[avt] Use of redundancy in rfc2793bis text transmission - optimizing interoperability

Gunnar Hellström <gunnar.hellstrom@omnitor.se> Wed, 14 April 2004 21:40 UTC

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Date: Wed, 14 Apr 2004 22:59:04 +0200
From: Gunnar Hellström <gunnar.hellstrom@omnitor.se>
To: avt@ietf.org
Cc: toip@snowshore.com
Subject: [avt] Use of redundancy in rfc2793bis text transmission - optimizing interoperability
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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 assure
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% )
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