Triple-Play Service Deployment

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Chapter 7: Troubleshooting Video Service in the Field
An IP packet typically carries seven video packets. A lost IP packet
event will normally create some kind of visible impairment. But, a
subscriber’s subjective response to, for example, minor pixelization
events caused by packet loss varies with the pattern or
distribution of the events. For the same loss rate different
distributions of loss will impact perceptions differently. Thus,
adding a metric to measure the number of packets lost in an
event—the period—and a metric for the number of times these
events are separated by at least one packet in the event—the
distance—will allow a better analysis of the spread of these loss
events (RFC3357).This can help in looking at the “bursty” nature of
the loss, which in turn can be helpful in determining the source of
the loss: buffer over runs, forward error correction (FEC) depth
setting threshold crossings, etc. Another packet analysis approach
defined in RFC4445 called Media Delivery Index (MDI) provides a
way to look at packet loss and jitter by calculating two metrics:
delay factor (DF) and media loss rate (MLR). DF is a jitter analysis
that indicates how long a data stream must be buffered, at its
nominal rate, to prevent packet loss. MLR is the count of lost or
out-of-sequence packets over time. However, mapping this kind of
analysis to perceived quality, or QoE is best accomplished by a
MOS algorithm.
Transaction quality
Transaction quality focuses on the availability and responsiveness of
the video service to the expectations of the user. For example, the
user may consider: “If I have subscribed to a set of broadcast TV
channels, can I gain access to them? If I can gain access, how long
does it take to change the channel? If I am watching a VoD movie
program and I want to pause the program for some reason and then
resume play, how responsive is the service to my commands?”
These perceptions of responsiveness can be measured with an
elapsed time approach.