Detailed interpretation of the concept of integrated cabling

In view of the current domestic structure of integrated wiring in the field of staff quality is uneven, the test methods and testing standards of the understanding of the deviation, this newspaper will be in the wiring system testing of the parameters involved in the test and the principle of some brief introduction, in order to stimulate the domestic industry elite to express ideas, Jointly promote the development of wiring industry.
If the new test standard of class five and six can be launched in the first quarter of next year according to the original plan of TIA, the domestic wiring product provider will face a severe test. The new test standard will add several parameters, such as equal-level remote crosstalk (elfext), Echo loss (return loss short loss), delay difference (Delay Skew). These new parameter requirements will make the previous one-person supervision, a few people construction wiring method becomes history, wiring dealer hand in the first five types of cable testing equipment will be eliminated. Testing will become an integral part of a cabling project.
According to the requirements of TSB-67 standard, four parameters, including wiring diagram, length, attenuation, and near-end crosstalk, should be included in the verification Test index of the structured cabling system. ISO also requires an additional parameter, ACR (attenuation to crosstalk). In view of the current development trend of the network and the gradual popularization of line six, Tia has made a supplement to the Test standard and test parameters of the integrated wiring system this year. Additional test parameters include:---http://bianceng.cn (learning computer)
　　
Wiring diagram
Length measurement

Near-end crosstalk (NEXT)

Cumulative Power NEXT (Powersum next,psnext)

Attenuation Amount (attenuation)

Attenuation to crosstalk ratio (attenuation Crosstalk RATE,ACR)

Distal crosstalk (fext) and the equal-level distal crosstalk (elfext)

Propagation delay (propagation Delay)

Delay variance (Delay Skew)

Structural return loss and return loss
　　
Frequency bandwidth
　　
Impedance (impedance)
　　
DC Loop Resistor
　　
Miscellaneous News
Wiring diagram
Wiring diagrams are used to indicate the way the wiring is wrong. Wiring diagrams of four to eight cores per cable can be expressed as:
　　
Correct pressure line position at each endpoint
　　
Whether or not the remote conduction
　　
Short circuit with two or more cores
　　
Staggered line Pair
　　
Reverse Line pair
　　
Bifurcation line pair
　　
Various other wiring errors
　　
The reverse is the polarity opposite to the end of the line pair. Interleaving refers to the two lines of the distal end to each other. Bifurcation means that each core line is in a one-to-one manner, but the physical line is separated from the location. In particular, the reader is reminded that the bifurcation line pair is often present, but the use of simple on-off instruments can not be accurately found out the wiring fault. In the 10BASE-T network, this kind of wiring fault because the network to the wiring system's request is looser but to the network overall operation does not have the big influence, but the high speed Ethernet test instrument, like 100BASE-TX test instrument Wiring Diagram Test function must be able to discover this kind of error. As the five types of verification equipment is expensive, users can choose the United States Microtest Company production of local area network detection instrument Microscanner, the instrument can comprehensively detect a variety of wiring problems, cheap and convenient and practical.

Length measurement
A test technique called TDR (Time Domain reflection measurement) was used to measure the length of copper cables. The tester emits a pulse wave from one end of the copper cable, and when the pulse waves travel, if the impedance changes, such as open circuit, short circuit, or abnormal wiring, some or all of the pulse wave energy will be reflected back to the tester. Based on the delay time of the back and forth pulse wave and the rate of NVP (rated propagation rate) of the known signal propagating in the copper cable, the tester can calculate the length of the pulse wave receiving end to the pulse wave return point. The NVP is expressed as a percentage of the speed of light (c), such as 0.75c or 75%.
The amplitude of the returned pulse wave is proportional to the degree of the impedance change, so a relatively large echo is returned in places where the impedance varies greatly, such as open or short circuit. The impedance variation (impedance anomaly) produced by bad contact produces a small amplitude echo.
The length of the measurement is accurate, depending on the NVP value. Therefore, the NVP value of the tester should be corrected with a known length data (which must be over 15 meters). But the precision of TDR is very difficult to reach 2%, at the same time, in the same cable of the NVP value between the lines, there are 4-6% differences. In addition, twisted-pair wires are also longer than the actual length of a cable itself. Pulse waves that run in longer cables can become jagged, which can also produce a nanosecond error. These are the factors that affect the accuracy of TDR measurement.
The pulse wave width of the tester is about 20 nanoseconds, and the propagation rate is about 3 nanoseconds/m, so the pulse wave is at 6 meters, which is the time when the pulse waves leave the tester. This is the tester in the measurement of the length of the "blind zone", so the length of the measurement will not be able to find the 6 meters may occur in the wiring problem (because there is no echo).
The tester must also be able to display the length of each line pair at the same time. If you can only get the length of a cable, it does not mean that each line pair is the same length.
Some of the early testers did not measure the length by TDR, but instead measured the change in the impedance by measuring the return loss in a frequency-domain way to calculate the length, which would be misjudged when the lines appeared to be of varying lengths.
Near-end crosstalk (NEXT)
When current flows through a wire, a certain electromagnetic field is generated that interferes with the signal on the adjacent conductor. The higher the frequency, the greater the effect. Twisted pair is the use of two wire stranded together, due to phase difference of 180 degrees to offset the interference between each other. The tighter the offset, the better the offsetting effect, and the higher the data transmission rate can be supported.
A near-end crosstalk is a crosstalk signal that is sensed from the sending line to the receiving end at the same side as the sender. When the crosstalk signal is too large, the receiver will not be able to determine whether the signal is a faint signal transmitted from the remote or crosstalk noise.
It should be noted that the greater the value (such as 45dB) of the lower next, the greater the difference between the signal sent and the crosstalk signal, the smaller the value of the high next (such as 20dB), which is to be avoided.
In order to meet the 5 specifications, the cable end of the non-stranded part of the length can not exceed 13 meters. The reasons that usually result in excessive next are:
　　
Use a jumper that is not a stranded wire.
　　
The terminal is not pressed according to the regulation.
　　
Use the old-fashioned 66 wiring block.
　　
Use a non-data-level connector.
　　
Use a voice-level cable.
　　
A coupler that uses a socket to the socket.
　　
In addition, note that when you measure the next value at both ends of the link, especially when the length is greater than 40 meters, the remote crosstalk is offset by the attenuation of the link, and the next value cannot be measured at the proximal end. The next value measured at both ends of the link is not the same, so all test criteria require that the next value be measured at both ends of the link.
Attenuation Amount (attenuation)
The intensity of the signal decreases with the length of the cable, which is called attenuation. It is expressed as a negative decibel number (db). The larger the number indicates the greater the attenuation, that is, the -10db is weaker than the -8db signal, in which the difference of 6dB indicates that the signal strength of the two is twice times different. For example, the -10db signal is twice times stronger than the -16db signal, four times times stronger than the -22db. The factors that affect attenuation are skin effects and insulation loss.
At a high frequency, the current density of the current in the conductor is no longer distributed evenly across the conductor, but is concentrated on the surface of the conductor, thereby reducing the current loss caused by the cross-section of the conductor. The skin effect is proportional to the square root of the frequency, so the higher the frequency, the greater the attenuation. This is why a single-strand cable is better conductive than a multiple-strand cable.
Temperature can also have an effect on the attenuation of some cables. Some insulating materials absorb the current that flows through the conductor, especially the PVC material used in the Category 3 cable, because the chlorine atoms of the PVC produce a pair of poles in the insulating material, and the oscillation of the dipole causes the electrical signals to lose part of the power. This situation can deteriorate further when the temperature is high. The higher the temperature, the more intense the oscillation of the bipolar oscillator, the greater the attenuation. That's why the standard temperature is 20 ℃.
In measuring attenuation, it is necessary to determine that the measurement is one-way, rather than measuring the amount of the loop attenuation, and then dividing the value by 2.
Attenuation to crosstalk ratio (ACR)
Because of the attenuation effect, the receiving end receives the weakest signal, but the receiver is also the strongest crosstalk signal. For unshielded cables, crosstalk is the most important noise that is sensed from the transmitter itself. The so-called ACR refers to the difference between crosstalk and attenuation amount. ACR reflects the performance of the cable, which is the richness of the signal at the receiving end, so the greater the ACR value the better. ACR targets are set in both ISO and IEEE standards, but Tia/eia 568A does not mention it.
Because the next value for each pair of pairs is not the same, the ACR value for each pair of pairs is also different. The ACR value of the cable is measured at the lowest ACR value. If it is compared to psnext, it is represented as a PSACR value.
Distal crosstalk (fext) and equal-level remote crosstalk (Elfext)
The fext is similar to next, but the signal is emitted from the near end, while crosstalk noise is measured remotely. Fext must also be measured from both ends of the link.
However, Fext is not a very effective test indicator. The length of the cable will have a significant effect on the measured Fext value because the intensity of the signal is related to the crosstalk caused by it and the attenuation of the signal at the transmitter end. Therefore, two of the same cable, because the length of different fext value, so it must be measured elfext value to replace the Fext value of the measurement. Exfext value is actually the Fext value minus the attenuation value, you can also understand the elfext as a remote ACR. Of course, as with Psnext, the Pselfext value corresponds to the Elfext value.
In order to measure Elfext, the dynamic range (sensitivity) of the tester must be 20dB lower than the measured signal.
Cumulative power Next (Powers Sum next)
Psnext is actually a formula, not a measurement step. The Psnext value is the algebra and derivation of the crosstalk of 3 pairs of lines against another pair of lines. Psnext and Elfext measurements are important test parameters for networks such as Gigabit Ethernet, which must use four pairs of wires to transmit signals. There are four sets of psnext values on each link.
Propagation delay (propagation Delay)
Propagation delay is the time required for a signal to pass from one end of the cable to the other, and it is also proportional to the NVP value. General 5-Class UTP latency is around 5~7 nanosecond (ns) per meter. ISO stipulates that the worst time delay for a 100-metre link is 1 microseconds (US). Delay time is one of the main reasons why a LAN has to have a length limit.
Delay variance (Delay Skew)
Delay variance is the transmission time difference between the maximum propagation delay and the smallest line pair in a UTP cable. Some cable manufacturers take into account the shortcomings of copper materials, a pair or two pairs of line pairs of other materials, which will produce a greater time difference. In particular, when running Gigabit Ethernet applications, too much time difference can result in simultaneous signals from four lines not reaching the receiving end at the same time. General requirements in the 100-meter link within the maximum time difference is 50 nanoseconds, but preferably within 35 nanoseconds.
Structural loss of return
The structural loss (Srl,structural return Loss) measures the consistency of the cable impedance. Because the cable's structure cannot be completely consistent, it can cause a small change in impedance. The variation of the impedance will cause the signal to wear out. Structural loss is associated with the design and manufacture of cables, and is not as often affected by the quality of construction as next. The SRL is expressed in db, and the higher the value, the better. Finish