Notes: Subject-Computer Network

                                                                           Unit-1

 Q1. What are nodes and links? DDU-2019-20 Node: Any communicating device in a network is called a Node. Node is the point of intersection in a Ans. network. It can send/receive data and information within a network. Examples of the node can be computers, laptops, printers, servers, modems, etc. Link: A link or edge refers to the connectivity between two nodes in the network. It includes the type of connectivity (wired or wireless) between the nodes and protocols used for one node to be able to communicate with the other. Nodes and Links 

 Q2. What is the network topology? DDU-2022-23 Network topology is a physical layout of the network, connecting the different nodes using the Ans. links. It depicts the connectivity between the computers, devices, cables, etc.

 Q3. What are the HTTP and the HTTPS protocol? HTTP is the Hyper Text Transfer Protocol which defines the set of rules and standards on how the Ans. information can be transmitted on the World Wide Web (WWW). It helps the web browsers and web servers for communication. It is a ‘stateless protocol’ where each command is independent with respect to the previous command. HTTP is an application layer protocol built upon the TCP. It uses port 80 by default. HTTPS is the Hyper Text Transfer Protocol Secure or Secure HTTP. It is an advanced and secured version of HTTP. On top of HTTP, SSL/TLS protocol is used to provide security. It enables secure transactions by encrypting the communication and also helps identify network servers securely. It uses port 443 by default. 

 Q4. Differentiate OSI Reference Model with TCP/IP Reference Model? DDU-2021-22 Ans. OSI Reference Model TCP/IP Reference Model 7 layered architecture 4 layered architecture Fixed boundaries and functionality for each layer Flexible architecture with no strict boundaries between layers Low Reliability High Reliability Vertical Layer Approach Horizontal Layer Approach 

 Q5. Define different types of network topology? Ans. The different types of network topology are given below: Bus Topology: DDU-2022-23  All the nodes are connected using the central link known as the bus.  It is useful to connect a smaller number of devices.  If the main cable gets damaged, it will damage the whole network. Star Topology:  All the nodes are connected to one single node known as the central node.  It is more robust.  If the central node fails the complete network is damaged.  Easy to troubleshoot.  Mainly used in home and office networks Ring Topology:  Each node is connected to exactly two nodes forming a ring structure  If one of the nodes are damaged, it will damage the whole network  It is used very rarely as it is expensive and hard to install and manage Mesh Topology:  Each node is connected to one or many nodes.  It is robust as failure in one link only disconnects that node.  It is rarely used and installation and management are difficult. Tree Topology:  A combination of star and bus topology also know as an extended bus topology.  All the smaller star networks are connected to a single bus.  If the main bus fails, the whole network is damaged. 

Q6. Define the 7 different layers of the OSI Reference Model? DDU-2022-23 Ans. Here the 7 layers of the OSI reference model: Layer Unit Exchanged Description Physical Bit  It is concerned with transmitting raw bits over a communication channel.  Chooses which type of transmission mode is to be selected for the transmission. The available transmission modes are Simplex, Half Duplex and Full Duplex., Data Link Frame  The main task of this layer is to transform a raw transmission facility into a line that appears free of undetected transmission errors.  It also allows detecting damaged packets using the CRC (Cyclic Redundancy Check) error-detecting, code.  When more than one node is connected to a shared link, Data Link Layer protocols are required to determine which device has control over the link at a given time.  It is implemented by protocols like CSMA/CD, CSMA/CA, ALOHA, and Token Passing. Network Packet  It controls the operation of the subnet.  The network layer takes care of feedback messaging through ICMP messages. Transport TPDU - Transaction Protocol Data Unit  The basic functionality of this layer is to accept data from the above layers, split it up into smaller units if needed, pass these to the network layer, and ensure that all the pieces arrive correctly at the other end.  The Transport Layer takes care of Segmentation and Reassembly. Session SPDU - Session Protocol Data Unit  The session layer allows users on different machines to establish sessions between them.  Dialogue control is using the full-duplex link as half-duplex. It sends out dummy packets from the client to the server when the client is ideal. Presentation PPDU - Presentation Protocol Data Unit  The presentation layer is concerned with the syntax and semantics of the information transmitted.  It translates a message from a common form to the encoded format which will be understood by the receiver. Application APDU - Application Protocol Data Unit  It contains a variety of protocols that are commonly needed by users.  The application layer sends data of any size to the transport layer. 

 Q7. Define the 4 different layers of the TCP/IP Reference Model? Ans. Layers of TCP/IP Layer Description Link Decides which links such as serial lines or classic Ethernet must be used to meet the needs of the connectionless internet layer. Internet  The internet layer is the most important layer which holds the whole architecture together.  It delivers the IP packets where they are supposed to be delivered. Transport Its functionality is almost the same as the OSI transport layer. It enables peer entities on the network to carry on a conversation. Application It contains all the higher-level protocols. 

 Q8. Explain different types of networks? Ans. Type Description PAN (Personal Area Network) Let devices connect and communicate over the range of a person. E.g. connecting Bluetooth devices. LAN (Local Area Network) It is a privately owned network that operates within and nearby a single building like a home, office, or factory MAN (Metropolitan Area Network) It connects and covers the whole city. E.g. TV Cable connection over the city WAN (Wide Area Network) It spans a large geographical area, often a country or continent. The Internet is the largest WAN GAN (Global Area Network) It is also known as the Internet which connects the globe using satellites. The Internet is also called the Network of WANs. 

 Q9. Explain Error Detection in Computer Network? DDU-2021-22 Ans. Error detection is a technique that is used to check if any error occurred in the data during the transmission. Some popular error detection methods are- Cyclic Redundancy Check-  Cyclic Redundancy Check (CRC) is an error detection method.  It is based on binary division. CRC Generator-  CRC generator is an algebraic polynomial represented as a bit pattern.  Bit pattern is obtained from the CRC generator using the following rule- NOTE: The power of each term gives the position of the bit and the coefficient gives the value of the bit. Example- Consider the CRC generator is x7 + x6 + x4 + x3 + x + 1. The corresponding binary pattern is obtained as- 11011011 Properties Of CRC Generator- The algebraic polynomial chosen as a CRC generator should have at least the following properties- Rule-01:  It should not be divisible by x.  This condition guarantees that all the burst errors of length equal to the length of polynomial are detected. Rule-02:  It should be divisible by x+1.  This condition guarantees that all the burst errors affecting an odd number of bits are detected. Important Notes- If the CRC generator is chosen according to the above rules, then-  CRC can detect all single-bit errors  CRC can detect all double-bit errors provided the divisor contains at least three logic 1’s.  CRC can detect any odd number of errors provided the divisor is a factor of x+1.  CRC can detect all burst error of length less than the degree of the polynomial.  CRC can detect most of the larger burst errors with a high probability. Steps Involved- Error detection using CRC technique involves the following steps- Step-01: Calculation Of CRC At Sender Side- At sender side,  A string of n 0’s is appended to the data unit to be transmitted.  Here, n is one less than the number of bits in CRC generator.  Binary division is performed of the resultant string with the CRC generator.  After division, the remainder so obtained is called as CRC.  It may be noted that CRC also consists of n bits. Step-02: Appending CRC To Data Unit- At sender side,  The CRC is obtained after the binary division.  The string of n 0’s appended to the data unit earlier is replaced by the CRC remainder. Step-03: Transmission To Receiver-  The newly formed code word (Original data + CRC) is transmitted to the receiver. Step-04: Checking at Receiver Side- At receiver side,  The transmitted code word is received.  The received code word is divided with the same CRC generator.  On division, the remainder so obtained is checked. The following two cases are possible- Case-01: Remainder = 0 If the remainder is zero,  Receiver assumes that no error occurred in the data during the transmission.  Receiver accepts the data. Case-02: Remainder ≠ 0 If the remainder is non-zero,  Receiver assumes that some error occurred in the data during the transmission.  Receiver rejects the data and asks the sender for retransmission.

 Q10. Differentiate between Full Duplex and Half Duplex modes of Transmission? Ans. Half-Duplex Mode – In half-duplex mode, each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa. The half-duplex mode is used in cases where there is no need for communication in both directions at the same time. The entire capacity of the channel can be utilized for each direction. Example: Walkie-talkie in which message is sent one at a time and messages are sent in both directions. Channel capacity=Bandwidth * Propagation Delay Advantages:  Half-duplex mode allows for bidirectional communication, which is useful in situations where devices need to send and receive data.  It is a more efficient mode of communication than simplex mode, as the channel can be used for both transmission and reception.  Half-duplex mode is less expensive than full-duplex mode, as it only requires one communication channel. Disadvantages:  Half-duplex mode is less reliable than Full-Duplex mode, as both devices cannot transmit at the same time. There is a delay between transmission and reception, which can cause problems in some applications.  There is a need for coordination between the transmitting and receiving devices, which can complicate the communication process. Full-Duplex Mode – In full-duplex mode, both stations can transmit and receive simultaneously. In full_duplex mode, signals going in one direction share the capacity of the link with signals going in another direction, this sharing can occur in two ways:  Either the link must contain two physically separate transmission paths, one for sending and the other for receiving.  Or the capacity is divided between signals traveling in both directions. Full-duplex mode is used when communication in both directions is required all the time. The capacity of the channel, however, must be divided between the two directions. Example: Telephone Network in which there is communication between two persons by a telephone line, through which both can talk and listen at the same time. Channel Capacity=2* Bandwidth*propagation Delay Advantages:  Full-duplex mode allows for simultaneous bidirectional communication, which is ideal for real-time applications such as video conferencing or online gaming.  It is the most efficient mode of communication, as both devices can transmit and receive data simultaneously.  Full-duplex mode provides a high level of reliability and accuracy, as there is no need for error correction mechanisms. Disadvantages:  Full-duplex mode is the most expensive mode, as it requires two communication channels.  It is more complex than simplex and half-duplex modes, as it requires two physically separate transmission paths or a division of channel capacity.  Full-duplex mode may not be suitable for all applications, as it requires a high level of bandwidth and may not be necessary for some types of communication. 

Unit-2           

 Q1. What is Coaxial Cable ?

 Ans. Copper conductor: A central conductor, which consists of copper. The conductor is the point at which data transmits. Insulator: Dielectric plastic insulation around the copper conductor. it is used to maintain the spacing between the center conductor and shield. Braided mesh: A braided mesh of copper helps to shield from electromagnetic interference, The braid provides a barrier against EMI moving into and out of the coaxial cable. Protective plastic layer: An external polymer layer, which has a plastic coating. It is used to protect internal layers from damages.

 Q2. What do you mean by Attenuation in Networking? 

 Ans. A coaxial cable is an electrical cable with a copper conductor and an insulator shielding around it and a braided metal mesh that prevents signal interference and cross talk. Coaxial cable is also known as coax. The core copper conductor is used for the transmission of signals and the insulator is used to provide insulation to the copper conductor and the insulator is surrounded by a braided metal conductor which helps to prevent the interference of electrical signals and prevent cross talk. This entire setup is again covered with a protective plastic layer to provide extra safety to the cable. Structure of Coaxial Cable Attenuation is the loss of signal strength in networking cables or connections. This typically is measured in decibels (dB) or voltage and can occur due to a variety of factors. It may cause signals to become distorted or indiscernible. An example of this is Wi-Fi signal and strength getting noticeably weaker the further that your device is from the router. When measuring attenuation in a wired network, the greater the signal strength over a long distance, the more effective the cable is. Less efficient cables will struggle with signal attenuation, and networking administrators may need to adjust the cable or insert amplifiers or repeaters in order to 

 Q3. How a Satellite Works ? 

 Ans. A satellite is a body that moves around another body in a particular path. A communication satellite is nothing but a microwave repeater station in space. It is helpful in telecommunications, radio and television along with internet applications. A repeater is a circuit, which increases the strength of the received signal and then transmits it. But, this repeater works as a transponder. That means, it changes the frequency band of the transmitted signal from the received one. The frequency with which, the signal is sent into the space is called as Uplink frequency. Similarly, the frequency with which, the signal is sent by the transponder is called as Downlink frequency. The following figure illustrates this concept clearly. The transmission of signal from first earth station to satellite through a channel is called as uplink. Similarly, the transmission of signal from satellite to second earth station through a channel is called as downlink. Uplink frequency is the frequency at which, the first earth station is communicating with satellite. The satellite transponder converts this signal into another frequency and sends it down to the second earth station. This frequency is called as Downlink frequency. In similar way, second earth station can also communicate with the first one. The process of satellite communication begins at an earth station. Here, an installation is designed to transmit and receive signals from a satellite in an orbit around the earth. Earth stations send the information to satellites in the form of high powered, high frequency (GHz range) signals. The satellites receive and retransmit the signals back to earth where they are received by other earth stations in the coverage area of the satellite. Satellite's footprint is the area which receives a signal of useful strength from the satellite.

 Q4. What is VSAT? 

 Ans. VSAT stands for Very Small Aperture Terminal. VSAT is of importance, especially in remote areas such as the hilly mountain regions, where Internet connectivity cannot be directly provided. There is no option left in such places through which the Internet can be accessed anyway. These places could be the Ocean region and the Sea region, where the citizens have a lack of utilities. In such cases, VSAT is one of the technologies that make Internet Connectivity possible so that people can access it. All the work is carried out in a workstation group where the sending and receiving of signals takes place. The data such as audio, video, etc, can be sent and received. Therefore, VSAT is considered to be a private Earth Station. This Earth Station is designed in a way such that the signals are transmitted and received with antenna size that is very small. 

 Q6. Ans. What is Microwave Transmission? Microwave transmission is the method of transmitting information using microwaves, a type of electromagnetic radiation. This method is commonly used in wireless communication systems such as cell phones, television and radio broadcasting, and satellite communication. What are the advantages and disadvantages of Microwave Transmission ? Advantages of Microwave Transmission Speed Microwave transmission allows for very fast data transfer, making it useful for things like live television broadcasts and internet connections. Distance Microwave transmission can cover long distances, making it useful for connecting remote areas to the rest of the world. Reliability Microwave transmission is often more reliable than other forms of wireless communication, such as satellite or cellular connections. Cost-effectiveness Setting up a microwave transmission system can be less expensive than laying cables or building towers for other types of transmission. Security Microwave transmissions can be encrypted, making them more secure than some other forms of wireless communication. Disadvantages of Microwave Transmission Weather interference disruptions in service. Heavy rain, snow, or fog can interfere with microwave transmission and cause Line-of-sight requirement Microwave transmission requires a clear line of sight between the transmitter and receiver, which can be affected by buildings or natural obstacles. Limited bandwidth The amount of information that can be sent through a microwave transmission is limited by the available bandwidth. Health concerns Some studies have suggested that prolonged exposure to microwaves from transmission towers could be harmful to human health. Vulnerability to interference Microwave transmissions can be disrupted by other electronic devices, such as radar systems or cell phones, that operate on the same frequency.

 Q7. Explain Infrared Transmission? 

 Ans. The electromagnetic waves having frequencies from 300 GHz to 400 THz (wavelengths from 1mm to 770 nm) are referred to as infrared (IR) waves. IR uses line-of-sight propagation. Infrared light is a transmission channel whose features are necessarily different from those of the radio frequencies. A fundamental property of infrared light is that it cannot penetrate the walls. This represents that it can easily include it within a room. Another advantage of infrared communication is massive bandwidth which is available for use, but has not been exploited to its full extent. The major disadvantage is that the sun creates emission in the infrared band. This can generate several interferences with IR transmission. Applications It can use the infrared signals for short-range communications. Wireless alternatives to linking tools, including a laptop to a printer. Infrared signals are used for transmission between keyboard, mouse, computers and printers. It can use an infrared band in the advancement of very huge-speed wireless LANs in future. Q8. What is Transmission Media ? Ans. Q 9. Ans.

 Q 10. Ans. o o o o o o o o o o Transmission media is a communication channel that carries the information from the sender to the receiver. Data is transmitted through the electromagnetic signals. The main functionality of the transmission media is to carry the information in the form of bits through LAN(Local Area Network). It is a physical path between transmitter and receiver in data communication. In a copper-based network, the bits in the form of electrical signals. In a fibre based network, the bits in the form of light pulses. In OSI(Open System Interconnection) phase, transmission media supports the Layer 1. Therefore, it is considered to be as a Layer 1 component. The electrical signals can be sent through the copper wire, fibre optics, atmosphere, water, and vacuum. The characteristics and quality of data transmission are determined by the characteristics of medium and signal. 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. Different transmission media have different properties such as bandwidth, delay, cost and ease of installation and maintenance. What do you mean by Distortion? DDU-2020-21 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 . What do you mean by Bandwidth , Latency and Throughput? Bandwidth is the maximum data transfer capacity of a network. It defines the theoretical limit of data that can be transmitted over the network in a given time. Bandwidth is often compared to the width of a road, determining the maximum number of vehicles (or data packets in a network) that can travel simultaneously . Throughput, on the other hand, is the amount of data that successfully travels through the network over capacity to handle data transfer, often seen as the actual infrastructure, the number of concurrent users, and the type of data being transferred . Latency refers to the time it takes for a packet of data to traverse from one point in the network to another. It is a measure of delay experienced by a packet, indicating the speed at which data travels across the network. Latency is often measured as round-trip time, which includes the time for a packet to travel from its source to its destination and for the source to receive a response. A network with low latency experiences less delay, thereby seeming faster to the end user.