What is a computer network? Types, devices, topologies, models of sharing and speed explained

A network is two or more devices connected so they can share data and resources: files, printers, an internet connection, a school management system or an M-Pesa till. Your phone on Wi-Fi at a café, the computers in a cyber, the CCTV cameras in a supermarket and the servers behind Safaricom, KRA's iTax and your bank are all parts of networks. The internet itself is a network of networks: millions of them connected together.

Networking is the foundation for almost every IT career: network and system administration, cybersecurity, cloud, telecoms, and even software development (every app talks over a network). This first unit gives you the vocabulary and big picture you'll build on in every later lesson.

Why do we need networks?

Without networks, every computer would be an island and data would move on flash disks.

Who uses networks, and where?

• Homes: a Wi-Fi router connecting phones, TVs and laptops to a fibre or 4G/5G internet line.
• Schools and universities: computer labs, staff networks, campus Wi-Fi, e-learning systems.
• Businesses: offices, supermarkets with tills and CCTV, banks linking branches, factories with sensors.
• Hospitals: patient records, lab machines and imaging systems.
• Government: eCitizen, KRA, county offices, the National Optic Fibre Backbone (NOFBI).
• Internet service providers (ISPs): Safaricom, Airtel, Zuku, Faiba and others running huge networks of fibre, towers and data centres.
• Data centres and cloud: thousands of servers connected by high-speed switches.

Types of networks by size

Two more terms you'll meet:

• SAN (Storage Area Network): a fast network connecting servers to shared storage in data centres.
• VPN (Virtual Private Network): an encrypted "tunnel" that makes a remote device or branch act as if it were on the private network (covered in the firewalls and VPN lesson).

The devices you will meet

Home "routers" from Safaricom, Zuku, Airtel or Faiba are usually modem/ONT + router + switch + access point + firewall in one box. In offices these are usually separate devices so each can be bigger and better managed.

Media: how the signal travels

The devices and cables lesson covers these in detail.

Network topologies

The topology is the shape of the network: how devices are connected.

Real networks are usually hybrids: a star in each office, connected by a ring or partial mesh of fibre between buildings.

Physical vs logical topology: the physical topology is how cables run; the logical topology is how data actually flows. Wi-Fi looks like a star physically (everyone to the AP) but devices share the same radio channel.

Client–server vs peer-to-peer

Speed and quality words

Bits vs bytes: 8 bits = 1 byte. Internet packages are sold in Mbps (megabits), but downloads show MB/s (megabytes). Divide by 8:

for mbps in [10, 20, 40, 100, 1000]:
    print(f"{mbps} Mbps package -> about {mbps / 8:.1f} MB/s at best")

size_gb = 4                       # a 4 GB movie
speed_mbps = 20
seconds = size_gb * 1000 * 8 / speed_mbps
print(f"Downloading {size_gb} GB at {speed_mbps} Mbps takes about {seconds / 60:.0f} minutes")

How a request travels: opening a website

When you type www.example.co.ke on your phone:

1. Your phone is connected to the Wi-Fi access point (wireless LAN).
2. It asks a DNS server for the website's IP address.
3. It sends the request to its default gateway (the home router).
4. The router forwards it to your ISP, which routes it across many routers and fibre links (the WAN/internet) to the web server's data centre.
5. The server replies; the reply travels back the same way, possibly through different routes.
6. All of this usually takes well under a second.

Each later lesson zooms into one part of this journey: addresses, DNS, routing, switching, Wi-Fi and security.

Careers that use networking

Network technician, network administrator/engineer, systems administrator, NOC (network operations centre) engineer at an ISP, cybersecurity analyst, cloud engineer, field engineer installing fibre and CCTV, IT support officer. Certifications like CompTIA Network+ and Cisco CCNA are covered in the careers lesson.

Summary

• A network connects devices to share data and resources; the internet is a network of networks.
• By size: PAN, LAN/WLAN, CAN, MAN, WAN; plus SAN and VPN.
• Routers join networks, switches connect devices in a LAN, APs add Wi-Fi, modems/ONTs connect to the ISP, firewalls filter traffic.
• Topologies: star (most common), bus, ring, mesh, hybrid; client–server vs peer-to-peer.
• Bandwidth is the maximum, throughput is what you get, latency is delay; divide Mbps by 8 for MB/s.

Learn more: Cloudflare Learning Center: What is a LAN? · Cisco Networking Academy (free courses)