Received-SPF: pass (sog-mx-4.v43.ch3.sourceforge.com: domain of gmail.com
	designates 209.85.220.182 as permitted sender)
	client-ip=209.85.220.182; envelope-from=gmaxwell@gmail.com;
	helo=mail-vc0-f182.google.com; 
MIME-Version: 1.0
In-Reply-To: <CA+iPb=GC7iw1LP6boyfX22oMO2k2=YcAuRhE0E3OzzJHYapsow@mail.gmail.com>
References: <CA+iPb=EaX=bvOjNtZ+LnYTMRLQQ9nFcrefAkBdv8eActoX_b8A@mail.gmail.com>
	<CABsx9T2PSa3MpfMMDCb8ACVF5vDOZOFLEK9zfP9PakgHA4U16w@mail.gmail.com>
	<CAPkFh0vKFnKRE-sd-Z9t1zB73VLPsiaQ3o=OYgBqqtUE4_rTaw@mail.gmail.com>
	<CA+iPb=GC7iw1LP6boyfX22oMO2k2=YcAuRhE0E3OzzJHYapsow@mail.gmail.com>
Date: Thu, 31 Jul 2014 14:29:40 -0700
Message-ID: <CAAS2fgS-KiP-tiy91Ah2hJ0pepA0OJDCG+Bv+redFtsqrUTevQ@mail.gmail.com>
From: Gregory Maxwell <gmaxwell@gmail.com>
To: Kaz Wesley <keziahw@gmail.com>
Content-Type: text/plain; charset=UTF-8
Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] Squashing redundant tx data in blocks on
 the wire
Precedence: list

On Thu, Jul 31, 2014 at 1:47 PM, Kaz Wesley <keziahw@gmail.com> wrote:
> trip to request the missing tx; if we could somehow get the "What's
> the Difference" approach to effectively operate on full transactions
> instead

I explain how to do this on the network block coding page.

Given that you know the sizes and orders of the transactions (e.g.
from a reconciliation step first), the sender sends non-syndromic
forward error correcting code data somewhat larger than their estimate
of how much data the user is missing.  Then you drop the data you know
into place and then recover the missing blocks using the fec.

There is no overhead in this approach except for FEC blocks that are
incompletely missing (and so must be completely discarded), and the
need to have the transmitted the transaction list and sizes first.
(note, that just more bandwidth, not an additional round trip).