Re: [Fecframe] Comments on: I-D Action:draft-ietf-fecframe-raptor-03.txt

[Thomas Stockhammer <[e-mail]>]

Mike,

thanks! I will integrate all your suggestions in a revised version. Before posting a revision, I will await any additional comments received by Fri, Dec 3rd.

Thomas

On Nov 23, 2010, at 8:09 PM, Luby, Michael wrote:

> Some comments on draft-ietf-fecframe-raptor-03.txt below.
> 
> General nits:
> 
> (1) Change "signalled" to "signaled"
> (2) Change "modelled" to "modeled"
> (3) Change "arbitary" to "arbitrary"
> (4) Change "thepadding" to "the padding"
> (5) Change "handware" to "hardware"
> 
> Particulars:
> 
> (6) Section 6.3.2 refers to Section 6.4 for the definition of I_repair: it
> vaguely says that
> 
> The ESI value placed into a repair
>   packet is given by the following formula:
> 
>  "ESI_repair = I_repair + SBL,
> 
>   where I_repair is the index of the repair symbol in the sequence of
>   repair symbols generated according to Section 6.4, where the first
>   repair symbol has index 0, the second index 1 etc. and SBL is the
>   Source Block Length."
> 
> If you look at Section 6.4, it just says that you shall use the Raptor in
> IETF RFC 5053 or the RaptorQ in the draft specification.  But, if you look
> into either Raptor or RaptorQ, you will see that the indexing of the repair
> symbols starts at K, where K is the SBL, and thus you need to reinterpret to
> understand the ESI K in the Raptor or RaptorQ specification corresponds to
> I_repair = 0, and then use this in the above, which gives you back exactly
> the same ESI as would have been specified by Raptor or RaptorQ.  This whole
> thing is overly confusing, and I think it would be better to just replace
> the above with:
> 
> "The ESI value placed into a repair packet is calculated as specified in
> Section 5.3.2 of [RFC5053] when [RFC5053] is used and as specified in
> Section 4.4.2 of [I-D.ietf-rmt-bb-fec-raptorq] when
> [I-D.ietf-rmt-bb-fec-raptorq] is used, where K=SBL."
> 
> 
> (7) Section 7.1, the second bullet point here is pretty confusing.  Suggest
> changing it from:
> 
> "A restricted set of possible source block sizes is specified.
>      This allows explicit operation sequences for encoding the
>      restricted set of block sizes to be pre-calculated and embedded in
>      software or handware."
> 
> To:
> "The possible choices of the source block size for a stream is restricted to
> a small specified set of sizes.  This allows explicit operation sequences
> for encoding and decoding the restricted set of source block sizes to be
> pre-calculated and embedded in software or hardware."
> 
> 
> (8) Section 7.3.2, similar comment to (6) above.  Suggest rewording:
> 
> "The ESI value placed into a repair
>   packet is given by the following formula:
> 
>   ESI_repair = I_repair + MSBL
> 
>   Where I_repair is the index of the repair symbol in the sequence of
>   repair symbols generated according to Section 6.4, where the first
>   repair symbol has index 0, the second index 1 etc. and MSBL is the
>   Maximum Source Block Length signalled in the FEC Scheme Specific
>   Information.  The Source Block Length field of the Repair FEC Payload
>   ID field SHALL be set to the number of symbols included in the Source
>   Packet Information of packets associated with the source block."
> 
> To:
> 
> "The ESI value placed into a repair packet is calculated as X + MSBL - SBL,
> where X would be the ESI value of the repair packet if the ESI were
> calculated as specified in Section 5.3.2 of [RFC5053] when [RFC5053] is used
> and as specified in Section 4.4.2 of [I-D.ietf-rmt-bb-fec-raptorq] when
> [I-D.ietf-rmt-bb-fec-raptorq] is used, where K=SBL. The value of SBL SHALL
> be at most the value of MSBL."
> 
> (9) Section 8.1.3:  The text for the second set of formats is a copy of the
> first set and should be changed.  Specifically, The ESI in the second set of
> formats should be specified as 24 bits, not 16 bits, and the ESI text should
> be listed third, not second (to match the order of the parameters in Fig.
> 7).
> 
> Mike 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> On 11/22/10 11:30 PM, "[e-mail]" <[e-mail]>
> wrote:
> 
>> A New Internet-Draft is available from the on-line Internet-Drafts
>> directories.
>> This draft is a work item of the FEC Framework Working Group of the IETF.
>> 
>> 
>> Title           : Raptor FEC Schemes for FECFRAME
>> Author(s)       : M. Watson, T. Stockhammer
>> Filename        : draft-ietf-fecframe-raptor-03.txt
>> Pages           : 21
>> Date            : 2010-11-22
>> 
>> This document describes Fully-Specified Forward Error Correction
>> (FEC) Schemes for the Raptor and RaptorQ codes and their application
>> to reliable delivery of media streams in the context of FEC
>> Framework.  The Raptor and RaptorQ codes are systematic codes, where
>> a number of repair symbols are generated from a set of source symbols
>> and sent in one or more repair flows in addition to the source
>> symbols that are sent to the receiver(s) within a source flow.  The
>> Raptor and RaptorQ codes offer close to optimal protection against
>> arbitrary packet losses at a low computational complexity.  Six FEC
>> Schemes are defined, two for protection of arbitrary packet flows,
>> two that are optimised for small source blocks and another two for
>> protection of a single flow that already contains a sequence number.
>> Repair data may be sent over arbitrary datagram transport (e.g.  UDP)
>> or using RTP.
>> 
>> A URL for this Internet-Draft is:
>> http://www.ietf.org/internet-drafts/draft-ietf-fecframe-raptor-03.txt
>> 
>> Internet-Drafts are also available by anonymous FTP at:
>> ftp://ftp.ietf.org/internet-drafts/
>> 
>> Below is the data which will enable a MIME compliant mail reader
>> implementation to automatically retrieve the ASCII version of the
>> Internet-Draft.
> 
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