User's Manual Part 2

Tech-X Flex
®
(NG2) Tech-X Flex User Guide - Firmware v06.50
6-47
Intro
Overview
Wi-Fi
Ethernet
System
IP/Video
MoCA
RF
Specs
The R-factor is a similar concept and is actually the mathematical component by which a MOS is
estimated. It is calculated using what is known as the “E-model” formula. This formula involves a
subjective summation of impairment and “advantage” factors, including the typical packet network
parameters such as jitter, latency, and loss. Like the MOS score, the higher the number, the better. An R-
factor result is presented as a percentage, where 80% loosely corresponds with an MOS score of 4, and
a factor of 50% corresponds with an MOS of 2.6.
While these types of measurement may help you view a snapshot summary of network quality, you
should remember that “real,” quantifiable network conditions are the only reliable means of judging
network integrity. Any means of numerically calculating the quality of the human experience is
necessarily subjective.
About gap and burst states
The software models the distribution of packet loss over the measurement duration, which allows for a
more detailed characterization of the packet loss experienced by the audio/video stream. This is a four-
state model in which two periods of loss exist, gap and burst periods, each of which has two states.
The stream is considered to be in a gap condition of loss when consecutive packet loss is less than or
equal to one packet. If two or more consecutive packets are lost, the stream is considered to be in a burst
condition. Following the entry into a burst period, 128 consecutive packets must be received in order to
return to the gap condition, a number determined though research of quality measurements. Note that
the successfully received packets will be considered to have arrived during a gap period.
Other test results
About packet delay variation (PDV)
Packet delay variation is a calculation based on the variation of a packet’s expected arrival time versus
its actual arrival time. Each packet has its own PDV, which is determined by:
| Expected time - Arrival time |
...noting the use of absolute values. So, if a packet is expected to arrive at time
1
but actually arrives at
time
2
, it has a PDV of | time
1
- time
2
|. Typically, individual PDVs are used for calculating an average for
multiple packets in a stream, or reporting the maximum PDV experienced during a measurement period.
NOTE: Packet delay variation is sometimes referred to as jitter. However, the use of PDV terminology
is preferred in this documentation due to its more specific definition.
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