Subject: Re: [nwcrg] [tsvwg] I-D Action: draft-ietf-tsvwg-rlc-fec-scheme-05.txt

From: Vincent Roca <[email-masked]>
Date: Thu, 24 May 2018 14:01:54 +0200

Dear all,

We have just posted a new version of our RLC FEC Schemes I-D, motivated by the use
of a new PRNG.

As already mentioned, the Park Miller Linear Congruential Generator has several flaws.
This was not an issue in RFC5170 because of the way it was used (many random values
obtained from the same seed). With the current document, we use it differently (many
seeds that will often be chosen in sequence) and these limits became obvious.

After a few hesitations, we moved to a brand new PRNG: the Tiny Mersenne Twister, 
32-bit version. This is a compact version of a renown PRNG: the Mersenne Twister, now 
widely used (see https://en.wikipedia.org/wiki/Mersenne_Twister <https://en.wikipedia.org/wiki/Mersenne_Twister>) and with provable quality
(it passes several key tests of the domain). We have the feeling the Tiny version is also 
quite popular, although more recent.

The compact version (TinyMT32) has been designed by the same authors and comes with
a reference C-language software, using a BSD license.
	http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/TINYMT/index.html <http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/TINYMT/index.html>
	https://github.com/MersenneTwister-Lab/TinyMT <https://github.com/MersenneTwister-Lab/TinyMT>
In fact this PRNG is defined by this implementation, version 1.1 (2015/4/24).

Therefore:
- we switched to this PRNG in the I-D as well as in our reference RLC codec;
- using seed 0 is now authorised and the I-D has been updated accordingly (no need to
  keep an unnecessary restriction);
- we added Annex A that reproduces a sub-set of the TinyMT32 reference software (see
  the I-D for differences with the original, mostly of editorial nature);

In terms of speed, there is no significant difference between Park Miller LCG and TinyMT32
(it may even be slightly faster). In terms of PRNG quality, we get rid of our issues :-)
I’m now going to contact TinyMT32 authors to let them know of this initiative.

The remaining of the I-D remains mostly unchanged WRT version -04.

Cheers,

  Vincent and Belkacem

> Le 24 mai 2018 à 13:33, [email-masked] a écrit :
> 
> 
> A New Internet-Draft is available from the on-line Internet-Drafts directories.
> This draft is a work item of the Transport Area Working Group WG of the IETF.
> 
>        Title           : Sliding Window Random Linear Code (RLC) Forward Erasure Correction (FEC) Schemes for FECFRAME
>        Authors         : Vincent Roca
>                          Belkacem Teibi
> 	Filename        : draft-ietf-tsvwg-rlc-fec-scheme-05.txt
> 	Pages           : 34
> 	Date            : 2018-05-24
> 
> Abstract:
>   This document describes two fully-specified Forward Erasure
>   Correction (FEC) Schemes for Sliding Window Random Linear Codes
>   (RLC), one for RLC over GF(2) (binary case), a second one for RLC
>   over GF(2^^8), both of them with the possibility of controlling the
>   code density.  They can protect arbitrary media streams along the
>   lines defined by FECFRAME extended to sliding window FEC codes.
>   These sliding window FEC codes rely on an encoding window that slides
>   over the source symbols, generating new repair symbols whenever
>   needed.  Compared to block FEC codes, these sliding window FEC codes
>   offer key advantages with real-time flows in terms of reduced FEC-
>   related latency while often providing improved packet erasure
>   recovery capabilities.
> 
> 
> The IETF datatracker status page for this draft is:
> https://datatracker.ietf.org/doc/draft-ietf-tsvwg-rlc-fec-scheme/
> 
> There are also htmlized versions available at:
> https://tools.ietf.org/html/draft-ietf-tsvwg-rlc-fec-scheme-05
> https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-rlc-fec-scheme-05
> 
> A diff from the previous version is available at:
> https://www.ietf.org/rfcdiff?url2=draft-ietf-tsvwg-rlc-fec-scheme-05
> 
> 
> Please note that it may take a couple of minutes from the time of submission
> until the htmlized version and diff are available at tools.ietf.org.
> 
> Internet-Drafts are also available by anonymous FTP at:
> ftp://ftp.ietf.org/internet-drafts/
>