LAN network cable. LAN Switching and Fast Ethernet Implementation


During the development of local networks, quite a lot of types of cables have appeared, and all of them are the result of increasingly complex standard requirements. Some of them have already become a thing of the past, and some are just beginning to be used, and thanks to them it has become possible to implement the much needed high speed data transmission.
In today's article I will talk about main types of cables And connectors, which have become widespread in the construction of wired local networks.

Coaxial cable

Coaxial cable- one of the first conductors used to create networks. Coaxial cable consists of a central conductor enclosed in thick insulation, a copper or aluminum braid and an outer insulating sheath: To work with coaxial cable, several different types of connectors:

Installed at the ends of the cable and used to connect to the T-connector and barrel connector. . It is a kind of tee that is used to connect a computer to the main line. Its design contains three connectors at once, one of which is connected to the connector on the network card, and the other two are used to connect the two ends of the trunk. . With its help, you can connect the broken ends of the highway or sharpen part of the cable to increase the radius of the network and connection additional computers and other network devices. . It is a kind of stub that blocks further propagation of the signal. Without it, the functioning of a network based on coaxial cable is impossible. A total of two terminators are required, one of which must be grounded.

Coaxial cable is quite susceptible to electromagnetic interference. From its use in local computer networks They gave up a long time ago.
Coaxial cable began to be mainly used to transmit signals from satellite dishes and other antennas. The coaxial cable received a second life as a backbone conductor of high-speed networks that combine the transmission of digital and analog signals, for example, cable television networks.

twisted pair

twisted pair is currently the most common cable for building local networks. The cable consists of pairs of intertwined copper insulated conductors. A typical cable has 8 conductors (4 pairs), although cables with 4 conductors (2 pairs) are also available. The colors of the internal insulation of conductors are strictly standard. The distance between devices connected by twisted pair cable should not exceed 100 meters.

Depending on the presence of protection - an electrically grounded copper braid or aluminum foil around the twisted pairs, there are types of twisted pair:

Unshielded twisted pair (UTP, unprotected twisted pair). Apart from conductors with their own plastic protection, no additional braids or grounding wires are used: Foiled twisted pair (F/UTP, foil twisted pair). All pairs of conductors of this cable have a common foil shield: Shielded twisted pair (STP, protected twisted pair). In a cable of this type, each pair has its own braided shielding, and there is also a common mesh screen for all: Screened Foiled twisted pair (S/FTP, foil shielded twisted pair). Each pair of this cable is in its own foil braid, and all pairs are placed in a copper shield: Screened Foiled Unshielded twisted pair, unprotected shielded twisted pair). Characterized by double screen copper braid and foil braid:

There are several categories of twisted pair cables, which are marked from CAT1 before CAT7. The higher the category, the more high quality cable and so best performance he has. Local computer networks of the Ethernet standard use twisted pair cable of the fifth category (CAT5) with a frequency band of 100 MHz. When laying new networks, it is advisable to use an improved cable CAT5e with a frequency band of 125 MHz, which better transmits high-frequency signals.

To work with a twisted pair cable, an 8P8C (8 Position 8 Contact) connector is used, called RJ-45:

Fiber optic cable

Fiber optic cable– the most modern data transmission medium. It contains several flexible glass light guides protected by heavy plastic insulation. The data transfer speed over optical fiber is extremely high, and the cable is absolutely free from interference. The distance between systems connected by optical fiber can reach 100 kilometers.

There are two main types of fiber optic cable - single-mode And multimode . The main differences between these types relate to different modes passage of light rays in the cable. To crimp a fiber optic cable, many connectors and connectors of different designs and reliability are used, among which the most popular are SC, ST, FC, LC, MU, F-3000, E-2000, FJ, etc.:
The use of optical fiber in local networks is limited by two factors. Although the optical cable itself is relatively inexpensive, prices for adapters and other equipment for fiber optic networks are quite high. Installation and repair of fiber optic networks requires high qualifications, and cable termination requires expensive equipment. Therefore, fiber optic cable is mainly used to connect segments large networks, high speed access to the Internet (for providers and large companies) and data transfer to long distances.

When designing and installing a LAN, as mentioned above, as standard systems data transmission, you can use a rather limited range of cables: cable with twisted pairs(UTP cable) categories 3, 4 or 5 with various types screens or without them (STP - shielding with copper braid, FTP - shielding with foil, SFTP - shielding with copper braid and foil), thin coaxial cable (RG-58) with different designs of the central core (RG-58/U - solid copper core, RG -58A/U - multi-core, RG-58C/U - special /military/ cable version RG-58A/U), thick coaxial cable (thick coaxial cable) and fiber optic cable (fiber optic cable single mode-single-mode multimode-multimode ). Moreover, each type of cable subsystem imposes certain restrictions on the network design:

MAXIMUM SEGMENT LENGTH

NUMBER OF NODES PER SEGMENT

POSSIBILITY OF OPERATING AT SPEEDS ABOVE 10Mbit/sec

FIRE SAFETY REQUIREMENTS AND APPLICATION OF CABLES

Fire safety rules divide cables into two categories: general use and plenum (approved for installation in ventilation shafts). This division is carried out based on the materials used in the manufacture of cables. The most common plastics used in the manufacture of cables are based on polyvinyl chloride (PVC). When burned, they release toxic gases. Therefore, PVC cables are prohibited for installation in ventilation shafts. Plenum spaces typically use Teflon-insulated cables.

BASIC OPERATING CHARACTERISTICS OF TWISTED PAIR CABLES.

All cables must have twisted pairs of wires; the use of cables with wires not twisted in pairs is not allowed. This applies even to short sections of flat cable. When using shielded twisted pair cables, it is recommended to ground the latter segments at one (and only one!) end. In practice, it is more convenient to do this at the end connected to the hub.

  • minimum bending radius - 5 cm
  • temperature during operation and storage:
    -35...+60С - for cable with PVC sheath
    -55...+200С - for cable with Teflon sheath
  • installation temperature:
    -20...+60С - for cable with PVC sheath
    -35...+200С - for cable with Teflon sheath
  • relative humidity:
    - 0...+100% - for a cable in a polyvinyl chloride sheath, accidental condensation is allowed
    - does not react to humidity, condensation and water splashes - for Teflon-sheathed cable
  • Possibility of outdoor use:
    - prohibited - for cables with a polyvinyl chloride sheath
    - allowed - for Teflon-sheathed cable
  • It is prohibited to use a thin coaxial cable for laying in the open air between two buildings that are not connected to each other (between buildings that do not have a common ground loop).


When installing new network It is advisable to use twisted pair cable in a work group. Fiber optic cables - on long highways and for communication between buildings. Thin coaxial cables are most justifiably used for organizing low-speed highways inside installation cabinets (see the material “Current practice in designing local networks”). Twisted pair cables and fiber optic cables allow you to upgrade your network, moving it from 10 to 100 Mbit technologies.

The most “moving” part of any LAN are subsystems working group. Adding new users, moving jobs and canceling them, and cable damage within a workgroup occur much more often than changes in trunk channels. That is why UTP cables are most convenient for organizing workgroup subsystems.

On long highways, optical fiber is certainly the most preferable, because it provides the longest permissible segment length, high security and noise immunity.



In order to avoid problems with the cable subsystem, when designing it, you can use the following rules (recommendations are given for the use of UTP cables):

  • if this is an office-type building network (for example, a bank or an office building itself), pledge one UTP cable for every 3-4 sq.m. premises. Workplaces in buildings of this type are subject to the most frequent moves and are very densely equipped with computers and office equipment;
  • if this is a network of an ordinary company or enterprise , double need for funds computer technology, which was stated to you by the Customer;
  • After installing the cable subsystem, be sure to install it certification for compliance with the requirements of category 5 (each link and patch cord). Even if you used quality components, installation and environmental factors may cause deterioration in performance. Print and save test results.

Following these rules will avoid problems with expansion cable network during transitions to new technologies both within the LAN itself and in telephone communications.

For subsystems based on thin coaxial cables, such recommendations cannot be made, because in such subsystems it is necessary to try to solve another problem - to minimize the number of jobs. Generally speaking, thin coaxial cable is not recommended for workgroup networks. Although the problem when using it is not the cable itself. The fact is that the wiring of a thin coaxial cable is open and users have access to it. Often the user incorrectly disconnects the cable, destroying the integrity of the cable segment. In this case, the entire network fails, and the operation of the network may be disrupted. software. The same consequences result from removing the terminator from the end of the cable segment and using cable sections with a different characteristic impedance. For these reasons, it is advisable to use thin coaxial cable only in tamper-proof locations, such as in a wiring closet. In addition, the bus topology of networks on a thin coaxial cable makes diagnosis difficult because the cable is common to multiple nodes. The malfunction can be caused by any node, any section of cable or any terminator. Finding a fault in such networks is usually quite difficult.

There are often situations when, after connecting a computer or laptop to the Internet using a network cable, the error “Network cable is not connected” appears. This is most likely not even an error, but simply the status of the network adapter, which can be observed in network connections.

It turns out that the computer does not respond to the connection in any way; the network cable is not connected, although it is connected to the computer and inserted into the network card connector. Icon on the notification panel with a red cross. Well, the Internet, of course, doesn’t work. This is what it looks like:

And most importantly, the cable is connected. From a router, modem, or directly from the provider’s equipment. This error can appear on both a PC and a laptop. It also doesn't matter which Windows is installed on your computer. Only in Windows 10 will the message “Network cable not connected” appear next to the “Ethernet” adapter, and in Windows 7 – next to “Connect via local network". And in Windows XP, a pop-up window with this error still appears if you hover your mouse over the connection icon. This also often happens.

The same goes for the connection method. Some people have a network cable coming directly from their provider (for example, Rostelecom), and for some via a modem, Wi-Fi router, or terminal.

What could be the problem?

There can be many reasons. We list the main ones:

  • The network cable is incorrectly or not fully connected.
  • The network cable is damaged. The contacts in the connector may have come loose (into which the network cable itself is crimped).
  • Hardware problems with the router, modem, provider equipment. Or the network card itself in your laptop or PC has broken down.
  • Problems with the network card settings. Most often, it cannot automatically determine the speed and duplex. I'll tell you about this in more detail.
  • There are some problems with the network card driver.
  • Viruses, firewalls, some programs. Yes, yes, they can also cause the “Network cable is not connected” error to appear.

How to find out the reason and what to do first?

  • First, restart your computer, modem, router (if you have one).
  • Disconnect the network cable and connect again. Also check the connection on the router (if the Internet is connected through it). Connect the cable to another LAN port. Pay attention to whether the LAN indicator on the router lights up after connecting the cable. You can see the instructions: .
  • If possible, connect via a different cable.
  • You can lightly move the network cable where it enters the connector. And at this moment look at the status of the network adapter on the computer. Perhaps the contacts are leaving there, and this way we can find out.
  • If you have another PC or laptop, try connecting it. This way we can find out what's going on.
  • If the Internet goes through a router, then try connecting the cable from the provider directly to the computer.

I would divide the solutions into software and hardware.

The network cable is not connected, although it is connected: solutions to the problem

1 I would try removing the network card from Device Manager. After a reboot it should recover automatically. Go to Device Manager (the easiest way to find it is through a search, or press the Win + R key combination and run the command devmgmt.msc).

By opening the tab " network adapters"find the network card. Depending on the manufacturer and driver, the name may be different. The name may contain "LAN". For example, on my laptop it is "Realtek PCIe GBE Family Controller". By the way, pay attention to whether there is a yellow icon. Click on it right click mouse and select "Remove device".

We confirm the deletion and restart the computer. Perhaps after a reboot everything will work and the computer will see the connected network cable.

2 Check the speed and duplex detection settings. In Device Manager, right-click on the network card (as I showed above) and select "Properties".

Next, go to the “Advanced” tab. In the list, find and select "Spread&Duplex". And in the drop-down menu on the left, set the value to "Auto Negotiation". But if you initially had it installed there this option, then try setting a different value. For example: "100 Mbps Full Duplex". You can also try different variants. Don't forget to click Ok and restart your computer.

It just often happens that the network card cannot automatically detect speed and duplex.

3 Network card driver. You need to try reinstalling it. Download the driver from the website of the manufacturer of the card itself (LAN), laptop, or motherboard your computer and start the installation. You can look at the article on this topic:.

Other reasons why the computer does not respond to the connection of the network cable

1 Network card failure. However, in this case, you most likely will not see it in the device manager. But it happens in different ways. To find out, you need to connect another cable to it. Connect to another router or provider. Or connect other devices to the same cable. 2 Problems with the provider. For example: an employee of the provider was connecting the Internet to another subscriber, and accidentally disconnected your cable from the equipment, or the cable was broken somewhere in the entrance. Or maybe someone cut it on purpose. In such cases, the message “Network cable is not connected” will appear. You need to contact your provider's support. Just before doing this, it would be good to make sure that the problem is not in the network card of your computer. It also often happens that the contacts on the connector into which the network cable from the provider is crimped are lost. You just need to do it again and correctly. Or call the experts. 3 Problem with the router. May be. But checking all this is very simple. Disconnect the Internet from the router (only if you don't have ADSL), and connect it directly to your computer. If the computer sees the network cable, then the problem is either in the router or in the cable with which you connect the PC to the router. You can also look at the article: . 4 The network cable is faulty. And this can happen. But, if we have a cable that we connect the computer to the router, then it is easy to check by connecting it to another device, or by connecting the cable from the provider directly to the computer’s network card.

Twisted pair - a type of communication cable, is one or more pairs of insulated conductors twisted together (with a small number of turns per unit length) to reduce mutual interference during signal transmission, and covered with a plastic sheath. One of the components of modern structured cabling systems. Used in telecommunications and computer networks as a network media in many technologies such as Ethernet, ARCNet and Token ring.

Currently, due to its low cost and ease of installation, it is the most common for building local networks.

(the dividing cord is visible between the pairs)

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

Unshielded twisted pair (UTP - Unshielded twisted pair)

Shielded twisted pair (STP)

Foiled twisted pair (FTP)

Foil shielded twisted pair (SFTP - Shielded Foiled twisted pair)

In some types of shielded cable, protection can also be used around each pair, individual shielding. Shielding provides better protection from electromagnetic interference, both external and internal, etc. The entire length of the screen is connected to a non-insulated drain wire, which unites the screen in case of division into sections due to excessive bending or stretching of the cable.

In addition to this, the cable is used single and multi-core. In the first case, each wire consists of one copper core, and in the second - of several.

A single-core cable does not require direct contact with connected peripherals. That is, as a rule, it is used for laying in boxes, walls, etc. followed by termination with sockets. This is due to the fact that copper strands are quite thick and with frequent bending they quickly break. However, such conductors are ideally suited for “cutting into” the connectors of socket panels.

In turn, a multi-core cable does not tolerate “cutting” into the connectors of socket panels (thin cores are cut), but behaves well when bent and twisted. Therefore, multi-core cable is used mainly for the manufacture of patch cords (PatchCord), connecting peripherals to sockets. In addition, stranded wire has less resistance to high-frequency signals (Skin effect).

Cables based on twisted pair copper unshielded are divided into 5 categories according to their electromechanical properties.

Category 1 cable is used in cases where data transfer speed requirements are minimal. It is usually used for analog and digital transmission voice and low-speed data transmission.

Category 3 cable was standardized in 1991. Then the Standard for Telecommunications Cabling Systems for Commercial Buildings (EIA-568) was developed, and subsequently the EIA-568A standard was created on its basis. This standard defines the electrical characteristics of Category 3 cables at 16 MHz, allowing this cable to be used for high-speed networking applications. Category 3 cable is designed for both data and voice transmission. The twisting pitch of the wires is three turns per 30.5 cm. Most cable systems in office buildings are built on the basis of this cable, through which voice and data are transmitted.

Category 4 cable is an improved version of the previous category. This cable must withstand tests at a signal transmission frequency of 20 MHz, while providing good noise immunity and low signal loss. This category is well suited for systems with extended distances up to 135 meters, as well as in networks Token Ring With throughput 16 Mbit/s. However, in practice it is almost never used.

Category 5 cable is specifically designed to support high-speed protocols. Their characteristics are determined in the range up to 100 MHz. Most high-speed standards are oriented towards Category 5 cable. It supports protocols with a data transfer rate of 100 Mbit/s FDDI with the physical standard TP-PMD, Fast Ethernet, 100VG-AnyLAN and faster ATM protocols with a speed of 155 Mbit/s, as well as the option Gigabit Ethernet at a speed of 1000 Mbit/s. A twisted-pair version of Gigabit Ethernet using 4-core UTP cable became the standard in 1999. Category 5 cable has replaced Category 3, and large building cabling systems are now built using this type of cable in combination with fiber optic cable.

UTP cables are available in 2- and 4-pair versions. Each pair of such cable has its own twist pitch and a specific color. In the 4-pair version, two pairs are for data transmission and two more are for voice transmission.

To connect the cables, RJ-45 sockets and plugs are used, which are eight-pin connectors and look similar to telephone connectors.

The main purpose of this cable is to support high-speed protocols over cable sections longer than Category 5 UTP cable, the maximum segment length of which should not exceed 100 meters. Category 7 cable is hardly advisable for use: the cost of a network based on it is close to the cost of a fiber-optic network, and the characteristics of fiber-optic cables are higher. Therefore, it is likely to gradually disappear in the near future, remaining only in the history of cable development.

Cables based on shielded twisted pair STP protect the transmitted signals well from external interference. The grounded screen used in this type of cable complicates installation, as it requires high-quality grounding and increases the cost of the cable itself. Shielded cable is used for data transmission only.

The main standard defining the parameters of shielded twisted pair cables is the IBM proprietary standard. In this standard, cables are divided not into categories, but into types (Type 1-type 9). Of these, the main one is the Type 1 cable. It consists of two pairs of wires and a conductive shielding braid, which is grounded. STP Type 1 cable is included in international standards.

Shielded pairs are also used in Type 2 cable. This cable is similar to Type1, with the addition of two pairs of unshielded wires for voice transmission. These cables are connected to the equipment using connectors designed by IBM.

Not all IBM standard cables are shielded. For example, Type 3 defines the characteristics of unshielded telephone cable, and Type 5 defines fiber optic cable.

Wireless technologies are certainly beginning to lead the way in organizing home and office networks, but they will never replace wired ones, and if this happens, it will not be in the near future. The majority of providers install their cables directly to the client, and only then the work begins WiFi routers. There are several types of local network cables; they differ in channel capacity, method of connection to the computer, installation method, and others. Let's consider in order how the standards changed, what they were, and what is used today.

What kind of cable is there for a local network?

The choice of conductor is initially always determined by the LAN topology, and the most common are coaxial wires and twisted pair. Fiber optic technologies are now widely used, but this is still a developing standard, used mainly for laying highways over long distances. It is not widely used for connecting the end user. So, LAN cable Ethernet comes in two types:

  • Coaxial - which is a single-core wire with a screen, separated from each other by insulating material or an air gap. Reminds me very much TV wire resistance 70 Ohm.
  • “Twisted pair” - consists of eight wires intertwined in pairs. Each core is marked with a separate color to simplify installation. The colors are fixed and described by specifications and all product manufacturers adhere to these rules.
  • Fiber optic or fiber optic - has a very complex design and is quite expensive to install. The signal in it is transmitted in the form of light pulses through special light guides.

In the 90s of the last century, exclusively coaxial wire was used to build local networks, and on its basis such well-known topologies as “bus” and “ring” were developed. A little later, the “star” topology based on twisted pair appeared, which is still the most popular and popular architecture for local and global networks. Now it's time to stop and describe each one used LAN cable separately.

Coaxial cable and connectors used

This type of wire is the oldest of the conductors. This cord has one supporting copper or aluminum core, which is covered with a thick layer of insulating material. Next comes the screen, made in the form of a tape encircling the central core of aluminum or copper. The top outer layer is a sheath that protects the cores from damage, made of polyethylene or polyvinyl chloride. There are several types of such cable used for LAN:

  • 10Base 5 is a thick type of conductor, with a cross-section of 12 mm and total resistance 50 Ohms for the 8th category and 75 Ohms for the 11th. The data transfer speed does not exceed 10 Mbit/s over distances between end nodes up to 500 meters.
  • 10Base 2 is thin, about 6 mm in diameter, most common for organizing home or small office networks. Its impedance is 50 ohms, but the maximum length is 185 meters at a speed of 10 Mbps.

Thanks to good insulation, the signal in the conductor is practically not extinguished, i.e. packets are not lost, and additional algorithms for checking transmitted or received information are not needed. The only drawback is the rather high cost of production and low speed, so it was subsequently supplanted by “twisted pair”.

“Twisted pair” - types and methods of crimping

LAN cable“twisted pair” got its name due to the fact that it consists of eight strands intertwined in pairs. Each core is insulated in a strictly specified color. Polyvinyl chloride or polyethylene is used as an external insulating material that protects the signal from electromagnetic interference. There are several types of such cable:

  • UTP (Unshelded Twisted Pair) is an unshielded modification, most often used for laying home or office networks when there are no strong interference to the transmitted signal.
  • FTP (Foiled Twisted Pair) - cable with additional screen made of aluminum foil under external insulation.
  • STP (Shelded Twisted Pair) - in addition to the general screen, it has an additional one for each pair separately.

Twisted pair has 7 categories, and the higher the category number, the more protected the wire is from electromagnetic radiation. For Ethernet networks Category 5 cable (CAT5) is used, which has a bandwidth of 100 MHz. When installing new facilities, it is recommended to use a more advanced modification of CAT5e for higher frequency signals with a bandwidth of 125 MHz.

Twisted pair is used to create connections at speeds from 100 Mbit/s to 40 Gbit/s, depending on the category and quality of the cable itself and its length between end devices. Typically the segment length should not exceed 100 m.

The wire must have a connector for connection to network devices. For twisted pair, an RJ-45 connector is used (8P8C - 8 position and 8 contacts). Inside the connector there are special grooves with contacts for each core. There are several options for crimping network cables: forward and reverse (crossover). Straight patch cord is used to connect a computer to a router or switch, or to connect an active network equipment between themselves. Cross is used quite rarely and serves to connect two computers to each other. Currently, almost all manufacturers install “smart” network cards, which do not care about the location of the wires in the connector, but it is advisable to adhere to the standards and arrange the wires as written in the specification. This will help avoid collisions in the operation of the entire network. To make a straight LAN cable The cores are arranged in the following order at both ends:

  • white-orange;
  • orange;
  • white-green;
  • blue;
  • white-blue;
  • green;
  • white-brown;
  • brown.

To make a patch cord for ease of work, special pliers are used - a crimper (or “crimp” in common parlance). The crimper allows you not only to clamp the wire evenly in the connector, but also to properly cut and strip the insulation. In exceptional cases, you can use a flat-head screwdriver or a knife, but then the quality will not be satisfactory. There are connectors that are clamped without a crimper, but they are designed for multi-core soft wires and may not be suitable for standard twisted pair cables.

Fiber optic cable

Optical fiber is the most advanced technology for transmitting signals over long distances at enormous speed. The difference in signal transmission is that light, rather than electricity, is used as an impulse. Light is transmitted through glass fiber strands and reflected from the inner walls of the conductor. You can simultaneously transmit several signals: they will not intersect or cancel each other. The speed of information transfer over such a cable is limited only by the capabilities of the network cards or adapters. The cable is not subject to interference and is made of non-flammable materials.

The cost of such a cable is relatively low compared to other conductors, but its installation can only be carried out by qualified employees using high-precision and expensive equipment, so it is almost impossible to use it at home. But such a conductor has found wide application for laying highways, because the distances between signal amplifiers can reach hundreds of kilometers. Some providers already provide a service for connecting optical fiber to the home, but end devices are still connected via twisted pair, which is why it is the fundamental standard for organizing a network.


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