Unit 1: Computer Networks — Long Questions

A computer network allows different devices such as computers, mobile phones, printers, and other digital devices to connect and communicate with each other using cables or wireless signals. It helps in sharing information, data, files, and resources quickly and easily between devices, saving time and effort.

Importance Computer networks are used in homes, schools, offices, and businesses, and modern life depends heavily on them for daily tasks. They support online learning and remote work, and businesses rely on networks for daily operations.

Uses in daily life 1. Internet browsing is a common example of network use.
2. Mobile phones use networks for calls, messages, and apps.
3. Schools use networks for online classes and learning systems.
4. Banks use networks for online transactions and ATMs.
5. Social media platforms work through computer networks.
6. Smart homes use networks to control devices.

Network architecture is the overall design of a computer network. It shows how computers, servers, and other devices are arranged and defines how data is transmitted across the network. Network architecture includes hardware, software, and communication rules, and a good architecture helps the network work efficiently and supports future expansion. A network works by breaking data into small packets, which travel through cables or wireless signals; networking devices guide the packets to the correct destination, and the receiving device reassembles the packets into the original data.

Main components (networking devices) 1. Network Interface Card (NIC): Allows a device to connect to a network (wired or wireless); each NIC has a unique MAC address, and a device cannot communicate on a network without it.
2. Switch: Connects devices and sends data to the correct device, improving network speed and efficiency.
3. Router: Connects different networks together, directs data packets using IP addresses, and connects local networks to the Internet.
4. Modem: Connects a local network to an Internet Service Provider (ISP); it converts digital data into signals for transmission and converts incoming signals back into digital form.
5. Wireless Access Point: Provides Wi-Fi connectivity, allowing wireless devices to connect to a network and extending wireless coverage.

The OSI (Open Systems Interconnection) model is a standard model used to understand network communication. It has seven layers, with each layer performing a different function; it is used for learning and designing networks and helps different systems communicate properly.

Layers and functions 1. Physical Layer: Sends raw data as electrical, optical, or radio signals over the medium; defines hardware aspects such as cables, connectors, voltage levels, and data transmission rates.
2. Data Link Layer: Ensures error-free data transfer between directly connected nodes; handles framing, error detection/correction, and controls access to the shared transmission medium.
3. Network Layer: Routes data from source to destination across different networks; manages logical addressing (IP addresses) and determines the best path for delivery.
4. Transport Layer: Provides reliable and ordered delivery of data between devices; performs error recovery, flow control, and segmentation of data.
5. Session Layer: Establishes, maintains, and terminates communication sessions between applications; manages session checkpoints and recovery.
6. Presentation Layer: Translates data into a format understandable by the application layer; handles encryption, compression, and format conversion.
7. Application Layer: Provides services directly to end users and applications; supports protocols like HTTP, FTP, and email services.

Lower layers handle physical data transfer, middle layers manage routing and delivery, and upper layers support user applications; each layer works independently, and together they ensure proper communication.

Network topology refers to the layout of a computer network — how devices and cables are arranged. Topology can be physical (actual connections) or logical (how data flows), and it affects network performance and maintenance.

Bus Topology All devices are connected to a single main cable, and data travels along this cable to each device.
Advantages: Simple and easy to install; requires less cable; cost-effective.
Disadvantages: Failure of the main cable affects the whole network; difficult to troubleshoot; performance decreases with more devices.

Star Topology All devices connect to a central hub or switch, and data passes through this central device.
Advantages: Easy to install and manage; failure of one device does not affect others; easy to detect faults.
Disadvantages: Failure of the central device stops the entire network; requires more cable; higher cost.

Ring Topology Devices are connected in a circular path, and data moves in one direction around the ring, with each device receiving and passing it along.
Advantages: Data flows in an organized manner; no data collision; equal access for all devices.
Disadvantages: Failure of one device affects the whole network; difficult to add/remove devices; rarely used today.

Mesh Topology Devices are connected to many other devices, so multiple paths exist for data transmission.
Advantages: Highly reliable and fault-tolerant; multiple paths for data; high security.
Disadvantages: Very expensive; complex installation; requires a large number of cables.

Computer networks are classified based on their size and coverage area, with different types used for different purposes. The most common types are LAN, WAN, and the Internet (Public WAN).

Local Area Network (LAN) Connects devices within a small area such as a home, school, or office. It provides high data transfer speed, is usually owned and managed by a single organization, commonly uses Ethernet and Wi-Fi, and is cost-effective and easy to maintain.

Wide Area Network (WAN) Covers a large geographic area and connects networks in different cities or countries. It uses leased lines, satellites, or the Internet; its data transfer speed is slower than LAN, and it is expensive to install and manage. The Internet is the largest example of a WAN.

The Internet (Public WAN) A global network connecting millions of devices, allowing sharing of information worldwide. Services like email, websites, and cloud storage use the Internet. It uses standard protocols for communication and supports education, business, and entertainment, playing an important role in daily life.

Networking devices are used to connect computers and other devices in a network and control the flow of data; each device has a specific role in communication.

1. Network Interface Card (NIC): Allows a device to connect to a network, either wired or wireless. Each NIC has a unique address called a MAC address, and it sends and receives data from the network; without a NIC, a device cannot communicate on a network.

2. Switch: Connects devices and sends data to the correct device, improving network speed and efficiency; switches are common in modern networks.

3. Router: Connects different networks together and directs data packets to their correct destination. Routers connect local networks to the Internet, use IP addresses to send data, and improve network security and control.

4. Modem: Connects a local network to an Internet Service Provider (ISP). It converts digital data into signals suitable for transmission and converts incoming signals back into digital form; it is used with cable, DSL, or fiber connections, and often works with routers.

5. Wireless Access Point: Provides Wi-Fi connectivity, allowing wireless devices to connect to a network. It extends wireless network coverage, improves signal strength and stability, and supports mobile connectivity, especially in large buildings and campuses.

A network protocol is a set of rules for communication. It defines how data is formatted and transmitted, and controls error handling and data delivery. All devices in a network must follow the same protocol to ensure smooth data exchange.

TCP/IP (Transmission Control Protocol/Internet Protocol): The main protocol used on the Internet. TCP ensures reliable data delivery, while IP handles the addressing and routing of data; together, TCP/IP enables communication between devices and is used in almost all networks.

HTTP (Hypertext Transfer Protocol) Used to transfer web pages between a web browser and a web server, allowing users to view websites. HTTP does not encrypt data; secure websites use HTTPS instead, which uses SSL/TLS encryption to protect sensitive information such as passwords and payment data from interception.

FTP (File Transfer Protocol) Used to upload and download files, allowing file sharing between computers. It is commonly used by web developers, can transfer large files, and secure versions of FTP are also available.

DNS (Domain Name System) Converts website names into IP addresses, making websites easy to access since users do not need to remember numbers. DNS servers perform this translation process and it plays a key role in Internet use.

An IP address is a unique number assigned to a device, where IP stands for Internet Protocol. It helps identify devices on a network, and data uses IP addresses to find its destination; every network device must have an IP address, as communication is not possible without it.

IPv4 An older version of IP addressing that uses 32-bit numeric addresses, for example 192.168.1.10, written as 4 numbers (each 0-255, i.e. 1 byte = 8 bits) separated by dots. It consists of a network part (identifies the local network) and a host part (identifies the specific device); IPv4 has a limited number of addresses (about 4.29 billion in total).

IPv6 The newer version with 128-bit addresses, written as 8 groups of 4 hexadecimal digits (each group = 16 bits) separated by colons, for example 2001:0db8:85a3:0000:0000:8a2e:0370:7334. It provides a much larger address space (about 3.4×10³8 addresses) and supports modern Internet needs, so it will never run out of addresses.

Default Gateway A default gateway connects a local network to other networks; it is usually a router. Data meant for outside networks goes through the gateway, which forwards it to the correct network, so Internet access depends on it.

Subnetting Subnetting divides a network into smaller parts called subnets. It reduces network traffic, improves performance, increases security, and is used by large networks for better management.