Parameters in Structured Cabling Certification

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The certification process of structured cabling network, is composed of twisted-pair cables (balanced) or optical fibers, requires specialized equipment and involves a number of parameters determined by ANSI / TIA-568-C (2009). Certifiers cables Fluke Networks (figure), for example, are global benchmark.

Fonte: Fluke Networks®

A number of tests required by the standard, the list:

• Termination setting (Wire Map)
• Cable Length
• Insertion loss (attenuation)
• Return Loss (impedance)
• Crosstalk (NEXT), PS-NEXT, ELNEXT and PS-ELNEXT
• Relationship Attenuation / Crosstalk (ACR)
• Vegetable propagating delay (Delay)
• Deviation in the propagation delay (Delay Skew)

The wiring pattern mapping is the simplest of them, and is to ensure that the wires sequence of the RJ-45 twisted pair cable connectors are in accordance with the T568A or T568B standard, as seen in the figure below.

I often organize other parameters in the following categories:

• crosstalk
• Impedance
• Mitigation

The crosstalk and crosstalk (crosstalk English) occurs when a particular wire pair produces another pair interference in nearby, either in the same or another cable. Crosstalk may receive multiple ratings, then I will detail the key in the sequence below:

• NEXT or Crosstalk
• FEXT and Far End Crosstalk
• AXT
• PS-NEXT
• PS-FEXT
• Etc...

The NEXT (Near End CrossTalk) or crosstalk concerns the interference between wire pairs at the same end of the same cable. It is a very sensitive parameter and higher values ​​indicate less noise (interference). In fact the results of the measured values ​​is negative, but the equipment that make the measurement does not show this negative signal. So a result of 30dB (-30dB) indicates less interference than a result of 10dB (-10dB).

The FEXT (Far End CrossTalk) or Far End Crosstalk respect to interference between wire pairs at opposite ends of a cable. The FEXT is not as serious as the NEXT because the crosstalk that occurs away from the transmitter creates less noise. The AXT (alien crosstalk) concerns the impact of interference between different pairs of wire cables that pass through the same conduit, for example when subjected to excessive pressure.

The PS-NEXT and PS-FEXT (PS Power Sum) consider the signal interference sum invested in three pairs on the fourth pair and are important in modern networks that use all four pairs of wires. In Fast Ethernet (100 Mbps) that uses only 1.2 pairs (TX) and 3.6 (RX), the crosstalk test between green and orange pairs (V - L) is sufficient because the other pairs are unused and do not generate interference. In the technology Gigabit Ethernet (1 Gbps) that uses all four pairs of wires in data transmission, the NEXT and FEXT traditional tests must be performed between all the possible pairs, which are:

• V - L
• V - A
• V - M
• L - A
• L - M
• A - M

Legenda: V (Verde), L (Laranja), A (Azul) e M (Marrom).

Impedance is a measure of the resistance (in ohms, Ω) should be uniform along the cable and connectors. The ANSI / TIA-568-C urges caution in excessive traction for drivers, unnecessary amendments and distortions of the cables because these actions impact negatively on the value of impedance, whose tolerance limit is 15%. For the record, the reference standard of a twisted-pair Cat5e cable is 100Ω.

Attenuation is expressed in dB and represents the reduction of signal amplitude along the cable (loss). Also degrades at higher frequencies, for which reason the devices do a measurement with different frequencies ranging from 64kHz to 100MHz (the CAT5e cable) or more in other categories.

Hug.

FreeGprsNetwork Team

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Parameters in Structured Cabling Certification