Chapter 9 VDSL Setup
VES1724-56 User’s Guide
100
signal with higher attenuation. With DPBO enabled on the CO (A), it decreases the PSD level and
reduces the crosstalk impact on other service lines.
Figure 52 DPBO Resolves Downstream Far-End Crosstalk
UPBO/DPBO Electrical Length
The distance between a cabinet and the central office is an important parameter in UPBO/DPBO
settings as we mentioned in the DPBO section on page 99. The electrical length is used instead of
the real physical distance according to G.997.1 format. Depending on the cable type the line used
and physical line length, you can calculate the electrical length (in dB). For example, the distance is
1 kilometer and you use 24 AWG cable type, the electrical length 20.5 dB is suggested to be used.
The following table displays the calculation from a real length to an electrical length.
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 ration of signal
power to noise power. A low SNR indicates poor line quality.
SOS
SOS is a system for realizing emergency rate reduction. In a DSL system, especially in VDSL2 that
uses wider frequency bandwidth and is deployed in the shorter loop than ADSL, far-end crosstalk
(FEXT) may cause bursts of CRC errors and force CPE devices to retrain. SOS efficiently removes or
Table 28 Real Length to Electrical Length
CABLE TYPE REAL LENGTH TO ELECTRICAL LENGTH A B C
22 AWG =16.2 x (cable length in kilometer) 0 0 0
24 AWG =20.5 x (cable length in kilometer) 0 1 0
26 AWG =25.8 x (cable length in kilometer) 0 1.0039065 -0.0039065
VDSL
CPE (B)
Line1 (150m)
Line2 (600m)
No-DPBO
DPBO
ADSL
CO (A)
ADSL
CPE (A)
VDSL
CO (B)
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