docs: Adding forwarding strategy example
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+
+Forwarding Strategies
+=====================
+
+ndnSIM provides simple ways to experiment with custom Interest/Data forwarding strategies.
+A new forwarding strategy can be implement completely different processing or override just specific actions/events of the :ndnsim:`forwarding strategy interface <ndn::ForwardingStrategy>`.
+Please refer to :ndnsim:`API documentation <ndn::ForwardingStrategy>` of the forwarding strategy interface, which lists all default actions/events.
+
+Writing your own custom strategy
+++++++++++++++++++++++++++++++++
+
+First step in creating your own strategy is to decide which existing strategy you want to extend. You can either use realize :ndnsim:`forwarding strategy interface <ndn::ForwardingStrategy>` (:ndnsim:`ndn::ForwardingStrategy::DoPropagateInterest` call must be implemented) or extended one of the available forwarding strategies (:ndnsim:`fw::BestRoute` or :ndnsim:`fw::Flooding`).
+The following example assumes that we are realizing :ndnsim:`forwarding strategy interface <ndn::ForwardingStrategy>`.
+
+The follwoing are template strategy h/cc files:
+
+.. literalinclude:: _static/code-samples/custom-strategy.h
+ :language: c++
+ :linenos:
+ :lines: 1-36,51-55,59-
+
+.. literalinclude:: _static/code-samples/custom-strategy.cc
+ :language: c++
+ :linenos:
+ :lines: 1-40,42-50,75-76,115-
+
+After having the template, we can fill the necesasry functionality.
+
+Let us say, that we want Interest be forwarded to first two best-metric faces specified by FIB.
+That is, if node has two or more alternative paths to forward the Interests, this Interest will be forwarded to the best two neighbors.
+The following implementation of CustomStrategy::DoPropagateInterest accomplishes the task:
+
+.. literalinclude:: _static/code-samples/custom-strategy.cc
+ :language: c++
+ :linenos:
+ :lines: 45-75
+ :emphasize-lines: 7-30
+
+After the compilation, you can use ``"ns3::ndn::fw::CustomStrategy"`` as a parameter to :ndnsim:`ndn::StackHelper::SetForwardingStrategy` helper method.
+
+ .. as well as NS_LOG=ndn.fw.CustomStrategy when running in a debug mode
+
+Extending strategy
+++++++++++++++++++
+
+If you need more customization for the forwarding strategy, there are many forwarding strategy events that can be overriden.
+For example, if we want to perform special logging of all forwarded, timed out, and satisfied Intersts, we can override the following events (for more events, refer to :ndnsim:`ForwardingStrategy API documentation <ForwardingStrategy>`):
+
+- :ndnsim:`DidSendOutInterest <ForwardingStrategy::DidSendOutInterest>`, which fired just after forwarding the Interest
+
+- :ndnsim:`WillEraseTimedOutPendingInterest <ForwardingStrategy::WillEraseTimedOutPendingInterest>`, which fired just before PIT entry is removed by timeout
+
+- :ndnsim:`WillSatisfyPendingInterest <ForwardingStrategy::WillSatisfyPendingInterest>`, which fired just before Interest will be satisfied.
+
+The highlighted ares of the following code demonstrates how it can be impelmented:
+
+.. literalinclude:: _static/code-samples/custom-strategy.h
+ :language: c++
+ :linenos:
+ :emphasize-lines: 37-50,56-58
+
+.. literalinclude:: _static/code-samples/custom-strategy.cc
+ :language: c++
+ :linenos:
+ :emphasize-lines: 41,51-74,77-114