Computer Networks - Unit 1

A computer network is a collection of interconnected devices, such as computers, servers, and mobile devices, that can share resources and communicate with each other. Scope refers to the geographical area covered by the network, which can be local (LAN), wide area (WAN), or personal (PAN).
Communication type refers to how data is transmitted, which can be either unicast (one-to-one), multicast (one-to-many), or broadcast (one-to-all). Connection type refers to how devices are connected, which can be wired (using cables) or wireless (using radio waves).

Broadcast networks allow data to be sent to all connected devices simultaneously, while point-to-point networks involve direct communication between two specific devices only.

Here are two key differences

• Addressing: Broadcast networks use a single broadcast address for all devices, while point-to-point networks use unique addresses for each device.
• Collision: Broadcast networks are prone to collisions, where multiple devices try to transmit at the same time, while point-to-point networks avoid collisions as only two devices communicate at a time.

LAN stands for Local Area Network, a network covering a small geographical area, such as a home, office, or school. A WAN, or Wide Area Network, connects devices over a large geographical area, such as across cities or countries.
Finally, a PAN, or Personal Area Network, is a small wireless network connecting personal devices, such as smartphones, laptops, and tablets, typically within a short range.

<p>The Open Systems Interconnection (OSI) Model is a conceptual framework that defines the different layers involved in network communication. It provides a standardized way to understand the different functions and protocols involved in transmitting data across a network. The OSI Model consists of seven layers:</p> <ol> <li> <p><strong>Physical Layer:</strong> Deals with the physical transmission of data bits over the network medium. Examples include connecting cables, transmitting electrical signals, and defining physical connectors.</p> </li> <li> <p><strong>Data Link Layer:</strong> Addresses the reliable transmission of data frames, often using error detection and correction mechanisms. It also handles access to the physical medium for various devices.</p> </li> <li> <p><strong>Network Layer:</strong> Responsible for routing data packets from source to destination, providing logical addressing, and managing congestion control.</p> </li> <li> <p><strong>Transport Layer:</strong> Establishes and manages connections between applications, providing reliable delivery of data segments, controlling the flow of data, and ensuring reliable data transfer (e.g., TCP).</p> </li> <li> <p><strong>Session Layer:</strong> Manages communication sessions between applications, coordinating the dialogue and synchronizing data exchange.</p> </li> <li> <p><strong>Presentation Layer:</strong> Handles data formatting, encryption, and decryption, ensuring data is presented in a format understandable by applications. This layer deals with data representation and conversion.</p> </li> <li> <p><strong>Application Layer:</strong> The highest layer, responsible for providing services to applications, including email, file transfer, web browsing, and remote login. It interacts directly with user applications.</p> </li> </ol> <p>*Example: * Let's explain the <strong>Physical Layer</strong>.</p> <p>The Physical Layer is the foundation of the OSI model. It deals with the actual physical transmission of data over the network medium, such as copper cables, optical fibers, or wireless signals. Functions of the Physical Layer include:</p> <ol> <li> <p><strong>Signal transmission:</strong> Defining the electrical, mechanical, and procedural characteristics of how data bits are represented as signals.</p> </li> <li> <p><strong>Physical addressing:</strong> Defining the physical addresses used to identify devices on the network.</p> </li> <li> <p><strong>Bit synchronization:</strong> Establishing a common clocking mechanism to coordinate the transmission and reception of bits.</p> </li> <li> <p><strong>Medium access control:</strong> Determining how devices share the physical medium, especially in shared environments like Ethernet.</p> </li> <li> <p><strong>Data encoding:</strong> Converting digital data into physical signals for transmission.</p> </li> </ol> Signup and view all the answers

<p>The Physical Layer is the lowest layer of the OSI model, responsible for the physical transmission of data bits over the network medium. Its main duties include:</p> <ol> <li> <p><strong>Physical interface:</strong> Defining the physical characteristics of the network medium, including connectors, cables, and signaling methods.</p> </li> <li> <p><strong>Bit encoding and decoding:</strong> Converting digital data into signals for transmission and vice versa.</p> </li> <li> <p><strong>Signal transmission:</strong> Transmitting and receiving signals over the physical medium.</p> </li> <li> <p><strong>Physical addressing:</strong> Implementing physical addresses for devices on the network.</p> </li> <li> <p><strong>Medium access control:</strong> Determining how devices share the physical medium, especially in shared environments like Ethernet.</p> </li> </ol> <p>The Data Link Layer, the second layer of the OSI model, focuses on reliable transmission of data frames across the physical medium. Its primary duties include:</p> <ol> <li> <p><strong>Error detection and correction:</strong> Protecting data from errors caused by the physical channel noise using techniques like checksums or parity bits.</p> </li> <li> <p><strong>Frame delimiting:</strong> Framing data into manageable units for transmission and adding headers and trailers for addressing and control information.</p> </li> <li> <p><strong>Flow control:</strong> Ensuring that data is transmitted at a rate that does not overwhelm the receiver.</p> </li> <li> <p><strong>Access control:</strong> Controlling access to the physical medium, resolving collisions and ensuring fair sharing of resources (e.g., using CSMA/CD in Ethernet).</p> </li> <li> <p><strong>Addressing:</strong> Using MAC (Media Access Control) addresses to identify devices at the data link layer.</p> </li> </ol> Signup and view all the answers

<p>These terms are essential for understanding how data is represented and transmitted in analog signals, which is often the case for physical layer communication.</p> <ul> <li> <strong>Amplitude:</strong> The height of a wave, representing the strength or intensity of the signal. Higher amplitude means a stronger signal.</li> <li> <strong>Frequency:</strong> The number of waves that pass a point in one second, measured in Hertz (Hz). Higher frequency means faster oscillations of the wave.</li> <li> <strong>Wavelength:</strong> The distance between two consecutive peaks or troughs of a wave. It is inversely proportional to frequency, meaning higher frequency results in shorter wavelengths.</li> <li> <strong>Bitrate:</strong> The number of bits transmitted per second, often measured in bits per second (bps). Higher bitrate means faster data transfer.</li> <li> <strong>Baud rate:</strong> The number of symbol changes per second, representing the rate at which the signal changes its state (e.g., voltage level). It can be equal to or lower than the bitrate.</li> <li> <strong>Signal:</strong> A varying physical quantity, such as voltage, current, or electromagnetic waves, used to represent data in a network.</li> </ul> Signup and view all the answers

<p>Fiber optic cables are a type of data transmission medium that uses light pulses to transmit data. They offer several advantages over traditional copper cables, including:</p> <ul> <li> <strong>Higher bandwidth:</strong> Fiber optics can support much higher data transmission rates than copper cables, making them ideal for high-speed data applications.</li> <li> <strong>Lower signal attenuation:</strong> Light signals travel longer distances with less degradation than electrical signals, resulting in lower signal loss.</li> <li> <strong>Immunity to electromagnetic interference:</strong> Fiber optics are not susceptible to electromagnetic interference (EMI), making them suitable for environments with high noise levels.</li> <li> <strong>Security:</strong> Fiber optic cables are more secure than copper cables, as it is difficult to tap into them without being detected.</li> <li> <strong>Smaller size and lighter weight:</strong> Fiber optic cables are thinner and lighter than copper cables, making them easier to install and manage.</li> </ul> Signup and view all the answers

<p>Twisted pair cables consist of two insulated wires twisted together, often in pairs, to reduce electromagnetic interference. This twisting technique helps to cancel out noise and improve signal quality. Advantages of twisted pair cables include:</p> <ul> <li> <strong>Cost effectiveness:</strong> Twisted pair cables are relatively inexpensive compared to other types of cables.</li> <li> <strong>Ease of installation:</strong> They are easy to install and work with, requiring standard connectors.</li> <li> <strong>Widely available:</strong> Twisted pair cables are widely available and compatible with various networking devices.</li> <li> <strong>Flexibility:</strong> They are flexible and can be easily routed around obstacles.</li> </ul> <p>However, twisted pair cables also have limitations. They are susceptible to cross-talk, where signals in one pair can interfere with signals in another pair. Moreover, twisted pair cables have limited bandwidth compared to fiber optic cables, and their performance deteriorates over long distances.</p> Signup and view all the answers

<p>Coaxial cable consists of a central conductor surrounded by an insulating layer, a metallic shield, and an outer insulating layer. This arrangement helps to reduce interference. Here's a comparison of twisted pair cables and coaxial cables:</p> <p><strong>Twisted Pair Cables</strong></p> <ul> <li> <strong>Structure:</strong> Consists of two insulated wires twisted together.</li> <li> <strong>Bandwidth:</strong> Limited bandwidth compared to coaxial cables.</li> <li> <strong>Cost:</strong> Relatively inexpensive.</li> <li> <strong>Susceptibility to interference:</strong> More susceptible to interference compared to coaxial cables.</li> <li> <strong>Installation:</strong> Easier to install.</li> </ul> <p><strong>Coaxial Cables</strong></p> <ul> <li> <strong>Structure:</strong> Consists of a central conductor surrounded by insulation, a metallic shield, and an outer insulating layer.</li> <li> <strong>Bandwidth:</strong> Higher bandwidth compared to twisted pair cables.</li> <li> <strong>Cost:</strong> More expensive than twisted pair cables.</li> <li> <strong>Susceptibility to interference:</strong> Less susceptible to interference compared to twisted pair cables.</li> <li> <strong>Installation:</strong> More difficult to install.</li> </ul> Signup and view all the answers

<p>The Open Systems Interconnection (OSI) Model is a conceptual framework that defines seven layers involved in network communication, providing a standardized way to understand the functions and protocols involved in data transmission. Each layer has specific responsibilities and interacts with adjacent layers to facilitate data flow.</p> <ol> <li> <p><strong>Physical Layer:</strong> Deals with the physical transmission of data bits over the network medium, including defining connectors, cables, voltage signals, and physical addressing.</p> </li> <li> <p><strong>Data Link Layer:</strong> Ensures reliable transmission of data frames across the physical medium by providing error detection and correction, frame delimiting, flow control, access control, and MAC addresses.</p> </li> <li> <p><strong>Network Layer:</strong> Handles the addressing and routing of data packets from source to destination, providing logical addressing, managing congestion control, and breaking data into smaller packets.</p> </li> <li> <p><strong>Transport Layer:</strong> Establishes and manages connections between applications, providing reliable data transfers, ensuring data integrity and flow control (e.g., TCP).</p> </li> <li> <p><strong>Session Layer:</strong> Manages communication sessions between applications, coordinating dialogue, synchronizing data exchange, and setting up, managing, and terminating sessions.</p> </li> <li> <p><strong>Presentation Layer:</strong> Handles data formatting, encryption, and decryption, ensuring data is presented in a format understandable by applications.</p> </li> <li> <p><strong>Application Layer:</strong> The highest layer, providing services to user applications, including email, file transfer, web browsing, and remote login, interacting with user applications directly.</p> </li> </ol> <p>Each layer builds upon the functionality provided by the layers below it, enabling the smooth and reliable exchange of data across computer networks.</p> Signup and view all the answers

<p>The OSI (Open Systems Interconnection) and TCP/IP (Transmission Control Protocol/Internet Protocol) models are both frameworks for understanding network communication, but they differ in their structure and scope.</p> <p><strong>OSI Model</strong></p> <ul> <li> <strong>Structure:</strong> Has seven well-defined layers, each with its specific function.</li> <li> <strong>Scope:</strong> More theoretical and focuses on general network communication principles.</li> <li> <strong>Implementation:</strong> Not widely implemented in its entirety.</li> </ul> <p><strong>TCP/IP Model</strong></p> <ul> <li> <strong>Structure:</strong> Has four main layers: Application, Transport, Internet, and Network Interface.</li> <li> <strong>Scope:</strong> More practical and focuses on the internet protocol suite.</li> <li> <strong>Implementation:</strong> Widely implemented as the foundation of the internet.</li> </ul> <p><strong>Key Differences</strong></p> <ul> <li> <strong>Number of layers:</strong> The OSI model has seven layers, while the TCP/IP model has four.</li> <li> <strong>Focus:</strong> The OSI model is more general and focuses on network communication principles, while the TCP/IP model is more practical and focuses on the internet protocol suite.</li> <li> <strong>Implementation:</strong> The OSI model is not widely implemented, while the TCP/IP model is the foundation of internet communication.</li> </ul> <p>Both the OSI and TCP/IP models serve as helpful abstractions for network engineers and professionals, even though their detailed implementation and usage vary.</p> Signup and view all the answers

<p>Network software plays a crucial role in managing and facilitating communication within a network. Here are some different types of network software:</p> <ul> <li> <strong>Network Operating Systems (NOS):</strong> Specialized operating systems designed for network devices like routers, switches, and firewalls. Examples include Cisco IOS and Juniper Junos.</li> <li> <strong>Protocol Stack Software:</strong> Implements protocols like TCP/IP, enabling communication between devices and managing data transmission.</li> <li> <strong>Network Management Software:</strong> Provides tools for monitoring, configuring, and troubleshooting network devices and services. Examples include SolarWinds Network Performance Monitor (NPM) and ManageEngine OpManager.</li> <li> <strong>Security Software:</strong> Protects networks from cyber threats, including firewalls, intrusion detection systems (IDS), intrusion prevention systems (IPS), antivirus software, and VPNs.</li> <li> <strong>Network Monitoring Software:</strong> Monitors network performance, identifying potential bottlenecks and performance issues. Examples include PRTG Network Monitor and ManageEngine NetFlow Analyzer.</li> <li> <strong>Network Simulation Software:</strong> Allows for testing and experimenting with network configurations and protocols in a virtual environment before deployment. Examples include Cisco Packet Tracer and GNS3.</li> <li> <strong>Network Analysis Software:</strong> Analyzes network traffic patterns to identify security risks, performance bottlenecks, and user activity trends. Examples include Wireshark and tcpdump.</li> </ul> <p>These are just some examples, and there are many other types of network software available, each serving a specific purpose in managing and optimizing a network.</p> Signup and view all the answers

<p>Framing is essential in data link layer communication because it involves dividing large blocks of data into smaller, manageable units called frames. Frames are used for reliable transmission, error detection, and flow control. Here are some primary reasons for framing:</p> <ul> <li> <strong>Efficient Transmission:</strong> Frames allow for the efficient transmission of data by breaking large blocks into smaller units suitable for transmission over the network.</li> <li> <strong>Error Detection:</strong> Frames include headers and trailers containing information about the frame, such as source and destination addresses, and checksums for error detection.</li> <li> <strong>Flow Control:</strong> Frames can be used to control the rate of data transmission, preventing the receiver from being overwhelmed by excessive data.</li> <li> <strong>Multiple Access:</strong> Frames help manage access to the shared physical medium, allowing multiple devices to use the network without interfering with each other.</li> </ul> <p><strong>Byte Stuffing</strong></p> <p>Byte stuffing is a framing method used to ensure that the frame does not contain a pattern identical to special control characters used to delimit the frame. This prevents confusion and ensures proper frame recognition by the receiver.</p> <p>For example, consider a frame that uses the character <code>ESC</code> (Escape Character) to mark the start and end of the frame. If the data within the frame contains the <code>ESC</code> character, it could be misinterpreted as a frame delimiter. To address this, byte stuffing inserts an additional character, usually <code>ESC</code>, before each <code>ESC</code> found within the data. This allows the receiver to identify the actual <code>ESC</code> characters used in the data, distinguishing them from frame delimiters.</p> Signup and view all the answers