Twisted pair in modern networks

We, Maltima Telecom specialists, continue to publish reference materials on telecom equipment and components to help specialists. This time we will talk about the twisted pair, the supply of which we are engaged in, among other things. This product passes input control in Russia: a part of the lot is tested by three different certifying testers, which show the whole picture by cable. If at least one tester detects a discrepancy, the cable does not start on sale.

When constructing structured cable networks, the physical medium of signal transmission, the role of which is usually performed by a twisted pair, is of particular importance. In the simplest case, it represents one or more pairs of insulated copper conductors, twisted between themselves and covered with a common sheath. The copper conductors themselves in such wires can be either solid (solid) or multicore (patch). If the former are usually used for laying in boxes and walls (they have less attenuation of the signal, they are convenient for embedding sockets), then the latter are better suited for connecting the final equipment to the sockets (they are more resistant to repeated bending).

For ease of use, individual twisted pairs are combined into cables containing 2, 4, 8 or more pairs. The most common currently are cables consisting of 4 twisted pairs. Despite the general principle of the device, such cables have different properties, the main among which is the band of transmitted frequencies, which directly depends on the resistance to external and mutual interference. It is for this parameter that cables with twisted pairs are usually divided into categories in accordance with the international standard ISO 11801. Consider these categories in more detail.
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Categories

Categories 1 and 2 are usually referred to as outdated cables with one or two pairs of wires, suitable for voice and modem communication, as well as digital signal transmission with a capacity of up to 4 Mbps.

Category 3 cables have a bandwidth of 16 MHz and are suitable for building local networks with a capacity of up to 100 Mbit / s to the specification of 100BASE-T4. Currently, cables of this category are mainly used for voice telephone communication.

The band of the transmitted frequencies of the 4th category cables is 20 MHz. They were also used to build 100BASE-T4 networks, but at the present time they are practically not used.

About cables 5 (5e) categories have heard, probably, everything. Suitable for organizing telephone communication and video transmission, they nevertheless became most widely used as the basis for creating local computer networks 10BASE-T, 100BASE-TX and 1000BASE-T due to the band of transmitted frequencies of 100 MHz.

More modern is the cable of the 6th category. Its bandwidth of transmitted frequencies is 250 MHz, which allows you to organize data transmission at a speed of 10 Gbit / s over a distance of 55 m. However, you shouldn’t focus on the last parameter. Practitioners point out that achieving sustainable channel performance over a distance of over 50 meters is difficult to achieve. Much more realistic is the figure of 30-35 m.

There is also a subcategory of this cable, known as 6A. In order to combat interference and increase the bandwidth of transmitted frequencies up to 500 MHz, these cables are equipped with either a common foil shield (F / UTP) or screens around each of the four twisted pairs (U / FTP). Due to the bandwidth of the transmitted frequencies increased up to 500 MHz, data transmission with a speed of 10 Gbit / s can be carried out over a distance of up to 100 m (the theoretical limit value).

The "youngest" cable category approved by the International Organization for Standardization (ISO) is the seventh. Designed for the most demanding to the physical medium of the SCS signal transmission, cables of this category provide a bandwidth of 600 MHz (1000 MHz for category 7A), and the data transfer rate is up to 40 Gbit / s (for category 7A). They are distinguished from cables of the sixth category by the presence of both a screen around each twisted pair and a common screen for all 4 pairs (F / FTP or S / FTP, depending on the manufacturing technology of the external screen - braid or foil, respectively).


SSTP twisted pair cable, 4 pairs, category 7a, single core, LSZH

Marking

Twisted pair shielding is used both to reduce external electromagnetic interference (common screen) and to minimize mutual interference between twisted pairs (individual screens). You can judge the design of a particular cable by marking it. So the letter F means the presence of a screen from a continuous sheet of foil, and the letter S - the presence of a shielding braid. The letter U indicates the absence of the screen. In this case, the first part of the marking contains information about the general screen, and the second about the individual. Thus, for example, SF / FTP marking means that in this cable each pair is shielded with foil, and there is also a double external foil and braid shield. In turn, the UTP marking indicates the absence of any protection against interference in addition to the twisting of the wires in pairs with variable pitch.

It should be noted that the differences between cables, even of one category can be very significant. So the most "running" is a simple cable designed for interior work. It is usually painted gray. Black color indicates that the cable is designed for external (street) works and has additional protection in the form of an outer shell of hydrophobic polyethylene. The voids between the twisted pairs are sometimes filled with a hydrophobic gel, and the cable itself may have an external reservation made of steel wire or tape. Finally, if the outer sheath of the cable is colored orange, this indicates its compliance with fire safety requirements. This cable emits less smoke and toxic substances when burning, and in addition, in the event of a fire, it will not become a channel for the further spread of fire.

Special features


Cable twisted pair 100 pairs UTP, category 5, single core

The variety of cables with twisted pairs due to the breadth of applications. In this regard, specific models may include additional functional elements. So outdoor cables designed for suspension on supports are equipped with an external steel cable that prevents deformation of the product under its own weight. Power elements, giving the cable greater strength, can be placed inside, near the central axis. For cables designed for interior use, there is a special cord of nylon fiber - a ripcord. Pulling it, you can cut the outer sheath of the cable without damaging the insulation of twisted pairs. Some models with a common screen, in addition to twisted pairs, contain an uninsulated drain wire, the task of which is to maintain electrical contact between the parts of the screen in case of damage to it when it is bent too much. This list can be continued, but the end is that, whatever the task of the designer of the SCS, there will always be exactly the twisted pair that is best suited.