Triple-Play Service Deployment

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Chapter 4: Troubleshooting the Copper Plant for IP Services
While physical layer testing is important for xDSL service,
application specific QoS testing is also important. Therefore, a test
set that supports voice, video, and data applications, in addition to
copper testing, provides the most efficient solution and enables
more seamless correlation of potential problems between
protocol layers. For example, excessive loss in data rate,
attenuation, and/or noise margin seen at the VDSL layer can be
more quickly isolated to cable faults, such as bridged taps, wet
sections, or excessive noise caused by pair imbalance or poor
bonding and grounding.
Turn-Up Sequence
(Simplified Overview)
IPTV Test
3 (Go/No-Go)
2 VDSL Test
1
Metallic Test
– Foreign Voltage
– Resistance
– Opens/Capactance
– Balance
– Noise
– Impulse Noise
Trouble Sequence
(Simplified Overview)
IPTV Test
3 (Go/No-Go)
2 VDSL Test
Metallic Test
– Foreign Voltage
– Resistance
– Opens/Capactance
– Balance
– Noise
– Impulse Noise
Figure 4.14 Typical turn-up (installation) and troubleshooting sequences
As an example, if in-service monitoring of the IPTV service reveals
excessive bursts of lost packets and VDSL errors (code violations,
CRC, uncorrected FEC errors, etc.) are observed, the problem often
can be isolated to excessive noise or impulse noise on the line
caused by pair imbalance or poor bonding and grounding. Recent
lab and field testing has shown this to be a major source of IPTV
degradation. Again, having the capability in a single instrument to
make this diagnosis quickly and accurately is essential.
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