Subject: Re: [nwcrg] [tsvwg] I-D Action: draft-ietf-tsvwg-rlc-fec-scheme-04.txt

From: Vincent Roca <[email-masked]>
Date: Fri, 18 May 2018 09:13:14 +0200

Dear all,

Here is an updated version of our I-D.

- It takes into accounts comments received by Jonathan Detchart
  (added section 3.6. Finite Fields Operations);

- Section 3.1. Possible Parameter Derivations 
  has been significantly improved for more precision;

- It also fixes a small bug (in parameter checks) in 
  section 3.5.  Coding Coefficients Generation Function;

We are not sure we will keep the current PRNG...
Even with the previous fix (i.e., ignoring the first value produced),
the Park-Miler minimal standard PRNG behaves badly when used
with seeds that are in sequence (e.g., the application generates
a repair symbol with seed s and then s+1, etc.) and when mapping
the PRNG output to a small range of value (especially with [0, 15]):
	Ij+1 = A * s (modulo M)
and:
	Ij+1 = A * (s+1) (modulo M)
scaled to [0, 15] have a certain probability to give the same value.
We are  currently experimenting with alternatives. Unfortunately we
only identified this side-effect recently. 

Cheers,

   Vincent and Belkacem

> Le 18 mai 2018 à 08:51, [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-04.txt
> 	Pages           : 31
> 	Date            : 2018-05-17
> 
> 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-04
> https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-rlc-fec-scheme-04
> 
> A diff from the previous version is available at:
> https://www.ietf.org/rfcdiff?url2=draft-ietf-tsvwg-rlc-fec-scheme-04
> 
> 
> 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/
>