Chapter 6 Basic Setting

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.

6.8.6Rate 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.

76

 

VES-1616F-3x Series User’s Guide