User's Manual Part 2

Tech-X Flex
®
(NG2) Tech-X Flex User Guide - Firmware v06.50
6-45
Intro
Overview
Wi-Fi
Ethernet
System
IP/Video
MoCA
RF
Specs
Protocol Independent Multicast (PIM) to build logical multicast trees and forward packets efficiently
between the multicast source and group members. Once multicast packets reach their destination
subnets, group members "listening" for packets with the specific IP multicast (destination) address will
receive and process the packets accordingly.
The IP address range of 224.0.0.0 - 239.255.255.255 is reserved for multicast packets. It should be
noted that these addresses are likely unroutable in a traditional sense on the destination subnets that
receive the packets. Rather, it is the suite of multicasting protocols that allows packets to be properly
forwarded and ultimately processed by the proper group member device(s). This is distinctly different
from unicast transmission, where IP packets are addressed for a specific source/destination pair and
exchanged exclusively between the two hosts.
Video quality measurement (VQM) overview and additional results descriptions
The following sections describe the quality measurement process in more detail, for the “VQM” mode of
analysis. For more information on MDI, see MDI measurement overview on page 6-48.
How the analysis works - An overview
The following metrics may be used to estimate the overall subjective quality of the audio/video stream,
some of which are also reported in the results:
• Audio/video packet details - Comprehensive metrics describing the number of MPEG packets
received, lost, and discarded.
• General audio/video stream information - Stream characteristics such as audio/video codec,
audio/video stream bit rate, video stream GOP size/structure, and video stream image size.
• Degradation factors - Identification and quantification of the factors which have caused degradation
of the video signal, such as codec, packet loss, and packets discarded due to buffer underrun and/or
overrun.
• General network metrics - Information on the overall packet transport network such as packet delay
variation and packet loss.
Quality is estimated based on general stream, packet, and frame characteristics that are known to have
a predictable impact on user experience. This methodology provides reliable measurements without the
need to decrypt a scrambled video signal. Packet loss is naturally the primary factor involved with
audio/video quality degradation, but the following types of considerations also affect quality calculations:
• Other problems related to network impairments, such as packet delay variation and out-of-sequence
packets.
• The inherent abilities of the codec and associated equipment to conceal network impairments such
as packet loss.
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