ZyXEL Communications VES-1616F-44, User Manual

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VES-1616F/1624F-44 User’s Guide
Chapter 6 Basic Setting 73
6.8.2 Configured Versus Actual Rate
You configure the maximum rate of an individual VDSL port by modifying its profile (see the
VDSL Profile Setup screen) or assigning the port to a different profile (see the Port Setup
screen). However, the actual rate varies depending on factor such as transmission range and
interference.
6.8.3 PSD
PSD (Power Spectral Density) defines the distribution of a VDSL line’s power in the
frequency domain. A PSD mask is a template that 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.