Network Topologies

Why This Matters

When the AP exam asks about networks, you're being tested on more than just naming shapes—you need to understand how network design choices affect fault tolerance, scalability, and performance. The College Board specifically emphasizes that networks should have redundant paths so that if one connection fails, data can still reach its destination. Every topology represents a different trade-off between these competing goals.

Think of network topologies as the blueprint for how computing devices work together. The exam loves to ask questions about single points of failure, redundancy, and why the Internet's design makes it so resilient. Don't just memorize which topology looks like what—know why each design succeeds or fails when connections break, and which scenarios call for each approach.

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Single-Path Architectures: Simple but Fragile

These topologies route data through a single pathway, making them cost-effective but vulnerable. When any link in the chain breaks, communication stops entirely.

Bus Topology

• Single central cable connects all devices—data travels in both directions along the bus, with each device listening for packets addressed to it
• Single point of failure (SPOF)—if the main cable breaks, the entire network goes down, violating fault tolerance principles
• Limited scalability—cable length restrictions and signal degradation make this impractical for growing networks

Ring Topology

• Circular pathway where each device connects to exactly two neighbors—data travels in one direction (or both in dual-ring configurations)
• Token-based transmission control—a token circulates to prevent data collisions, but any single device failure disrupts the entire ring
• Predictable performance—works efficiently for small networks, but adding devices requires reconfiguring the entire loop

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Centralized Architectures: Easy Management, Central Risk

These topologies funnel all traffic through a central device. The hub or root node simplifies management but creates a critical vulnerability.

Star Topology

• Central hub or switch connects to every device individually—each connection is independent, so one device failure doesn't affect others
• Centralized management simplifies troubleshooting—but the hub itself becomes a single point of failure for the entire network
• Easy to add or remove devices—dedicated connections support scalability better than bus or ring designs

Tree Topology

• Hierarchical structure combining star and bus characteristics—a root node branches into multiple levels of subordinate nodes
• Segmentation supports large organizations—networks can be divided into manageable sections, improving organization
• Root node failure is catastrophic—if the top-level node goes down, all downstream devices lose connectivity

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Redundant Architectures: Built for Fault Tolerance

These topologies include multiple paths between devices, directly supporting the Internet's design principle that data should find alternate routes when connections fail.

Mesh Topology

• Every device interconnects with multiple (or all) other devices—if one path fails, data automatically routes through an alternative connection
• Highest redundancy and fault tolerance—exemplifies the Internet's resilience design where subsequent data takes different routes after failures
• Full mesh vs. partial mesh—full mesh connects every device to every other (expensive), while partial mesh strategically places redundant links where they matter most

Hybrid Topology

• Combines two or more topology types—such as star-bus or star-ring configurations tailored to specific network needs
• Balances competing priorities—can leverage mesh redundancy in critical areas while using simpler topologies elsewhere to manage costs
• Complex design and management—requires careful planning to ensure redundant paths exist where fault tolerance is essential

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Quick Reference Table

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Self-Check Questions

1. Which two topologies both suffer from single points of failure but at different levels (cable vs. device)?

2. If an FRQ describes a network where "subsequent data will be sent via a different route if a connection fails," which topology best demonstrates this principle, and why?

3. Compare and contrast star and tree topologies: what management advantage do they share, and how do their failure vulnerabilities differ?

4. A company needs high fault tolerance in their data center but wants to minimize cabling costs in office areas. Which topology approach would you recommend, and what concept does this illustrate?

5. Why does the College Board emphasize redundancy and multiple paths in network design? Identify which topologies meet this requirement and which do not.