2: Network Topologies (Bus, Star, Ring, Mesh)

Section 2: Network Topologies (Bus, Star, Ring, Mesh)

A network's topology defines the physical or logical arrangement of devices and the connections between them. It is a fundamental concept that influences a network's cost, performance, and reliability. The four primary physical topologies are Bus, Star, Ring, and Mesh.

Bus Topology In a bus topology, all devices are connected to a single central cable, called the bus or backbone. Data transmitted by one device travels along the bus and is seen by all other devices, but only the intended recipient accepts and processes it. This topology is simple and inexpensive to implement, requiring less cabling than alternatives. However, it has significant drawbacks. A break in the main cable brings the entire network segment down. Performance also degrades under heavy traffic due to data collisions, making it largely obsolete in modern wired networks.

Star Topology The star topology is the most common layout in modern LANs. Here, every network device connects to a central networking device, such as a switch or hub. This central node manages all data traffic. The primary advantage is robustness; if one cable fails, only that single connection is affected, and the rest of the network remains operational. This makes it easy to troubleshoot and add new devices. The disadvantage is that the entire network relies on the central device; if it fails, the whole network goes down.

Ring Topology In a ring topology, devices are connected in a closed loop, where each device is connected directly to two others. Data travels in one direction around the ring (unidirectional) or in both directions (bidirectional in more modern implementations like Token Ring). Each device acts as a repeater, retransmitting the signal to the next. This prevents signal degradation over distance. The major flaw is that a single node or cable failure can break the loop and disrupt the entire network, unless a dual-ring design is used for redundancy.

Mesh Topology A mesh topology provides the highest level of fault tolerance. In a full mesh topology, every device is interconnected with every other device. This creates multiple paths for any data packet to take. If one link fails, the network can automatically reroute traffic along an alternative path. While this offers exceptional redundancy and reliability, it is extremely expensive and complex to implement and manage due to the sheer amount of cabling required (the formula $n(n-1)/2$ connections for n devices). A partial mesh topology, where only critical devices have multiple connections, offers a more practical compromise.