Q.Define the term topology. What are the popular network topologies?

Network Topology

Topology refers to the physical or logical arrangement of nodes (computers, switches, routers) and the connecting links in a network. It defines how devices are interconnected and how data flows between them. The topology determines the network's performance, reliability, fault tolerance, and cost.

Topologies are classified into two categories:

• Physical topology: the actual layout of cables and devices.
• Logical topology: the path data takes through the network, regardless of physical layout.

Popular Network Topologies

1. Bus Topology

All devices connect to a single central cable (the bus or backbone). Data travels in both directions along the bus. Terminators are placed at both ends to prevent signal reflection. Simple and inexpensive, but a failure in the backbone brings down the entire network.

2. Star Topology

All devices connect to a central hub or switch. Data passes through the central device to reach its destination. Easy to install and manage; failure of one node does not affect others. However, if the central hub fails, the entire network goes down.

3. Ring Topology

Devices are connected in a closed loop; each device has exactly two neighbors. Data travels in one direction (unidirectional) or both directions (bidirectional). A token-passing mechanism often controls access. Failure of a single node or link can disrupt the entire network unless redundancy is built in.

4. Mesh Topology …

What is Network Topology?

Topology describes the layout or structure of a network — how computers, servers, switches, routers, and other devices (collectively called nodes) are interconnected by communication links. The term comes from the Greek topos (place) and logos (study), literally the study of arrangement.

We distinguish two perspectives:

• Physical topology: the actual geometric placement of cables and devices — where things sit in space.
• Logical topology: the path data takes through the network, which may differ from the physical wiring.

Understanding topology is essential because it determines the network's cost, scalability, fault tolerance, and performance. Different topologies suit different scenarios: a small office, a campus, a data center, or a wide-area network each demand different trade-offs.

Popular Network Topologies

1. Bus Topology

A single backbone cable (the bus) runs through the network, and every node taps into it via a T-connector or drop line. Data travels in both directions along the bus; terminators at each end absorb signals to prevent reflection.

Advantages:

• Simple and inexpensive for small networks.
• Requires less cable than star.

Disadvantages:

• A break in the backbone brings down the entire network.
• Performance degrades as more nodes are added (collision domain).
• Difficult to troubleshoot.

Use case: Early Ethernet (10BASE2, 10BASE5) used bus topology; rarely deployed today.

2. Star Topology

Every node connects to a central device — a hub, switch, or router — via its own dedicated cable. All communication passes through the central device.

Advantages:

• Easy to install and manage.
• Failure of one node does not affect others.
• Easy to detect and isolate faults.
• Scalable: adding a node requires only one new cable.

Disadvantages:

• Central device is a single point of failure.
• Requires more cable than bus.
• Cost of the central switch/hub.

Use case: The dominant topology in modern LANs (Ethernet with switches).

3. Ring Topology

Nodes are connected in a closed loop. Each node has exactly two neighbors; data travels in one direction (unidirectional ring) or both (bidirectional ring). A token-passing protocol often controls access.

Advantages:

• No collisions (token-based access).
• Predictable performance under load.

Disadvantages:

• A single node or cable failure breaks the loop (unless dual-ring is used).
• Adding or removing nodes disrupts the network.
• Troubleshooting is harder than star.

Use case: Token Ring (IEEE 802.5), FDDI (Fiber Distributed Data Interface). Largely obsolete in LANs but the concept survives in some MANs.

4. Mesh Topology

Every node connects directly to every other node (full mesh) or to several others (partial mesh).

Full Mesh:

• $n$ nodes require $\frac{n(n-1)}{2}$ links.
• Extremely fault-tolerant: multiple paths between any two nodes.
• High cost and complexity.

Partial Mesh:

• Only critical nodes have redundant links.
• Balances cost and reliability.

Advantages:

• Robust: failure of one link does not isolate any node.
• High bandwidth: dedicated links.
• Secure: point-to-point links.

Disadvantages:

• Expensive (cabling, ports).
• Complex installation and maintenance.

Use case: WANs, the Internet backbone, wireless mesh networks (Wi-Fi mesh systems).

5. Tree (Hierarchical) Topology

A root node connects to one or more second-level nodes, which in turn connect to third-level nodes, forming a hierarchy. It is essentially a collection of star topologies arranged in a tree structure.

Advantages:

• Scalable: easy to expand by adding branches.
• Centralized management at each level.
• Fault isolation: a failure in one branch does not affect others.

Disadvantages:

• Root node and backbone are single points of failure.
• More cable than star.

Use case: Large organizations with departmental LANs connected to a backbone; cable TV networks. …