Computer Networks PDF

COMPUTER NETWORKS A network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network. Apart from computers, networks include networking...

COMPUTER NETWORKS A network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network. Apart from computers, networks include networking devices like switch, router, modem, etc. Networking devices are used to connect multiple computers in different settings. For communication, data in a network is divided into smaller chunks called packets. These packets are then carried over a network. In a communication network, each device that is a part of a network and that can receive, create, store or send data to different network routes is called a node. In the context of data communication, a node can be a device such as a modem, hub, bridge, switch, router, digital telephone handset, a printer, a computer or a server. 1 Benefits of computer networks 1. Resource Sharing Networks allow multiple devices to share resources like printers, scanners, and storage. Reduces the need for duplicate hardware, saving costs and space. For example, in an office network, all users can share a single printer. 2. Improved Communication Networks provide various communication tools such as email, instant messaging, video conferencing, and VoIP. Enables fast, reliable, and real-time communication among users, even across long distances. This is essential for businesses, allowing teams to collaborate efficiently. 3. Data Sharing and Collaboration Networks enable users to easily share files, documents, and data across connected devices. Facilitates collaborative work as multiple users can access and work on shared files, improving productivity and teamwork. Cloud-based systems like Google Drive are examples. 4. Centralized Data Management In a network, data can be stored and managed centrally on servers. Ensures better organization and security of data. Centralized backup and data management also reduce the risk of data loss, making it easier to maintain data integrity and security policies. 5. Internet Access Sharing Computer networks allow multiple devices to share a single internet connection. Saves costs by eliminating the need for multiple internet subscriptions in a home or office. All devices on the network can access the internet simultaneously through routers. 6. Increased Storage Efficiency Through network storage devices like Network Attached Storage (NAS), users can store and retrieve data centrally. This offers more efficient use of storage space, reduces redundancy, and provides easier access to shared storage resources. It also simplifies data backup and recovery processes. 7. Enhanced Security Networks enable administrators to apply consistent security policies and monitor access to data and resources. Centralized security protocols can be implemented, such as firewalls, antivirus software, and user authentication systems, to protect against unauthorized access and threats. 8. Scalability 2  Networks can easily expand by adding new devices or upgrading infrastructure. As a business grows, additional devices and users can be integrated into the network without major disruption, ensuring future-proof growth potential. 9. Cost Efficiency Computer networks reduce costs by allowing shared use of hardware and software resources. Instead of purchasing separate printers, storage, or software licenses for each computer, the network allows resource sharing. Centralized IT management also reduces maintenance and operational costs. 10. Remote Access and Flexibility Computer networks enable users to access resources remotely, either through Virtual Private Networks (VPNs) or cloud-based systems. This allows employees to work from any location, enabling remote work and flexibility. It also ensures continuous access to network resources even outside the office. 11. Easy Software and File Management Software and file updates can be managed centrally across all networked devices. System administrators can install, update, or patch software on all devices from a central location, saving time and ensuring that all users have the latest versions of software. 12. Load Balancing and Redundancy Networks can distribute workloads across multiple devices and provide redundancy. Ensures optimal use of system resources, reduces system overloads, and increases reliability through failover systems, which protect against downtime if one server fails. 13. Real-time Monitoring and Troubleshooting Networks allow centralized monitoring of devices and data traffic. Administrators can detect issues, manage performance, and troubleshoot problems more easily, reducing network downtime and enhancing performance. 14. Support for E-commerce and Online Services Networks form the backbone of internet-based services such as e-commerce, online banking, and cloud computing. Enables businesses to reach global markets, provide services, and interact with customers via online platforms, expanding business opportunities. 15. Disaster Recovery Networks facilitate regular data backups and redundancy mechanisms, which are vital for disaster recovery. 3  In case of data loss or hardware failure, having a network backup ensures that data can be restored quickly, minimizing downtime and operational impact. Type of Connection A network is two or more devices connected through links. A link is a communications pathway that transfers data from one device to another. There are two possible types of connections: point-to-point and multipoint. Point-to-Point A point-to-point connection provides a dedicated link between two devices. The entire capacity of the link is reserved for transmission between those two devices. Most point-to-point connections use an actual length of wire or cable to connect the two ends, but other options, such as microwave or satellite links, are also possible When you change television channels by infrared remote control, you are establishing a point-to-point connection between the remote control and the television's control system. Multipoint A multipoint (also called multi-drop) connection is one in which more than two specific devices share a single link In a multipoint environment, the capacity of the channel is shared, either spatially or temporally. If several devices can use the link simultaneously, it is a spatially shared connection. If users must take turns, it is a timeshared connection. 4  Transmission Media Computer network transmission media refers to the physical paths or materials through which data is transmitted between devices on a network. There are two main categories: wired (guided) and wireless (unguided) transmission media. 1. Wired (Guided) Transmission Media Wired media involve physical cables that guide data from one device to another. The most common types include: a) Twisted Pair Cable In this type of transmission media, two insulated conductors of a single circuit are twisted together to improve electromagnetic compatibility. These are the most widely used transmission medium cables. These are packed together in protective sheaths. They reduce electromagnetic radiation from pairs and crosstalk between the neighbouring pair. Overall, it improves the rejection of external electromagnetic interference 5  - Unshielded Twisted Pair (UTP): - Widely used in local area networks (LANs). - Consists of pairs of wires twisted around each other to reduce electromagnetic interference. - Example: Ethernet cables (e.g., CAT5, CAT6). - Pros: Cheap, easy to install. - Cons: Susceptible to interference and signal degradation over long distances. - Shielded Twisted Pair (STP): - Similar to UTP but with a shielding layer to protect against electromagnetic interference. - Used in environments with high interference. - Pros: Better protection against interference than UTP. - Cons: More expensive and less flexible than UTP. b) Coaxial Cable - Has a single copper conductor at its core, with a layer of insulation and shielding. - Commonly used in older Ethernet networks and for cable television. - Pros: More resistant to interference and can carry signals over longer distances compared to twisted pair cables. - Cons: Bulkier and more expensive than twisted pair cables. 6  c) Fiber Optic Cable - Uses light pulses to transmit data through thin strands of glass or plastic fibers. - Two types: - Single-mode fiber: Transmits data over long distances using a single light mode. - Multi-mode fiber: Uses multiple light modes, ideal for shorter distances. - Pros: Extremely high bandwidth, long-distance transmission, immune to electromagnetic interference. - Cons: Expensive and requires specialized equipment for installation and maintenance. 2. Wireless (Unguided) Transmission Media Wireless media use electromagnetic waves to transmit data through the air, without the need for physical cables. a) Radio Waves - Used in wireless local area networks (Wi-Fi), cellular networks, and Bluetooth connections. 7  - Typically has a short to medium-range transmission. - Pros: Convenient for mobile and portable devices, can cover large areas with the right equipment. - Cons: Susceptible to interference and limited bandwidth compared to wired media. b) Microwaves - Used for point-to-point communication, such as satellite and long-distance transmission between relay stations. - Requires line-of-sight between transmission points. - Pros: Can transmit large amounts of data over long distances. - Cons: Affected by weather conditions and physical obstructions. c) Infrared - Used for short-range communication, often in devices like remote controls or between personal devices (e.g., infrared ports). - Requires line-of-sight and is typically used for small data transfers. - Pros: Secure and less prone to interference. - Cons: Short-range and requires direct line-of-sight, so its applications are limited. d) Satellite - Uses satellites orbiting the Earth to provide long-range communication. - Commonly used for global broadcasting and data transmission to remote areas. - Pros: Can cover vast distances, including areas without traditional infrastructure. - Cons: Expensive, affected by latency, and sensitive to weather conditions. 8 Types Of Computer Networks Computer networks can be classified based on several factors such as geographical scope, the type of technology used, or the purpose they serve. Here are the main types of computer networks: 1. Personal Area Network (PAN) - Scope: Very small, usually within a range of a few meters. - Purpose: Connects devices such as smartphones, tablets, laptops, and wearable devices around a single person. - Examples: Bluetooth connections, USB connections. - Types: - Wired PAN: Devices are connected via cables (USB). - Wireless PAN: Devices are connected using wireless technologies (Bluetooth, infrared). 2. Local Area Network (LAN) - Scope: Limited to a small geographic area, like a single building, home, or office. - Connects devices such as computers, printers, and servers to share resources like files and internet connections. LAN is comparatively secure as only authentic users in the network can access other computers or shared resources. Users can print documents using a connected printer, upload/download documents and software to and from the local server. Such LANs provide the short range communication with the high speed data transfer rates. These types of networks can be extended up to 1 km. Data transfer in LAN is quite high, and usually varies from 10 Mbps (called Ethernet) to 1000 Mbps (called Gigabit Ethernet), where Mbps stands for Megabits per second. Ethernet is a set of rules that decides how computers and other devices connect with each other through cables in a local area network or LAN. - Examples: School network, office network. 9  - Types: - Wired LAN: Devices are connected using Ethernet cables. - Wireless LAN (WLAN): Devices are connected using wireless technologies (Wi-Fi). 3. Metropolitan Area Network (MAN) - Scope: Covers a city or a large campus, typically larger than a LAN but smaller than a WAN. - Purpose: Connects multiple LANs within a city or a large geographical area. Cable TV network or cable based broadband internet services are examples of MAN. This kind of network can be extended up to 30-40 km. Sometimes, many LANs are connected together to form MAN - Examples: City-wide Wi-Fi networks, university campus networks. - Types: - Wired MAN: Utilizes fiber-optic or copper cables to connect LANs. - Wireless MAN: Uses wireless communication for city-wide connectivity (WiMAX). 10  4. Wide Area Network (WAN) - Scope: Covers a large geographic area, such as multiple cities, countries, or continents. - Purpose: Connects multiple LANs or MANs over long distances. The Internet is the largest WAN that connects billions of computers, smartphones and millions of LANs from different continents. - Examples: The internet, corporate WANs. - Types: - Enterprise WAN: Used by businesses to connect their offices in different locations. - Global WAN: Includes large public networks like the internet. 5. Campus Area Network (CAN) - Scope: Covers a specific campus area, like a university, corporate campus, or military base. - Purpose: Connects various buildings within a campus to share resources and provide connectivity. - Examples: University campus network, military base networks. - Types: - Wired CAN: Uses fiber-optic cables or Ethernet. - Wireless CAN: Utilizes Wi-Fi for wireless communication within the campus. 11 6. Virtual Private Network (VPN) - Scope: Extends a private network across a public network, such as the internet. - Purpose: Provides secure communication by creating encrypted connections over less secure networks. - Examples: Corporate VPN for remote access to internal systems, personal VPN for secure browsing. - Types: - Remote Access VPN: Allows individual users to securely connect to a private network. - Site-to-Site VPN: Connects two or more networks, often in different physical locations. 7. Storage Area Network (SAN) - Scope: Dedicated network for data storage, typically used in large organizations. - Purpose: Provides high-speed access to consolidated storage resources. - Examples: Networked storage for data centers or enterprise environments. - Types: - Fibre Channel SAN: Uses Fibre Channel technology for fast data transmission. - iSCSI SAN: Uses Internet Protocol (IP) for linking data storage devices. 12  8. Enterprise Private Network (EPN) - Scope: Used by large organizations to connect multiple locations or departments. - Purpose: Provides secure, private communication and data sharing across an organization. - Examples: Corporate networks connecting different branches. - Types: - Wired EPN: Uses physical connections like Ethernet or fiber-optic cables. - Wireless EPN: Uses wireless technologies for connectivity. 9. Home Area Network (HAN) - Scope: Limited to a home environment. - Purpose: Connects devices such as computers, smartphones, smart appliances, and IoT devices within a home. - Examples: Home Wi-Fi network, smart home setups. - Types: - Wired HAN: Uses Ethernet cables for device connections. - Wireless HAN: Uses Wi-Fi or Bluetooth for connectivity. 13 10. Global Area Network (GAN) - Scope: Covers worldwide or global regions, linking multiple WANs. - Purpose: Enables global communication and connectivity between networks. - Examples: The internet is a type of GAN. - Types: - Satellite-based GAN: Uses satellite communication for global coverage. - Terrestrial-based GAN: Uses undersea cables and terrestrial networks for global connectivity. 14  11. Wireless Sensor Network (WSN) - Scope: Typically used for monitoring environments, deployed across large areas. - Purpose: Connects distributed sensors to collect data for various applications like environmental monitoring, healthcare, or industrial automation. - Examples: Smart agriculture networks, military surveillance systems. - Types: - Environmental WSN: For monitoring natural environments like forests or oceans. - Industrial WSN: For industrial applications like monitoring equipment in a factory. These types of computer networks serve different purposes based on scale, technology, and application, from small home networks to vast global networks. Network Type Scope Purpose Examples Types Wired PAN, Very small, a few Connects personal Bluetooth Personal Area Wireless PAN meters around an devices for individual connections, USB Network (PAN) (Bluetooth, individual. use. connections Infrared) Wired LAN Small geographic Connects devices to Local Area Office network, (Ethernet), area, like a building share resources Network (LAN) school network Wireless LAN (Wi- or office. within a limited area. Fi) Metropolitan Connects multiple Wired MAN (Fiber- City-wide Wi-Fi, Area Network City or large campus. LANs across a city or optic), Wireless university network (MAN) large area. MAN (WiMAX) Large geographic Connects multiple Wide Area The internet, Enterprise WAN, area, across cities or LANs or MANs over Network (WAN) corporate WANs Global WAN countries. long distances. 15  Wired CAN Specific campus like a Connects buildings Campus Area University network, (Ethernet, Fiber), university or within a campus to Network (CAN) military base Wireless CAN (Wi- company. share resources. Fi) Extends a private Provides secure Remote Access Virtual Private Corporate VPN, network over the communication over VPN, Site-to-Site Network (VPN) personal VPN internet. public networks. VPN Dedicated to data Provides high-speed Storage Area Fibre Channel SAN, storage, often in data access to centralized Data center storage Network (SAN) iSCSI SAN centers. storage resources. Provides secure Large organizations, Wired EPN Enterprise Private internal connecting multiple Corporate networks (Ethernet, Fiber), Network (EPN) communication and locations. Wireless EPN resource sharing. Connects home Wired HAN devices such as Home Area Home Wi-Fi, smart (Ethernet), Home environment. computers, Network (HAN) home setups Wireless HAN (Wi- smartphones, and Fi, Bluetooth) IoT. Enables global Satellite-based Global Area Worldwide, linking communication and The internet GAN, Terrestrial- Network (GAN) multiple WANs. network based GAN connectivity. Connects sensors to Smart agriculture, Environmental Wireless Sensor Deployed over large collect and transmit industrial WSN, Industrial Network (WSN) areas for monitoring. environmental data. monitoring WSN 16  Network Topologies Network topologies describe the layout or arrangement of different elements (links, nodes, etc.) in a computer network. The two main types of topologies are physical and logical topologies. Below are the common types of network topologies. 1. Bus Topology - Physical Layout: All devices are connected to a single central cable, known as the "bus" or backbone. - Data Flow: Data sent from one device travels in both directions until it reaches the destination. - Pros: - Simple to set up and requires less cable compared to other topologies. - Cost-effective for small networks. - Cons: - The entire network shuts down if the central bus cable fails. - Limited cable length and number of devices. - Troubleshooting can be difficult when issues arise. 2. Star Topology - Physical Layout: All devices are connected to a central hub, switch, or router. - Data Flow: Data passes through the hub before reaching its destination. - Pros: - Easy to install and manage. - Failure of a single device does not affect the entire network. - Easy to add or remove devices. - Cons: 17  - If the central hub fails, the entire network is disrupted. - More cabling is required compared to bus topology. 3. Ring Topology - Physical Layout: Devices are connected in a circular pattern, with each device connected to exactly two others. - Data Flow: Data travels in one direction (unidirectional) or both directions (bidirectional) around the ring. - Pros: - Data is transmitted in a predictable sequence, making it easier to manage network traffic. - Can work efficiently in smaller networks. - Cons: - A failure in any cable or device breaks the entire network unless a dual-ring topology is used. - Adding or removing devices can disrupt the network. 4. Mesh Topology - Physical Layout: Every device is connected to every other device, either fully (full mesh) or partially (partial mesh). 18  - Data Flow: Data can take multiple paths to reach its destination, providing redundancy. - Pros: - High fault tolerance; network continues to operate even if multiple links fail. - Can handle high traffic due to multiple paths. - Cons: - Expensive to implement due to the large number of connections. - Complex and difficult to manage. 5. Tree Topology - Physical Layout: A hierarchical topology where star-configured networks are connected to a central bus. - Data Flow: Data can flow from the root to the leaves and vice versa. - Pros: - Scalable; ideal for larger networks that need hierarchical structure. - Easy to manage and maintain due to the clear structure. - Cons: - If the central bus (backbone) fails, the whole network can fail. - More cabling and hardware are required than in simpler topologies. 19 6. Hybrid Topology - Physical Layout: A combination of two or more different types of topologies (e.g., star-bus, star-ring). - Data Flow: Follows the rules of the combined topologies. - Pros: - Flexible and scalable, as it can combine the strengths of various topologies. - Suitable for complex networks with different segments. - Cons: - Can be expensive and difficult to design and manage due to its complexity. 7. Point-to-Point Topology - Physical Layout: A direct link between two devices (nodes). - Data Flow: Data flows directly between the two connected devices. - Pros: 20  - Simple to establish and manage. - High bandwidth and reliable connection between two devices. - Cons: - Limited to only two devices; not scalable for larger networks. 8. Point-to-Multipoint Topology - Physical Layout: One device is connected to multiple devices, with all communication going through the central device. - Data Flow: The central node communicates with several nodes individually. - Pros: - Efficient for communication between a central device and multiple receivers. - Cons: - The central device can become a bottleneck if it has to handle many connections. Comparison Overview: - Bus: Simple but prone to failure. - Star: Reliable but reliant on the central hub. - Ring: Efficient but fragile to link failures. - Mesh: Redundant but costly and complex. - Tree: Scalable but dependent on the backbone. - Hybrid: Flexible but complex. Topology Physical Layout Data Flow Pros Cons Failure of the bus Devices connected to a Data travels in Simple to set up, Bus affects the entire single central cable both directions on cost-effective for Topology network, difficult to (bus). the bus. small networks. troubleshoot. Easy to Central hub failure Data passes install/manage, Star Devices connected to a disables the entire through the failure of one Topology central hub or switch. network, more cabling central hub. device doesn't required. affect others. 21  Failure of one device affects the entire Data travels in Predictable data Ring Devices connected in a network, one or both flow, suitable for Topology circular pattern. adding/removing directions. smaller networks. devices can disrupt the network. High fault Expensive and complex Mesh Every device connected Data can take tolerance, multiple to implement, requires Topology to every other device. multiple paths. paths prevent a lot of cabling. downtime. Failure of the central Star networks Data flows from Scalable, good for Tree backbone can take connected to a central root to leaves and larger networks Topology down the network, backbone (bus). vice versa. with hierarchy. more cabling required. Combination of two or Follows rules of Flexible, scalable, Hybrid Expensive, complex to more topologies (e.g., the combined combines strengths Topology design and manage. star-bus, star-ring). topologies. of topologies. Data flows directly Simple, high Point-to- Direct link between two Limited to two devices, between two bandwidth, reliable Point devices. not scalable. devices. connection. Central node Efficient for Point-to- One device connected communicates Central device can centralized Multipoint to multiple devices. with multiple become a bottleneck. communication. devices. 22  Network Hardware Computer network hardware consists of physical devices that are used to connect, manage, and facilitate communication between computers and other devices in a network. Below is an overview of key network hardware components: 1. Network Interface Card (NIC) - Purpose: Allows a computer or device to connect to a network. - Function: Converts data into electrical signals that can be transmitted over the network. Each NIC has a MAC address, which helps in uniquely identifying the computer on the network - Types: Can be wired (Ethernet NIC) or wireless (Wi-Fi NIC). - Location: Installed inside computers, laptops, or other devices. - Example: Ethernet cards, Wi-Fi adapters. 2. Switch - Purpose: Connects multiple devices within the same network (typically a Local Area Network, LAN). - Function: Forwards data to the appropriate device by using MAC addresses. A switch is a networking device that plays a central role in a Local Area Network (LAN). Like a hub, a network switch is used to connect multiple computers or communicating devices. When data arrives, the switch extracts the destination address from the data packet and looks it up in a table to see where to send the packet. Thus, it sends signals to only selected devices instead of sending to all. It can forward multiple packets at the same time. A switch does not forward the signals which are noisy or corrupted. It drops such signals and asks the sender to resend it. - Managed vs. Unmanaged: - Managed Switch: Allows configuration of features like VLANs, monitoring, and traffic control. 23  - Unmanaged Switch: Offers basic connectivity with no configuration. - Example: Cisco Catalyst switch. 3. Router - Purpose: Connects different networks together, including LANs, Wide Area Networks (WANs), or the internet. A router is a network device that can receive the data, analyse it and transmit it to other networks. A router connects a local area network to the internet. Compared to a hub or a switch, a router has advanced capabilities as it can analyse the data being carried over a network, decide/alter how it is packaged, and send it to another network of a different type. For example, data has been divided into packets of a certain size. Suppose these packets are to be carried over a different type of network which cannot handle bigger packets. In such a case, the data is to be repackaged as smaller packets and then sent over the network by a router. - Function: Routes data packets between networks by using IP addresses. - Home vs. Enterprise: Home routers typically combine router, switch, and access point functionalities, while enterprise routers are more specialized. - Example: Linksys, TP-Link routers. 24  4. Hub - Purpose: Connects multiple devices in a network through wires. Data arriving on any of the lines are sent out on all the others. The limitation of Hub is that if data from two devices come at the same time, they will collide. - Function: Broadcasts data to all devices in the network, regardless of the destination. - Types: Active hubs (amplify signals) and passive hubs (do not amplify). - Example: Basic networking hubs (largely obsolete, replaced by switches). 5. Modem - Purpose: Connects a network to the internet by converting digital signals from a computer to analog signals used by telephone lines (and vice versa). Modem stands for ‘MOdulator DEModulator’. It refers to a device used for conversion between analog signals and digital bits. computers store and process data in terms of 0s and 1s. However, to transmit data from a sender to a receiver, or while browsing the internet, digital data are converted to an analog signal and the medium (be it free- space or a physical media) carries the signal to the receiver. There are modems connected to both the source and destination nodes. The modem at the sender’s end acts as a modulator that converts the digital data into analog signals. The modem at the receiver’s end acts as a demodulator that converts the analog signals into digital data for the destination node to understand. - Types: - DSL Modem: For digital subscriber lines. - Cable Modem: For internet via cable TV networks. - Fiber Modem: For fiber-optic internet. 25  - Example: Motorola cable modems. 6. Access Point (AP) - Purpose: Provides wireless devices access to a wired network. - Function: Connects to a wired network and allows wireless devices to communicate with it. - Standalone vs. Router-integrated: Can be standalone or integrated into a router. - Example: Ubiquiti wireless access points, TP-Link APs. 7. Firewall - Purpose: Protects the network by controlling incoming and outgoing traffic based on security rules. - Function: Monitors and filters network traffic to prevent unauthorized access or attacks. - Types: - Hardware Firewall: A physical device installed in the network. - Software Firewall: Installed on individual devices (like a PC). - Example: Cisco ASA, Fortinet hardware firewalls. 8. Gateway 26  - Purpose: Acts as a "gate" between different networks, often different protocol types. It is a key access point that acts as a “gate” between an organisation's network and the outside world of the Internet - Function: Converts and routes data between different types of networks, such as between a LAN and a WAN or between the internet and a private network. Gateway serves as the entry and exit point of a network, as all data coming in or going out of a network must first pass through the gateway in order to use routing paths. Besides routing data packets, gateways also maintain information about the host network's internal connection paths and the identified paths of other remote networks. If a node from one network wants to communicate with a node of a foreign network, it will Notes 2024- 25 Computer Networks 191 pass the data packet to the gateway, which then routes it to the destination using the best possible route. - Example: Broadband gateways for home networks, enterprise-level gateways. 9. Repeater - Purpose: Extends the range of a network by amplifying and retransmitting signals. - Function: Receives weak signals, boosts them, and sends them along the network to maintain signal strength over long distances. - Types: Can be used in both wired and wireless networks. - Example: Wireless repeaters, Ethernet repeaters. 10. Bridge 27  - Purpose: Connects and filters traffic between two or more network segments, typically within a LAN. - Function: Divides traffic into smaller segments to reduce congestion by forwarding only relevant traffic. - Types: Can be used in both wired and wireless environments. - Example: Network bridges for Ethernet segments. 11. Load Balancer - Purpose: Distributes network traffic across multiple servers or devices. - Function: Ensures that no single server becomes overloaded, improving performance and reliability. - Types: Hardware and software load balancers. - Example: F5 Networks BIG-IP load balancers. 12. Proxy Server - Purpose: Acts as an intermediary between a client and the server from which the client requests services. - Function: Manages requests and improves security by hiding the client’s IP address and controlling internet traffic. - Types: Forward proxy (for outbound traffic) and reverse proxy (for inbound traffic). - Example: Squid, HAProxy. 28 13. Network Attached Storage (NAS) - Purpose: Provides centralized storage accessible over a network. - Function: Allows multiple users and devices to store and retrieve data over a network. - Example: Synology, QNAP NAS devices. 29 Hardware Purpose Function Types Example Network Converts data to Enables a device to connect Wired (Ethernet), Ethernet NIC, Wi-Fi Interface Card signals for to a network. Wireless (Wi-Fi) Adapter (NIC) transmission. Connects multiple devices in Forwards data based Managed, Cisco Catalyst Switch a LAN. on MAC addresses. Unmanaged Switch Routes data between Connects different networks, Linksys, TP-Link Router networks using IP Home, Enterprise like LANs to the internet. Router addresses. Basic Networking Connects multiple devices, Sends data to all Hubs (obsolete, Hub Active, Passive broadcasting data to all. connected devices. replaced by switches) Converts digital Connects a network to the Motorola Cable Modem signals to analog and DSL, Cable, Fiber internet. Modem vice versa. Enables wireless Provides wireless access to a devices to Standalone, Router- Ubiquiti Access Access Point (AP) wired network. communicate with a integrated Point, TP-Link AP network. Filters network traffic Protects the network from Cisco ASA, Fortinet Firewall based on security Hardware, Software unauthorized access. Firewall rules. Routes and converts Broadband Acts as a bridge between data between Broadband, Gateways, Gateway different networks or different network Enterprise Enterprise protocols. types. Gateways Amplifies and Extends the range of a Wireless Repeaters, Repeater retransmits weak Wired, Wireless network. Ethernet Repeaters signals. Divides network Connects and filters traffic Ethernet Bridge, Bridge traffic and forwards Wired, Wireless between network segments. Wireless Bridge relevant data. Prevents servers from Distributes traffic across being overloaded, F5 Networks BIG-IP Load Balancer Hardware, Software multiple servers. improving Load Balancer performance. Manages requests Acts as an intermediary and improves Forward Proxy, Proxy Server Squid, HAProxy between a client and server. security by hiding Reverse Proxy client IPs. Network Allows users to store Centralized storage Consumer, Synology, QNAP Attached Storage and retrieve data accessible over the network. Enterprise NAS (NAS) from a network. 30 31  Identifying Nodes in a Networked Communication Each node in a network should be uniquely identified so that a network device can identify the sender and receiver and decide a routing path to transmit data. Let us explore further and know how each node is distinguished in a network. MAC Address MAC stands for Media Access Control. The MAC address, also known as the physical or hardware address, is a unique value associated with a network adapter called a NIC. The MAC address is engraved on NIC at the time of manufacturing and thus it is a permanent address and cannot be changed under any circumstances. The machine on which the NIC is attached, can be physically identified on the network using its MAC address. Each MAC address is a 12-digit hexadecimal numbers (48 bits in length), of which the first six digits (24 bits) contain the manufacturer’s ID called Organisational Unique Identifier (OUI) and the later six digits (24 bits) represents the serial number assigned to the card by the manufacturer. A sample MAC address looks like: IP Address IP address, also known as Internet Protocol address, is also a unique address that can be used to uniquely identify each node in a network. The IP addresses are assigned to each node in a network that uses the Internet Protocol for communication. Thus, if we know a computer’s IP address, we can communicate with that computer from anywhere in the world. However, unlike MAC address, IP address can change if a node is removed from one network and connected to another network. The initial IP Address called version 4 (IPV4 in short), is a 32 bit numeric address, written as four numbers separated by periods, where each number is the decimal (base-10) representation for an 8-bit binary (base-2) number and each can take any value from 0 - 255. A sample IPV4 address looks like: 192.168.0.178 With more and more devices getting connected to the Internet, it was realised that the 32-bit IP address will not be sufficient as it offers just under 4.3 billion unique addresses. Thus, a 128 bits IP address, called IP version 6 (IPV6 in short) was proposed. An IPv6 address is represented by eight groups of hexadecimal (base-16) numbers separated by colons. A sample IPV6 address looks like: 2001:CDBA:0000:0000:0000:0000:3257:9652 Internet, Web and the Internet of Things 32 The Internet is the global network of computing devices including desktop, laptop, servers, tablets, mobile phones, other handheld devices, printers, scanners, routers, switches, gateways, etc. Moreover, smart electronic appliances like TV, AC, refrigerator, fan, light, etc. can also communicate through a network. The list of such smart devices is always increasing e.g., drones, vehicles, door lock, security camera. The Internet is evolving every day and it is difficult to visualise or describe each and every aspect of the architecture of the Internet. Computers are either connected to a modem through a cable or wirelessly (WiFi). That modem, be it wired or wireless, is connected to a local Internet Service Provider (ISP) who then connects to a national network. Many such ISPs connect together forming a regional network and regional networks connect together forming a national network, and such country-wise networks form the Internet backbone. The World Wide Web (WWW) The World Wide Web (WWW) or web in short, is an ocean of information, stored in the form of trillions of interlinked web pages and web resources. The resources on the web can be shared or accessed through the Internet. Sir Tim Berners-Lee — a British computer scientist invented the revolutionary World Wide Web in 1990 by defining three fundamental technologies that lead to creation of web: HTML – HyperText Markup Language. It is a language which is used to design standardised Web Pages so that the Web contents can be read and understood from any computer. Basic structure of every webpage is designed using HTML. URI – Uniform Resource Identifier. It is a unique address or path for each resource located on the web. It is also known as Uniform Resource Locator (URL). Every page on the web has a unique URL. Examples are: https://www.mhrd.gov.in,http:// www.ncert.nic.in,http://www.airindia.in, etc. URL is sometimes also called web address. However, a URL is not only the domain name. It contains other information that completes a web address, as depicted below: http://www.ncert.nic.in/textbook/textbook.htm URL Domain Name HTTP – The HyperText Transfer Protocol is a set of rules which is used to retrieve linked web pages across the web. The more secure and advanced version is HTTPS. Many people confuse the web with the Internet. The Internet as we know is the huge global network of interconnected computers, which may or may not have any file or webpage to share with the world. The web on the other hand is the interlinking of collection of Webpages on these computers which are accessible over the Internet. WWW today gives users access to a vast collection of information created and shared by people across the world. It is today the most popular information retrieval system Domain Name System The Internet is a vast ocean where information is available in the form of millions of websites. Each website is stored on a server which is connected to the Internet, which means each server has an IP address. Every device connected to the Internet has an IP address. To access a website, we need to enter its IP address on our web 33 browser. But it is very difficult to remember the IP addresses of different websites as they are in terms of numbers or strings. However, it is easier to remember names, and therefore, each computer server hosting a website or web resource is given a name against its IP address. These names are called the Domain names or hostnames corresponding to unique IP addresses assigned to each server. For easy understanding, it can be considered as the phonebook where instead of remembering each person’s phone number, we assign names to their numbers. For example, IP addresses and domain names of some websites are as follows: DNS Server Instead of remembering IP addresses, we assign a domain name to each IP. But, to access a web resource, a browser needs to find out the IP address corresponding to the domain name entered. Conversion of the domain name of each web server to its corresponding IP address is called Domain Name Resolution. It is done through a server called DNS server. Thus, when we enter a URL on a web browser, the HTTP protocol approaches a computer server called DNS server to obtain the IP address corresponding to that domain name. After getting the IP address, the HTTP protocol retrieves the information and loads it in our browser. In Figure 10.20, an example is shown in which the HTTP requests a DNS server for corresponding IP addss, and the server sends back an IP address. 34 Network Protocols Network protocols are the foundational rules and conventions that enable devices to communicate over networks. They define how data is transmitted, formatted, and processed, ensuring seamless interaction between diverse hardware and software systems. 1. What Are Network Protocols? At their core, network protocols are sets of standardized rules that dictate how data is exchanged between devices in a network. These protocols ensure that information sent from one device can be accurately received and interpreted by another, regardless of differences in hardware or software. 2. The OSI and TCP/IP Models Network protocols are often categorized based on the layers of the OSI (Open Systems Interconnection) or TCP/IP (Transmission Control Protocol/Internet Protocol) models. These models provide a framework for understanding how different protocols interact within a network. a. OSI Model (7 Layers): 1. Physical Layer: Deals with the physical connection between devices (e.g., cables, switches). 2. Data Link Layer: Manages node-to-node data transfer and error detection (e.g., Ethernet). 3. Network Layer: Handles routing and forwarding of data packets (e.g., IP). 4. Transport Layer: Ensures reliable data transfer (e.g., TCP, UDP). 5. Session Layer: Manages sessions or connections between applications. 6. Presentation Layer: Translates data formats (e.g., encryption, compression). 7. Application Layer: Interfaces directly with end-user applications (e.g., HTTP, FTP). b. TCP/IP Model (4 Layers): 1. Link Layer: Combines OSI's Physical and Data Link layers. 2. Internet Layer: Similar to OSI's Network layer (e.g., IP). 3. Transport Layer: Aligns with OSI's Transport layer (e.g., TCP, UDP). 4. Application Layer: Encompasses OSI's Session, Presentation, and Application layers (e.g., HTTP, FTP). 3. Common Network Protocols Here’s an overview of some widely used network protocols across different layers: 35 a. Application Layer Protocols: - HTTP/HTTPS (HyperText Transfer Protocol/Secure): Foundation of data communication for the World Wide Web. HTTPS includes encryption for secure communication. - FTP/SFTP (File Transfer Protocol/Secure): Used for transferring files between client and server. - SMTP/IMAP/POP3 (Email Protocols): Internet Access Message Protocol/Post Office Protocol Version 3.. Facilitate sending and receiving emails. - DNS (Domain Name System): Translates domain names to IP addresses. - SSH (Secure Shell): Provides secure remote login and command execution. b. Transport Layer Protocols: - TCP (Transmission Control Protocol): Ensures reliable, ordered, and error-checked delivery of data. - UDP (User Datagram Protocol): Offers faster, connectionless data transmission without guarantees, suitable for real-time applications. c. Internet Layer Protocols: - IP (Internet Protocol): Core protocol for routing and addressing packets of data. - IPv4: 32-bit addressing scheme. - IPv6: 128-bit addressing scheme to accommodate more devices. - ICMP (Internet Control Message Protocol): Used for diagnostic and error messages (e.g., ping). d. Link Layer Protocols: - Ethernet: Dominant wired networking technology for local area networks (LANs). - Wi-Fi (IEEE 802.11): Wireless networking technology. - ARP (Address Resolution Protocol): Maps IP addresses to physical MAC addresses. 4. Specialized Network Protocols Beyond the standard protocols, several specialized protocols cater to specific needs: - BGP (Border Gateway Protocol): Manages how packets are routed across the internet through autonomous systems. - MPLS (Multi-Protocol Label Switching): Enhances speed and control over data flows in large networks. 36 - SNMP (Simple Network Management Protocol): Facilitates network device management and monitoring. - VoIP Protocols (e.g., SIP, RTP): Enable voice communication over IP networks. 5. Security Protocols Security is paramount in networking, and several protocols ensure data integrity, confidentiality, and authentication: - TLS/SSL (Transport Layer Security/Secure Sockets Layer): Encrypt data between client and server, securing web traffic. - IPsec (Internet Protocol Security): Secures IP communications by authenticating and encrypting each IP packet. - Kerberos: Provides network authentication using secret-key cryptography. - HTTPS (combines HTTP with TLS/SSL): Secures web browsing. 6. Emerging and Modern Network Protocols As technology evolves, new protocols emerge to address contemporary challenges: - QUIC (Quick UDP Internet Connections): Developed by Google, it aims to reduce latency for web traffic. - HTTP/3: Built on QUIC, it offers improved performance over its predecessors. - WebSocket: Enables full-duplex communication channels over a single TCP connection, useful for real-time applications. - IoT Protocols (e.g., MQTT, CoAP): Designed for efficient communication in Internet of Things (IoT) environments. 37 What is the OSI Model? The OSI model is a layered framework that helps network architects and engineers visualize how data is transmitted over a network. It consists of seven layers stacked upon each other in order from the lowest to the highest level. Each OSI layer has its protocols and functions, which enable communication between two endpoints on different networks. Network stacks are complex, multi-layered systems that map application-layer data structures to bits transferred over physical media and back again. The Open Systems Interconnection (OSI) Model is a conceptual framework that provides a protocol-agnostic description of how the various layers of a network stack combine to enable network communications. The goal of the OSI model is to enable diverse communication systems to better interoperate using standard communication protocols. Layer 1: Physical Layer in OSI Purpose and functions The Physical layer of OSI is basically the first and lowest layer in the OSI model. Its purpose is establishing, maintain, and terminate communication between two endpoints on different networks. It does this by defining the connection type (wired or wireless), medium of transmission (fibre optic cable, copper wire, etc.), signal types (analogue or digital) and electric voltages used 38 in data transmission. The physical layer also handles issues related to synchronization and addressing at the media level. In addition, it defines how devices interact with each other at a hardware level so that data can be sent between them successfully. Hardware devices and protocols associated with the physical layer The Physical layer in OSI involves several hardware devices, such as modems, multiplexers, repeaters, and transceivers. The protocols used at this layer include Ethernet (IEEE 802.3), Token Ring (IEEE 802.5), High-Level Data Link Control (HDLC) and Point-to-Point Protocol (PPP). Layer 2: Data Link Layer in OSI Purpose and functions The Data Link Layer provides reliable data transmission over a physical communication link. It handles the physical addressing of each node and ensures that data is properly transferred between two connected nodes on a network. This OSI layer also defines how the network will handle data errors, retransmitting lost packets, and flow control mechanisms such as windowing. Hardware devices and protocols associated with the data link layer The Data Link Layer In OSI involves several hardware devices, such as frames, bridges, repeaters, and switches. The protocols used at this layer include Ethernet (IEEE 802.2), Logical Link Control (LLC) and High-Level Data Link Control (HDLC). Layer 3: Network Layer in OSI Purpose and functions This OSI Layer is mainly responsible for routing data packets from one node to another on a network. It establishes logical paths between endpoints (nodes) on a network and determines the best route for each packet to take to reach its destination. This OSI layer also handles addressing, subnetting, packet fragmentation and reassembly, and traffic congestion control mechanisms if needed. Hardware devices and protocols associated with the network layer 39 The Network Layer involves several hardware devices, such as routers and gateways. The protocols used at this layer include Internet Protocol (IP), IPX, AppleTalk, and Address Resolution Protocol (ARP). Layer 4: Transport Layer in OSI Purpose and functions The Transport Layer is primarily responsible for providing reliable end-to-end delivery of data packets across a network. It segments large data units into smaller ones (called frames) so that they can be transferred more efficiently between nodes on a network. This layer in OSI also handles the retransmission of lost or damaged packets and flow control mechanisms such as sliding windows. Hardware devices and protocols associated with the transport layer The Transport Layer in OSI involves several hardware devices, such as bridges, repeaters, and switches. The protocols used at this layer include Transmission Control Protocol (TCP), User Datagram Protocol (UDP), Real-Time Protocol (RTP) and Stream Control Transmission Protocol (SCTP). Layer 5: Session Layer in OSI Purpose and functions The Session Layer in OSI is majorly responsible for creating, maintaining, and managing the communication between two endpoints (nodes) on a network. It establishes logical (virtual) connections between host systems, coordinates data exchange between nodes, handles token- passing mechanisms to control access to shared resources on a network, and provides security measures such as encryption for data integrity. Hardware devices and protocols associated with the session layer The Session Layer involves several hardware devices, such as routers or gateways. The protocols used at this layer include Network File System Protocol (NFS), Remote Procedure Call (RPC), and Secure Shell (SSH). 40 Layer 6: Presentation Layer in OSI Purpose and functions The Presentation Layer in OSI is for converting data from one format to some other so that it can be understood by both endpoints (nodes) on a network. It translates application data sent across a network into an agreed-upon format and compresses it if needed to reduce overall transmission time. This layer in OSI also provides security measures such as encryption to ensure data integrity. Hardware devices and protocols associated with the presentation layer The Presentation Layer involves several hardware devices, such as switches and routers. The protocols used at this layer include Hypertext Transfer Protocol or HTTP, Simple Mail Transfer Protocol or SMTP, Secure Sockets Layer (SSL) and Transport Layer Security (TLS). Layer 7: Application Layer in OSI Purpose and functions The Application Layer provides services to end-users, such as file transfer, web browsing, email, and chat. This OSI layer can also provide access to network resources, such as databases and printers. Hardware devices and protocols associated with the application layer The Application Layer in OSI involves several hardware devices, such as servers and gateways. The protocols used at this layer include Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), Simple Mail Transfer Protocol (SMTP) and Secure Sockets Layer (SSL). 41 Comparison of the 7 Layers of OSI Model Let’s look at the comparison of 7 layers of OSI Models in details here; OSI Layer Purpose and Functions Hardware Devices & Common Problems Protocols OSI Layer 1: Data’s physical and Network cards, hubs, Faulty connections between Physical electrical transmission over switches, routers, etc. two nodes, inadequate a network connection Protocols include bandwidth Ethernet and PPP OSI Layer 2: Providing reliable link-level Network cards, hubs, Misconfigured or Data Link data transfer between two switches, routers, etc. incompatible hardware nodes Protocols used include devices, protocol mismatch Ethernet and PPP errors OSI Layer 3: Routing packets from the Network cards, routers, Inefficient path selection Network source to the destination and gateways. algorithms, incorrect data Protocols used include format or incorrect routing IP, ICMP, ARP, OSPF, information BGP, etc OSI Layer 4: Providing reliable end-to- Network cards, routers, Inefficient path selection Transport end communication and gateways. algorithms, incorrect data between two nodes in a Protocols used include format network TCP and UDP OSI Layer 5: Establishing and Network cards, routers, Missing or corrupted session Session maintaining a session and gateways. data between two applications Protocols used include SNMP, Telnet, and RPC OSI Layer 6: Converting data between Network cards, routers, Conversions errors caused by Presentation different formats and and gateways. incorrect data format or ensuring end-to-end data Protocols used include coding errors integrity SSL/TLS, S-HTTP, and SSH OSI Layer 7: Responsible for providing Network cards, servers, Misconfigured routers or Application end-user services, such as gateways. Protocols gateways, inadequate file transfer, web browsing, used include HTTP, bandwidth, signal interference email, and chat. FTP, SMTP, and due to electrical noise or radio SSL/TLS waves 42