TANDBERG E5780, Справочное руководство

Страница: 289 / 298

ProMPEG FEC Support for IP Streaming in E57xx Encoders
Reference Guide: evolution 5000 E5780 and E5782 Encoder Page K-5
ST.RE.E10135.4
K.2.4 Recommendations for use of ProMPEG FEC
Overview
There are no official recommendations within the ProMPEG Code of Practice #3 release 2
regarding which parameters give the best results.
The first decision to be made is which Encapsulation mode to use, as this has a large effect
on the added overhead. Column only or Row and Column mode, this decision will be
determined by the packet loss characteristics of the network and the importance of data
integrity over the network. This information will be different for every network and service
provider, therefore TANDBERG Television cannot offer recommendations in this reference
guide.
The following information has been added to help demonstrate the difference in data
protection provided by each FEC scheme.
Column-Only Mode Performance
For every 10 fold improvement in Channel Packet Loss Ratio (PLR) there is approximately a
100 fold improvement in the outgoing PLR.
Row and Column Mode Performance
For every 10 fold improvement in Channel PLR there is approximately a 1000 fold
improvement in the outgoing PLR.
Size of the Matrix
The final decision to be made is the size of matrix to be used. Simply by adding a Column only
FEC scheme, irrespective of dimension reduces the Mean Time To Failure (MTBF) massively.
The difference in coding gain between a small matrix and a big matrix is small compared to
the massive gain of actually adding a FEC scheme. A large matrix would therefore probably
be preferred for most service providers as the IP packet overhead is lower. However using a
large matrix means that the latency to decode the transport stream is increased. Using a small
matrix will reduce the latency of the system but will obviously significantly increase the
overhead.