Chapter 02: Network basics & Cabling

Network Topologies

Star Topology

Think of this system as resembling a power strip with various devices plugged into it. In this case, instead of a power strip you have a network hub, and instead of devices requiring electricity you have devices needing and providing data. These devices might include computers, network-equipped printers, cable or DSL modems, a local network backbone, or even other hubs. Star topology networks are connected by twisted pair cabling, which looks like the cabling used in modular phone systems. Twisted pair cables and other devices are rated according to category (typically just called cat): Cat 3 uses two pairs of twisted wires as the standard for regular telephone service. Star topology networks usually use cat 5 twisted pair cabling, which has four twisted pairs and terminates in connectors called RJ-45s. (Your phone is connected with RJ- 11s.) You may have up to 1024 nodes — distinct machines or devices — on a star topology network, at speeds of up to 100 MB per second. The newest networking technology provides even faster speeds.

Bus Topology

If star topology resembles a power strip with many devices plugged into it, bus topology physically resembles strings of old-fashioned Christmas tree lights, hooked together one after another. Of course, on your network there’s a lot more going on than what happens on a string of lights. On a bus topology network one machine is plugged to the next, which is plugged to the next, and so on. Two types of coaxial cable hold bus topology networks together: RG-8, often called Thicknet because of the thickness of the cable, and RG-58, often called Thinnet because it is thinner than RG-8. RG-8 is familiar at least in general form to anyone involved in amateur radio or anyone who has ever hooked up cable television. With this kind of topology, each end of the cable is specifically terminated by use of a “terminating resistor.” Bus topology networks are limited to 30 machines. They were a very common style in early networks. While considered highly reliable, bus topology networks are not very fault tolerant because the failure of any device on the cable causes the entire network to fail. Also, their potential bandwidth (datahandling capacity) is limited to 10 MB per second. Nearly all modern networks use some type of star topology with cat 5 or better cabling.

Ring Topology

Imagine those Christmas tree lights again. This time the end of the string plugs into its beginning, creating a loop. Popularized by IBM’s Token Ring system, ring networks are relatively difficult to set up but do offer high-bandwidth capabilities.

Tree Topology

Although you almost certainly won’t undertake this system at the outset, you should know about it anyway. A tree network involves a high-speed “backbone” that is connected in the fashion of bus topology. However, instead of connecting individual machines, it connects groups of star topology subnetworks. Many network backbones use fiber-optic cabling to achieve high throughput.

Ultimately, your choice of network is determined by the equipment you already own and the amount of money you have to spend. If you are setting up a new network, speed, ease of configuration, and relatively low cost all argue in favor of establishing a star topology network.