Re: [dtn-interest] some comments on draft-zinky-dtnrg-erasure-coding-extension

["Ivancic, William D. (GRC-RHN0)" <[e-mail]>]

  
> The intent of the ALC protocol suite is also trying to send large data
> objects, but many of the details are different. ALC really is designed for IP
> multicast, with reasonable error-rates.

Agreed.

>The DTN Erasure Coding has to deal
> with the case of extreme bundle loss, when contact times are short relative to
> the transmission time of the object. The way DTN Erasure coding deals with
> this problem is to basically make every bundle a "repair symbol" and to flood
> redundant, but not duplicate, repair symbols into the DTN in hopes that a
> enough get through in time. The key to this case is that no Encoding Bundle
> carries unique information, all the bundles have to be completely
> interchangeable. 

The main concern I have with breaking large bundles into small bundles is
forwarding table bloat.  What happens if I take a 1Gbyte bundle and break it
into a bunch of 64Kbyte Erasure code bundles?   This is of particularly
concern with the current specification that has all these time-stamps that
have to be managed.

If we got rid of creation and expiration times and just had a few QoS queues
with different storage times, this may simplify things greatly.

Everything really is deployment specific.


> 6) Feedback messages - are these more general?
> 
> Feedback messages are out of scope of these internet drafts. This section just
> tries to enumerate the different types. We are still experimenting with the
> usefulness of each type, but the usefulness is highly dependent on the
> end-to-end channel characteristics.

I would suspect for different deployment environments, one would use
different redundancies rather than feedback.  Feedback characteristics will
also be deployment specific.  Thus, the ability to not assume anything about
feedback is highly desirable.


> Which diagrams do you recommend based on the limitation of ascii art.
> Example diagrams can be found in the EC slideshow.
> https://dist-systems.bbn.com/papers/2011/Zinky/ErasureCodingExtBlockSpec-IRTF-
> 2011-07-25-Rev1-2-2.pdf
> 
> Will Ivancic suggests:
> Slide 8 for section 3.3.3
> Slide 13 for section 4.2
> Slide 30 for the Bundle Data Object description.

 JAVE  is a nice ASCII Art Utility.
www.jave.de/
Note, I have no financial stake here.  I just find it useful.  In theory, I
cannot endorse anything (being a US Govt employee) so consider this just a
statement that I have used the  program and it has worked well for me.  :-)

- Will