ZyXEL Communications IES4005M User Manual page 168

Chapter 24 VDSL
Figure 43 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 of DPBO settings
as mentioned in
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, if the distance is 1 kilometer
and you use 24 AWG cable type, the electrical length 20.5 dB is recommended.
The following table displays the calculation from a real length to an electrical length.
Table 114 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 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.
RFI (Radio Frequency Interference)
RFI is induced noise on the lines by surrounding radio frequency electromagnetic radiation from
sources such as AM and HAM radio stations. Since VDSL uses a much larger frequency range that
overlaps with other radio frequency systems, signals from VDSL lines and other radio systems
interfere with each other. To avoid performance degradation due to RFI, set the switch to not
transmit VDSL signals in the RFI band defined by the regulatory bodies (ETSI and ANSI). You can
also configure your own RFI bands on the system.
168
VDSL
CO (A)
No-DPBO
DPBO
Section on page 167. The electrical length is used instead of the real physical
REAL LENGTH TO ELECTRICAL LENGTH
=16.2*(cable length in kilometer)
=20.5*(cable length in kilometer)
=25.8*(cable length in kilometer)
ADSL
Line 2 (600 m)
CPE (B)
VDSL
Line 1 (150 m)
CPE (A)
A B
0 0
0 1
0 1.0039065
C
0
0
-0.0039065
IES4005M User's Guide