Remember our articles about OSI Interworking Layers, and Physical Layer particularly? So, here’s a key element, cornerstone of networks today – twisted pair cable.
Twisted pair, as it is clear from the name is made of pairs of wires that are twisted around each other. Each wire is having its own shell, but also there is an outer shell that is protecting the whole cable. There could be multiple pairs in a wire, depending on the cable type.
The resistance to the crosstalk in a pair is depending on the amount of twists per foot or the twist ratio. Too much twist will increase attenuation and amount of cable required, but too small twist results in a cross-talk. It is critical for manufacturers to find optimal twist ratio in order to produce high-quality cable.
Figure 1. Twisted Pair cable.
Today, there are thousands of different twisted pair cables that are available on the market. Differences may be in amount of twists (twist ratio), amount of pairs in cable (between 1 and 4200), type of copper used, shielding type and material. Most common type of twisted pair nowadays is the four-wire cable used for networking.
Using twisted pair cable is beneficial because the price is low, cable is easy to install, it can be used for multiple topologies like star or star-hybrid. Drawback is the distance that signal can travel without repeater. Although the distance is great, it is shorter than coax. There are two main types of twisted pair: STP and UTP – they are discussed in detail in the next article – STP vs UTP cable.
