spectrum: Add getter for propagation delay model

src/spectrum/model/spectrum-channel.cc

@@ -19,6 +19,7 @@
 
 #include "spectrum-channel.h"
 
+#include <ns3/abort.h>
 #include <ns3/double.h>
 #include <ns3/log.h>
 #include <ns3/pointer.h>
@@ -167,7 +168,7 @@ SpectrumChannel::GetSpectrumTransmitFilter() const
 void
 SpectrumChannel::SetPropagationDelayModel(Ptr<PropagationDelayModel> delay)
 {
-    NS_ASSERT(!m_propagationDelay);
+    NS_ABORT_MSG_IF(m_propagationDelay, "Error, called SetPropagationDelayModel() twice");
     m_propagationDelay = delay;
 }
 
@@ -191,4 +192,10 @@ SpectrumChannel::GetPropagationLossModel()
     return m_propagationLoss;
 }
 
+Ptr<PropagationDelayModel>
+SpectrumChannel::GetPropagationDelayModel() const
+{
+    return m_propagationDelay;
+}
+
 } // namespace ns3

src/spectrum/model/spectrum-channel.h

@@ -92,7 +92,10 @@ class SpectrumChannel : public Channel
         Ptr<PhasedArraySpectrumPropagationLossModel> loss);
 
     /**
-     * Set the propagation delay model to be used
+     * Set the propagation delay model to be used.  This method will abort
+     * the simulation if there exists a previously set propagation delay model
+     * (i.e., unlike propagation loss models, multiple of which can be chained
+     * together, there is only one propagation delay model).
      * \param delay Ptr to the propagation delay model to be used.
      */
     void SetPropagationDelayModel(Ptr<PropagationDelayModel> delay);
@@ -116,6 +119,12 @@ class SpectrumChannel : public Channel
      */
     Ptr<PropagationLossModel> GetPropagationLossModel();
 
+    /**
+     * Get the propagation delay model that has been set on the channel.
+     * \returns a pointer to the propagation delay model.
+     */
+    Ptr<PropagationDelayModel> GetPropagationDelayModel() const;
+
     /**
      * Add the transmit filter to be used to filter possible signal receptions
      * at the StartTx() time.  This method may be called multiple