Triple-Play Service Deployment

92
TDR Response (V)
7.3
3.6
Figure 4.2 TDR trace of load coil
0
-3.6
-7.3
1
0 600 1200 1800 2400 3000 3600
Distance (Feet)
Chapter 4: Troubleshooting the Copper Plant for IP Services
Loop length
Attenuation of a loop increases as loop length increases. If the loop
is too long, the modems may not synch at all, or will have a low
data rate. Because of this, there is a maximum length for a pair to
be acceptable for ADSL. This length depends on wire gauge,
gauge changes, and overall line condition. The approximate
maximum length is 18,000 feet for ADSL, 15,000 feet for ADSL2,
and 18,000 feet for ADSL2+. To obtain rated levels of bandwidth
associated with ADSL2+, however, the loop must be shorter than
8,000 feet. Loop lengths for VDSL2 are considerably lower. One
major service provider has set 2,300 feet as a conservative starting
point for its rollout but has considered extending to 3,000 feet or
more if conditions are acceptable. Between 2,300 and 3,000 feet,
results of other measurements are closely examined to be sure they
are well within limits. A fault condition that may be tolerable on a
2,000 foot loop could impair performance on a 3,000 foot loop.