User's Manual

Chapter 18 Maintenance and Troubleshooting
Resolving problems
SmartClass TPS User’s Guide
156 22035456, Rev 001 May 2014
Video test problems
Individual program flows should be analyzed to ensure that both content quality and network perfor-
mance parameters are within desired network specifications. The suggested thresholds are listed
below:
Packet loss = less than or equal to 0.1%
Packet jitter = less than or equal to 5 msec*
PCR jitter = less than or equal to 5 msec*
Error indicator = zero count
IGMP latency = less than or equal to 200 msec
*Specific STB/decoder designs may be able to tolerate higher levels of jitter based on larger
buffer designs. Less than or equal to 10 msec may be acceptable.
Five to ten msec is a conservative PCR jitter level. As network designs and STBs increase
buffer sizes, the acceptable level will rise. The acceptable level for a particular network is a
company-specific issue.
When these measurements are made simultaneously on more than one channel, then content
problems can be easily separated from distribution network problems, a critical determination for
problem resolution.
Issue
I have continuity errors.
Resolution
Packet loss (continuity error) problems are typically seen on all channels/programs coming to the
premise because they are not source or content related. If packet loss is present, analysis of the
physical layer at the xDSL interface or Ethernet interface will aid in sectionalization. If no physical
layer errors are present, then packet loss is most likely being caused by the distribution network not
from the access network. Congestion is most likely at issue.
Looking further into the temporal component can help pinpoint the issue. The answers to the
following questions can help find the problem area(s). Are packets being lost during known peak
traffic times during the day? Are they coming in bursts with intervals with no loss? Are they random
single or small packet loss events?
Bursts of loss might be more symptomatic of buffer overflows related to heavy traffic. Random
single or small events might be more related to noise hits on the access network impacting packet
flows. DSL loop performance in the access network may be pushing the bandwidth limits when
signal to noise margins are low and the addition of a second or third channel flow reaches 100%
capacity of the loop. The copper may be poorly balanced allowing high impulse noise to impact the
data flows. In-home wiring may be introducing noise which also can damage data flows.
Issue
I have a PCR jitter result that is higher than expected.
Resolution
PCR jitter problems may be due to content quality problems as outlined previously or overall
network packet jitter. By evaluating more than one channel/program at a time, this can be deter-
mined. If excessive PCR jitter is present at more than one channel, network jitter is most likely at
fault. If excessive PCR jitter is present on only one channel, then a source problem as described
above is normally the cause.