Network topologies represent the physical side of the network, and they form part of the foundation of our overall system. Before we explore too far, the first thing you need to understand is that you must consider two opposing yet related concepts in this article: the physical layout of the network and the logical layout of the network. The physical layout of a network relates directly to the wiring and cabling that connects devices. Some of the common layouts we’ll cover are the bus, ring, star, mesh, and hybrid topologies. The logical layout of the network equates to the methodology of access to the network, the stuff you can’t readily see or touch, or the flow of information and other data. We’ll get to the logical side, but first let’s break down each physical design:
- Bus The bus topology lays out all connecting nodes in a single run that acts as the common backbone connection for all connected devices. As with the public transport of the same name, signals get on, travel to their destination, and get off. The bus is the common link to all devices and cables. The downside to its simplicity is its vulnerability; all connectivity is lost if the bus backbone is damaged. The best way to envision this vulnerability is to think of those strings of Christmas lights that go completely out when one light burns out or is removed. Although not seen in its purest form in today’s networks, the concept still applies to particular segments.
- Ring Ring topologies are as true to their names as bus layouts. Essentially the backbone, or common connector of the network, is looped into a ring; some ring layouts use a concentric circle design to provide redundancy if one ring fails. Each client or node attaches to the ring and delivers packets according to its designated turn or the availability of the token.
- Star The star layout is one of the most common because of its ease of setup and isolation of connectivity problems should an issue arise. A star topology attaches multiple nodes to a centralized network device that ties the network together. Think of it as looking like an old-style wagon wheel or the wheels on a bike. The hub is the centerpiece of the wheel, and the spokes of the wheel are the legs of the star. The center could be a hub or a switch; as long as it acts as a central point of connection, you have a star topology. Stars are popular for numerous reasons, but the biggest reason has long been its resistance to outages. Unlike nodes in bus and ring topologies, a single node of a star can go offline without affecting other nodes.
- Mesh A mesh topology is essentially a web of cabling that attaches a group of clients or nodes to each other. It can look a little messy and convoluted, and it can also make troubleshooting a bear. However, this setup is often used for mission-critical services because of its high level of redundancy and resistance to outages. The largest network in the world, the Internet, which was designed to survive nuclear attack, is built as one large mesh network.
- Hybrid Hybrid topologies are by far the most common layout in use today. Rarely will you encounter a pure setup that strictly follows the topologies previously listed. Our net- works of today are complex and multifaceted. More often than not, current networks are the offspring of many additions and alterations over many years of expansion or logistical changes. A hybrid layout combines different topologies into one mixed topology; it takes the best of other layouts and uses them to its advantage.
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