What is a Network?#

A network is officially defined as a &group or system of interconnected people or items.

So, by this definition, train stations connected to each other with rail tracks make up a railway network. People who follow each other on Twitter make up an online social network.

Similarly, computers connected to each other with cable or wireless radio make up a computer network.

Why Computer Networks?#

There are two main purposes of computer networks: Communication using computers and sharing of resources.

A Brief History of Networking#

The 50s: Cold War#

The concept of networking began during the Cold War, primarily due to the rivalry between the United States and the Soviet Union. After the Soviet Union successfully launched Sputnik, the first satellite, the United States was caught off-guard.

In response, the U.S. government established the Advanced Research Projects Agency (ARPA) to drive scientific discoveries and technological advancements.

The 60s - 70s: ARPANET#

ARPA was meant to facilitate research. But their computers could not talk to each other. ARPA sent out a request for the design of a network that would allow computers across the entire country to talk to each other.

A network called the ARPANET was developed over the course of a year. In September 1969, the ARPANET was turned on. It initially connected four universities: MIT, UCLA, Stanford, and the University of Utah.

Over the ’70s, other computer networks just like ARPANET sprang up. While the computers on one network could communicate via a default way to communicate set by the network administrator of each network, the computers on different networks could not communicate since every network had its own language or protocol.

Then, a standardized protocol called the Transmission Control Protocol(TCP) was invented.

The 80s: Protocols#

TCP/IP became the foundational protocol suite for networking, establishing the rules for data transmission. ARPANET was fully migrated to TCP/IP.

Computers were added to the Internet at an increasing rate. These computers were primarily from government, academic, and research organizations. Much to the surprise of the engineers, the early popularity of the Internet was driven by the use of electronic mail.

The 90s: The World Wide Web (WWW)?#

The World Wide Web (WWW) is a system of interlinked hypertext documents accessed via the internet. It was invented by Tim Berners-Lee in 1989 to facilitate the sharing of information through hyperlinks, which allow users to navigate between different web pages easily.

Why Do We Need Protocols?#

Protocols are essential in networking because they define the rules for communication between different devices. Without standard protocols, devices and applications wouldn’t be able to communicate effectively, leading to chaos and inefficiency.

The Internet Society (ISOC) and other standard-setting organizations create and maintain these protocols to ensure consistency and interoperability across the internet.

How Are We Connected?#

Connections between networks are made via physical and wireless methods:

• Physical Connections: Most of the world’s internet traffic relies on physical cables, including fiber-optic cables laid across the ocean floors, which connect continents and enable high-speed data transfer.

• Wireless Connections: These include radio waves used in Wi-Fi, Bluetooth (for short-range communication), and mobile networks like 3G, 4G, LTE, and 5G (for long-range communication).

What is an ISP?#

An Internet Service Provider (ISP) is a company that provides internet access to users. ISPs are interconnected with other ISPs to form a vast network. Some ISPs are “Tier 1” providers, meaning they own the infrastructure that forms the backbone of the internet and can connect to any other network without paying fees.

What is an IP Address?#

An IP (Internet Protocol) address is a unique identifier assigned to each device connected to a network, enabling it to communicate with other devices. It’s similar to a phone number, allowing computers to find and communicate with each other.

When you connect to the internet, your ISP assigns you a public IP address. Within your local network, devices are assigned private IP addresses by your router through DHCP (Dynamic Host Configuration Protocol).

Network Address Translation (NAT) allows multiple devices on a local network to share a single public IP address. When data is sent to your public IP, NAT directs it to the correct device within your network.

• Ports: These are 16-bit numbers that help direct data to the correct application on a device. For example, web traffic usually uses port 80 for HTTP. There are 65,536 possible port numbers, with the first 1024 reserved for system use.

Internet Speed#

• 1 Mbps (Megabit per second): Equals 1 million bits of data transmitted every second.
• 1 Gbps (Gigabit per second): Equals 1 billion bits per second.

Local Area Network (LAN)#

A LAN is a network that covers a small geographic area, like a home, school, or office building. It typically uses Ethernet cables or Wi-Fi to connect devices.

Metropolitan Area Network (MAN)#

A MAN covers a larger area, like a city, and is typically made up of multiple LANs.

Wide Area Network (WAN)#

A WAN spans large geographic areas, often a country or continent, and typically uses fiber-optic cables or satellite links to connect different networks.

What is a Modem?#

A modem converts digital data from a computer into analog signals that can be transmitted over telephone or cable lines, and vice versa.

What is a Router?#

A router is a device that directs data packets between networks, determining the best path for data to travel.

Network Topologies#

Bus Topology#

All devices share a single communication line. Only one device can send data at a time. If the main cable fails, the entire network goes down.

Ring Topology#

Devices are connected in a circular manner. Data travels in one direction. If one connection fails, the network is disrupted.

Star Topology#

All devices are connected to a central hub. If the central device fails, the entire network is affected.

Tree Topology#

A combination of star and bus topologies, providing a hierarchical network structure.

Mesh Topology#

Every device is connected to every other device. This provides high reliability but is expensive to implement.