Triple-Play Service Deployment

Chapter 4: Troubleshooting the Copper Plant for IP Services
Max. Downstream Speed (Mbps)
100
50
45
40
35
30
25
20
15
10
5
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Loop Length (k ft)
Figure 4.3 xDSL downstream speed as a function of loop length
VDSL2
VDSL
ADSL2+
ADSL2
One way to test loop length is to use an opens meter on a
disconnected pair. An opens meter measures capacitance, and
since cable specifications in North America require that all wiring
used for outside plant have a constant capacitance of .083 mf per
mile between tip and ring, an opens meter can measure the
capacitance of an open pair and convert the measurement to
distance. The capacitance between tip and ground or ring and
ground, however, is dependent upon the cable fill type. As a result,
to accurately measure opens tip to ground or ring to ground, the
test set must be configured for the proper fill type. Since bridged
taps add capacitance, this length includes any bridged taps for all
opens results. Wet sections of cable also add capacitance and if
present, will increase the length for opens results. Some test sets
allow the entry of custom values for capacitance per distance unit
for unique cable types.
93