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Attenuation defines a signal’s loss over distance. As a signal travels down a cable, it loses strength. The unit “dB,” or decibel, defines the amount of attenuation by measuring a signal’s strength. Factors that influence attenuation include conductor size, material type, and frequency of operation and distance. Lower values are better.
POWER SUM NEXT
Power Sum NEXT (near-end crosstalk) indicates the effect that the energized pairs have on the non-energized pair. Good numbers are critical in applications such as Gigabit Ethernet that require 4-pair technology (full-duplex mode).
FEXT (far-end crosstalk) is crosstalk measured at the end of the cable opposite the signal source. ELFEXT measurements compensate for the effects of varying cable lengths so that all cable can be certified to the same limit. Without good ELFEXT numbers, a channel less than 100 meters can suffer increased collisions, retries and server utilization, slowing a network and causing lost sessions or network drop-offs.
ACR (attenuation-to-crosstalk ratio) shows the usable bandwidth of a system. Also expressed in decibels, larger ACR numbers indicate more usable bandwidth.
Propagation delay is the time interval required for the signal to be transmitted from one end of the circuit to the other.
Return loss indicates how much signal will be lost due to reflected energy, also known as echo. Return loss becomes a factor in full-duplex transmission because a portion of the signal is “reflected” back to the transmitting end, disrupting transmission. Return loss can result in signal jitters, meaning dropped packets, more transmissions, slower speeds and frustrated users.
ACR (attenuation-to-crosstalk ratio) shows the usable bandwidth of a system. Also expressed in decibels, larger ACR numbers indicate more usable bandwidthDelay skew defines the timing difference of the slowest and fastest pairs in a multi-pair signal traveling down a cable. When all four pairs are activated, it is important that the signals arrive close to the same time. When the difference in time is too great, the receiving device is unable to reassemble the signal. This will ultimately cause errors and lost data.