ZyXEL Communications VDSL SWITCH VES-1616F-3X, Руководство пользователя

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Chapter 6 Basic Setting
VES-1616F-3x Series User’s Guide
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6.8.3 PSD
PSD (Power Spectral Density) defines the distribution of a VDSL line’s power in the
frequency domain. A PSD mask specifies the maximum allowable PSD for a line.
6.8.4 UPBO
In a network with varying telephone wiring lengths, the PSD on each line is different. This
causes crosstalk between the lines. Enable UPBO (Upstream Power Back Off) to allow the
switch to adjust the transmit PSD of all lines based on a reference line length so that the PSD
at the receiving end is the same.
6.8.5 Latency Modes
There are two latency modes: interleave and fast.
• Interleave
Interleave delay is the wait (in milliseconds) that determines the size of a single block of
data to be interleaved (assembled) and then transmitted. Interleave delay is used when
transmission error correction (Reed- Solomon) is necessary due to a less-than-ideal
telephone line. The bigger the delay, the bigger the data block size, allowing better error
correction to be performed.
Reed-Solomon codes are block-based error correcting codes with a wide range of
applications. The Reed-Solomon encoder takes a block of digital data and adds extra
"redundant" bits. The Reed-Solomon decoder processes each block and attempts to correct
errors and recover the original data.
• Fast
Fast mode means no interleaving takes place and transmission is faster (a “fast channel”).
This would be suitable if you have a good line where little error correction is necessary.
6.8.6 Rate Adaption
Rate adaption is the ability of a device to adjust from the configured transmission rate to the
attainable transmission rate automatically depending on the line quality. The VDSL
transmission rate then stays at the new rate or adjusts if line quality improves or deteriorates.
The switch determines line quality using the Signal-to-Noise Ratio (SNR). SNR is the ratio of
the amplitude of the actual signal to the amplitude of noise signals at a given point in time. A
low SNR indicates poor line quality.
If you disable transmission rate adjustment and the attainable speeds cannot match configured
speeds, then the VDSL link may go down or link communications may be sporadic due to line
errors and consequent retransmissions
Enable the switch to adjust to a new lower rate when the line quality deteriorates until the
connection is broken. The switch will first disconnect and then re-establish the line connection
to maintain connectivity. However, the new line rate might be lower or higher than the
configured line rate.