[avt] Use of redundancy in rfc2793bis text transmission

Sorry, I sent a message to the list yesterday that was chopped off just
before the important part - the proposed text section in RFC2793bis.

Here is the full message:
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I often get comments on the real time interactive text conversation
transport RFC2793bis, that it must more clearly require the use of
redundancy to achieve good success rate in text transmission even in bad
network conditions.

Next version of draft-ietf-avt-rfc2793bis is about to be published, and I
would like to have  agreeable wording on this issue.

A traditional requirement for basic text conversation quality is that no
more than 1% characters may be lost in conditions where voice
communications is barely usable. Where characters are dropped marks for
missing text should be inserted in the received text. A higher quality
level, called good text quality requires no more than 0.2% characters to be
dropped. This is of course no exact scientific measure and many factors
influence both the loss and the perception of usability of voice
conversation, but it gives a fair design goal.

With voice coding and transmission schemes prevailing today, voice gets
barely usable around 20% packet loss.

Therefore, in order to assure proper interoperability with the required
quality level for text at 20% packet loss, we need to require one original
and two redundant transmissions according to RFC2198. ( lowering text loss
to 0.8% ). We also have to require that RFC 2198 is supported as the
default mechanism. Otherwise we may have the risk that two UAs propose
different protection methods against loss, and we end up in a situation
without protection, that gives us 20% text loss at 20% packet loss. That
can not be called interoperability.

In order to be assured proper interoperability, but give room for use of
other methods in specific applications and known network conditions, I want
to get agreement to introduce this section in RFC 2793 bis:

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"4. Protection against loss of data

For reduction of data loss in case of packet loss, redundant data SHOULD be
included in the packets following the procedures in RFC 2198 [3].  If the
application and the end to end network conditions are not known to require
other methods or parameters, this method MUST be used, transmitting the
original text and two redundant generations.

As an alternative (or in addition) to redundancy, Forward Error Correction
mechanisms MAY be used when transmitting text, as per RFC 2733 [8] or any
other mechanism with the purpose of increasing the reliability of text
transmission.

There are also other mechanisms for increasing robustness of transmission
that MAY be applied."
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Regards
Gunnar

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Gunnar Hellström
Omnitor AB
Renathvägen 2
SE 121 37 Johanneshov
SWEDEN
+46 8 556 002 03
Mob: +46 708 204 288
www.omnitor.se
Gunnar.Hellstrom@Omnitor.se
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[avt] Use of redundancy in rfc2793bis text transmission - optimizing interoperability