Network Topologies

How Devices Are Arranged

The physical or logical arrangement of devices in a network is called its topology. Topology determines how data flows, how fault-tolerant the network is, and how easy it is to add or remove devices. There are several common topologies, each with its own strengths and weaknesses.

Bus Topology

All devices are connected to a single central cable called the bus. Data sent by one device travels along the bus in both directions until it reaches the intended recipient.

  ┌──────┐  ┌──────┐  ┌──────┐  ┌──────┐
  │ PC 1 │  │ PC 2 │  │ PC 3 │  │ PC 4 │
  └──┬───┘  └──┬───┘  └──┬───┘  └──┬───┘
     │         │         │         │
  ═══╧═════════╧═════════╧═════════╧═══  ← Bus (coaxial cable)

• Advantage: Simple and cheap — requires less cable than other topologies.
• Disadvantage: If the bus cable breaks, the entire network goes down. Difficult to troubleshoot.

Bus topology was common in early Ethernet networks (10Base2, 10Base5) but is rarely used today.

Star Topology

Every device connects to a central hub or switch. All data passes through the hub, which forwards it to the destination. This is the most common topology in modern networks.

         ┌──────┐
         │ PC 1 │
         └──┬───┘
            │
  ┌──────┐  │  ┌──────┐
  │ PC 2 ├──┼──┤ PC 3 │
  └──────┘  │  └──────┘
         ┌──┴───┐
         │Switch│
         └──┬───┘
            │
         ┌──┴───┐
         │ PC 4 │
         └──────┘

• Advantage: If one cable breaks, only that device is affected — the rest of the network keeps working. Easy to add new devices.
• Disadvantage: If the central hub/switch fails, the entire network goes down. Requires more cable than bus.

Ring Topology

Devices are connected in a circle. Data travels in one direction around the ring, passing through each device until it reaches its destination.

        ┌──────┐
    ┌───┤ PC 1 ├───┐
    │   └──────┘   │
  ┌─┴──┐        ┌──┴─┐
  │PC 4│        │PC 2│
  └─┬──┘        └──┬─┘
    │   ┌──────┐   │
    └───┤ PC 3 ├───┘
        └──────┘

• Advantage: Equal access for all devices — no device can dominate the network.
• Disadvantage: If one device or cable fails, the entire ring breaks. Adding or removing devices disrupts the ring.

Ring topology was used in IBM's Token Ring networks but has largely been replaced by star topology.

Mesh Topology

Every device connects to every other device, or at least to multiple other devices. This provides maximum redundancy — if one path fails, data can take an alternate route.

       ┌──────┐
   ┌───┤ PC 1 ├───┐
   │   └──┬┬──┘   │
   │      ││      │
  ┌┴──┐   ││   ┌──┴┐
  │PC ├───┘└───┤PC │
  │ 2 │   ┌┐   │ 3│
  └─┬─┘   ││   └─┬┘
    │     ││     │
    └─────┤├─────┘
     ┌────┘└────┐
     │  ┌────┐  │
     └──┤PC 4├──┘
        └────┘

• Advantage: Extremely reliable — multiple paths mean the network survives failures. High security — data can take different routes.
• Disadvantage: Expensive — requires a lot of cabling and ports. Complex to manage and configure.

Full mesh is impractical for large networks (the number of connections grows as n*(n-1)/2), but partial mesh is used in wide-area networks and critical infrastructure.

Tree Topology

A combination of star and bus topologies. Star networks are connected to a central bus, creating a hierarchical structure. This is common in large organizational networks where departments are organized hierarchically.

            ┌────────┐
            │ Root   │
            │ (Hub)  │
            └───┬────┘
        ┌───────┴───────┐
    ┌───┴───┐       ┌───┴───┐
    │ Switch│       │ Switch│
    └───┬───┘       └───┬───┘
   ┌────┼────┐     ┌────┼────┐
   │    │    │     │    │    │
  PC1  PC2  PC3   PC4  PC5  PC6