point-to-point-layout: Doc for Dumbbell Helper (Contributions from GCI 2018)
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Mohit P. Tahiliani
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src/point-to-point-layout/doc/point-to-point-dumbbell.rst
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src/point-to-point-layout/doc/point-to-point-dumbbell.rst
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.. include:: replace.txt
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.. highlight:: cpp
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Point to Point Dumbbell Topology Helper
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---------------------------------------
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This is an introduction to dumbbell topology helper to complement the
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``PointToPointDumbbellHelper`` doxygen.
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Model Description
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*****************
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The |ns3| :cpp:class:`PointToPointDumbbellHelper` class is used to create nodes, add
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point-to-point connections between them and position them in a dumbbell type
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layout. It provides several functions that give complete control over the node
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creation, IPv4/IPv6 address assignment and node positioning (defining bounding
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box).
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It accepts the number of leaf nodes that are to be created on the left, number
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of leaf nodes to be created on the right, and the ``PointToPointHelper``
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objects for the left side, right side and router nodes. These
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``PointToPointHelper`` objects define Device and Channel attributes for the
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nodes in the respective ``NodeContainer`` for left, right and router nodes. It
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then connects all the left leaf nodes to the left router and all the right
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leaf nodes to the right router. Thus, all the left leaf nodes are connected
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to the left router, which is connected to the right router, and the right
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router is connected to all the right leaf nodes.
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It provides a feature to position the nodes in a dumbbell type layout to help
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visualize the topology. This is achieved through a function called
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``BoundingBox`` which requires coordinate limits as parameters, and then
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positions all the nodes within the limits specified to it in a dumbbell layout
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which is described later in this documentation.
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It also provides a function ``InstallStack`` which takes a
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``InternetStackHelper`` object for installing the ``InternetStack`` on the
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nodes, function ``AssignIpv4Addresses`` which takes ``Ipv4AddressHelper``
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objects for the left, right and router nodes for assigning IPv4 address to
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each node. It provides a function ``AssignIpv6Addresses`` which takes a
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``Ipv6Address`` address base and a ``Ipv6Prefix`` prefix for assigning
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IPv6Adddress to every node.
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Node Positioning
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================
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The algorithm used by the ``BoundingBox`` function to position the leaf nodes
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and router nodes uses properties of a circle to correctly place the nodes even
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when the user specified coordinate constraints are not enough to place nodes
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accurately.
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It accepts the minimum upper left X-axis coordinate, minimum upper left Y-axis
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coordinate, maximum lower right X-axis coordinate and maximum lower right Y-
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axis coordinate. These limits are used by the algorithm to position the nodes
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in a dumbbell type layout. It automatically adjusts the nodes according to the
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parameters passed to it, and if the parameters specified are too less than
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required, it positions them in a straight line.
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This feature is useful if the user wants to visualize the topology using any
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supported visualization tool such as PyViz or NetAnim.
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Using PointToPointDumbbellHelper
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================================
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A dumbbell topology with point-to-point links can be configured by using the
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``PointToPointDumbbellHelper``. The first task is to create two
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``PointToPointHelper`` objects: one for the leaf nodes and the other for the
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router nodes as shown below::
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PointToPointHelper p2pLeaf;
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p2pLeaf.SetDeviceAttribute ("DataRate", StringValue ("10Mbps"));
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p2pLeaf.SetChannelAttribute ("Delay", StringValue ("2ms"));
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PointToPointHelper p2pRouter;
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p2pRouter.SetDeviceAttribute ("DataRate", StringValue ("5Mbps"));
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p2pRouter.SetChannelAttribute ("Delay", StringValue ("10ms"));
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After creating the ``PointToPointHelper`` objects, we need to instantiate the
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``PointToPointDumbbellHelper``::
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PointToPointDumbbellHelper dumbbell (nLeftLeaf, p2pLeaf, nRightLeaf,
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p2pLeaf, p2pRouter);
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It is also possible to create two separate ``PointToPointHelper`` objects for
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left leaf nodes and right leaf nodes. In this case, a total of three
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``PointToPointHelper`` objects should be created: one for the left leaf nodes,
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one for right leaf nodes and one for the router nodes as shown below::
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PointToPointHelper p2pLeft;
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p2pLeft.SetDeviceAttribute ("DataRate", StringValue ("10Mbps"));
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p2pLeft.SetChannelAttribute ("Delay", StringValue ("2ms"));
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PointToPointHelper p2pRight;
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p2pRight.SetDeviceAttribute ("DataRate", StringValue ("15Mbps"));
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p2pRight.SetChannelAttribute ("Delay", StringValue ("5ms"));
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PointToPointHelper p2pRouter;
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p2pRouter.SetDeviceAttribute ("DataRate", StringValue ("5Mbps"));
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p2pRouter.SetChannelAttribute ("Delay", StringValue ("10ms"));
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In this case, we instantiate the ``PointToPointDumbbellHelper`` as shown below::
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PointToPointDumbbellHelper dumbbell (nLeftLeaf, p2pLeft, nRightLeaf,
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p2pRight, p2pRouter);
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After this, we can tell the helper to position the nodes in a dumbbell layout.
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This is done to improve the visualization of the topology and can be achieved
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by calling the ``BoundingBox`` function::
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// ulx -> Minimum Upper Left X coordinate
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// uly -> Minimum Upper Left Y coordinate
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// lrx -> Maximum Lower Right X coordinate
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// lry -> Maximum Lower Right Y coordinate
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dumbbell.BoundingBox (ulx, uly, lrx, lry);
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Next, we need to install an Internet Stack on the nodes. We have to
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instantiate a ``InternetStackHelper`` object for this, and pass it as a
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parameter to ``InstallStack`` function::
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InternetStackHelper stack;
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dumbbell.InstallStack (stack);
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Subsequently, we have to assign a IPv4/IPv6 address to the nodes as shown
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below::
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// IPv4
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Ipv4AddressHelper leftIp, rightIp, routerIp;
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leftIp.SetBase ("10.1.1.0", "255.255.255.0");
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rightIp.SetBase ("10.2.1.0", "255.255.255.0");
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routerIp.SetBase ("10.3.1.0", "255.255.255.0");
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dumbbell.AssignIpv4Addresses (leftIp, rightIp, routerIp);
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For IPv6 address::
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// IPv6
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Ipv6Address addrBase ("2001:1::");
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Ipv6Prefix prefix (64)
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dumbbell.AssignIpv6Addresses (addrBase, prefix);
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Example
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*******
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The example for this helper is `dumbbell-animation.cc` located in
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``src/netanim/examples``. The following command shows the available command-
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line options for this example::
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$ ./waf --run "dumbbell-animation --PrintHelp"
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The following command sets up a dumbbell topology with the default
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configuration::
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$ ./waf --run dumbbell-animation
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The following command sets up a dumbbell topology with 6 left leaf nodes and 9
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right leaf nodes::
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$ ./waf --run "dumbbell-animation --nLeftLeaf=6 --nRightLeaf=9"
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The following command sets up a dumbbell topology with 10 left leaf nodes and
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10 right leaf nodes::
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$ ./waf --run "dumbbell-animation --nLeaf=10"
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The expected output from the previous commands is a XML file to playback the
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animation using NetAnim.
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