 1. Therefore, it is considered to be as a Layer 1 component. o The electrical signals can be sent through the copper wire, fibre optics, atmosphere, water, and vacuum. o The characteristics and quality of data transmission are determined by the characteristics of medium and signal. o Transmission media is of two types are wired media and wireless media. In wired media, medium characteristics are more important whereas, in wireless media, signal characteristics are more important. o Different transmission media have different properties such as bandwidth, delay, cost and ease of installation and maintenance. o The transmission media is available in the lowest layer of the OSI reference model, i.e., Physical layer. Some factors need to be considered for designing the transmission media: o Bandwidth: All the factors are remaining constant, the greater the bandwidth of a medium, the higher the data transmission rate of a signal. o Transmission impairment: When the received signal is not identical to the transmitted one due to the transmission impairment. The quality of the signals will get destroyed due to transmission impairment. o Interference: An interference is defined as the process of disrupting a signal when it travels over a communication medium on the addition of some unwanted signal. Causes Of Transmission Impairment: o Attenuation: Attenuation means the loss of energy, i.e., the strength of the signal decreases with increasing the distance which causes the loss of energy. o Distortion: Distortion occurs when there is a change in the shape of the signal. This type of distortion is examined from different signals having different frequencies. Each frequency component has its own propagation speed, so they reach at a different time which leads to the delay distortion. o Noise: When data is travelled over a transmission medium, some unwanted signal is added to it which creates the noise. Classification Of Transmission Media: o Guided Transmission Media o UnGuided Transmission Media o Guided Transmission Media in Computer Network Introduction Communication is an essential component of the vast field of computer networks, which depends on a variety of transmission methods to enable data exchange. In this procedure, guided transmission media also referred to as bounded or wired media, are essential. These media are the actual channels that direct signals 15 between connected devices in a network. We shall examine the different types, traits, and uses of guided transmission medium in computer networks as we dig into their complexities in this article. Types of Guided Transmission Media 1. Twisted Pair Cable: o Description: To try to reduce electromagnetic interference, insulated copper wires are twisted together in pairs to create twisted pair cables. Twisted pair is a physical media made up of a pair of cables twisted with each other. A twisted pair cable is cheap as compared to other transmission media. Installation of the twisted pair cable is easy, and it is a lightweight cable. The frequency range for twisted pair cable is from 0 to 3.5KHz. o Characteristics: Twisted pair cables have become common in LANs and phone lines. They are available in two types: unprotected twisted pair and shielded twisted pair. A twisted pair consists of two insulated copper wires arranged in a regular spiral pattern. The degree of reduction in noise interference is determined by the number of turns per foot. Increasing the number of turns per foot decreases noise interference. Types of Twisted pair: Unshielded Twisted Pair: An unshielded twisted pair is widely used in telecommunication. Following are the categories of the unshielded twisted pair cable: o Category 1: Category 1 is used for telephone lines that have low-speed data. o Category 2: It can support upto 4Mbps. o Category 3: It can support upto 16Mbps. o Category 4: It can support upto 20Mbps. Therefore, it can be used for long-distance communication. o Category 5: It can support upto 200Mbps. Advantages Of Unshielded Twisted Pair: Advertisement o It is cheap. o Installation of the unshielded twisted pair is easy. o It can be used for high-speed LAN. Disadvantage: o This cable can only be used for shorter distances because of attenuation. Shielded Twisted Pair A shielded twisted pair is a cable that contains the mesh surrounding the wire that allows the higher transmission rate. Characteristics Of Shielded Twisted Pair: o The cost of the shielded twisted pair cable is not very high and not very low. o An installation of STP is easy. o It has higher capacity as compared to unshielded twisted pair cable. o It has a higher attenuation. o It is shielded that provides the higher data transmission rate. Disadvantages o It is more expensive as compared to UTP and coaxial cable. o It has a higher attenuation rate. 16 Coaxial Cable o Coaxial cable is very commonly used transmission media, for example, TV wire is usually a coaxial cable. o The name of the cable is coaxial as it contains two conductors parallel to each other. o It has a higher frequency as compared to Twisted pair cable. o The inner conductor of the coaxial cable is made up of copper, and the outer conductor is made up of copper mesh. The middle core is made up of non-conductive cover that separates the inner conductor from the outer conductor. o The middle core is responsible for the data transferring whereas the copper mesh prevents from the EMI(Electromagnetic interference). Coaxial cable is of two types: 1. Baseband transmission: It is defined as the process of transmitting a single signal at high speed. 2. Broadband transmission: It is defined as the process of transmitting multiple signals simultaneously. Advantages Of Coaxial cable: o The data can be transmitted at high speed. o It has better shielding as compared to twisted pair cable. o It provides higher bandwidth. Disadvantages Of Coaxial cable: o It is more expensive as compared to twisted pair cable. o If any fault occurs in the cable causes the failure in the entire network. Fibre Optic o Fibre optic cable is a cable that uses electrical signals for communication. o Fibre optic is a cable that holds the optical fibres coated in plastic that are used to send the data by pulses of light. o The plastic coating protects the optical fibres from heat, cold, electromagnetic interference from other types of wiring. o Fibre optics provide faster data transmission than copper wires. Diagrammatic representation of fibre optic cable: Basic elements of Fibre optic cable: o Core: The optical fibre consists of a narrow strand of glass or plastic known as a core. A core is a light transmission area of the fibre. The more the area of the core, the more light will be transmitted into the fibre. o Cladding: The concentric layer of glass is known as cladding. The main functionality of the cladding is to provide the lower refractive index at the core interface as to cause the reflection within the core so that the light waves are transmitted through the fibre. o Jacket: The protective coating consisting of plastic is known as a jacket. The main purpose of a jacket is to preserve the fibre strength, absorb shock and extra fibre protection. 17 Following are the advantages of fibre optic cable over copper: o Greater Bandwidth: The fibre optic cable provides more bandwidth as compared copper. Therefore, the fibre optic carries more data as compared to copper cable. o Faster speed: Fibre optic cable carries the data in the form of light. This allows the fibre optic cable to carry the signals at a higher speed. o Longer distances: The fibre optic cable carries the data at a longer distance as compared to copper cable. o Better reliability: The fibre optic cable is more reliable than the copper cable as it is immune to any temperature changes while it can cause obstruct in the connectivity of copper cable. o Thinner and Sturdier: Fibre optic cable is thinner and lighter in weight so it can withstand more pull pressure than copper cable. 4. Guided Media Connectors: o Description: Connectors are parts that connect parts of guided media so that continuous communication channels may be created. o Characteristics: To be able to offer stable and efficient communication in computer networks, a variety of connectors are important, such as BNC connectors for coaxial cables and RJ-45 connectors for twisted pair cables. Applications of Guided Transmission Media 1. Local Area Networks (LANs): In local area networks (LANs), guided transmission media, particularly coaxial and twisted pair cables, are often utilized to link computers and other devices within a specific geographic region. 2. Wide Area Networks (WANs): Due to their high bandwidth and ability to transfer data over long distances without a significant signal loss, optical fiber cables are the preferred choice for wide-area networks. 3. Internet Backbone Networks: A lot of data can be easily and quickly sent across continents due to the internet core, which is made up of high-capacity fiber connections. 4. Telecommunication Networks: A lot of data can be easily and quickly sent across continents due to the internet core, which is made up of high-capacity fiber connections. Advantages of Guided Transmission Media 1. Reliability: High levels of stability are provided by guided transmission mediums such as optical fibers and twisted pair cables. Because these media are real, there is less chance of interference or signal loss, ensuring safe and constant communication. 2. Security: When compared to wireless options guided transmission methods give a more secure communication environment. Because these media are led, it is more difficult for hackers to intercept signals, which improves network security in general. 3. Higher Bandwidth: Higher bandwidths are ensured by guided media, especially optical fibers, than by many wireless choices. These are perfect for applications with high data transfer requirements since this enables the transmission of greater amounts of data at faster speeds. 4. Less Susceptible to Interference: Compared to wireless transmission twisted pair and coaxial cables are less sensitive to electromagnetic interference. This feature assures signal integrity and makes them useful for high electrical noise settings. 5. Predictable Performance: Media with guided transmission provide consistent performance properties. Because these media allow for more accurate control and management of signal behavior, they are perfect for applications where stability is important. 6. Suitable for Long Distances: 18 Optical fibers, in particular, have a low signal reduction, making them perfect for long-distance communication. They are also important for fast data transmission over big geographical regions and core networks. 7. Cost-Effective for Short Distances: When compared to building wireless infrastructure, guided transmission mediums such as twisted pair cables can be cheaper for relatively short distances. They are also preferred choices for some connections between devices and local area networks. Disadvantages of Guided Transmission Media 1. Limited Mobility: The infrastructure physically attaches devices connected through guided media. These media are less suited to applications that require continuous movement, like mobile communication, because of this restriction on mobility and flexibility. 2. Vulnerability to Physical Damage: Even cables guided transmission media are at risk of physical harm. Communication can be interrupted by the construction of the environment or accidental cuts. These situations require maintenance and repair. 3. Cost for Long Distances: Since optical fibers and other guided media are great for long-distance communication, the initial installation costs of these systems can be high. For companies with small budgets, this cost may be a problem. 4. Limited Bandwidth for Some Types: Compared to wireless technologies, a few guided transmission media types, such as twisted pair cables, may have lower bandwidth sizes. For applications that require high data transfer rates, this may be an issue. 5. Infrastructure Dependency: Media that is guided mostly depends upon physical infrastructure. Any network upgrades or changes require major adjustments to the current infrastructure that may result in delays and extra expenses. 6. Environmental Impact: There can be environmental effects from the production and disposal of guided transmission media, particularly cables. The creation of more environmentally friendly and sustainable alternatives is becoming more and more important as technology develops. UnGuided Transmission Advertisement o An unguided transmission transmits the electromagnetic waves without using any physical medium. Therefore it is also known as wireless transmission. o In unguided media, air is the media through which the electromagnetic energy can flow easily. Unguided transmission is broadly classified into three categories: Radio waves o Radio waves are the electromagnetic waves that are transmitted in all the directions of free space. o Radio waves are omnidirectional, i.e., the signals are propagated in all the directions. o The range in frequencies of radio waves is from 3Khz to 1 khz. o In the case of radio waves, the sending and receiving antenna are not aligned, i.e., the wave sent by the sending antenna can be received by any receiving antenna. o An example of the radio wave is FM radio. Applications Of Radio waves: o A Radio wave is useful for multicasting when there is one sender and many receivers. 19  o An FM radio, television, cordless phones are examples of a radio wave. Advantages Of Radio transmission: o Radio transmission is mainly used for wide area networks and mobile cellular phones. o Radio waves cover a large area, and they can penetrate the walls. o Radio transmission provides a higher transmission rate. Microwaves Microwaves are of two types: o Terrestrial microwave o Satellite microwave communication. Terrestrial Microwave Transmission o Terrestrial Microwave transmission is a technology that transmits the focused beam of a radio signal from one ground-based microwave transmission antenna to another. o Microwaves are the electromagnetic waves having the frequency in the range from 1GHz to 1000 GHz. o Microwaves are unidirectional as the sending and receiving antenna is to be aligned, i.e., the waves sent by the sending antenna are narrowly focussed. o In this case, antennas are mounted on the towers to send a beam to another antenna which is km away. o It works on the line of sight transmission, i.e., the antennas mounted on the towers are the direct sight of each other. Characteristics of Microwave: o Frequency range: The frequency range of terrestrial microwave is from 4-6 GHz to 21-23 GHz. o Bandwidth: It supports the bandwidth from 1 to 10 Mbps. o Short distance: It is inexpensive for short distance. o Long distance: It is expensive as it requires a higher tower for a longer distance. o Attenuation: Attenuation means loss of signal. It is affected by environmental conditions and antenna size. Advantages Of Microwave: o Microwave transmission is cheaper than using cables. o It is free from land acquisition as it does not require any land for the installation of cables. o Microwave transmission provides an easy communication in terrains as the installation of cable in terrain is quite a difficult task. o Communication over oceans can be achieved by using microwave transmission. Disadvantages of Microwave transmission: o Eavesdropping: An eavesdropping creates insecure communication. Any malicious user can catch the signal in the air by using its own antenna. o Out of phase signal: A signal can be moved out of phase by using microwave transmission. o Susceptible to weather condition: A microwave transmission is susceptible to weather condition. This means that any environmental change such as rain, wind can distort the signal. o Bandwidth limited: Allocation of bandwidth is limited in the case of microwave transmission. Satellite Microwave Communication o A satellite is a physical object that revolves around the earth at a known height. o Satellite communication is more reliable nowadays as it offers more flexibility than cable and fibre optic systems. 20  o We can communicate with any point on the globe by using satellite communication. How Does Satellite work? The satellite accepts the signal that is transmitted from the earth station, and it amplifies the signal. The amplified signal is retransmitted to another earth station. Advantages Of Satellite Microwave Communication: o The coverage area of a satellite microwave is more than the terrestrial microwave. o The transmission cost of the satellite is independent of the distance from the centre of the coverage area. o Satellite communication is used in mobile and wireless communication applications. o It is easy to install. o It is used in a wide variety of applications such as weather forecasting, radio/TV signal broadcasting, mobile communication, etc. Disadvantages Of Satellite Microwave Communication: o Satellite designing and development requires more time and higher cost. o The Satellite needs to be monitored and controlled on regular periods so that it remains in orbit. o The life of the satellite is about 12-15 years. Due to this reason, another launch of the satellite has to be planned before it becomes non-functional. Infrared o An infrared transmission is a wireless technology used for communication over short ranges. o The frequency of the infrared in the range from 300 GHz to 400 THz. o It is used for short-range communication such as data transfer between two cell phones, TV remote operation, data transfer between a computer and cell phone resides in the same closed area. Characteristics Of Infrared: o It supports high bandwidth, and hence the data rate will be very high. o Infrared waves cannot penetrate the walls. Therefore, the infrared communication in one room cannot be interrupted by the nearby rooms. o An infrared communication provides better security with minimum interference. o Infrared communication is unreliable outside the building because the sun rays will interfere with the infrared waves. Digital Communication Digital communication is made from two words digital and communication. Digital refers to the discrete time-varying signal. Communication refers to the exchange of information between two or more sources. Digital refers to the discrete time-varying signal. Communication refers to the exchange of information between two or more sources. Digital communication refers to the exchange of digital information between the sender and receiver using different devices and methods. The data transmission using analog methods for long-distance communication suffers from distortion, delays, interferences, and other losses. To overcome these problems, the digitization and sampling of signals using different techniques help in making the transmission process more efficient, clear, and accurate. Digital communication is a popular technology used today in electronics. It allows us to access video conferencing, digital meetings, online education, etc. The data can travel upto long distances within a second with the help of the internet and other modes of digital communication. It not only saves money but also saves time and effort. It has also raised the standard of an individual's social, political, and economic life. Data communication vs. digital communication What is Communication? Communication refers to the exchange of information using a specific medium, such as vacuum, space, wireless medium, wired medium, etc. Good communication always transmits information with reduced attenuation and noise. The received signal is the same as the transmitted signal with clear information. Communication is a two-way process of sharing information. In digital terms, communication refers to the exchange of digital information from the transmitter to the receiver. 21 The components of a communication system are the transmitter, communication channel, and receiver. The transmitter transmits the data to the communication channel, which further sends it to the receiver. Various devices are used in cascade or parallel with the transmitters and receivers for different purposes, such as modulation, demodulation, noise removal, sampling, etc. The devices include modulators, filters, amplifiers, encoders, and decoders. Signals A signal is an electromagnetic wave that carries information from one place to another, using a specific propagation medium, such as air, vacuum, water, and solid. In electronics, the signal is defined as a current, voltage, or wave carrying information. It can travel short distances or long distances depending on the requirements. The speed of a signal wave is equal to the speed of light. The signals are categorized as analog signal and digital signals. Analog refers to the data transmission in continuous form, while digital refers to the data transmission in the discrete form. It is also known as the transmission in the form of bits, 0 (LOW) and 1 (HIGH). The waveforms of the analog and digital signal are shown below: The noise in analog signals is high as compared to digital signal. It is due to the thresholding and high bandwidth of the digital signals. Hence, electronic noise affects analog signals more than digital signals. Filters are generally used in analog communication at transmitting and receiving ends to remove the noise. Digital Signal We can represent various physical quantities using digital signals, such as voltage and current. A signal represented in the form of discrete values is known as digital signal. It is transmitted in the form of bits. Only two bits (0 and 1) work in different combinations. A digital signal can take only one value at a time from the set of finite possible values. Digital signal is nothing but the representation of the analog data in the discrete form. For example, The above two waveforms are the analog and digital waveforms. The digital waveform depicts the information in discrete bands of analog levels. 22 The binary signal is also known as the logic signal because both represent two bands, HIGH and LOW. 0 and 1 are also represented as the numbers in Boolean domain. HIGH = 1 = TRUE LOW = 0 = FALSE A digital system represents a continuous waveform switching between the discrete values called bitstreams in a communication system. It allows cost savings with reduced transmission time. The noise interference during the transmission can be effectively removed using the data redundancy process or data compression, where the data is encoded using fewer bits than the original information. Digital vs. Analog The digital computers were the first technologies used to store the digital record with a large size occupying the space of a room. The later inventions created new history and today digital computers are used to store millions of data with a size similar to rice grain. The differences between digital communication and analog communication are listed in the below table: Category Digital Communication Analog Communication Definition It uses digital signals with discrete values It uses analog signals for for transmitting data represented in the form transmitting data. of two binary digits 0 and 1. Signal The digital signal represents one bit at a The analog signal represents time. continuous values at a time. Noise Immunity Good Poor Error Probability Low High Coding Yes No The digital communication system uses an encoder and decoder to convert the information into bits and vice-versa. Flexible More flexible Less flexible Cost High cost Low cost Power Low High consumption Data transmission More accurate Less accurate Signal The digital signals are represented by a The analog signals are represented representation square wave. by a sine wave or cosine wave. Examples Clock signals Audio signals, speech signals, sound waves, pressure waves, video signals, etc. Applications Digital watches, Compact Disks, computers, Radar, Telephony, etc. etc. What is Multiplexing? Multiplexing is a technique used to combine and send the multiple data streams over a single medium. The process of combining the data streams is known as multiplexing and hardware used for multiplexing is known as a multiplexer. Multiplexing is achieved by using a device called Multiplexer (MUX) that combines n input lines to generate a single output line. Multiplexing follows many-to-one, i.e., n input lines and one output line. 23 Demultiplexing is achieved by using a device called Demultiplexer (DEMUX) available at the receiving end. DEMUX separates a signal into its component signals (one input and n outputs). Therefore, we can say that demultiplexing follows the one-to-many approach. Why Multiplexing? o The transmission medium is used to send the signal from sender to receiver. The medium can only have one signal at a time. o If there are multiple signals to share one medium, then the medium must be divided in such a way that each signal is given some portion of the available bandwidth. For example: If there are 10 signals and bandwidth of medium is100 units, then the 10 unit is shared by each signal. o When multiple signals share the common medium, there is a possibility of collision. Multiplexing concept is used to avoid such collision. o Transmission services are very expensive. History of Multiplexing o Multiplexing technique is widely used in telecommunications in which several telephone calls are carried through a single wire. o Multiplexing originated in telegraphy in the early 1870s and is now widely used in communication. o George Owen Squier developed the telephone carrier multiplexing in 1910. Concept of Multiplexing o The 'n' input lines are transmitted through a multiplexer and multiplexer combines the signals to form a composite signal. o The composite signal is passed through a Demultiplexer and demultiplexer separates a signal to component signals and transfers them to their respective destinations. Advantages of Multiplexing: o More than one signal can be sent over a single medium. o The bandwidth of a medium can be utilized effectively. Multiplexing Techniques Multiplexing techniques can be classified as: Frequency-division Multiplexing (FDM) o It is an analog technique. o Frequency Division Multiplexing is a technique in which the available bandwidth of a single transmission medium is subdivided into several channels. 24  o In the above diagram, a single transmission medium is subdivided into several frequency channels, and each frequency channel is given to different devices. Device 1 has a frequency channel of range from 1 to 5. o The input signals are translated into frequency bands by using modulation techniques, and they are combined by a multiplexer to form a composite signal. o The main aim of the FDM is to subdivide the available bandwidth into different frequency channels and allocate them to different devices. o Using the modulation technique, the input signals are transmitted into frequency bands and then combined to form a composite signal. o The carriers which are used for modulating the signals are known as sub-carriers. They are represented as f1,f2..fn. o FDM is mainly used in radio broadcasts and TV networks. Advantages Of FDM: o FDM is used for analog signals. o FDM process is very simple and easy modulation. o A Large number of signals can be sent through an FDM simultaneously. o It does not require any synchronization between sender and receiver. Disadvantages Of FDM: o FDM technique is used only when low-speed channels are required. o It suffers the problem of crosstalk. o A Large number of modulators are required. o It requires a high bandwidth channel. Applications Of FDM: o FDM is commonly used in TV networks. o It is used in FM and AM broadcasting. Each FM radio station has different frequencies, and they are multiplexed to form a composite signal. The multiplexed signal is transmitted in the air. Wavelength Division Multiplexing (WDM) 25  o Wavelength Division Multiplexing is same as FDM except that the optical signals are transmitted through the fibre optic cable. o WDM is used on fibre optics to increase the capacity of a single fibre. o It is used to utilize the high data rate capability of fibre optic cable. o It is an analog multiplexing technique. o Optical signals from different source are combined to form a wider band of light with the help of multiplexer. o At the receiving end, demultiplexer separates the signals to transmit them to their respective destinations. o Multiplexing and Demultiplexing can be achieved by using a prism. o Prism can perform a role of multiplexer by combining the various optical signals to form a composite signal, and the composite signal is transmitted through a fibre optical cable. o Prism also performs a reverse operation, i.e., demultiplexing the signal. Time Division Multiplexing o It is a digital technique. o In Frequency Division Multiplexing Technique, all signals operate at the same time with different frequency, but in case of Time Division Multiplexing technique, all signals operate at the same frequency with different time. o In Time Division Multiplexing technique, the total time available in the channel is distributed among different users. Therefore, each user is allocated with different time interval known as a Time slot at which data is to be transmitted by the sender. o A user takes control of the channel for a fixed amount of time. o In Time Division Multiplexing technique, data is not transmitted simultaneously rather the data is transmitted one-by-one. o In TDM, the signal is transmitted in the form of frames. Frames contain a cycle of time slots in which each frame contains one or more slots dedicated to each user. o It can be used to multiplex both digital and analog signals but mainly used to multiplex digital signals. There are two types of TDM: o Synchronous TDM o Asynchronous TDM Synchronous TDM o A Synchronous TDM is a technique in which time slot is preassigned to every device. o In Synchronous TDM, each device is given some time slot irrespective of the fact that the device contains the data or not. o If the device does not have any data, then the slot will remain empty. 26  o In Synchronous TDM, signals are sent in the form of frames. Time slots are organized in the form of frames. If a device does not have data for a particular time slot, then the empty slot will be transmitted. o The most popular Synchronous TDM are T-1 multiplexing, ISDN multiplexing, and SONET multiplexing. o If there are n devices, then there are n slots. Concept Of Synchronous TDM In the above figure, the Synchronous TDM technique is implemented. Each device is allocated with some time slot. The time slots are transmitted irrespective of whether the sender has data to send or not. Disadvantages Of Synchronous TDM: o The capacity of the channel is not fully utilized as the empty slots are also transmitted which is having no data. In the above figure, the first frame is completely filled, but in the last two frames, some slots are empty. Therefore, we can say that the capacity of the channel is not utilized efficiently. o The speed of the transmission medium should be greater than the total speed of the input lines. An alternative approach to the Synchronous TDM is Asynchronous Time Division Multiplexing. Asynchronous TDM o An asynchronous TDM is also known as Statistical TDM. o An asynchronous TDM is a technique in which time slots are not fixed as in the case of Synchronous TDM. Time slots are allocated to only those devices which have the data to send. Therefore, we can say that Asynchronous Time Division multiplexor transmits only the data from active workstations. o An asynchronous TDM technique dynamically allocates the time slots to the devices. o In Asynchronous TDM, total speed of the input lines can be greater than the capacity of the channel. o Asynchronous Time Division multiplexor accepts the incoming data streams and creates a frame that contains only data with no empty slots. o In Asynchronous TDM, each slot contains an address part that identifies the source of the data. o The difference between Asynchronous TDM and Synchronous TDM is that many slots in Synchronous TDM are unutilized, but in Asynchronous TDM, slots are fully utilized. This leads to the smaller transmission time and efficient utilization of the capacity of the channel. o In Synchronous TDM, if there are n sending devices, then there are n time slots. In Asynchronous TDM, if there are n sending devices, then there are m time slots where m is less than n (m