Cables

Twisted Pair

Twisted pair is two separately charged wires twisted around each other. One wire carries the electrical signal and the other is the ground. This is common for phone lines and inexpensive LANs. The reason the wires are twisted around each other is to reduce "crosstalk", which is electrical interference generated by the two wires. This results in noise (crosstalk) being carried evenly by the two wires in the pair, which causes the noise to cancel itself out. 

Generally more than one pair is contained within a cable. For example, the phone company may run 2 or 4 pairs to an apartment to allow for additional lines being installed at a future date. 

There are specific standards for making twisted pairs. In general, the higher the transmission rate across the wire the more strict the standard. This standard includes gauge (the diameter of the wire), how the wire is twisted and the number of twists per foot. 

Twisted pair comes in two forms: shielded, which has an electromagnetic shield around the pairs, and unshielded, which does not. 

Unshielded Twisted Pair 

UTP (Unshielded Twisted Pair) is a twisted pair contained in a plastic sheath. The most common use for unshielded twisted pair is standard telephone lines. UTP comes in the following standards: 

The difference between the standards is the higher category numbers are more rigid in their definitions, use thicker gauge cables and have more twists per foot. 

The cables are connected to various hardware using RJ-45 connectors. These are the small plastic connectors used today to hook phone lines into the phone jack. 

UTP is one of the cheapest and easiest types of cabling to install. However, the distance of the cables is limited to just a few hundred feet since the signal tends to degrade rapidly. The cables are also very susceptible to electromagnetic interference. 

Shielded Twisted Pair 

Shielded twisted pair consists of one or more pairs of wires twisted around each other (similarly to unshielded twisted pair) and protected by a sheathing wrapped around the copper wire. The purpose of this sheathing is to reduce outside electrical interference. STP is harder to install than UTP because the cable must be grounded. This requires special connectors and installation techniques. Since the shielding reduces interference, greater transmission speeds are possible than with UTP. 

STP speeds typically hover around 16mps but can go up to 144mps and even 500mps. 

Coaxial Cable 

Coaxial cable is what you will typically find connecting your television set to your cable television network. It consists of a central conductor surrounded by insulation, which is in turn surrounded by another conductor. Finally, the whole cable is surrounded by an insulating plastic case. 

In addition to it's well known usage in cable TV connections, this type of cable is also used for 10Base5 and 10Base2 Ethernet connections. This wire is very resistant to electromagnetic interference. However, it is also very expensive to install. 

This type of cable was invented in 1929, and was used by AT&T in the first cross-continental cable system in 1940. 

Fiber Optic 

This kind of cable consists of light conducting glass fibers in a plastic sheath. Light is used instead of electrical impulses to carry information. These cables are ideal for high-speed applications (up to 2gps) due to their high reliability and immunity from electromagnetic interference. However, fiber optic tends to be more difficult to install due to the relative fragility of the cables themselves and the complexity of the systems to convert to light impulses.