Dev Docs: Add Section About Headers-First IBD

* Add flowchart illustration to blocks-first section to match new headers-first flowchart * Add new headers-first initial block download (IBD) section * Revise Block Broadcasting section * Add paragraph about orphan block handling in headers-first to the Orphan Blocks section
2025-07-27 01:36:13 +00:00 · 2015-02-05 15:44:05 -05:00 · 2015-02-05 15:44:05 -05:00 · 72cc5f7f9e
commit 72cc5f7f9e
parent 7dcf67d5a8
18 changed files with 772 additions and 4 deletions
--- a/img/dev/en-blocks-first-flowchart.dot
+++ b/img/dev/en-blocks-first-flowchart.dot
@ -0,0 +1,32 @@
+digraph {
+// This file is licensed under the MIT License (MIT) available on
+// http://opensource.org/licenses/MIT.
+
+size=6.25;
+rankdir=TB
+splines = "true";
+ranksep = 0.2;
+nodesep = 0.9;
+
+edge [ penwidth = 1.75, fontname="Sans" ]
+node [ penwidth = 1.75, shape = "none", fontname="Sans"]
+graph [ penwidth = 1.75, fontname="Sans" ]
+
+fsbc [ label = "Fully-Synced Block Chain?", style = "filled" ];
+listen [ label = "Listen For New Blocks (Inv)" ];
+request_blocks [ label = "Request Blocks (GetData)" ];
+request_invs [ label = "Request Inventories (GetBlocks)" ];
+have_invs [ label = "Have Inventories?", style = "filled" ];
+
+fsbc -> have_invs [ label = "  No" ];
+fsbc -> listen [ label = "Yes", constraint = false ];
+have_invs -> request_invs [ label = "  No" ];
+
+have_invs -> request_blocks [ label = "Yes", constraint=false ];
+
+listen -> request_blocks [ style = "invis" ];
+
+
+
+label = "\ \nOverview Of Blocks-First Initial Blocks Download (IBD)"
+}
--- a/img/dev/en-blocks-first-flowchart.png
+++ b/img/dev/en-blocks-first-flowchart.png
--- a/img/dev/en-blocks-first-flowchart.svg
+++ b/img/dev/en-blocks-first-flowchart.svg
@ -0,0 +1,62 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
+ "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
+<!-- Generated by graphviz version 2.38.0 (20140413.2041)
+ -->
+<!-- Title: %3 Pages: 1 -->
+<svg width="450pt" height="173pt"
+ viewBox="0.00 0.00 450.00 173.11" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+<g id="graph0" class="graph" transform="scale(0.801425 0.801425) rotate(0) translate(4 212)">
+<title>%3</title>
+<polygon fill="white" stroke="none" points="-4,4 -4,-212 557.5,-212 557.5,4 -4,4"/>
+<text text-anchor="middle" x="276.75" y="-22.8" font-family="Sans" font-size="14.00"> </text>
+<text text-anchor="middle" x="276.75" y="-7.8" font-family="Sans" font-size="14.00">Overview Of Blocks&#45;First Initial Blocks Download (IBD)</text>
+<!-- fsbc -->
+<g id="node1" class="node"><title>fsbc</title>
+<polygon fill="lightgrey" stroke="none" stroke-width="1.75" points="218,-208 21,-208 21,-172 218,-172 218,-208"/>
+<text text-anchor="middle" x="119.5" y="-186.3" font-family="Sans" font-size="14.00">Fully&#45;Synced Block Chain?</text>
+</g>
+<!-- listen -->
+<g id="node2" class="node"><title>listen</title>
+<text text-anchor="middle" x="450.5" y="-186.3" font-family="Sans" font-size="14.00">Listen For New Blocks (Inv)</text>
+</g>
+<!-- fsbc&#45;&gt;listen -->
+<g id="edge2" class="edge"><title>fsbc&#45;&gt;listen</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M218.363,-190C255.697,-190 298.464,-190 337.033,-190"/>
+<polygon fill="black" stroke="black" stroke-width="1.75" points="337.265,-193.5 347.265,-190 337.265,-186.5 337.265,-193.5"/>
+<text text-anchor="middle" x="282.75" y="-196.8" font-family="Sans" font-size="14.00">Yes</text>
+</g>
+<!-- have_invs -->
+<g id="node5" class="node"><title>have_invs</title>
+<polygon fill="lightgrey" stroke="none" stroke-width="1.75" points="190.5,-141 48.5,-141 48.5,-105 190.5,-105 190.5,-141"/>
+<text text-anchor="middle" x="119.5" y="-119.3" font-family="Sans" font-size="14.00">Have Inventories?</text>
+</g>
+<!-- fsbc&#45;&gt;have_invs -->
+<g id="edge1" class="edge"><title>fsbc&#45;&gt;have_invs</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M119.5,-171.922C119.5,-165.702 119.5,-158.5 119.5,-151.6"/>
+<polygon fill="black" stroke="black" stroke-width="1.75" points="123,-151.19 119.5,-141.19 116,-151.19 123,-151.19"/>
+<text text-anchor="middle" x="133.5" y="-152.8" font-family="Sans" font-size="14.00"> &#160;No</text>
+</g>
+<!-- request_blocks -->
+<g id="node3" class="node"><title>request_blocks</title>
+<text text-anchor="middle" x="450.5" y="-119.3" font-family="Sans" font-size="14.00">Request Blocks (GetData)</text>
+</g>
+<!-- listen&#45;&gt;request_blocks -->
+<!-- request_invs -->
+<g id="node4" class="node"><title>request_invs</title>
+<text text-anchor="middle" x="119.5" y="-52.3" font-family="Sans" font-size="14.00">Request Inventories (GetBlocks)</text>
+</g>
+<!-- have_invs&#45;&gt;request_blocks -->
+<g id="edge4" class="edge"><title>have_invs&#45;&gt;request_blocks</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M190.508,-123C234.937,-123 293.028,-123 343.029,-123"/>
+<polygon fill="black" stroke="black" stroke-width="1.75" points="343.241,-126.5 353.241,-123 343.241,-119.5 343.241,-126.5"/>
+<text text-anchor="middle" x="272" y="-129.8" font-family="Sans" font-size="14.00">Yes</text>
+</g>
+<!-- have_invs&#45;&gt;request_invs -->
+<g id="edge3" class="edge"><title>have_invs&#45;&gt;request_invs</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M119.5,-104.922C119.5,-98.7016 119.5,-91.4999 119.5,-84.5999"/>
+<polygon fill="black" stroke="black" stroke-width="1.75" points="123,-84.1896 119.5,-74.1896 116,-84.1896 123,-84.1896"/>
+<text text-anchor="middle" x="133.5" y="-85.8" font-family="Sans" font-size="14.00"> &#160;No</text>
+</g>
+</g>
+</svg>
--- a/img/dev/en-headers-first-flowchart.dot
+++ b/img/dev/en-headers-first-flowchart.dot
@ -0,0 +1,37 @@
+digraph {
+// This file is licensed under the MIT License (MIT) available on
+// http://opensource.org/licenses/MIT.
+
+size=6.25;
+rankdir=TB
+splines = "true";
+ranksep = 0.2;
+nodesep = 0.9;
+
+edge [ penwidth = 1.75, fontname="Sans" ]
+node [ penwidth = 1.75, shape = "none", fontname="Sans"]
+graph [ penwidth = 1.75, fontname="Sans" ]
+
+fsbc [ label = "Fully-Synced Block Chain?", style = "filled" ];
+fshc [ label = "Fully-Synced Header Chain?", style = "filled" ];
+more_headers_than_blocks [ label = "More Headers Than Blocks?", style = "filled" ];
+listen_for_new_blocks [ label = "Listen For New Blocks (Inv)" ];
+request_blocks [ label = "Request Blocks (GetData)" ];
+request_headers [ label = "Request Headers (GetHeaders)" ];
+
+fsbc -> fshc [ label = "  No" ];
+fshc -> more_headers_than_blocks [ label = "No" ];
+fshc -> request_headers [ label = "  No" ];
+
+fsbc -> listen_for_new_blocks [ label = "Yes", constraint=false ];
+fshc -> request_blocks [ label = "Yes", constraint=false ];
+request_blocks -> more_headers_than_blocks [ dir=back, label = "   Yes" ];
+
+//request_headers -> fshc [ style = "dotted", constraint = false ];
+//request_blocks -> fsbc [ style = "dotted", constraint = false ];
+
+
+
+
+label = "\ \nOverview Of Headers-First Initial Blocks Download (IBD)"
+}
--- a/img/dev/en-headers-first-flowchart.png
+++ b/img/dev/en-headers-first-flowchart.png
--- a/img/dev/en-headers-first-flowchart.svg
+++ b/img/dev/en-headers-first-flowchart.svg
@ -0,0 +1,78 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
+ "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
+<!-- Generated by graphviz version 2.38.0 (20140413.2041)
+ -->
+<!-- Title: %3 Pages: 1 -->
+<svg width="450pt" height="175pt"
+ viewBox="0.00 0.00 450.00 174.51" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+<g id="graph0" class="graph" transform="scale(0.807899 0.807899) rotate(0) translate(4 212)">
+<title>%3</title>
+<polygon fill="white" stroke="none" points="-4,4 -4,-212 553,-212 553,4 -4,4"/>
+<text text-anchor="middle" x="274.5" y="-22.8" font-family="Sans" font-size="14.00"> </text>
+<text text-anchor="middle" x="274.5" y="-7.8" font-family="Sans" font-size="14.00">Overview Of Headers&#45;First Initial Blocks Download (IBD)</text>
+<!-- fsbc -->
+<g id="node1" class="node"><title>fsbc</title>
+<polygon fill="lightgrey" stroke="none" stroke-width="1.75" points="213.5,-208 16.5,-208 16.5,-172 213.5,-172 213.5,-208"/>
+<text text-anchor="middle" x="115" y="-186.3" font-family="Sans" font-size="14.00">Fully&#45;Synced Block Chain?</text>
+</g>
+<!-- fshc -->
+<g id="node2" class="node"><title>fshc</title>
+<polygon fill="lightgrey" stroke="none" stroke-width="1.75" points="219.5,-141 10.5,-141 10.5,-105 219.5,-105 219.5,-141"/>
+<text text-anchor="middle" x="115" y="-119.3" font-family="Sans" font-size="14.00">Fully&#45;Synced Header Chain?</text>
+</g>
+<!-- fsbc&#45;&gt;fshc -->
+<g id="edge1" class="edge"><title>fsbc&#45;&gt;fshc</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M115,-171.922C115,-165.702 115,-158.5 115,-151.6"/>
+<polygon fill="black" stroke="black" stroke-width="1.75" points="118.5,-151.19 115,-141.19 111.5,-151.19 118.5,-151.19"/>
+<text text-anchor="middle" x="129" y="-152.8" font-family="Sans" font-size="14.00"> &#160;No</text>
+</g>
+<!-- listen_for_new_blocks -->
+<g id="node4" class="node"><title>listen_for_new_blocks</title>
+<text text-anchor="middle" x="446" y="-186.3" font-family="Sans" font-size="14.00">Listen For New Blocks (Inv)</text>
+</g>
+<!-- fsbc&#45;&gt;listen_for_new_blocks -->
+<g id="edge4" class="edge"><title>fsbc&#45;&gt;listen_for_new_blocks</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M213.863,-190C251.197,-190 293.964,-190 332.533,-190"/>
+<polygon fill="black" stroke="black" stroke-width="1.75" points="332.765,-193.5 342.765,-190 332.765,-186.5 332.765,-193.5"/>
+<text text-anchor="middle" x="278.25" y="-196.8" font-family="Sans" font-size="14.00">Yes</text>
+</g>
+<!-- more_headers_than_blocks -->
+<g id="node3" class="node"><title>more_headers_than_blocks</title>
+<polygon fill="lightgrey" stroke="none" stroke-width="1.75" points="514.5,-74 307.5,-74 307.5,-38 514.5,-38 514.5,-74"/>
+<text text-anchor="middle" x="411" y="-52.3" font-family="Sans" font-size="14.00">More Headers Than Blocks?</text>
+</g>
+<!-- fshc&#45;&gt;more_headers_than_blocks -->
+<g id="edge2" class="edge"><title>fshc&#45;&gt;more_headers_than_blocks</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M192.771,-104.922C232.969,-96.0945 282.167,-85.291 323.668,-76.1776"/>
+<polygon fill="black" stroke="black" stroke-width="1.75" points="324.476,-79.5837 333.492,-74.0203 322.974,-72.7466 324.476,-79.5837"/>
+<text text-anchor="middle" x="299.5" y="-85.8" font-family="Sans" font-size="14.00">No</text>
+</g>
+<!-- request_blocks -->
+<g id="node5" class="node"><title>request_blocks</title>
+<text text-anchor="middle" x="446" y="-119.3" font-family="Sans" font-size="14.00">Request Blocks (GetData)</text>
+</g>
+<!-- fshc&#45;&gt;request_blocks -->
+<g id="edge5" class="edge"><title>fshc&#45;&gt;request_blocks</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M219.73,-123C257.72,-123 300.669,-123 338.863,-123"/>
+<polygon fill="black" stroke="black" stroke-width="1.75" points="338.981,-126.5 348.981,-123 338.981,-119.5 338.981,-126.5"/>
+<text text-anchor="middle" x="284.25" y="-129.8" font-family="Sans" font-size="14.00">Yes</text>
+</g>
+<!-- request_headers -->
+<g id="node6" class="node"><title>request_headers</title>
+<text text-anchor="middle" x="115" y="-52.3" font-family="Sans" font-size="14.00">Request Headers (GetHeaders)</text>
+</g>
+<!-- fshc&#45;&gt;request_headers -->
+<g id="edge3" class="edge"><title>fshc&#45;&gt;request_headers</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M115,-104.922C115,-98.7016 115,-91.4999 115,-84.5999"/>
+<polygon fill="black" stroke="black" stroke-width="1.75" points="118.5,-84.1896 115,-74.1896 111.5,-84.1896 118.5,-84.1896"/>
+<text text-anchor="middle" x="129" y="-85.8" font-family="Sans" font-size="14.00"> &#160;No</text>
+</g>
+<!-- request_blocks&#45;&gt;more_headers_than_blocks -->
+<g id="edge6" class="edge"><title>request_blocks&#45;&gt;more_headers_than_blocks</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M431.998,-95.9964C428.049,-88.6617 423.851,-80.8669 420.256,-74.1896"/>
+<polygon fill="black" stroke="black" stroke-width="1.75" points="428.981,-97.7767 436.804,-104.922 435.145,-94.4579 428.981,-97.7767"/>
+<text text-anchor="middle" x="449" y="-85.8" font-family="Sans" font-size="14.00"> &#160;&#160;Yes</text>
+</g>
+</g>
+</svg>
--- a/img/dev/en-headers-first-moving-window.dot
+++ b/img/dev/en-headers-first-moving-window.dot
@ -0,0 +1,45 @@
+digraph {
+// This file is licensed under the MIT License (MIT) available on
+// http://opensource.org/licenses/MIT.
+
+size="6.25";
+rankdir=LR
+nodesep=0.2;
+ranksep=0.3;
+splines="false"
+
+edge [ penwidth = 1.75, fontname="Sans", dir=none ]
+node [ penwidth = 1.75, shape = "box", fontname="Sans", ]
+graph [ penwidth = 1.75, fontname="Sans", fontsize = 16 ]
+
+subgraph cluster_verified {
+    graph [ penwidth = 0 ];
+    node [ style = "filled" ];
+
+    block0 [ width=0, style = "invis", label = "" ];
+    block1 [ label = "1\nDownloaded\nFrom Node A" ];
+    block2 [ label = "2\nDownloaded\nFrom Node B" ];
+
+
+    label = "Downloaded And Validated\n "
+}
+
+block0 -> block1;
+block1 -> block2;
+block2 -> block3 -> block4 -> block5;
+
+block5 -> block6 [ minlen = 2 ];
+
+block6 [ style = "invis", width = 0, label = "" ];
+
+subgraph cluster_download_window {
+    block3 [ label = "3\nRequested\nFrom Node A" ];
+    block4 [ label = "4\nDownloaded\nFrom Node B", style = "filled" ];
+    block5 [ label = "5\nRequested\nFrom Node B" ];
+
+    label = "Download Window\nBlocks Not Validated Yet"
+}
+
+label = " \nSimulated Headers-First Download Window (Real Window Is Much Larger)"
+
+}
--- a/img/dev/en-headers-first-moving-window.png
+++ b/img/dev/en-headers-first-moving-window.png
--- a/img/dev/en-headers-first-moving-window.svg
+++ b/img/dev/en-headers-first-moving-window.svg
@ -0,0 +1,86 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
+ "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
+<!-- Generated by graphviz version 2.38.0 (20140413.2041)
+ -->
+<!-- Title: %3 Pages: 1 -->
+<svg width="450pt" height="116pt"
+ viewBox="0.00 0.00 450.00 115.68" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+<g id="graph0" class="graph" transform="scale(0.635593 0.635593) rotate(0) translate(4 178)">
+<title>%3</title>
+<polygon fill="white" stroke="none" points="-4,4 -4,-178 704,-178 704,4 -4,4"/>
+<text text-anchor="middle" x="350" y="-27.2" font-family="Sans" font-size="16.00"> </text>
+<text text-anchor="middle" x="350" y="-9.2" font-family="Sans" font-size="16.00">Simulated Headers&#45;First Download Window (Real Window Is Much Larger)</text>
+<g id="clust1" class="cluster"><title>cluster_verified</title>
+<polygon fill="none" stroke="black" stroke-width="0" points="8,-52 8,-166 279,-166 279,-52 8,-52"/>
+<text text-anchor="middle" x="143.5" y="-149.2" font-family="Sans" font-size="16.00">Downloaded And Validated</text>
+<text text-anchor="middle" x="143.5" y="-131.2" font-family="Sans" font-size="16.00"> </text>
+</g>
+<g id="clust2" class="cluster"><title>cluster_download_window</title>
+<polygon fill="none" stroke="black" stroke-width="1.75" points="287,-52 287,-166 662,-166 662,-52 287,-52"/>
+<text text-anchor="middle" x="474.5" y="-149.2" font-family="Sans" font-size="16.00">Download Window</text>
+<text text-anchor="middle" x="474.5" y="-131.2" font-family="Sans" font-size="16.00">Blocks Not Validated Yet</text>
+</g>
+<!-- block0 -->
+<!-- block1 -->
+<g id="node2" class="node"><title>block1</title>
+<polygon fill="lightgrey" stroke="black" stroke-width="1.75" points="144,-113.5 39,-113.5 39,-60.5 144,-60.5 144,-113.5"/>
+<text text-anchor="middle" x="91.5" y="-98.3" font-family="Sans" font-size="14.00">1</text>
+<text text-anchor="middle" x="91.5" y="-83.3" font-family="Sans" font-size="14.00">Downloaded</text>
+<text text-anchor="middle" x="91.5" y="-68.3" font-family="Sans" font-size="14.00">From Node A</text>
+</g>
+<!-- block0&#45;&gt;block1 -->
+<g id="edge1" class="edge"><title>block0&#45;&gt;block1</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M17.0533,-87C17.8357,-87 27.1458,-87 38.8907,-87"/>
+</g>
+<!-- block2 -->
+<g id="node3" class="node"><title>block2</title>
+<polygon fill="lightgrey" stroke="black" stroke-width="1.75" points="271,-113.5 166,-113.5 166,-60.5 271,-60.5 271,-113.5"/>
+<text text-anchor="middle" x="218.5" y="-98.3" font-family="Sans" font-size="14.00">2</text>
+<text text-anchor="middle" x="218.5" y="-83.3" font-family="Sans" font-size="14.00">Downloaded</text>
+<text text-anchor="middle" x="218.5" y="-68.3" font-family="Sans" font-size="14.00">From Node B</text>
+</g>
+<!-- block1&#45;&gt;block2 -->
+<g id="edge2" class="edge"><title>block1&#45;&gt;block2</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M144.064,-87C151.193,-87 158.517,-87 165.651,-87"/>
+</g>
+<!-- block3 -->
+<g id="node4" class="node"><title>block3</title>
+<polygon fill="none" stroke="black" stroke-width="1.75" points="400,-113.5 295,-113.5 295,-60.5 400,-60.5 400,-113.5"/>
+<text text-anchor="middle" x="347.5" y="-98.3" font-family="Sans" font-size="14.00">3</text>
+<text text-anchor="middle" x="347.5" y="-83.3" font-family="Sans" font-size="14.00">Requested</text>
+<text text-anchor="middle" x="347.5" y="-68.3" font-family="Sans" font-size="14.00">From Node A</text>
+</g>
+<!-- block2&#45;&gt;block3 -->
+<g id="edge3" class="edge"><title>block2&#45;&gt;block3</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M271.156,-87C278.984,-87 287.062,-87 294.89,-87"/>
+</g>
+<!-- block4 -->
+<g id="node5" class="node"><title>block4</title>
+<polygon fill="lightgrey" stroke="black" stroke-width="1.75" points="527,-113.5 422,-113.5 422,-60.5 527,-60.5 527,-113.5"/>
+<text text-anchor="middle" x="474.5" y="-98.3" font-family="Sans" font-size="14.00">4</text>
+<text text-anchor="middle" x="474.5" y="-83.3" font-family="Sans" font-size="14.00">Downloaded</text>
+<text text-anchor="middle" x="474.5" y="-68.3" font-family="Sans" font-size="14.00">From Node B</text>
+</g>
+<!-- block3&#45;&gt;block4 -->
+<g id="edge4" class="edge"><title>block3&#45;&gt;block4</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M400.064,-87C407.193,-87 414.517,-87 421.651,-87"/>
+</g>
+<!-- block5 -->
+<g id="node6" class="node"><title>block5</title>
+<polygon fill="none" stroke="black" stroke-width="1.75" points="654,-113.5 549,-113.5 549,-60.5 654,-60.5 654,-113.5"/>
+<text text-anchor="middle" x="601.5" y="-98.3" font-family="Sans" font-size="14.00">5</text>
+<text text-anchor="middle" x="601.5" y="-83.3" font-family="Sans" font-size="14.00">Requested</text>
+<text text-anchor="middle" x="601.5" y="-68.3" font-family="Sans" font-size="14.00">From Node B</text>
+</g>
+<!-- block4&#45;&gt;block5 -->
+<g id="edge5" class="edge"><title>block4&#45;&gt;block5</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M527.064,-87C534.193,-87 541.517,-87 548.651,-87"/>
+</g>
+<!-- block6 -->
+<!-- block5&#45;&gt;block6 -->
+<g id="edge6" class="edge"><title>block5&#45;&gt;block6</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M654.229,-87C675.25,-87 695.351,-87 698.935,-87"/>
+</g>
+</g>
+</svg>
--- a/img/dev/en-ibd-getheaders.dot
+++ b/img/dev/en-ibd-getheaders.dot
@ -0,0 +1,57 @@
+digraph {
+// This file is licensed under the MIT License (MIT) available on
+// http://opensource.org/licenses/MIT.
+
+size=6.25;
+rankdir=LR
+splines = "false";
+ranksep = 0.4;
+nodesep = 0.1;
+
+edge [ penwidth = 1.75, fontname="Sans" ]
+node [ penwidth = 1.75, shape = "box", fontname="Sans"]
+graph [ penwidth = 1.75, fontname="Sans" ]
+
+ibd -> getblocks:f1 -> sync;
+
+ibd [ label = "IBD\nNode", shape="none" ];
+sync [ label = "Sync\nNode", shape="none" ];
+
+getblocks [ shape="plaintext", label=<
+    <table border="2" cellborder="1" cellpadding="1">
+      <tr>
+        <td colspan="4" port="f1" border="0" cellpadding="4"><b>GetHeaders Message</b></td>
+      </tr>
+
+      <tr>
+        <td colspan="4" border="0"><i>Message Header</i></td>
+      </tr>
+
+      <tr>
+        <td border="1"><i>Start String</i><br/><font face="courier">f9beb4d9</font></td>
+        <td border="1" cellpadding="4"><i>Command</i><br/><font face="courier">getheaders</font></td>
+        <td border="1"><i>Size</i><br/><font face="courier">69</font></td>
+        <td border="1"><i>Checksum</i><br/><font face="courier">f5fcbcad</font></td>
+      </tr>
+
+      <tr>
+        <td colspan="4" border="0"><i>Payload</i></td>
+      </tr>
+
+      <tr>
+        <td colspan="2"><i>Protocol Version</i><br /><font face="courier">70002</font></td>
+        <td colspan="2"><i>Header Hash Count</i><br /><font face="courier">1</font></td>
+      </tr>
+
+      <tr>
+        <td colspan="4"><i>Header Hashes (Highest-Height First)</i><br /><font face="courier">6fe28c0ab6f1b3...d6190000000000</font></td>
+      </tr>
+
+      <tr>
+        <td colspan="4"><i>Stopping Hash (Zero Is "No Stop")</i><br /><font face="courier">00000000000000...00000000000000</font></td>
+      </tr>
+
+    </table>>];
+
+label = "First getheaders message sent from Initial Blocks Download (IBD) node"
+}
--- a/img/dev/en-ibd-getheaders.png
+++ b/img/dev/en-ibd-getheaders.png
--- a/img/dev/en-ibd-getheaders.svg
+++ b/img/dev/en-ibd-getheaders.svg
@ -0,0 +1,65 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
+ "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
+<!-- Generated by graphviz version 2.38.0 (20140413.2041)
+ -->
+<!-- Title: %3 Pages: 1 -->
+<svg width="450pt" height="216pt"
+ viewBox="0.00 0.00 450.00 215.93" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+<g id="graph0" class="graph" transform="scale(0.863724 0.863724) rotate(0) translate(4 246)">
+<title>%3</title>
+<polygon fill="white" stroke="none" points="-4,4 -4,-246 517,-246 517,4 -4,4"/>
+<text text-anchor="middle" x="256.5" y="-7.8" font-family="Sans" font-size="14.00">First getheaders message sent from Initial Blocks Download (IBD) node</text>
+<!-- ibd -->
+<g id="node1" class="node"><title>ibd</title>
+<text text-anchor="middle" x="27" y="-226.3" font-family="Sans" font-size="14.00">IBD</text>
+<text text-anchor="middle" x="27" y="-211.3" font-family="Sans" font-size="14.00">Node</text>
+</g>
+<!-- getblocks -->
+<g id="node2" class="node"><title>getblocks</title>
+<text text-anchor="start" x="171" y="-219.3" font-family="Sans" font-weight="bold" font-size="14.00">GetHeaders Message</text>
+<text text-anchor="start" x="199.5" y="-197.3" font-family="Sans" font-style="italic" font-size="14.00">Message Header</text>
+<polygon fill="none" stroke="black" points="95.5,-151.5 95.5,-189.5 179.5,-189.5 179.5,-151.5 95.5,-151.5"/>
+<text text-anchor="start" x="97.5" y="-174.3" font-family="Sans" font-style="italic" font-size="14.00">Start String</text>
+<text text-anchor="start" x="104" y="-160.3" font-family="Courier,monospace" font-size="14.00">f9beb4d9</text>
+<polygon fill="none" stroke="black" points="181.5,-151.5 181.5,-189.5 274.5,-189.5 274.5,-151.5 181.5,-151.5"/>
+<text text-anchor="start" x="193" y="-174.3" font-family="Sans" font-style="italic" font-size="14.00">Command</text>
+<text text-anchor="start" x="186.5" y="-160.3" font-family="Courier,monospace" font-size="14.00">getheaders</text>
+<polygon fill="none" stroke="black" points="276.5,-151.5 276.5,-189.5 324.5,-189.5 324.5,-151.5 276.5,-151.5"/>
+<text text-anchor="start" x="286" y="-174.3" font-family="Sans" font-style="italic" font-size="14.00">Size</text>
+<text text-anchor="start" x="292" y="-160.3" font-family="Courier,monospace" font-size="14.00">69</text>
+<polygon fill="none" stroke="black" points="326.5,-151.5 326.5,-189.5 418.5,-189.5 418.5,-151.5 326.5,-151.5"/>
+<text text-anchor="start" x="336" y="-174.3" font-family="Sans" font-style="italic" font-size="14.00">Checksum</text>
+<text text-anchor="start" x="339" y="-160.3" font-family="Courier,monospace" font-size="14.00">f5fcbcad</text>
+<text text-anchor="start" x="229.5" y="-138.3" font-family="Sans" font-style="italic" font-size="14.00">Payload</text>
+<polygon fill="none" stroke="black" points="95.5,-98.5 95.5,-130.5 274.5,-130.5 274.5,-98.5 95.5,-98.5"/>
+<text text-anchor="start" x="128.5" y="-118.3" font-family="Sans" font-style="italic" font-size="14.00">Protocol Version</text>
+<text text-anchor="start" x="164" y="-104.3" font-family="Courier,monospace" font-size="14.00">70002</text>
+<polygon fill="none" stroke="black" points="276.5,-98.5 276.5,-130.5 418.5,-130.5 418.5,-98.5 276.5,-98.5"/>
+<text text-anchor="start" x="279.5" y="-118.3" font-family="Sans" font-style="italic" font-size="14.00">Header Hash Count</text>
+<text text-anchor="start" x="343" y="-104.3" font-family="Courier,monospace" font-size="14.00">1</text>
+<polygon fill="none" stroke="black" points="95.5,-64.5 95.5,-96.5 418.5,-96.5 418.5,-64.5 95.5,-64.5"/>
+<text text-anchor="start" x="127.5" y="-84.3" font-family="Sans" font-style="italic" font-size="14.00">Header Hashes (Highest&#45;Height First)</text>
+<text text-anchor="start" x="129" y="-70.3" font-family="Courier,monospace" font-size="14.00">6fe28c0ab6f1b3...d6190000000000</text>
+<polygon fill="none" stroke="black" points="95.5,-30.5 95.5,-62.5 418.5,-62.5 418.5,-30.5 95.5,-30.5"/>
+<text text-anchor="start" x="138.5" y="-50.3" font-family="Sans" font-style="italic" font-size="14.00">Stopping Hash (Zero Is &quot;No Stop&quot;)</text>
+<text text-anchor="start" x="129" y="-36.3" font-family="Courier,monospace" font-size="14.00">00000000000000...00000000000000</text>
+<polygon fill="none" stroke="black" stroke-width="2" points="92,-28 92,-237 421,-237 421,-28 92,-28"/>
+</g>
+<!-- ibd&#45;&gt;getblocks -->
+<g id="edge1" class="edge"><title>ibd&#45;&gt;getblocks:f1</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M54.2826,-222.5C64.8835,-222.5 76.4737,-222.5 84.4768,-222.5"/>
+<polygon fill="black" stroke="black" stroke-width="1.75" points="84.5,-226 94.5,-222.5 84.5,-219 84.5,-226"/>
+</g>
+<!-- sync -->
+<g id="node3" class="node"><title>sync</title>
+<text text-anchor="middle" x="486" y="-226.3" font-family="Sans" font-size="14.00">Sync</text>
+<text text-anchor="middle" x="486" y="-211.3" font-family="Sans" font-size="14.00">Node</text>
+</g>
+<!-- getblocks&#45;&gt;sync -->
+<g id="edge2" class="edge"><title>getblocks:f1&#45;&gt;sync</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M419.5,-222.5C419.5,-222.5 433.372,-222.5 448.348,-222.5"/>
+<polygon fill="black" stroke="black" stroke-width="1.75" points="448.736,-226 458.736,-222.5 448.736,-219 448.736,-226"/>
+</g>
+</g>
+</svg>
--- a/img/dev/en-ibd-headers.dot
+++ b/img/dev/en-ibd-headers.dot
@ -0,0 +1,67 @@
+digraph {
+// This file is licensed under the MIT License (MIT) available on
+// http://opensource.org/licenses/MIT.
+
+size=6.25;
+rankdir=LR
+splines = "false";
+ranksep = 0.2;
+nodesep = 0.1;
+
+edge [ penwidth = 1.75, fontname="Sans" ]
+node [ penwidth = 1.75, shape = "box", fontname="Sans"]
+graph [ penwidth = 1.75, fontname="Sans" ]
+
+ibd -> inv:f1 -> sync [ dir = "back" ];
+
+ibd [ label = "IBD\nNode", shape="none" ];
+sync [ label = "Sync\nNode", shape="none" ];
+
+inv [ shape="plaintext", label=<
+    <table border="2" cellborder="1">
+      <tr>
+        <td colspan="4" port="f1" border="0" cellpadding="4"><b>Headers Message</b></td>
+      </tr>
+
+      <tr>
+        <td colspan="4" border="0"><i>Message Header</i></td>
+      </tr>
+
+      <tr>
+        <td border="1"><i>Start String</i><br/><font face="courier">f9beb4d9</font></td>
+        <td border="1"><i>Command</i><br/><font face="courier">headers</font></td>
+        <td border="1"><i>Size</i><br/><font face="courier">162003</font></td>
+        <td border="1"><i>Checksum</i><br/><font face="courier">a65b2b77</font></td>
+      </tr>
+
+      <tr>
+        <td colspan="4" border="0"><i>Payload</i></td>
+      </tr>
+
+      <tr>
+        <td colspan="4"><i>Number Of Headers (Max 2,000 In Reply To GetHeaders) </i><br /><font face="courier">2000</font></td>
+      </tr>
+
+      <tr>
+        <td colspan="4">
+        <table border="0">
+          <tr>
+            <td><i>80-byte Block Headers + 0x00 (The Empty Tx Count)</i></td>
+          </tr>
+          <tr>
+            <td><font face="courier">010000006fe28cab...ff001d01e3629900</font></td>
+          </tr>
+          <tr>
+            <td><font face="courier">010000004860eb18...ff001d08d2bd6100</font></td>
+          </tr>
+          <tr>
+            <td colspan="2"><i>...............1,998 more block headers...............</i></td>
+          </tr>
+
+        </table>
+        </td>
+      </tr>
+    </table>>];
+
+label = "First headers message reply sent to Initial Blocks Download (IBD) node"
+}
--- a/img/dev/en-ibd-headers.png
+++ b/img/dev/en-ibd-headers.png
--- a/img/dev/en-ibd-headers.svg
+++ b/img/dev/en-ibd-headers.svg
@ -0,0 +1,61 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
+ "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
+<!-- Generated by graphviz version 2.38.0 (20140413.2041)
+ -->
+<!-- Title: %3 Pages: 1 -->
+<svg width="450pt" height="216pt"
+ viewBox="0.00 0.00 450.00 216.44" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+<g id="graph0" class="graph" transform="scale(0.778547 0.778547) rotate(0) translate(4 274)">
+<title>%3</title>
+<polygon fill="white" stroke="none" points="-4,4 -4,-274 574,-274 574,4 -4,4"/>
+<text text-anchor="middle" x="285" y="-7.8" font-family="Sans" font-size="14.00">First headers message reply sent to Initial Blocks Download (IBD) node</text>
+<!-- ibd -->
+<g id="node1" class="node"><title>ibd</title>
+<text text-anchor="middle" x="27" y="-254.3" font-family="Sans" font-size="14.00">IBD</text>
+<text text-anchor="middle" x="27" y="-239.3" font-family="Sans" font-size="14.00">Node</text>
+</g>
+<!-- inv -->
+<g id="node2" class="node"><title>inv</title>
+<text text-anchor="start" x="213.5" y="-247.3" font-family="Sans" font-weight="bold" font-size="14.00">Headers Message</text>
+<text text-anchor="start" x="227.5" y="-224.3" font-family="Sans" font-style="italic" font-size="14.00">Message Header</text>
+<polygon fill="none" stroke="black" points="80,-181.5 80,-215.5 219,-215.5 219,-181.5 80,-181.5"/>
+<text text-anchor="start" x="109.5" y="-202.3" font-family="Sans" font-style="italic" font-size="14.00">Start String</text>
+<text text-anchor="start" x="116" y="-188.3" font-family="Courier,monospace" font-size="14.00">f9beb4d9</text>
+<polygon fill="none" stroke="black" points="221,-181.5 221,-215.5 324,-215.5 324,-181.5 221,-181.5"/>
+<text text-anchor="start" x="237.5" y="-202.3" font-family="Sans" font-style="italic" font-size="14.00">Command</text>
+<text text-anchor="start" x="243.5" y="-188.3" font-family="Courier,monospace" font-size="14.00">headers</text>
+<polygon fill="none" stroke="black" points="326,-181.5 326,-215.5 395,-215.5 395,-181.5 326,-181.5"/>
+<text text-anchor="start" x="346" y="-202.3" font-family="Sans" font-style="italic" font-size="14.00">Size</text>
+<text text-anchor="start" x="335.5" y="-188.3" font-family="Courier,monospace" font-size="14.00">162003</text>
+<polygon fill="none" stroke="black" points="397,-181.5 397,-215.5 490,-215.5 490,-181.5 397,-181.5"/>
+<text text-anchor="start" x="407" y="-202.3" font-family="Sans" font-style="italic" font-size="14.00">Checksum</text>
+<text text-anchor="start" x="410" y="-188.3" font-family="Courier,monospace" font-size="14.00">a65b2b77</text>
+<text text-anchor="start" x="257.5" y="-167.3" font-family="Sans" font-style="italic" font-size="14.00">Payload</text>
+<polygon fill="none" stroke="black" points="80,-124.5 80,-158.5 490,-158.5 490,-124.5 80,-124.5"/>
+<text text-anchor="start" x="86" y="-145.3" font-family="Sans" font-style="italic" font-size="14.00">Number Of Headers (Max 2,000 In Reply To GetHeaders) </text>
+<text text-anchor="start" x="268" y="-131.3" font-family="Courier,monospace" font-size="14.00">2000</text>
+<polygon fill="none" stroke="black" points="80,-30.5 80,-122.5 490,-122.5 490,-30.5 80,-30.5"/>
+<text text-anchor="start" x="93" y="-105.3" font-family="Sans" font-style="italic" font-size="14.00">80&#45;byte Block Headers + 0x00 (The Empty Tx Count)</text>
+<text text-anchor="start" x="133.5" y="-83.3" font-family="Courier,monospace" font-size="14.00">010000006fe28cab...ff001d01e3629900</text>
+<text text-anchor="start" x="133.5" y="-62.3" font-family="Courier,monospace" font-size="14.00">010000004860eb18...ff001d08d2bd6100</text>
+<text text-anchor="start" x="127" y="-42.3" font-family="Sans" font-style="italic" font-size="14.00">...............1,998 more block headers...............</text>
+<polygon fill="none" stroke="black" stroke-width="2" points="77,-28 77,-265 493,-265 493,-28 77,-28"/>
+</g>
+<!-- ibd&#45;&gt;inv -->
+<g id="edge1" class="edge"><title>ibd&#45;&gt;inv:f1</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M64.0987,-250.5C72.4781,-250.5 79,-250.5 79,-250.5"/>
+<polygon fill="black" stroke="black" stroke-width="1.75" points="64.0976,-247 54.0976,-250.5 64.0976,-254 64.0976,-247"/>
+</g>
+<!-- sync -->
+<g id="node3" class="node"><title>sync</title>
+<text text-anchor="middle" x="543" y="-254.3" font-family="Sans" font-size="14.00">Sync</text>
+<text text-anchor="middle" x="543" y="-239.3" font-family="Sans" font-size="14.00">Node</text>
+</g>
+<!-- inv&#45;&gt;sync -->
+<g id="edge2" class="edge"><title>inv:f1&#45;&gt;sync</title>
+<path fill="none" stroke="black" stroke-width="1.75" d="M501.038,-250.5C505.35,-250.5 510.609,-250.5 515.902,-250.5"/>
+<polygon fill="black" stroke="black" stroke-width="1.75" points="501,-247 491,-250.5 501,-254 501,-247"/>
+</g>
+</g>
+</svg>