Cables used to build the infrastructure of computer networks are produced in a wide range of varieties. Among the most popular - coaxial, twisted pair, as well as fiber. What is the specificity of each of them? What are the features of mounting the most common - twisted pair?
Cable types: coaxial
Among the most historically early types of cables used in network connections are coaxial. In terms of thickness, it roughly corresponds to the network power cable for the computer, designed to work with a 220 V socket.
The structure of the coaxial design is as follows: in the middle - a metal conductor, it is thick, usually plastic insulated. On top of it - a braid of copper or aluminum. The outer layer is an insulating shell.
The connection of a network cable of this type can be carried out by:
- BNC connector;
- BNC terminator;
- BNC-barrel connector.
Let's consider their specifics in more detail.
The BNC connector assumes placement on the ends of the cable, it is used for connection with T- or barrel-connectors. BNC-terminator is used as an insulating barrier, preventing the signal from moving along the cable. The correct functioning of the network without this element is unworkable in some cases. Connecting via a coaxial network cable involves the use of two terminators, one of which requires grounding. The BNC-T connector is used to connect the PC to the backbone. In its structure there are three slots. The first is connected to the network card of the computer, with the help of the other two, the connection of the different ends of the trunk is made. Another type of connector for coaxial cable is BNC-barrel. It is used to connect different ends of the trunk, or to increase the radius of the computer network.
Among the useful features of coaxial designs - there is no problem with deciding how to connect two network cables of this type. It is enough to ensure a reliable contact of the conductor cores, of course, with the technology of interface insulation and screen mesh. However, the coaxial cable is quite sensitive to electromagnetic interference. Therefore, in the practice of building computer networks, it is now used quite rarely. However, it is indispensable in the organization of infrastructure for the transmission of television signals - from cymbals or cable providers.
The most probably network cables today are called "twisted pair". Why this name? The fact is that in the structure of the cable of this type there are pairwise conductors. They are made of copper. The standard cable of this type includes 8 cores (in total, thus 4 pairs), but there are also samples with four conductors. The so-called pinout of a network cable of this type (correlating each core with a function) involves the use of isolation of a specific color on each conductor.
The outer insulation of the twisted pair is made of PVC, which provides sufficient protection for conductive elements from electromagnetic interference. There are shielded cables of the type in question - FTP and STP. In the first, the corresponding foil is located on top of all cores, in the second - on each of the conductors. There is an unshielded modification of the twisted pair - UTP. As a rule, cables with foil are more expensive. But it makes sense to apply them only if there is a need for high-quality data transmission over a relatively large distance. For home networks is quite suitable unshielded version of the twisted pair.
There are several classes of the corresponding type of structures, each of them is designated as CAT with a number from 1 to 7. The higher the corresponding figure, the better the materials providing the signal transmission. Modern network cables for a computer for Ethernet data exchange in home networks require the compliance of elements with the CAT5 class. In the connections where twisted pair is used, connectors are used which will correctly classify as 8P8C, but there is also their unofficial name - RJ-45. It can be noted that cables corresponding to at least the CAT5 and CAT6 classes can transmit data at speeds close to the maximum for the type of design under consideration - up to 1 Gbit / s.
Perhaps the most modern and fast network cables for a computer are fiber-optic. In their structure there are light-conducting elements from glass, which are protected by strong plastic insulation. Among the key advantages that these network cables have for the computer are high immunity from interference. Also, through the fiber can transmit data over a distance of about 100 km. The connection of cables of this type with the devices can be carried out by means of various types of connectors. Among the most common - SC, FC, F-3000.
What does this high-tech network cable look like for a computer? The photo of the fiber-optic structure is below.
The intensity of the practical use of optical fiber is limited by the relatively high cost of the equipment necessary to transmit data through it. However, recently many Russian providers are actively using this network cable for the Internet. According to IT experts, with the expectation that the relevant investment will pay off in the future.
Evolution of cable infrastructure
With the example of the three mentioned types of cables, we can trace some evolution in the aspect of building the infrastructure of computer networks. So, initially when data was transmitted via the Ethernet standard, it was coaxial structures that were involved. In this case, the maximum distance to which a signal could be sent from one device to another did not exceed 500 meters. The maximum data transfer rate on the coaxial cable was about 10 Mbit / s. The use of twisted pair has significantly increased the dynamics of file sharing in computer networks - up to 1 Gbit / s. Also, it was possible to transmit data in duplex mode (one device could both receive signals and send them). With the advent of fiber, the IT industry was able to transfer files at a speed of 30-40 Gbit / s or more. In many respects thanks to this technology, computer networks successfully connect countries and continents.
Of course, when working with a PC, many other types of cables used in the installation of computer networks are used. Theoretically, for similar purposes, you can use, for example, a USB cable, though it will not be very effective, in particular, due to the fact that within the USB standard, data can be transmitted for a short distance - about 20 m.
How to connect a twisted pair
Twisted-pair, as we noted above, is today the most common type of cable for the design of computer networks. However, its practical use is characterized by some nuances. In particular, they reflect such an aspect as the pinout of the network cable, which we mentioned above. It is important to know how to properly place the wires in the area of their contact with the RJ-45 connector. The procedure by which a twisted pair is connected to the corresponding element is called crimping, since in the course of its carrying out a special tool is used that presupposes a force effect on the structure.
Nuances of crimping
During this procedure, the connectors are securely fixed to the ends of the twisted pair. The number of contacts in them corresponds to the number of cores - in both cases there are 8 such elements. There are several schemes within which a twisted pair can be crimped.
Next, we will consider the relevant specifics. But to begin with, the person who works with the cable should take the connectors in their hands correctly. They should be held so that the metal contacts are located on top.
Plastic latch should be directed towards the one who carries out crimping. On the left in this case will be the 1st contact, on the right - the 8th. Numbering is an extremely important nuance of working with a twisted pair. So, what kind of crimping schemes are used by network infrastructure specialists?
First, there is a network cable scheme, called EIA / TIA-568A. It assumes the location of the cores in relation to the metal contacts of the connector in the following order:
- for 1 contact: white-green;
- for the 2-nd: green;
- for the third: white-orange;
- for the 4th: blue;
- for the 5th: white-blue;
- for the 6th: orange;
- for the 7th: white-brown;
- for the 8th: brown.
There is another scheme - EIA / TIA-568B. It assumes the arrangement of the veins in the following order:
- for 1 contact: white-orange;
- for the 2nd: orange;
- for the third: white-green;
- for the 4th: blue;
- for the 5th: white-blue;
- for the 6th: green;
- for the 7th: white-brown;
- for the 8th: brown.
How to connect the network cable to the connector, you now know. But it is useful to study the specifics related to various schemes for connecting a twisted pair to one or other device.
Crimp and connection type
For example, when connecting a PC to a router or switch, you must use a direct connection method. If there is a need to organize the exchange of files between two computers without using a router, then you can use the cross-connect method. The difference between the marked schemes is small. With a direct connection method, the cable must be crimped with the same pin. When crossed, one end is 568A, the other 568B.
A twisted pair is characterized by one interesting feature. With a direct connection scheme, the device can use not 4 pairs of conductors, but 2. That is, with the help of one cable it is permissible to connect two computers at the same time to the network. Thus, you can save on the cable or make a connection, if it is very necessary to do it, and there is no twisted pair at hand. However, in this case, the maximum data rate will not be 1 Gb / s, but 10 times less. But to organize the work of a home network, this is acceptable in most situations.
How in this case to distribute veins? Regarding the contacts on the connectors for connecting the first computer :
- 1 contact: white-orange vein;
- 2nd: orange;
- 3rd: white-green;
- 6th: green.
That is, 4, 5, 7 and 8 cores are not used in this scheme. In turn, on the connectors for connecting the second computer:
- 1 contact: a white-brown vein;
- 2nd: brown;
- 3rd: white-blue;
- 6th: blue.
It can be noted that when implementing a cross-connection scheme, you should always use all 8 conductors in a twisted pair. Also, if the user needs to implement data transfer between devices at a speed of 1 Gbit / s, the pinout will need to be carried out according to a special scheme. Let's consider its features.
Cross-connection at gigabit speed
The first connector of the cable should be crimped in accordance with diagram 568B. The second assumes the following comparison of cores and contacts on the connector:
- 1 contact: white-green vein;
- 2nd: green;
- 3rd: white-orange;
- 4th: white-brown;
- 5th: brown;
- 6th: orange;
- 7th: blue;
- 8th: white and blue.
The circuit is quite similar to the 568A, but it changes the position of the blue and brown pairs of conductors.
Compliance with the noted rules for correlating the color of wires and contacts on the 8P8C connector is the most important factor in ensuring the functionality of the network infrastructure. The person designing it needs to be careful when installing the relevant elements. It happens that the computer does not see the network cable - this is often due to the incorrect crimp of the twisted pair.
How to properly compress the cable
Let's consider some technical nuances. The main device, which in this case is involved, is the crimper. It is similar to pliers, but it is adapted to work with computer cables of the appropriate type.
The design of the crimper requires the presence of special knives, designed to cut the structure. Also sometimes crimpers are equipped with a small device for stripping the insulation of twisted pair. In the central part of the tool - special nests, adapted to the thickness of the cable structure.
The optimal algorithm for the actions of a person squeezing a twisted pair can be as follows.
- First of all, it is necessary to cut off a cable section of a suitable length - its exact measurements will thus be required.
- After this, remove the external insulation - approximately 3 cm at the end of the cable. The main thing at the same time is not to damage the insulation of the veins by accident.
- Then it is necessary to arrange the conductors in relation to the connection diagrams to the connector discussed above. After smoothly cut the ends of the strands, so that the length of each of them outside the outer layer of insulation was about 12 mm.
- Next, you need to put the connector on the cable so that the wires remain in the order that corresponds to the connection scheme, and each of them entered the desired channel. The veins should be moved until the resistance of the plastic wall of the connector is felt.
- After the appropriate placement of the cores inside the connector, the PVC sheath must be located inside the connector housing. If this can not be done, it may be necessary to pull the veins and slightly shorten them.
Once all the elements of the structure are positioned correctly, you can crimp the cable by inserting the connector into a special socket on the crimper and gently pressing the tool handle all the way.