Re: [dtn-interest] Question

[jzinky <[e-mail]>]

Emmanuel,
I think that the Tetrys algorithm could be implemented on top of the Erasure Coding Extension internet draft. 
  http://tools.ietf.org/id/draft-irtf-dtnrg-zinky-erasure-coding-extension-00.txt

I would be interested to see what parameters Tetrys needs to add to the Bundle header for sending source bundles and repair bundles. Also, the headers for the Selective acknowledgement (SACK) bundles.

If  Tetrys can use the GF(2) field, then the Random Binary FEC scheme can be used to encode the coefficients using the Windowed Binary Array: FEC Scheme Type = 3.

If Tetrys uses a higher field you would need to define a new FEC Scheme Type and Parameters. It looks like these parameters would include the pseudo-random number generator seed and the range of coefficient indexes. 

It is interesting that Tetyrs needs SACK feedback messages. These have not been defined in the Erasure Coding Extension. Did you use administrative bundles and store the SACK parameters in an extension block or did you just create a new new bundle type and store the parameters in the payload?

Do you see any fields that are missing in the Erasure Coding Extension.
For example, how to you signal that the stream is terminated?  
and how do you pad the last bundle?

On Jan 31, 2013, at 5:55 AM, Emmanuel Lochin wrote:

> Hi Sitaraman
> 
> Thanks for your interest. We are currently working on these aspects for deep space communication on top of a DTN architecture with CNES (the French space agency).
> In particular, we seek to integrate erasure coding inside the DTN architecture.
> Note that there is also an IETF draft on this subject : http://www.ietf.org/id/draft-zinky-dtnrg-erasure-coding-objects-00.txt
> 
> Emmanuel
> 
> On 31/01/2013 02:34, [e-mail] wrote:
>> I should rather say "in addition to" instead of "as opposed to" in the below
>>> Hi Emmanuel,
>>>  This looks great to me, thanks for this pointer. Only one scenario comes
>>> to mind, if it so happens that the expected bundle loss rate, even if for
>>> brief periods, is underestimated. Such scenarios could perhaps be
>>> relevant in space as intense disturbances for brief period is more likely
>>> than a steady noise, and with Tetrys, it would be inefficient to have the
>>> expected bundle loss rate set at its peak.
>>>  I am tending to think while Tetrys could be a default scheme running in
>>> the DTN, DSN, there is needed a scheme that can put out fires
>>> occasionally?
>>> Sitaraman
>>>> Hi Sitaraman
>>>> 
>>>>> Thanks much for this pointer, it will help me learn this aspect.
>>>>> In general a question remains that i have, for the group as  whole.
>>>>> A lot seems to have already been done  and literature and code
>>>>> available
>>>>> in FEC and Erasure Codes as has been made available from  the
>>>>> discussion
>>>>> on this group  Do these complement or can they replace loss (chunks
>>>>> of
>>>>> data compeletely lost so that there is not anything to decode from)
>>>>> handling mechansims?
>>>> Concerning this point, you'll find a study that uses such scheme to
>>>> rebuild lost chunks in "Robust streaming in delay tolerant networks":
>>>> see http://oatao.univ-toulouse.fr/4111/
>>>> The erasure coding scheme is a specific elastic-window encoding scheme
>>>> named Tetrys: see http://websites.isae.fr/tetrys/
>>>> 
>>>> Emmanuel