When organizing computer networks in households and small offices about the category network lan you don’t have to think about the cable, since at short distances and low speeds of information data transfer this issue is not relevant. Networks can be made from almost any cable, plugs and sockets that the market offers. Currently, for the creation of computer networks, as a rule, unshielded twisted-pair cable is used. UTP category CAT5, as it is not expensive and provides sufficient data transfer rate for the consumer.

The lan categories of twisted pair cables are classified in the EIA / TIA-568 specification and in the international standard ISO 11801. In Russia, there are two GOST R 53246-2008 (a copy of the American ANSI / TIA / EIA-568B) and GOST R 53245-2008 (developed on basis technical regulations one of major manufacturers twisted pair cables). On the page, I have given only part of the information from the documents, which will help to create a computer network with skill.

The design of the twisted pair lan cable is determined by the required data transfer rate. Cables are unshielded and shielded and are designated as follows.

The screen performs two tasks at once, reduces the radiation of electromagnetic fields by themselves twisted pair into the surrounding space and protects them from external electromagnetic fields. Shielded lan cables are used exclusively when laying trunk lines and in industrial premises with large electromagnetic fields. In everyday life and offices, as a rule, an unshielded UTP cable is used.

The cores of twisted pairs in lan cables are of two types, from a single conductor and stranded. The core diameter in single-core twisted pairs is 0.51 mm. Cables with single-core conductors are used for mounting networks in boxes, cable channels and along walls. In addition, it is easier to mount it in communication devices. With stranded conductors, the cable is used only where it can be subjected to frequent bending, for example, connecting a computer to an RJ-45 socket, they are also called patch cords. The attenuation of the signal in a cable made of multi-core twisted pairs is greater than that of a cable made of single-core conductors. For crimping multicore twisted pairs, special RJ-45 connectors are needed. They differ in that the teeth in the lamellas are set apart, like a saw.

The sheath of lan twisted pair cables is typically made of PVC with chalk added to make it brittle when stripped and comes in three colors to indicate the application.

In the form of lan twisted pair cables are round and flat. On the cable sheath, every meter or foot (0.3 m) is marked with a manufacturer, cable category, footage and other information. This allows you to determine the length of the laid line without a ruler.

As can be seen from the marking in the photo, this cable is designed to operate at temperatures environment up to 75°C, UTP - unshielded, 4PR - has 4 twisted pairs, EIA/TIA-568 - complies with EIA/TIA-568 specification, marks on the cable in feet.

Inside the sheath, parallel to the twisted pairs, you can often find a nylon thread, which serves to increase the mechanical strength of the cable as a whole, and also allows you to cut along the sheath when cutting the cable without damaging the twisted pairs. To do this, you need to free the twisted pairs from the sheath for a couple of centimeters, grab the thread and pull it in the opposite direction. The sheath will easily cut along the cable. This thread is also called a split thread.

As technological capabilities have improved, the number of categories has increased, and has now reached seven. The main criterion for classifying a lan cable into one of the categories is its high-speed capabilities for transmitting information data. Speed ​​is measured in Mbps. The larger the number, the greater the amount of information that a twisted-pair cable can pass per unit of time.

Twisted pairs in a lan cable have a wave impedance of 100 ± 25 ohms, all additional connections, including twists, make a change in the resistance value, which reduces the data transfer rate. The influence on extended sections of networks is especially important.

Currently, in practice, everywhere to build local networks and the Internet is used lan cable twisted pairs of category CAT5e, data is transmitted, as a rule, only on 2 pairs,

To create communication networks, computer and communication, cables are used, made according to special technology. Their veins are twisted in pairs with each other. Such products are called "twisted pair". There are two main types of cables of this design: ftp and utp.

UTP (top) and shielded FTP (bottom)

Twisted Pair Features

The main problem in the protection of communication lines is their protection from interference. The signal amplitudes in the line are much smaller than those of the surrounding electrical equipment: in power cable lines, electric motors, household appliances, overhead power lines. Taking into account the degree of development of electrification, it is not difficult to imagine the number of electromagnetic pickups affecting communication cables along their entire route.

In addition, the cores inside the cable itself act on each other, creating mutual interference. When communication lines were carried out using the same technology as electrical ones (in the form overhead lines with wires on insulators), interference from adjacent conductors and high-voltage power lines was minimized by regularly changing the location of the line conductors relative to each other. This technical trick called a transposition.

Transposition on the example of a power line

The twisted pair in modern cable is the same transposition, but done with high density. The veins are twisted together in pairs. This achieves the minimum influence of individual pairs of wires on each other and increases the protection from external interference.

However, the protective properties of twisted-pair cables are reduced to nothing if the conditions for their laying are violated. The bending radius of such products is strictly limited and usually should not be less than eight diameters. If this is not taken into account, then geometric changes occur inside the cable, sometimes irreparable, worsening its noise immunity.

The twisted pair bending radius must be at least 8 cable diameters

Shielding of communication cables

However, twisting the cores does not always help to completely eliminate the effect of interference on the useful signal. In this case, the introduction of shielding shells into the design helps. Shielding can be applied to both individual pairs of cores and all cores inside the cable. These methods are applied both separately and together, in this case each pair of cores is shielded and, additionally, all cores together.

However, this method of protection is effective only if the equipment cases connected by a cable are grounded. Otherwise, the screen shells themselves become a source of interference, accumulating them along the entire path of the line.

Depending on the presence, absence and number of screens, a letter is added to the cable brand, meaning:

• U - no screen;
• S - common screen in the form of a metal braid;
• F - a screen of copper or aluminum foil or metallized tape around the cores of each pair or all as a whole.

The full designation of the brand consists of the above letters written through a fraction. The numerator indicates the protection of individual cores, the denominator indicates the protection of the entire cable. Next, the letters "TP" are added, denoting "twisted pair", in translation - twisted pair.

For example, the designation U/FTP means that the cable does not have a protective shield of individual pairs of cores, but contains a common shield. There are also combinations of their two letters, for example "SF" - a metal braid and foil are used together.

It should be borne in mind that when using foil for shielding, its outer surface is covered with a dielectric layer. Therefore, when connecting the screen, you need to use only it inner surface for contact connection.

If the screen is made of foil, then a metal wire of small cross section runs parallel to it. It is necessary for better contact when connected to grounding devices. It also eliminates possible breaks in the foil screen that occur in places of kinks, as if shunting the places of breaks.

Which cable is better: with or without a shield?

Which one is better to use cable when laying communication networks, utp or ftp? It would seem that the use of shielded cables solves all problems with noise immunity, and unshielded cables only partially cope with the task.

It wasn't there. Recall the ability of the screen to accumulate interference in the absence of grounding. If the equipment to which it is connected does not have a connection to the ground loop (or its own ground loop, which is mandatory for servers), then using ftp will only make the situation worse.

In addition, ftp cables are very sensitive to low-frequency interference, the level of which is manufacturing enterprises quite high due to the presence of power electrical equipment. No matter how hard you try, the laying of communication cables is still impossible at a sufficient distance from existing power lines. And the cable products passing through them always radiate pickups around them. In addition, interference is emitted by electric motors and induction elements. Do not forget about the impulse noise that occurs during the operation of switching devices.

Another utp cable, unlike ftp, has a lower attenuation value of the useful signal. That greatly affects the long length of the communication line.

Therefore, when deciding which cable to choose, unshielded or ftp, you need to focus on whether the equipment has the ability to connect a shield, the presence or absence of low-frequency interference, and overall length communication lines.

Even when choosing a cable, you need to pay attention to the material of its sheath. If it passes through open areas on the street, then it must be protected from exposure sun rays. To do this, the outer shell is made of polyethylene, usually it is black. But the polyethylene sheath that protects the cable from sunlight, temperature fluctuations and precipitation supports combustion. Therefore, indoors they can not be laid openly.

For indoor use, the enclosure must be non-flammable and must not emit halogens (fluorine, chlorine, bromine or iodine). They are not only strong oxidizing agents, but also poisonous to humans. Flame-retardant sheaths are indicated by adding the letters LS (low smoke) to the cable marking for imported products or “ng” for Russian products. Not emitting halogens are additionally labeled HF (halogen free).

Types of cable used in networks

Depending on the presence of protection - electrically grounded copper braid or aluminum foil around twisted pairs, the types of this technology are determined:

• unshielded twisted pair(English) UTP - Unshielded twisted pair) - without a protective screen;
• foil twisted pair(English) FTP - Foiled twisted pair), ) - there is one common external screen in the form of a foil;
• shielded twisted pair(English) STP - Shielded twisted pair) - there is protection in the form of a screen for each pair and a common external screen in the form of a grid;
• foil shielded twisted pair(English) S/FTP - Screened Foiled twisted pair ) - an outer shield of copper braid and each pair in a foil braid;
• unprotected shielded twisted pair (SF/UTP- or from English. Screened Foiled Unshielded twisted pair).The difference from other types of twisted pairs is the presence of a double outer shield made of copper braid and foil.

Shielding provides better protection from electromagnetic pickups, both external and internal, etc. The screen along the entire length is connected to an uninsulated drain wire, which unites the screen in case of division into sections in case of excessive bending or stretching of the cable.

Depending on the structure of the conductors, the cable is used single-core and multi-core. In the first case, each wire consists of one copper core and is called a core-monolith, and in the second - from several and is called a core-bundle.

A single-core cable does not imply direct contacts with connected peripherals. That is, as a rule, it is used for laying in boxes, walls, etc., followed by termination with sockets. This is related to the fact that copper conductors quite thick and with frequent bends quickly break. However, for "cutting" into the connectors of the socket panels, such cores are the best suited.

In its turn stranded cable does not tolerate “cutting” into the connectors of socket panels (thin cores are cut), but it behaves remarkably when bending and twisting. Besides, stranded wire has more signal attenuation. Therefore, multi-core cable is mainly used for the manufacture of patch cords (eng. patch cord) connecting the periphery with sockets.

twisted pair cable design

A twisted pair cable consists of several twisted pairs. The conductors in pairs are made of solid copper wire 0.4-0.6 mm thick. In addition to metric, the American AWG system is used, in which these values ​​\u200b\u200bare 22-26AWG. Standard 4-pair cables generally use 0.51mm (24AWG) conductors. The thickness of the conductor insulation is about 0.2 mm, the material is usually polyvinyl chloride (English abbreviation PVC), for higher quality samples of category 5 - polypropylene (PP), polyethylene (PE). Particularly high-quality cables are insulated with foamed (cellular) polyethylene, which ensures low dielectric losses, or Teflon, providing a wide operating temperature range

Also inside the cable there is a so-called “breaking thread” (usually kapron), which is used to facilitate cutting the outer sheath - when pulled, it makes a longitudinal cut on the sheath, which opens access to the cable core, without damaging the insulation of the conductors. Also, the tear thread, due to its high tensile strength, performs a protective function.

The outer sheath of 4-pair cables is 0.5-0.9 mm thick depending on the cable category and is usually made of PVC with chalk added to increase brittleness. This is necessary for an accurate break at the place of the incision with the blade of the cutting tool. In addition, for the manufacture of the sheath, polymers are used that do not support combustion and do not emit halogens when heated (such cables are labeled as LSZH - Low Smoke Zero Halogen). Cables that do not support combustion and do not emit smoke are allowed to be laid and used in closed areas where air flows from the air conditioning and ventilation system can pass (the so-called plenum areas).

In general, colors do not indicate special properties, but their use makes it easy to distinguish between communications with different functional purpose both during installation and maintenance. The most common cable sheath color is grey. External cables have a black outer sheath. Orange color usually indicates non-combustible material shells.

Separately, it is necessary to note the marking. In addition to information about the manufacturer and type of cable, it necessarily includes meter or foot marks.

The shape of the outer sheath of a twisted pair cable can be different. Most often used round form. Flat cable can be used for under carpeting.

Cables for outdoor laying they must have a moisture-resistant polyethylene sheath, which is applied (as a rule) with a second layer over the usual, polyvinyl chloride. In addition, it is possible to fill voids in the cable with water-repellent gel and armor with corrugated tape or steel wire.

Cable categories

Telecoil with cable model 1933

There are several categories of twisted pair cable, which are numbered from CAT1 to CAT7 (the correct category or category, the abbreviation "CAT", "Cat" should be written with a dot - "Cat.", Because the category and the cat are different things) and determine the effective throughput frequency range. cable more high category usually contains more pairs of wires and each pair has more turns per unit length. Unshielded twisted pair categories are described in the EIA/TIA 568 standard ( american standard wiring in commercial buildings) and in the international standard ISO 11801, as well as GOST R 53246-2008 and GOST R 53245-2008 (translations of one of the manufacturer's manuals).

• CAT1(bandwidth 0.1 MHz) - telephone cable, only one pair (in Russia a cable is used and no twists at all - “ noodles"- her characteristics are not worse, but the influence of interference is greater). In the USA it was used earlier, only in a "twisted" form. Used only for voice or data transmission using a modem.

• CAT2(frequency band 1 MHz) - an old type of cable, 2 pairs of conductors, supported data transfer at speeds up to 4 Mbit / s, used in Token ring and Arcnet networks. Now sometimes found in telephone networks.

• CAT4(frequency band 20 MHz) - the cable consists of 4 twisted pairs, was used in token ring, 10BASE-T, 100BASE-T4 networks, the data transfer rate does not exceed 16 Mbps over one pair, is not used now.

• CAT5(frequency band 100 MHz) - 4-pair cable, used in the construction of 100BASE-TX local networks and for laying telephone lines, supports data rates up to 100 Mbps when using 2 pairs.

• CAT5e(band 125 MHz) - 4-pair cable, enhanced category 5. Data rates up to 100 Mbps when using 2 pairs and up to 1000 Mbps when using 4 pairs. Category 5e cable is the most common and is used to build computer networks. Sometimes there is a two-pair category 5e cable. The advantages of this cable are lower cost and smaller thickness.

• CAT6(frequency band 250 MHz) - used in Fast Ethernet and Gigabit Ethernet networks, consists of 4 pairs of conductors and is capable of transmitting data at speeds up to 1000 Mbps and up to 10 gigabits at a distance of up to 50 m. Added to the standard in June 2002.

• CAT6a(frequency band 500 MHz) - used in Ethernet networks, consists of 4 pairs of conductors and is capable of transmitting data at speeds up to 10 Gb / s and is planned to be used for applications operating at speeds up to 40 Gb / s. Added to the standard in February 2008 .

• CAT7(frequency band 600-700 MHz) - the specification for this type of cable is approved only international standard ISO 11801, data rate up to 10 Gbps. This category of cable has an overall shield and shields around each pair. The seventh category, strictly speaking, is not UTP, but S/FTP (Screened Fully Shielded Twisted Pair).

• CAT7a(frequency band 1200 MHz) - designed for data transmission at speeds up to 40 Gbps.

Each individual twisted pair, which is part of a cable intended for data transmission, must have a characteristic impedance of 100 ± 15 Ohm, otherwise the shape of the electrical signal will be distorted and data transmission will become impossible. The cause of data transmission problems can be not only a poor-quality cable, but also the presence of "twists" in the cable and the use of sockets of a lower category than the cable.

Types of cable used in networks.

* Shielding provides better protection against electromagnetic interference, both external and internal, etc. The shield is connected along its entire length to an uninsulated drain wire, which integrates the shield in case of division into sections due to excessive bending or stretching of the cable. LANs operating at 100 or 1000 Mbps use mostly unshielded cables. However, it is worth noting that for high-speed networks of 10 Gb / s, 40 Gb / s, 100 Gb / s, the standards determine the use of shielded cables only.

Main difference is the presence and appearance of the screen. The twisted-pair shield serves to protect the signal from external interference. For example, when it is not possible to lay a twisted pair cable separately from power cables. In addition, each manufacturer may add other designations depending on the cable design, for example:

Thus, the U/UTP 4 cat.5e solid 24AWG LSZH marking translates as follows: - unshielded cable, contains 4 pairs of 2 cores, category 5, solid - single-wire core, 24 AWG - diameter 0.51 mm, LSZH - halogen-free cable with low smoke emission.

conductor material.

Conductors in pairs are made of copper, aluminum and bimetal (copper-plated aluminum). Initially, the conductor material was exclusively copper. However, copper has a drawback - it is a high cost, in connection with this, aluminum, and later bimetallic twisted pair, appeared on the market, which is cheaper than copper. But is it beneficial similar savings in the long term? To get a high-quality and long-term working network, and even more so to pass certification, it is possible only when using copper conductors.

solid care	stranded
Suitable for long distance transmission. It is used for mounting the horizontal SCS subsystem.	Flexible and easy to handle. It is mainly used for making patch cords.

The cross section of each core of a twisted pair is marked in accordance with the AWG (American Wire Gauge) standard. The most common conductors are 26 AWG (section 0.13 mm²), 24 AWG (0.2 - 0.28 mm²) and 22 AWG (0.33 - 0.44 mm²). The conductor cross section is understood as the direct cross section of the conductive material without the thickness of its insulation.
It is necessary to pay attention to the fact that the smaller the AWG, the thicker the conductors and the better the twisted pair cable in terms of characteristics, since the cross section is larger and the resistance is lower. That is, a 22 AWG twisted-pair cable will outperform a 24 AWG twisted-pair cable. But such a cable will be more expensive, since there is more copper in it.
Category 5e cables have 24 AWG conductors, and higher quality cat.6a, cat.7, cat.7a cables are 23 AWG, and some manufacturers use 22 AWG twisted pair conductors.

rj-45 cat.5 (24AWG)	rj-45 cat.6 (23AWG)	rj-45 cat.6a, 7 (22/23AWG)

Categories of twisted pair cable.

The design of twisted pair cable.

* Each individual twisted pair that is part of the data cable must have a characteristic impedance of 100 ± 15 ohms, otherwise the shape of the electrical signal will be distorted and data transmission will become impossible. The cause of problems with data transfer, as well as big losses signal, there can be not only a low-quality cable, but also the presence of "twisting" in the cable and the use of sockets of a lower category than the cable.

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24.01.2008 Carol Everett Oliver

Category 5e still accounts for the majority of horizontal cabling installations. But according to a recent study by FTM Consulting, Category 6 is increasingly used in new projects and is expected to overtake Category 5e in the coming year. The positions of the latter will be significantly weakened, and it will be used only in already operated and low-budget installations. Yet questions about the purposes of a Category 6 installation are being asked over and over again.

Modern data and voice applications such as Gigabit Ethernet to the desktop are rated for Category 5e. This solution has the necessary features in accordance with the TIA 568-B specification. However, Category 6 provides better signal integrity over a wider bandwidth, which can be critical for a cable system to support more demanding applications in the future. Category 5e is defined in the frequency band up to 100 MHz, while Category 6 is defined in the 250 MHz band. In addition, significant improvements in the design and manufacturing process of Category 6 offer additional benefits beyond greater bandwidth. Considering the ever-increasing need for bandwidth, which, according to Moore's law, doubles every year and a half, the need for speed and capacity can make a cable system obsolete if the requirements for it change.

Category 6 uses larger diameter conductors and a smaller twist pitch to improve basic electrical characteristics, for example, crosstalk (see Figure 1). Separators are installed on some Category 6 cables to further separate the pairs. Reducing attenuation and increasing conductor size makes Category 6 cable significantly more robust, which is essential for applications that require more bandwidth and provides sustainable work networks during sudden temperature fluctuations. In addition, some Category 6 cables are designed and manufactured to provide exceptional balance. This will achieve immunity to noise, both internal and external to the cable.

Let's take a closer look at how physical differences affect the functioning of the network. The laboratory at the Nexans Data Communications Competence Center (DCCC) conducted several comparative tests to determine the signal integrity parameters for Category 5e and Category 6 cabling systems various manufacturers. You can decide how important this is when choosing a cable system.

REDUCE ERRORS

As found in previous studies, Category 6 is less error prone than Category 5e, and the test was carried out on several transceivers at once with different characteristics. Tests in the DCCC lab compared the number of errors (Cyclic Redundancy Check, CRC) for Category 5e and 6 when using a Gigabit Ethernet transceiver. Many people mistakenly believe that all transceivers are the same. However, in reality, even transceivers from the same manufacturer differ. Three devices were chosen for the experiment. Gigabit Ethernet packets were transmitted over a full 100 m path with three connectors, first Category 5e, then Category 6.

Test results show a 13-fold reduction in CRC errors when using Category 6. Changing cabling to Category 6 improves the signal-to-noise ratio of the entire transport system, so transceivers can receive Ethernet packets more consistently and without errors. Thus, the best performance of Category 6 wiring translates into greater network reliability. This additional headroom allows you to install network components that would otherwise result in long downtime and additional costs.

Structured cabling systems are often installed in high temperature areas, such as above-ceiling spaces, where temperature differences often reach 25°C during the day. These fluctuations affect the characteristics of the cable. DCCC conducted a series of tests in which 1000BaseT signals were transmitted over 90 m over Category 5e, 6 and Enhanced Category 6 cabling. various stages In testing, the temperature was raised with an adjustable heater from 20 to 70°C in 10°C increments.

It turned out that at high temperatures the error rate with Category 5e wiring is significantly higher than with Category 6 wiring (see Figure 2). In the case of Enhanced Category 6 cabling, errors were even rarer.

In addition to heating from external heat sources, cables are exposed to applications such as Power over Ethernet (PoE). To support power delivery over structured cabling, industry standards have defined electrical and physical requirements for PoE applications. The IEEE 2003 802.3af standard defines a methodology for providing power over balanced wiring to connected end devices. Voltage power limited physical characteristics And regulatory requirements. The 802.3af standards are designed to be compatible with existing equipment, so the recommendations are for Category 5e power since most networks use 10BaseT or 100BaseTX technologies.

Applications that require both power and data over the same twisted-pair cable, such as VoIP phones or surveillance cameras, will eventually need more power. The IEEE 802.3 specification, known as PoE Plus, which has been in development for two years, is expected to be approved soon. As a result, the power allowed for transmission over twisted pair will increase from 13 to 60 watts. As can be seen from the test results (see above), cable performance deteriorates with increasing temperature due to higher insertion loss (Insertion Loss). This may adversely affect the allowable maximum length fixed line or transmission path. Installation of cables with the best performance, such as Category 6, is in line with general industry trends. They use larger diameter conductors to minimize insertion loss while increasing current transfer capability.

NOISE RESISTANCE

Increased sensitivity to external noise becomes critical as the data rate increases, when more high speeds signaling and complex coding. External sources of noise - power lines, air conditioning units, elevators, electrical equipment and interference from neighboring cables - cause voltage spikes, the so-called electrical fast transient (EFT). They can drastically affect the functioning copper cables and lead to errors. There is a direct relationship between balance and immunity to noise. Balanced Category 6 cable is 50% more resistant to noise than Category 5e.

In the DCCC tests, Category 5e, 6, and Enhanced Category 6 cable was subjected to various levels of EFT while carrying Gigabit Ethernet packets. The relationship between errors and impulse noise was calculated and displayed graphically. There are significant performance differences between balanced and unbalanced cables, as well as between Category 5e and Category 6 (see Figure 3).

RATIONALE FOR INVESTMENT

One of the main reasons for choosing Category 5e is cost savings. Larger conductor diameter, smaller twist pitch and difficult process production conditions high cost Category 6 cables. But everything is relative.

Yes, in terms of materials Category 6 is 30-50% more expensive. But in reality, if we take into account the total cost information system, this discrepancy turns out to be negligible. In computer system building projects, all costs are usually divided into the following four categories:

Software (51%);

Equipment (22%);

Network infrastructure (20%);

Training and documentation (7%).

At the same time, it should be taken into account that 20% of investments in network infrastructure are distributed between passive and active components, as well as the costs of design and project management. Of this amount, wiring accounts for less than half, and only 35% of the remainder for cables. So cables for local systems account for less than 3% of the total project budget. The cost of moving from Category 6 to Category 5e is less than 1% of the total costs.

Research shows that during life cycle telecommunications wiring has been replaced by at least two generations network equipment. The conclusion is clear: Cabling designers and installers should opt for better wiring. If you want to cable system supports existing and future applications, then, given the benefits of Category 6, investment in it seems to be the minimum necessary. If noise, temperature fluctuations, rising speeds do not matter to you, then Category 5e is quite enough. The choice is yours.