ZyXEL VES1724-56B2 User Guide - 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) VDSL CO (A) No-DPBO DPBO Line2 (600m) ADSL CPE (B) Line1 (150m) VDSL CPE (A) 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. Table 28 Real Length to Electrical Length CABLE TYPE REAL LENGTH TO ELECTRICAL LENGTH A 22 AWG =16.2 x (cable length in kilometer) 0 24 AWG =20.5 x (cable length in kilometer) 0 26 AWG =25.8 x (cable length in kilometer) 0 B 0 1 1.0039065 C 0 0 -0.0039065 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 VES1724-56 User's Guide