ZyXEL Communications VES1724-56 User Manual page 100

Chapter 9 VDSL Setup
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
ADSL
CO (B)
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
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.
Table 28 Real Length to Electrical Length
CABLE TYPE
22 AWG
24 AWG
26 AWG
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
100
VDSL
CO (A)
No-DPBO
DPBO
DPBO section on
REAL LENGTH TO ELECTRICAL LENGTH
=16.2 x (cable length in kilometer)
=20.5 x (cable length in kilometer)
=25.8 x (cable length in kilometer)
ADSL
Line2 (600m)
CPE (B)
VDSL
Line1 (150m)
CPE (A)
page 99. The electrical length is used instead of
A B
0 0
0 1
0 1.0039065
C
0
0
-0.0039065
VES1724-56 User's Guide