In the early 1980s, the first personal computers were launched on the market. All users were thrilled with their own computer on the table. After a while, however, they knew they needed to communicate with others. There has been a rapid development of networks. In many cases, several organizations have used several technologies at a time. This, along with the other cabling used in the building for the transmission of the telephone, the industrial television, has created a clutter of cables. Any changes and maintenance were very costly.
Therefore, a universal cabling system based on a twisted pair was created. Structured cabling features are designed to deliver a wide range of applications.
At present, the most widely used transmission medium in the LAN is a twisted pair called UTP (Unshielded Twisted Pair). The basic parameter of this cable is the 100 ohm impedance. In Europe, however, a shielded modification of this cable is used - shielding is carried out at the level of the whole bundle, thus it is a protective film under the plastic cable wrapper. The designation is dependent on the manufacturer for this modification. Some manufacturers call it STP (Shielded Twisted Pair) or FTP (Foiled Twisted Pair). It does not matter what the label is, but it is necessary to realize that these modern cables have the same impedance as UTP cables - 100 ohm. These cables are not identical to conventional STP cables with a 150 ohm impedance and usually have individual shielded pairs. UTP cables can be used for a wide range of currently-used technologies - Ethernet Fast Ethernet, Gigabit Ethernet, Token Ring and ATM. A topology that is twisted by a twisted pair is a star. The common designation for twisted pair networks is structured cabling. The basics of the 10Base-T standard, which is the modification of Ethernet for UTP cables, was laid by SynOptics, now part of Nortel Networks.
Definition of generic cabling for four classes of line:
Relationship between categories and class depending on channel length
Cable type Class A Class B Class C Class D Class D + Class E
CAT 3 2 Km 200 m 100 m - - -
CAT 4 3 Km 260 m 150 m - - -
CAT 5 3 Km 260 m 160 m 100 m - -
CAT 5E 3 Km 260 m 160 m 100 m 100 m -
CAT 6 3 Km 260 m 160 m 100 m 100 m 100 m
Channel lengths include interconnection cables with a maximum length of 10 m.
Recently, the most common transmission medium in Ethernet LAN networks was the coaxial cable (in Token Ring twinned networks). The advantage was the price and ease of execution. Disadvantages are susceptibility to failure and technological limitations (number of nodes, speed). The typical coaxial cable topology is the bus.
In LAN networks, fiber optic cables are used to bridle longer distances. For shorter distances (about 260 m to 2 km depending on technology) multimode (or multidirectional) for larger singlemod (or single-mode) distances. Like UTP cables, optical cables can be used for the full range of up-to-date technologies. Optical cables are also used to connect buildings where it is necessary to connect the outdoor environment, even at relatively short distances. Optical cables will provide galvanic isolation of potential and will not destroy the infrastructure in the event of a lightning strike. A typical coaxial cable topology is a star.
There are places where optic connections can not be used. This could be due to the excessive cost of cable laying or even the impossibility of laying cables. In that case, wireless technologies are used. These have been developed over time to be used as an alternative to local networks based on cable systems. The disadvantage is the price and the relatively low speed so far. This, on the contrary, does not hinder the use of wireless networks to connect to the Internet - here it achieves more than an interesting price / performance ratio.
For long distances, leased data circuits are operated by one of the service providers (usually a telecom operator).
For the correct UTP cable connection, it is most important to stick to the standards, and these are two TIA / EIA-T568A and TIA / EIA-T568B. Both are equivalent and have the same transmission parameters.
To connect a 100Mb network, you need a UTP cable (twisted pair) that will have RJ-45 connectors. When using a 4-pair cable, the individual pairs are used as shown in the figure. Only two pairs (green and orange) are used for data transmission. A blue pair can be used to run a telephone line while the brown pair is left as a reserve. So, in fact, we only need a cable with two pairs (possibly shielded).
It is also possible to see how individual RJ-45 connectors are numbered (connector and socket). It follows from the description that if we only have a pair with two pairs, we only connect the contacts 1,2 and 3,6.
But if we want to have 100Mb network we need to connect all 4 pairs of cable.
Here are a few important points that should be followed: