Unit IV — Network Topologies & Types (LAN, WAN, MAN)
A computer network is a collection of interconnected devices that share resources and data. Networks are described by their topology (physical/logical arrangement) and type (geographic scale).
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Network Topologies
Topology refers to the arrangement of nodes (computers) and links (connections) in a network.
1. Bus Topology
- All devices connected to a single shared communication line (bus).
- Data travels in both directions along the bus.
- Advantages: Simple, cheap, easy to install for small networks.
- Disadvantages: Single point of failure (bus breaks → entire network down); performance degrades as nodes increase; collisions.
- Example: Early Ethernet (10Base2 coaxial).
2. Star Topology
- All devices connect to a central hub or switch.
- Most widely used today.
- Advantages: Easy to add/remove devices; failure of one node doesn't affect others; easy to troubleshoot.
- Disadvantages: Central hub is a single point of failure; requires more cable than bus.
- Example: Modern home/office Ethernet with a switch.
3. Ring Topology
- Each device connects to exactly two neighbouring devices, forming a closed loop.
- Data travels in one direction (token-based — Token Ring protocol).
- Advantages: Predictable performance; no collisions.
- Disadvantages: Failure of one node can break the ring; adding/removing nodes disrupts the network.
- Example: IBM Token Ring networks.
4. Mesh Topology
- Every device has a dedicated point-to-point connection to every other device.
- Full Mesh: N devices → N(N−1)/2 connections.
- Partial Mesh: Some, not all, devices are fully connected.
- Advantages: Highly reliable; multiple paths for data; no traffic congestion.
- Disadvantages: Expensive; difficult to install and maintain.
- Example: Internet backbone, military networks.
5. Tree Topology (Hierarchical)
- A hybrid of star and bus — star networks connected to a central bus backbone.
- Devices arranged in a hierarchical parent-child structure.
- Advantages: Scalable; easy to manage large networks.
- Disadvantages: Backbone failure affects entire network.
- Example: University campus networks.
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Topology Comparison Table
| Topology | Cable Cost | Reliability | Scalability | Failure Impact |
|---|---|---|---|---|
| Bus | Low | Low | Low | Whole network |
| Star | Moderate | High | High | Single node |
| Ring | Moderate | Moderate | Moderate | Whole ring |
| Mesh | High | Very High | Low | Minimal |
| Tree | Moderate | Moderate | High | Subtree/backbone |
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Network Types by Geographic Scale
| Type | Full Form | Coverage | Speed | Example |
|---|---|---|---|---|
| LAN | Local Area Network | Room to building | 100 Mbps–10 Gbps | Office network, home Wi-Fi |
| MAN | Metropolitan Area Network | City-wide | 10–100 Mbps | City cable TV, university campus |
| WAN | Wide Area Network | Country/global | Variable (slower) | Internet, corporate intranets |
LAN Characteristics:
- Privately owned; limited geographic area.
- High speed, low error rate, low cost.
- Technologies: Ethernet (IEEE 802.3), Wi-Fi (IEEE 802.11).
MAN Characteristics:
- Covers a city; may be public or private.
- Used to connect multiple LANs in a city.
WAN Characteristics:
- Covers very large distances (national, international).
- Uses leased lines, satellite, fibre optic backbones.
- The Internet is the largest WAN.
Key Takeaway: The five topologies (bus, star, ring, mesh, tree) each have distinct trade-offs in cost, reliability, and scalability. Star topology dominates modern LANs. LAN/MAN/WAN classification by geographic scale is a standard exam topic — know their coverage areas, typical speeds, and examples.