Triple-Play Service Deployment

Chapter 4: Troubleshooting the Copper Plant for IP Services
Wideband Noise
High frequency noise can have a negative impact on xDSL service,
causing bit errors or in the worst case complete loss of synchronization
between the ATU-R and ATU-C. The table below lists
common noise sources and the corresponding frequencies and
tones. To measure noise, use a test set capable of wideband noise
measurements rather than one designed only for voice-band
noise measurements. It should support noise measurement
across the wideband range up to 30MHz to cover the ADSL/2/2+
and VDSL1/2 frequency spectrums.
Noise Source Noise
Frequency (kHz)
ADSL Tone # Tone Frequency (kHz)
ISDN BRI 40 9 38.8125
HDSL passband center 196 45 194.0625
HDSL passband max 392 91 392.4375
HDSL2 274 64 276
T1 passband center 772 179 772
E1 passband center 1024 237 1022
Table 4.2 Noise sources and tones
To filter only for noise that will affect ADSL, the technician must set
the tester use a “G” Filter. For VDSL2, use of a test set that has
selectable filters applicable to the VDSL band plan in use is
essential. However, the standards bodies have not yet defined
filters that adequately cover the VDSL spectrum. JDSU has defined
a set of “J” filters which do cover the VDSL spectrum. For example,
the J-20K8 filter, which provides a 20KHz to 8MHz band width,
should be selected for noise testing of VDSL pairs employing this
band plan. To ensure accuracy, the far end should be terminated
with a 100 Ω resistance for any noise measurement. Wideband
noise is measured in dBm, and is usually a number below zero. For
example, the maximum noise depends on the attenuation and
desired line rate. A typical requirement for VDSL is that measured
wideband noise should be below -50 dBm.
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