Learning Objectives

By the end of this chapter, you will be able to:

  • Define a computer network and list its benefits.
  • Differentiate between PAN, LAN, MAN, and WAN.
  • Differentiate between client-server and peer-to-peer networks.
  • Describe the common network topologies: Bus, Star, Ring, Mesh, Tree, and Hybrid.
  • Choose a suitable topology for a given situation.

What is a Computer Network?

A computer network is a collection of two or more computers and other hardware devices connected together to share resources and exchange data.

Benefits of networking: sharing printers and internet connections, sharing files and databases, communication (email, chat, video calls), centralized backup and security, and lower costs than giving every computer its own resources.

Network Types

Networks are often classified by their geographical scope.

  • Personal Area Network (PAN): Connects devices around one person, such as a phone, smartwatch, and Bluetooth earphones (a few meters).

  • Local Area Network (LAN): A network that connects computers within a limited geographical area, such as a single building or a school campus. Most LANs are used to share resources like printers and files.

  • Metropolitan Area Network (MAN): Covers a city or large campus, for example a cable or fiber network linking offices across Kathmandu Valley.

  • Wide Area Network (WAN): A network that covers a broad geographical area, such as a city, country, or even the entire globe. A WAN is often a collection of interconnected LANs. The most well-known example of a WAN is the Internet.

flowchart LR
    LAN["LAN: one office or building"] --> MAN["MAN: offices across a city"]
    MAN --> WAN["WAN: country or world (the Internet)"]

Figure 1: LAN, MAN, and WAN Scope

Type Coverage Speed Ownership Example
PAN A few meters Low to moderate Individual Phone connected to earbuds
LAN Building or campus High Single organization College computer lab
MAN City High ISP, city, or large organization Fiber ring linking city offices
WAN Country or world Varies Telecom companies, many owners Bank network across Nepal; Internet

Client-server vs peer-to-peer

Networks can also be classified by how computers relate to one another. In a client-server network, a dedicated server provides files, applications, or printing to clients. In a peer-to-peer (P2P) network, every computer is equal and shares its own resources; this is cheap but suits only small networks.

Network Topologies

Network topology refers to the physical layout or arrangement of the devices on a network. The most common topologies are:

  • Bus Topology: All devices are connected to a single central cable, called the bus or backbone.
    • Advantage: Cheap and easy to set up for a few devices; uses little cable.
    • Disadvantage: If the main cable fails, the entire network goes down.
  • Star Topology: All devices are connected to a central hub or switch. This is the most common topology used in modern LANs.
    • Advantage: If one cable fails, only that single device is affected. The rest of the network continues to function.
    • Disadvantage: If the central switch fails, the whole network stops; more cable is needed.
  • Ring Topology: All devices are connected in a closed loop or ring. Data travels around the ring in one direction.
    • Advantage: Orderly data flow with no collisions.
    • Disadvantage: If one device or cable fails, it can break the ring and take down the entire network.
  • Mesh Topology: Every device is connected to many (in a full mesh, all) other devices.
    • Advantage: Very reliable; data can take another path if one link fails.
    • Disadvantage: Expensive and complex because of the many links. Used for internet backbones and bank data centers.
  • Tree (Hierarchical) Topology: Several star networks connected to a central backbone, like branches of a tree.
    • Advantage: Easy to expand building by building or floor by floor.
    • Disadvantage: Failure of the backbone affects all branches.
  • Hybrid Topology: A combination of two or more topologies, which is what most real organizations use.
flowchart TB
  subgraph Star[Star topology]
    SW((Switch))
    SW --- A1[PC]
    SW --- A2[PC]
    SW --- A3[Printer]
    SW --- A4[PC]
  end
  subgraph Ring[Ring topology]
    R1[PC] --- R2[PC]
    R2 --- R3[PC]
    R3 --- R4[PC]
    R4 --- R1
  end

Comparison of topologies

Topology Cost Reliability Ease of expansion Typical use
Bus Low Low (backbone is a weak point) Limited Old or temporary small networks
Star Moderate Good (switch is a weak point) Easy Offices, labs, homes
Ring Moderate Low unless dual ring Difficult Some older and fiber networks
Mesh High Very high Difficult Backbones, critical systems
Tree Moderate Good Very easy Multi-floor or multi-building sites

Scenario

A college in Pokhara has a computer lab, a library, and an admin building. Inside each building, PCs connect to a switch (star). The three switches connect to a core switch over fiber (tree). The college’s connection to its ISP and other campuses forms part of a WAN. Overall, the college network is a hybrid topology.

Summary

A computer network is a group of connected computers that can share resources. Networks are classified by size, from PANs around one person to LANs, MANs, and WANs, the largest WAN being the Internet. They can also be client-server or peer-to-peer. The physical layout of a network is its topology. While older networks used Bus and Ring topologies, the modern standard for LANs is the more robust and reliable Star topology, with mesh used where very high reliability is needed and tree or hybrid layouts used in larger organizations.

Key Takeaways

  • A network is a collection of connected computers.
  • PANs are personal, LANs are local, MANs are city-wide, and WANs are wide-area. The Internet is a WAN.
  • Network topology is the physical layout of the network.
  • Star topology is the most common modern LAN topology.
  • Mesh is the most reliable but most expensive; most real networks are hybrid.

Discussion Questions

  1. What type of network do you have in your home or school (LAN or WAN)?
  2. Why is the Star topology more reliable than the Bus or Ring topology?
  3. Can you think of a situation where a Bus topology might still be useful?

Exam-Style Questions

Short answer

  1. What is a computer network? List three benefits.
  2. Differentiate between LAN and WAN.
  3. What is mesh topology? Where is it used?

Long answer

  1. Explain different network topologies with their advantages and disadvantages.
  2. A company has offices on three floors of a building. Suggest a suitable network type and topology, and justify your answer.