Twisted pair cable

Color code table of 25 pairs

In telecommunications, twisted pair cable is a type of cable that has two insulated electrical conductors intertwined to cancel out interference from outside sources and crosstalk from adjacent cables. It was invented by Alexander Graham Bell in 1881.

Description

Twisted pair cable consists of groups of copper wires twisted together in pairs in a helical fashion. This is done because two parallel wires make up a simple antenna. When the wires are helically intertwined, the waves cancel, so the interference produced by them is reduced, which allows better data transmission.

Thus, the interleaved form allows to reduce electrical interference both outside and from nearby pairs and allows data to be transmitted more reliably. A twisted pair cable is made up of a group of twisted pairs (usually 2, 4 or 25 pairs), covered by an insulating material. Each of these pairs is identified by a color.

The intertwining of cables that carry a signal in differential mode (that is, one is the invert of the other), has two main reasons:

1. If the waveform that travels through a cable is A(t) And in the other is -A(t) and n(t) is added noise equally on both cables during the road to the receiver, we will have: A(t) + n(t) on one cable and the other -A(t) + n(t) When making the difference in the receiver, we'll be with 2A(t) and we will have removed the noise (reject to the common mode).
2. If we think of the magnetic field that will produce this current in the cable and we take into account that one is next to the other and that in the other the current will go in the opposite direction, then the senses of the magnetic fields will be opposite and the module will be practically the same, so we will remove the fields outside the cable, thus avoiding any parasite current in nearby cables.

History

In the history of telecommunications, twisted pair cable has played a fundamental role. This type of cable is the most common and originated as a solution to connect telephones, terminals and computers on the same wiring, since it is enabled for data communication allowing transmissions with higher frequencies. Previously, in Europe, telephone systems used untwisted pair cables to communicate.

Early telephones used telegraph lines, or open single-conductor wires from ground circuits. In the 1880s, electric streetcars were installed in many cities in the United States, which induced noise on these circuits. Lawsuits on this issue being futile, the telephone companies turned to balanced circuit systems, which had the added benefit of reduced attenuation, and therefore provided greater range.

When electric power distribution became increasingly common, this measure proved insufficient. Two cables, strung on either side of the crossbars on utility poles, shared the route with the electrical power lines. Within a few years, the increasing use of electricity brought increased interference again, so engineers devised a method called "conductor transposition" to cancel out the interference.

In this method, the conductors swapped their position once for every several poles. In this way, the two cables would receive similar electromagnetic interference from power lines, but alternatively through one or the other cable. This represented a rapid implementation of braiding, at the rate of about four braids per kilometer, or six per mile. These balanced open-wire lines with periodic transpositions still exist today in some rural areas of the United States.

Twisted pair cables were invented by Scotsman Alexander Graham Bell in 1881 who filed an application with the United States Patent Office on June 4 of that year, being granted one month and 15 days later. In 1900, the entire American telephone line network was either twisted pair or open wire with the transposition to interference protection. Today, most of the millions of kilometers of twisted pairs in the world are fixed in overhead facilities, owned by telephone companies, and used for voice service, and are only handled or even seen by telephone workers.

Twisted Pair Cable Types

Armoured braided pair cable (STP)

• Unshielded twisted pair (UTP) or non-screened or non-armoured pair cable: Contains braided pairs that are used for different local network technologies. It is low cost and easy to use, but it produces more errors than other cable types and has limitations to work large distances without signal regeneration. Its characteristic impedance is 100 ohms.
• Shielded twisted pair (STP) or braided or armored pair cable: Contains braided pairs surrounded every pair of a protective cover made of aluminum. It is used in computer networks such as Ethernet or Token Ring. It is more expensive than the armorless version and its characteristic impedance is 150 ohms.
• Foiled twisted pair (FTP) or braided pair cable with global display: Contains braided pairs, all surrounded by a protective cover made of aluminum. It is similar to the previous case but the latter is more used in outdoor wireless equipment. its characteristic impedance is 120 ohms.

Categories

The specification 568A Commercial Building Wiring Standard of the EIA/TIA (Electronic Industries Alliance (EIA) and the Telecommunications Industry Association (TIA) specifies the type of UTP cable that will be used in each situation and construction.Depending on the transmission speed, it has been divided into different categories according to this table:

Transmission characteristics

You are limited in distance, bandwidth and data rate. Also note that attenuation is a function strongly dependent on frequency. Interference and external noise are also important factors, which is why external coverings and braiding are used. For analog signals, amplifiers are required every 5 or 6 kilometers, for digital signals every 2 or 3. In point-to-point analog signal transmissions, the bandwidth can reach up to 250 kHz. In long-distance digital signal transmission, the data rate is not too large, it is not very effective for these applications or devices. In local networks that support local computers, the data rate can reach 10 Mbps (Ethernet), 100 Mbps (Fast Ethernet), 1 Gbps (Gigabit Ethernet), and 10 Gbps (10 Gigabyte Ethernet).

Available settings

• Cross-Setting: This end-of-wire configuration in the RJ45 connector is used when we want to connect two devices equal to the same cable, such as a PC with another PC.
• Direct configuration: This end-of-wire configuration in the RJ45 connector is used when we want to connect two different devices with the same cable, such as a PC with a Switch.

Advantages and Disadvantages

Advantages

• Low cost in your hiring.
• High number of workstations per segment.
• Facility for performance and troubleshooting.
• It may be previously wired anywhere or anywhere.

Disadvantages

• High-speed error rates.
• Limited bandwidth.
• Lower immunity to noise.
• Low immunity to the diaphony.
• High cost of equipment.
• Limited distance (100 meters per segment).

Wiring Certification

ANSI/TIA/EIA-568-B.2 establishes certification parameters for the following items:

WIRE MAP: Checks that the wire map matches the installation check standard performed.

LENGTH: The length in all pairs of the cable tested based on the propagation measurement, its delay and the average NVP value. A copper cable structure may not exceed 99m, and in the case of FO it will depend on the type of fiber used.

INSERTION LOSS: Also called ATTENUATION, it checks the signal loss of the links due to their insertion.

NEAR-END CROSS-TALK LOSS: It is specified as NEXT (near end cross talk) and measures the interference that one pair makes over another at the same near end. Check pair by pair with their respective nearby this interference or induction. It is measured over the entire frequency range.

TOTAL NEAR-CARD LOSSES: Called PSNEXT, it performs a check on how the combined data transmission by the rest of the nearby pairs affects a pair, therefore it should be performed for a pair with the 8 pairs that make up the cable. It is measured over the entire frequency range.

NEAR-END CROSS-TALK LOSS PAIR-TO-PAIR: FEXT (far end cross talk) measures the interference that a pair of wires at the far end causes on the affected wire pair at the same end. ELFEXT measures the intensity of the near-end crosstalk at the far end relative to the attenuated signal arriving at the end of the cable. 24 pairs of possible combinations are produced and tested.

TOTAL NEAR-END CLEARANCE LOSSES (PSELFEXT): ELFEXT is a combined parameter that combines the effect of the FEXT of three pairs with respect to a single pair, PSELFEXT will perform the sum of all these combinations.

RETURN LOSS: RETURN LOSS measures the total loss of energy reflected in each pair of wires. It is measured at both ends and in each pair, and all for the entire frequency range.

DELAY SKEW CERTIFICATION: This parameter displays the difference in propagation delay between the four pairs. The pair with the smallest propagation delay is the biased delay reference 0.

Facilities that have these parameters within the ranges specified by ANSI/TIA/EIA-568-B.2 are called certified facilities. There is specific instrumentation that performs these checks in a few seconds; however, this certification must be carried out at all network ports, so certifying an installation can be arduous and extended work over time.

Minor variants of twisted pair cable

• Braided piece: it is a braided pair that is intentionally added inductance, very common in telecommunications lines, except for some frequencies. Added inducers are known as Pupin coils and reduce distortion.
• Braided joint: A variant of the braided pair cable in which the pairs are joined individually to increase the robustness of the cable. The electrical specifications of the cable are maintained despite rude handling.
• Tape braided cable: it is a variant of the tape cable standard where the adjacent drivers are in slave mode and braided. The braided pairs are slightly slaves of each other in tape format. Periodically, along the tape there are small sections without braiding to allow connectors and printed circuit headers to be finished using the usual IDC tape cable techniques.