Network Basics: Complex Network Topologies
Physicists say that the universe is expanding, and network administrators know they’re right. A simple bus or star topology is suitable only for small networks, with a dozen or so computers. But small networks inevitably become large networks as more computers are added. For larger networks, it’s common to create more complicated topologies that combine stars and buses.
A bus can be used to connect several stars. In this case, two or more hubs or switches are connected to each other using a bus. Each of these hubs or switches is then the center of a star that connects two or more computers to the network.
This type of arrangement is commonly used in buildings that have two or more distinct workgroups. The bus that connects the switches is sometimes called a backbone.
Another way to expand a star topology is to use a technique called daisy-chaining. When you use daisy-chaining, a switch is connected to another switch as if it were one of the nodes on the star. Then, this second switch serves as the center of a second star.
In a ring topology, packets are sent around the circle from computer to computer. Each computer looks at each packet to decide whether the packet was intended for it. If not, the packet is passed on to the next computer in the ring.
Years ago, ring topologies were common in LANs, as two popular networking technologies used rings: ARCNET and Token Ring. ARCNET is still used for certain applications such as factory automation, but is rarely used in business networks. Token Ring is still a popular network technology for IBM midrange computers. Although plenty of Token Ring networks are still in existence, not many new networks use Token Ring any more.
Ring topology was also used by FDDI, one of the first types of fiber-optic network connections. FDDI has given way to more efficient fiber-optic techniques, however. So ring networks have all but vanished from business networks.
Another type of network topology, known as mesh, has multiple connections between each of the nodes on the network. The advantage of a mesh topology is that if one cable breaks, the network can use an alternative route to deliver its packets.
Mesh networks aren’t very practical in a LAN setting. For example, to network eight computers in a mesh topology, each computer would have to have seven network interface cards, and 28 cables would be required to connect each computer to the seven other computers in the network. Obviously, this scheme isn’t very scalable.
However, mesh networks are common for metropolitan or wide area networks. These networks use devices called routers to route packets from network to network. For reliability and performance reasons, routers are usually arranged in a way that provides multiple paths between any two nodes on the network in a meshlike arrangement.