Network

A computer network is a collection of interconnected devices that can exchange data and share resources. The Internet is the largest example of this, a global network of networks.

Internet

The Internet is a global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices.

It is a vast network of networks that allows for the sharing of information and resources on a global scale.

A Brief History of the Internet

The internet's origins can be traced back to the Cold War era, with its development driven by military and academic needs for a resilient and decentralized communication network.

• 1969: The ARPANET (Advanced Research Projects Agency Network) was launched by the U.S. Department of Defense. This was the first packet-switching network and served as the direct predecessor to the modern internet.

• 1971: As the network expanded to connect more institutions, the first network email was sent, marking a significant milestone in digital communication.

• 1983: ARPANET officially adopted the TCP/IP protocol, establishing a universal standard for how data would be transmitted across different networks.

• 1986: The NSFNET (National Science Foundation Network) was created, providing a high-speed "backbone" to connect university computer networks across the U.S. and facilitate academic research.

• 1990: ARPANET was officially decommissioned, having successfully laid the groundwork for a global, interconnected network.

• 1991: The World Wide Web, developed by Tim Berners-Lee at CERN, became publicly available, making the internet more accessible and user-friendly through a system of hyperlinks and graphical browsers.

• 1995: NSFNET was decommissioned, and the internet transitioned into a fully commercialized entity, opening the door for businesses, e-commerce, and the general public.

• 2000s–Present: The internet has experienced explosive growth, connecting billions of people worldwide and enabling transformative technologies like cloud computing, the Internet of Things (IoT), and social media.

Network Components and Concepts

Types of Networks

Computer networks can be broadly categorized based on their physical connections and the number of "hops" data must take to travel between devices.

Computer Network
│
├── Wired Network
│   ├── Single Hop (e.g., Ethernet)
│   └── Multi-Hop
│
└── Wireless Network
    ├── Purely Wireless
    │   ├── Single Hop (e.g., Bluetooth)
    │   └── Multi-Hop (e.g., Ad-hoc Networks)
    │
    └── Wired cum Wireless
        ├── Single Hop (e.g., Wi-Fi)
        └── Multi-Hop (e.g., GSM)

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Network Interface Card (NIC)

A Network Interface Card (NIC) is a crucial hardware component that allows a device to connect to a network. It functions as a translator, converting digital data from the computer into electrical signals for wired networks, or radio signals for wireless networks that can be sent over the network medium.

• Installation: Can be integrated directly into the motherboard or added as an external device (e.g., via USB).

• Connectivity: Can be wired (Ethernet) or wireless (Wi-Fi).

  • Wired NIC: Uses an Ethernet cable with an RJ-45 connector.
  • Wireless NIC: Connects using radio waves (Wi-Fi).

Every NIC is assigned a unique MAC address, which serves as a permanent, physical identifier for the device on a local network.

Cables:

• Straight-Through Cable: Connects devices of different types (e.g., a PC to a switch).

• Cross-Over Cable: Connects devices of the same type (e.g., a PC to another PC).

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MAC (Media Access Control) Address

A MAC address is a unique hardware identifier assigned to a NIC. It operates at the data link layer (Layer 2) of the OSI model and is used for communication within a local network segment.

• Format: A 48-bit (6-byte) hexadecimal address, typically written as 00:1A:2B:3C:4D:5E.

• Structure is of 2 parts:

  • OUI (Organizationally Unique Identifier): The first 24 bits, which identify the manufacturer.

  • Device Identifier: The last 24 bits, which are unique to the specific device.

• MAC Addressing Types:

  • Unicast: Sent to a single, specific device.

  • Multicast: Sent to a select group of devices.

  • Broadcast: Sent to all devices on the network (FF:FF:FF:FF:FF:FF).

You can find your device's MAC address using these common commands:

• Windows: getmac or ipconfig /all

• Linux/macOS: ifconfig or ip a

Networking Devices

Hub, Switch, Bridge, Router, Brouter, Gateway, Workstation

Hub

A hub is a basic networking device that operates at the physical layer (Layer 1) of the OSI model. It connects multiple devices in a LAN but lacks intelligence;

when it receives data on one port, it broadcasts that data to all other ports. This can lead to frequent data collisions and makes hubs inefficient for modern networks.

• Does not learn MAC addresses or perform traffic filtering.

• Only one device can transmit at a time, which can cause data collisions.

Switch

A switch is a more advanced device that connects devices within a LAN that operates at the data link layer (Layer 2). Unlike a hub, a switch learns the MAC addresses of connected devices and forwards data only to the intended recipient.

This significantly reduces network congestion and collisions, and it allows for full-duplex communication, where devices can send and receive data simultaneously.

Bridge

A bridge is a device that connects two separate LAN segments, making them function as a single network. It also operates at Layer 2 and uses MAC addresses to filter traffic, forwarding data only when the destination is on the other segment.

While bridges improve efficiency, they have been largely replaced by more scalable switches.

Router

A router is a key networking device that operates at the network layer (Layer 3). Its primary function is to connect different networks (such as a home LAN and the internet) and route data packets between them based on their IP addresses.

Modern routers often include features like DHCP for IP address assignment, NAT for sharing a single public IP by mapping private IP to public IP addresses, and built-in firewalls for security.

Supports dynamic routing protocols such as RIP, OSPF, and BGP.

Brouter

A brouter, or bridge router, is a hybrid device that combines the functions of a bridge and a router. It can route packets for known network protocols and bridge traffic for all other, unknown protocols.

Brouters were useful in older, multi-protocol environments but are now rare.

Gateway

A gateway is a network node that connects two networks with different transmission protocols. It acts as a protocol translator, enabling communication between disparate systems.

For example, a VoIP gateway might translate between the internet's TCP/IP protocol and the public telephone network's protocol. Gateways can operate at any layer of the OSI model.

Workstation

In networking, a workstation is a high-performance computer designed for a single user, typically for technical or scientific applications. It acts as a client on the network, accessing shared resources, and is generally more powerful than a standard personal computer.

Network Architecture and Protocols

Network Topology

Network topology refers to the physical and logical arrangement of nodes and connections in a network. Common types include bus, star, ring, and mesh topologies.

Network Types

• LAN (Local Area Network): A network that connects computers and other devices within a limited geographical area, such as a single building or office.

• MAN (Metropolitan Area Network): A network that spans a larger area, like a city or a large campus, and often connects multiple LANs.

• WAN (Wide Area Network): A network that covers a broad geographic area, such as a country or continent. The internet is the world's largest WAN. Typically uses technologies like leased lines, satellite links, or fiber optic cables.

Protocol

A protocol in computer networking is a standard set of rules that define how computers communicate with each other over a network.

A network protocol is a standardized set of rules that governs how data is formatted, transmitted, and received by network devices. Protocols ensure that devices can communicate with each other in an orderly and efficient manner.

The Network Edge and Access Technologies

The network edge is where end-user devices (like computers, smartphones, and servers) connect to the larger network or the internet. These end systems are also called hosts because they host applications such as browsers, servers.

It is the starting or ending point of data in the network where communication with the Internet begins or ends.

Home Access Networks

Several technologies are used to connect homes to the internet:

• DSL (Digital Subscriber Line): Uses existing telephone lines (twisted-pair copper wire) to provide internet access. Data and voice calls are transmitted over different frequencies, allowing for simultaneous use.

• Cable Internet: Delivered through the same coaxial cable network used for cable television. It is a shared medium, meaning bandwidth is shared among users in a neighborhood.

• FTTH (Fiber to the Home): Provides a direct fiber optic connection to the home, offering very high speeds and symmetrical upload and download rates.

• Dial-Up: An older technology that uses a modem and a standard telephone line to connect to the internet. It is very slow and does not allow for simultaneous phone and internet use.

• Satellite Internet: Provides internet access via satellites, making it a good option for rural or remote areas where other options are not available. It typically has higher latency due to the long distance the signal must travel.

Physical Media

Physical media are the transmission pathways that carry data signals in a network. They can be divided into two main categories:

Guided Media

Guided media provide a physical path for the signals, such as a wire or cable.

• Twisted-Pair Copper Wire: The most common type of guided media, used in telephone lines and Ethernet cables. It consists of pairs of insulated copper wires twisted together to reduce electromagnetic interference.

• Coaxial Cable: Has a central copper conductor surrounded by insulation and a braided metal shield. It offers better protection from interference than twisted-pair and is commonly used for cable TV and internet.

• Fiber Optic Cable: Transmits data as pulses of light through thin strands of glass or plastic. It is immune to electromagnetic interference and can transmit data at extremely high speeds over long distances.

Unguided Media

Unguided media, or wireless media, transmit data through the air or space.

• Terrestrial Radio: Uses electromagnetic waves to transmit data. It is used in technologies like Wi-Fi, Bluetooth, and cellular networks, providing mobility and eliminating the need for physical cables.

• Satellite Radio: Transmits data between ground stations and satellites orbiting the Earth. It is used for satellite internet and other long-distance communication. Geostationary satellites are in a high orbit and have high latency, while Low Earth Orbit (LEO) satellites, like those used by Starlink, are closer to Earth and have lower latency.