6.Cable types. Coaxial cable.

is an electrical cable consisting of a central wire and metal braid, separated by a dielectric layer and placed in a common outer jacket. Coaxial cable until recently was the most widely distributed, due to its high noise immunity , and higher than in the twisted pair, allowed data rates (up to 500Mbit /s) than the maximum transmission distance (up to a kilometer or more)The main application of the coaxial cable is on the local computer networks with the topology of the "bus." In this case, the ends of the cable must be installed to prevent the termination of internal reflections, one (and only one!) Of termination must be grounded There are two types of coaxial cable:  1)Thin cable with a diameter of about 0.5 cm, more flexible;  2)Thick cable having a diameter of about 1 cm, much tougher. It is a classic version of the coaxial cable, which has almost completely replaced the more modern thin cable.Thin cable is used to transfer to smaller distances than fat, as it attenuates the signal is stronger. But with a thin cable is much easier to work: you can quickly navigate to each computer, and requires a thick rigid fixation on the wall of a room. Cables have better noise immunity and protection against eavesdropping, but they are a little more expensive than usual. It is now believed that the coaxial cable is out of date, in most cases it can replace the twisted pair or fiber optic cable. The device is a coaxial cable: 1 - inner conductor, 2 - insulation (solid polyethylene) 3 - the outer conductor, 4 - shell (light proof poly ethylene)

7.Twisted pair and its main categories.

Modern Ethernet technology generally uses a twisted pair (TP) to interconnect devices. Because TP is the most commonly encountered type of network cabling. Twisted pair cables consist of one or more pairs of insulated copper wires that are twisted together and housed in a protective jacket. Twisted pair uses pulses of electricity to transmit data. In twisted pair cabling, the number of twists per unit length affects the amount of resistance that the cable has to interference.

There are three types of twisted pair cable: unshielded twisted pair, shielded twisted pair, and screened twisted pair.

Unshielded twisted pair (UTP) is the most commonly encountered type of network cable in North America and many other areas. Shielded cables (ScTP and F-UTP) are used almost exclusively in European countries.

UTP cable is inexpensive, offers a high bandwidth, and is easy to install. This type of cable is used to connect workstations, hosts and network devices. It can come with many different numbers of pairs inside the jacket, but the most common number of pairs is four. Each pair is identified by a specific color code.

Unfortunately both STP and ScTP are very expensive, not as flexible, and have additional requirements due to the shielding that make them difficult to work with. They has some categories:

-Category 3 Cable (UTP) used for voice communication,most often used for phone lines

-Category 7 Cable (ScTP) used for data transmission, individual pairs are wrapped in a shield and then the entire four pairs wrapped in another shield, supports 1000 Mbps-10 Gbps,though 10 Gbps is not recommended