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Re: [dtn] [EXTERNAL] Alexey Melnikov's Discuss on draft-ietf-dtn-bpbis-22: (with DISCUSS and COMMENT)

"Burleigh, Scott C (US 312B)" <scott.c.burleigh@jpl.nasa.gov> Mon, 10 February 2020 17:08 UTC

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From: "Burleigh, Scott C (US 312B)" <scott.c.burleigh@jpl.nasa.gov>
To: Alexey Melnikov <aamelnikov@fastmail.fm>, The IESG <iesg@ietf.org>
CC: "draft-ietf-dtn-bpbis@ietf.org" <draft-ietf-dtn-bpbis@ietf.org>, Fred Templin <fred.l.templin@boeing.com>, "dtn-chairs@ietf.org" <dtn-chairs@ietf.org>, "dtn@ietf.org" <dtn@ietf.org>, Benjamin Schwartz <bemasc@google.com>
Thread-Topic: [EXTERNAL] Alexey Melnikov's Discuss on draft-ietf-dtn-bpbis-22: (with DISCUSS and COMMENT)
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Date: Mon, 10 Feb 2020 17:08:13 +0000
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Subject: Re: [dtn] [EXTERNAL] Alexey Melnikov's Discuss on draft-ietf-dtn-bpbis-22: (with DISCUSS and COMMENT)
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Thanks, Alexey.  I would expect an implementer who is coding section 5.9 of the spec would normally read section 5.8 as well, but maybe not.  I will gladly add some clarifying text in the Reassembly section as well.

Scott

-----Original Message-----
From: Alexey Melnikov <aamelnikov@fastmail.fm> 
Sent: Monday, February 10, 2020 3:39 AM
To: Burleigh, Scott C (US 312B) <scott.c.burleigh@jpl.nasa.gov>; The IESG <iesg@ietf.org>
Cc: draft-ietf-dtn-bpbis@ietf.org; Fred Templin <fred.l.templin@boeing.com>; dtn-chairs@ietf.org; dtn@ietf.org; Benjamin Schwartz <bemasc@google.com>
Subject: Re: [EXTERNAL] Alexey Melnikov's Discuss on draft-ietf-dtn-bpbis-22: (with DISCUSS and COMMENT)

Hi Scott,
Quickly replying to a single issue:

On Sat, Feb 8, 2020, at 12:45 AM, Burleigh, Scott C (US 312B) wrote:
> > ## Section 5.8
> > 
> > Clarity: The insistence, here and earlier, that a bundle is only 
> > fragmented into two packets, and that this can then be performed 
> > recursively, seems unhelpful.  Bundles can be fragmented into 
> > arbitrarily many pieces, and this binary subdivision concept is not 
> > actually present in the protocol.  I suggest removing it from the 
> > text as well.
> > 
> > 		Why is this unhelpful?  It's the formal procedure by which bundles 
> > are fragmented.  Let's not remove it.
> 
> I think saying that a bundle can only be fragmented into 2 pieces is a 
> lie, because the algorithm says that it can be fragmented into more 
> than 2. I found this text to be confusing as well. Just say that it 
> can be fragmented into 2 or more non overlapping fragments.
> 
> 	***	It is absolutely not a lie.  A bundle can be fragmented into 
> exactly 2 pieces, each of which is a bundle.  There is no defined 
> mechanism for fragmenting a single 		bundle into 3 pieces, or 4, other 
> than the recursive exercise of the binary fragmentation mechanism 
> defined in detail in section 5.8.  But I will try to make this
> 		clearer in the text.

Think of it from the point of view of a receiving system: if there were several nodes before it, it can't rely on only being 2 fragments, it has to expect arbitrary number of them.

So the text you have is possibly helpful for the sending system, but not for the receiving one.

Best Regards,
Alexey

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