diff --git a/doc/design/Seq.graphml b/doc/design/Seq.graphml
new file mode 100644
index 000000000..8ddc9353a
--- /dev/null
+++ b/doc/design/Seq.graphml
@@ -0,0 +1,234 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<graphml xmlns="http://graphml.graphdrawing.org/xmlns" xmlns:java="http://www.yworks.com/xml/yfiles-common/1.0/java" xmlns:sys="http://www.yworks.com/xml/yfiles-common/markup/primitives/2.0" xmlns:x="http://www.yworks.com/xml/yfiles-common/markup/2.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:y="http://www.yworks.com/xml/graphml" xmlns:yed="http://www.yworks.com/xml/yed/3" xsi:schemaLocation="http://graphml.graphdrawing.org/xmlns http://www.yworks.com/xml/schema/graphml/1.1/ygraphml.xsd">
+  <!--Created by yEd 3.14.2-->
+  <key attr.name="Description" attr.type="string" for="graph" id="d0"/>
+  <key for="port" id="d1" yfiles.type="portgraphics"/>
+  <key for="port" id="d2" yfiles.type="portgeometry"/>
+  <key for="port" id="d3" yfiles.type="portuserdata"/>
+  <key attr.name="url" attr.type="string" for="node" id="d4"/>
+  <key attr.name="description" attr.type="string" for="node" id="d5"/>
+  <key for="node" id="d6" yfiles.type="nodegraphics"/>
+  <key for="graphml" id="d7" yfiles.type="resources"/>
+  <key attr.name="url" attr.type="string" for="edge" id="d8"/>
+  <key attr.name="description" attr.type="string" for="edge" id="d9"/>
+  <key for="edge" id="d10" yfiles.type="edgegraphics"/>
+  <graph edgedefault="directed" id="G">
+    <data key="d0"/>
+    <node id="n0">
+      <data key="d5"/>
+      <data key="d6">
+        <y:ShapeNode>
+          <y:Geometry height="60.72000000000003" width="64.55999999999995" x="-371.08000000000004" y="-960.3600000000001"/>
+          <y:Fill color="#FFCC00" transparent="false"/>
+          <y:BorderStyle color="#000000" type="line" width="1.0"/>
+          <y:NodeLabel alignment="center" autoSizePolicy="content" fontFamily="Dialog" fontSize="12" fontStyle="plain" hasBackgroundColor="false" hasLineColor="false" height="18.1328125" modelName="custom" textColor="#000000" visible="true" width="11.587890625" x="26.486054687499973" y="21.293593750000014">T<y:LabelModel>
+              <y:SmartNodeLabelModel distance="4.0"/>
+            </y:LabelModel>
+            <y:ModelParameter>
+              <y:SmartNodeLabelModelParameter labelRatioX="0.0" labelRatioY="0.0" nodeRatioX="0.0" nodeRatioY="0.0" offsetX="0.0" offsetY="0.0" upX="0.0" upY="-1.0"/>
+            </y:ModelParameter>
+          </y:NodeLabel>
+          <y:Shape type="diamond"/>
+        </y:ShapeNode>
+      </data>
+    </node>
+    <node id="n1">
+      <data key="d5"/>
+      <data key="d6">
+        <y:ShapeNode>
+          <y:Geometry height="30.0" width="30.0" x="-585.0" y="-945.0"/>
+          <y:Fill color="#CCFFCC" transparent="false"/>
+          <y:BorderStyle color="#000000" type="line" width="1.0"/>
+          <y:NodeLabel alignment="center" autoSizePolicy="content" fontFamily="Dialog" fontSize="12" fontStyle="plain" hasBackgroundColor="false" hasLineColor="false" height="18.1328125" modelName="custom" textColor="#000000" visible="true" width="19.890625" x="5.0546875" y="5.93359375">C1<y:LabelModel>
+              <y:SmartNodeLabelModel distance="4.0"/>
+            </y:LabelModel>
+            <y:ModelParameter>
+              <y:SmartNodeLabelModelParameter labelRatioX="0.0" labelRatioY="0.0" nodeRatioX="0.0" nodeRatioY="0.0" offsetX="0.0" offsetY="0.0" upX="0.0" upY="-1.0"/>
+            </y:ModelParameter>
+          </y:NodeLabel>
+          <y:Shape type="ellipse"/>
+        </y:ShapeNode>
+      </data>
+    </node>
+    <node id="n2">
+      <data key="d5"/>
+      <data key="d6">
+        <y:ShapeNode>
+          <y:Geometry height="30.0" width="30.0" x="-478.04" y="-945.0"/>
+          <y:Fill color="#99CCFF" transparent="false"/>
+          <y:BorderStyle color="#000000" type="line" width="1.0"/>
+          <y:NodeLabel alignment="center" autoSizePolicy="content" fontFamily="Dialog" fontSize="12" fontStyle="plain" hasBackgroundColor="false" hasLineColor="false" height="18.1328125" modelName="custom" textColor="#000000" visible="true" width="18.05078125" x="5.974609375" y="5.93359375">S1<y:LabelModel>
+              <y:SmartNodeLabelModel distance="4.0"/>
+            </y:LabelModel>
+            <y:ModelParameter>
+              <y:SmartNodeLabelModelParameter labelRatioX="0.0" labelRatioY="0.0" nodeRatioX="0.0" nodeRatioY="0.0" offsetX="0.0" offsetY="0.0" upX="0.0" upY="-1.0"/>
+            </y:ModelParameter>
+          </y:NodeLabel>
+          <y:Shape type="ellipse"/>
+        </y:ShapeNode>
+      </data>
+    </node>
+    <node id="n3">
+      <data key="d5"/>
+      <data key="d6">
+        <y:ShapeNode>
+          <y:Geometry height="30.0" width="30.0" x="-122.60000000000014" y="-945.0"/>
+          <y:Fill color="#CCFFCC" transparent="false"/>
+          <y:BorderStyle color="#000000" type="line" width="1.0"/>
+          <y:NodeLabel alignment="center" autoSizePolicy="content" fontFamily="Dialog" fontSize="12" fontStyle="plain" hasBackgroundColor="false" hasLineColor="false" height="18.1328125" modelName="custom" textColor="#000000" visible="true" width="19.890625" x="5.0546875" y="5.93359375">C2<y:LabelModel>
+              <y:SmartNodeLabelModel distance="4.0"/>
+            </y:LabelModel>
+            <y:ModelParameter>
+              <y:SmartNodeLabelModelParameter labelRatioX="0.0" labelRatioY="0.0" nodeRatioX="0.0" nodeRatioY="0.0" offsetX="0.0" offsetY="0.0" upX="0.0" upY="-1.0"/>
+            </y:ModelParameter>
+          </y:NodeLabel>
+          <y:Shape type="ellipse"/>
+        </y:ShapeNode>
+      </data>
+    </node>
+    <node id="n4">
+      <data key="d5"/>
+      <data key="d6">
+        <y:ShapeNode>
+          <y:Geometry height="30.0" width="30.0" x="-229.56000000000012" y="-945.0"/>
+          <y:Fill color="#99CCFF" transparent="false"/>
+          <y:BorderStyle color="#000000" type="line" width="1.0"/>
+          <y:NodeLabel alignment="center" autoSizePolicy="content" fontFamily="Dialog" fontSize="12" fontStyle="plain" hasBackgroundColor="false" hasLineColor="false" height="18.1328125" modelName="custom" textColor="#000000" visible="true" width="18.05078125" x="5.974609375" y="5.93359375">S2<y:LabelModel>
+              <y:SmartNodeLabelModel distance="4.0"/>
+            </y:LabelModel>
+            <y:ModelParameter>
+              <y:SmartNodeLabelModelParameter labelRatioX="0.0" labelRatioY="0.0" nodeRatioX="0.0" nodeRatioY="0.0" offsetX="0.0" offsetY="0.0" upX="0.0" upY="-1.0"/>
+            </y:ModelParameter>
+          </y:NodeLabel>
+          <y:Shape type="ellipse"/>
+        </y:ShapeNode>
+      </data>
+    </node>
+    <node id="n5">
+      <data key="d5"/>
+      <data key="d6">
+        <y:ShapeNode>
+          <y:Geometry height="18.715277777777715" width="82.08333333333326" x="-255.60166666666674" y="-879.3576388888889"/>
+          <y:Fill color="#C0C0C0" transparent="false"/>
+          <y:BorderStyle color="#000000" type="line" width="1.0"/>
+          <y:NodeLabel alignment="center" autoSizePolicy="content" fontFamily="Dialog" fontSize="12" fontStyle="plain" hasBackgroundColor="false" hasLineColor="false" height="18.1328125" modelName="custom" textColor="#000000" visible="true" width="41.587890625" x="20.24772135416663" y="0.29123263888891415">Queue<y:LabelModel>
+              <y:SmartNodeLabelModel distance="4.0"/>
+            </y:LabelModel>
+            <y:ModelParameter>
+              <y:SmartNodeLabelModelParameter labelRatioX="0.0" labelRatioY="0.0" nodeRatioX="0.0" nodeRatioY="0.0" offsetX="0.0" offsetY="0.0" upX="0.0" upY="-1.0"/>
+            </y:ModelParameter>
+          </y:NodeLabel>
+          <y:Shape type="rectangle"/>
+        </y:ShapeNode>
+      </data>
+    </node>
+    <node id="n6">
+      <data key="d5"/>
+      <data key="d6">
+        <y:ShapeNode>
+          <y:Geometry height="18.715277777777715" width="82.08333333333326" x="-504.08166666666665" y="-879.3576388888889"/>
+          <y:Fill color="#C0C0C0" transparent="false"/>
+          <y:BorderStyle color="#000000" type="line" width="1.0"/>
+          <y:NodeLabel alignment="center" autoSizePolicy="content" fontFamily="Dialog" fontSize="12" fontStyle="plain" hasBackgroundColor="false" hasLineColor="false" height="18.1328125" modelName="custom" textColor="#000000" visible="true" width="41.587890625" x="20.24772135416663" y="0.29123263888891415">Queue<y:LabelModel>
+              <y:SmartNodeLabelModel distance="4.0"/>
+            </y:LabelModel>
+            <y:ModelParameter>
+              <y:SmartNodeLabelModelParameter labelRatioX="0.0" labelRatioY="0.0" nodeRatioX="0.0" nodeRatioY="0.0" offsetX="0.0" offsetY="0.0" upX="0.0" upY="-1.0"/>
+            </y:ModelParameter>
+          </y:NodeLabel>
+          <y:Shape type="rectangle"/>
+        </y:ShapeNode>
+      </data>
+    </node>
+    <edge id="e0" source="n0" target="n4">
+      <data key="d9"/>
+      <data key="d10">
+        <y:PolyLineEdge>
+          <y:Path sx="0.0" sy="0.0" tx="0.0" ty="0.0"/>
+          <y:LineStyle color="#000000" type="dashed" width="1.0"/>
+          <y:Arrows source="none" target="standard"/>
+          <y:EdgeLabel alignment="center" configuration="AutoFlippingLabel" distance="2.0" fontFamily="Dialog" fontSize="12" fontStyle="plain" hasBackgroundColor="false" hasLineColor="false" height="18.1328125" modelName="free" modelPosition="anywhere" preferredPlacement="anywhere" ratio="0.5" textColor="#000000" visible="true" width="54.8359375" x="6.2584301757812" y="-23.026406250000264">Dispatch<y:PreferredPlacementDescriptor angle="0.0" angleOffsetOnRightSide="0" angleReference="absolute" angleRotationOnRightSide="co" distance="-1.0" frozen="true" placement="anywhere" side="anywhere" sideReference="relative_to_edge_flow"/>
+          </y:EdgeLabel>
+          <y:BendStyle smoothed="false"/>
+        </y:PolyLineEdge>
+      </data>
+    </edge>
+    <edge id="e1" source="n4" target="n3">
+      <data key="d9"/>
+      <data key="d10">
+        <y:PolyLineEdge>
+          <y:Path sx="0.0" sy="0.0" tx="0.0" ty="0.0"/>
+          <y:LineStyle color="#000000" type="dashed" width="1.0"/>
+          <y:Arrows source="none" target="standard"/>
+          <y:EdgeLabel alignment="center" configuration="AutoFlippingLabel" distance="2.0" fontFamily="Dialog" fontSize="12" fontStyle="plain" hasBackgroundColor="false" hasLineColor="false" height="18.1328125" modelName="free" modelPosition="anywhere" preferredPlacement="anywhere" ratio="0.5" textColor="#000000" visible="true" width="44.41796875" x="13.971013183593755" y="-23.66640625000025">Deliver<y:PreferredPlacementDescriptor angle="0.0" angleOffsetOnRightSide="0" angleReference="absolute" angleRotationOnRightSide="co" distance="-1.0" frozen="true" placement="anywhere" side="anywhere" sideReference="relative_to_edge_flow"/>
+          </y:EdgeLabel>
+          <y:BendStyle smoothed="false"/>
+        </y:PolyLineEdge>
+      </data>
+    </edge>
+    <edge id="e2" source="n1" target="n2">
+      <data key="d9"/>
+      <data key="d10">
+        <y:PolyLineEdge>
+          <y:Path sx="0.0" sy="0.0" tx="0.0" ty="0.0"/>
+          <y:LineStyle color="#000000" type="dashed" width="1.0"/>
+          <y:Arrows source="none" target="standard"/>
+          <y:EdgeLabel alignment="center" configuration="AutoFlippingLabel" distance="2.0" fontFamily="Dialog" fontSize="12" fontStyle="plain" hasBackgroundColor="false" hasLineColor="false" height="18.1328125" modelName="free" modelPosition="anywhere" preferredPlacement="anywhere" ratio="0.5" textColor="#000000" visible="true" width="94.556640625" x="43.54167968749999" y="-36.46640625000032">Publish QoS1/2<y:PreferredPlacementDescriptor angle="0.0" angleOffsetOnRightSide="0" angleReference="absolute" angleRotationOnRightSide="co" distance="-1.0" frozen="true" placement="anywhere" side="anywhere" sideReference="relative_to_edge_flow"/>
+          </y:EdgeLabel>
+          <y:BendStyle smoothed="false"/>
+        </y:PolyLineEdge>
+      </data>
+    </edge>
+    <edge id="e3" source="n2" target="n0">
+      <data key="d9"/>
+      <data key="d10">
+        <y:PolyLineEdge>
+          <y:Path sx="0.0" sy="0.0" tx="0.0" ty="0.0"/>
+          <y:LineStyle color="#000000" type="dashed" width="1.0"/>
+          <y:Arrows source="none" target="standard"/>
+          <y:BendStyle smoothed="false"/>
+        </y:PolyLineEdge>
+      </data>
+    </edge>
+    <edge id="e4" source="n1" target="n0">
+      <data key="d9"/>
+      <data key="d10">
+        <y:PolyLineEdge>
+          <y:Path sx="0.0" sy="0.0" tx="-32.24675781249998" ty="0.0">
+            <y:Point x="-464.4087997380702" y="-990.0"/>
+          </y:Path>
+          <y:LineStyle color="#000000" type="dashed" width="1.0"/>
+          <y:Arrows source="none" target="standard"/>
+          <y:EdgeLabel alignment="center" configuration="AutoFlippingLabel" distance="2.0" fontFamily="Dialog" fontSize="12" fontStyle="plain" hasBackgroundColor="false" hasLineColor="false" height="18.1328125" modelName="free" modelPosition="anywhere" preferredPlacement="anywhere" ratio="0.5" textColor="#000000" visible="true" width="80.330078125" x="53.093395996093705" y="-79.45582275390632">Publish Qos0<y:PreferredPlacementDescriptor angle="0.0" angleOffsetOnRightSide="0" angleReference="absolute" angleRotationOnRightSide="co" distance="-1.0" frozen="true" placement="anywhere" side="anywhere" sideReference="relative_to_edge_flow"/>
+          </y:EdgeLabel>
+          <y:BendStyle smoothed="false"/>
+        </y:PolyLineEdge>
+      </data>
+    </edge>
+    <edge id="e5" source="n4" target="n5">
+      <data key="d9"/>
+      <data key="d10">
+        <y:PolyLineEdge>
+          <y:Path sx="0.0" sy="0.0" tx="0.0" ty="0.0"/>
+          <y:LineStyle color="#000000" type="dashed" width="1.0"/>
+          <y:Arrows source="none" target="standard"/>
+          <y:BendStyle smoothed="false"/>
+        </y:PolyLineEdge>
+      </data>
+    </edge>
+    <edge id="e6" source="n2" target="n6">
+      <data key="d9"/>
+      <data key="d10">
+        <y:PolyLineEdge>
+          <y:Path sx="0.0" sy="0.0" tx="0.0" ty="0.0"/>
+          <y:LineStyle color="#000000" type="dashed" width="1.0"/>
+          <y:Arrows source="none" target="standard"/>
+          <y:BendStyle smoothed="false"/>
+        </y:PolyLineEdge>
+      </data>
+    </edge>
+  </graph>
+  <data key="d7">
+    <y:Resources/>
+  </data>
+</graphml>
diff --git a/doc/design/Seq.png b/doc/design/Seq.png
new file mode 100644
index 000000000..b77f682a1
Binary files /dev/null and b/doc/design/Seq.png differ