diff --git a/modules/dnn/include/opencv2/dnn/dict.hpp b/modules/dnn/include/opencv2/dnn/dict.hpp
index 463d314bee574e5d98d6a6fc3b54179fe32573e5..059ce9b28ef562e192107c0fb3de8d378000f8fa 100644
--- a/modules/dnn/include/opencv2/dnn/dict.hpp
+++ b/modules/dnn/include/opencv2/dnn/dict.hpp
@@ -60,13 +60,13 @@ CV__DNN_INLINE_NS_BEGIN
 struct CV_EXPORTS_W DictValue
 {
     DictValue(const DictValue &r);
-    DictValue(bool i)           : type(Param::INT), pi(new AutoBuffer<int64,1>) { (*pi)[0] = i ? 1 : 0; }       //!< Constructs integer scalar
-    DictValue(int64 i = 0)      : type(Param::INT), pi(new AutoBuffer<int64,1>) { (*pi)[0] = i; }       //!< Constructs integer scalar
-    CV_WRAP DictValue(int i)    : type(Param::INT), pi(new AutoBuffer<int64,1>) { (*pi)[0] = i; }       //!< Constructs integer scalar
-    DictValue(unsigned p)       : type(Param::INT), pi(new AutoBuffer<int64,1>) { (*pi)[0] = p; }       //!< Constructs integer scalar
-    CV_WRAP DictValue(double p)         : type(Param::REAL), pd(new AutoBuffer<double,1>) { (*pd)[0] = p; }     //!< Constructs floating point scalar
-    CV_WRAP DictValue(const String &s)  : type(Param::STRING), ps(new AutoBuffer<String,1>) { (*ps)[0] = s; }   //!< Constructs string scalar
-    DictValue(const char *s)            : type(Param::STRING), ps(new AutoBuffer<String,1>) { (*ps)[0] = s; }   //!< @overload
+    explicit DictValue(bool i)           : type(Param::INT), pi(new AutoBuffer<int64,1>) { (*pi)[0] = i ? 1 : 0; }       //!< Constructs integer scalar
+    explicit DictValue(int64 i = 0)      : type(Param::INT), pi(new AutoBuffer<int64,1>) { (*pi)[0] = i; }       //!< Constructs integer scalar
+    CV_WRAP explicit DictValue(int i)    : type(Param::INT), pi(new AutoBuffer<int64,1>) { (*pi)[0] = i; }       //!< Constructs integer scalar
+    explicit DictValue(unsigned p)       : type(Param::INT), pi(new AutoBuffer<int64,1>) { (*pi)[0] = p; }       //!< Constructs integer scalar
+    CV_WRAP explicit DictValue(double p)         : type(Param::REAL), pd(new AutoBuffer<double,1>) { (*pd)[0] = p; }     //!< Constructs floating point scalar
+    CV_WRAP explicit DictValue(const String &s)  : type(Param::STRING), ps(new AutoBuffer<String,1>) { (*ps)[0] = s; }   //!< Constructs string scalar
+    explicit DictValue(const char *s)            : type(Param::STRING), ps(new AutoBuffer<String,1>) { (*ps)[0] = s; }   //!< @overload
 
     template<typename TypeIter>
     static DictValue arrayInt(TypeIter begin, int size);    //!< Constructs integer array
diff --git a/modules/dnn/include/opencv2/dnn/dnn.hpp b/modules/dnn/include/opencv2/dnn/dnn.hpp
index d6b29cfcf3354f1c2bbd353bb787c859bbc0b194..8b2cba9ce1f1cb5957716f26a7ad3f9a843f575f 100644
--- a/modules/dnn/include/opencv2/dnn/dnn.hpp
+++ b/modules/dnn/include/opencv2/dnn/dnn.hpp
@@ -134,7 +134,7 @@ CV__DNN_INLINE_NS_BEGIN
     class BackendNode
     {
     public:
-        BackendNode(int backendId);
+        explicit BackendNode(int backendId);
 
         virtual ~BackendNode(); //!< Virtual destructor to make polymorphism.
 
@@ -277,18 +277,18 @@ CV__DNN_INLINE_NS_BEGIN
          * Each layer input and output can be labeled to easily identify them using "%<layer_name%>[.output_name]" notation.
          * This method maps label of input blob to its index into input vector.
          */
-        virtual int inputNameToIndex(String inputName);
+        virtual int inputNameToIndex(String inputName);  // FIXIT const
         /** @brief Returns index of output blob in output array.
          *  @see inputNameToIndex()
          */
-        CV_WRAP virtual int outputNameToIndex(const String& outputName);
+        CV_WRAP virtual int outputNameToIndex(const String& outputName);  // FIXIT const
 
         /**
          * @brief Ask layer if it support specific backend for doing computations.
          * @param[in] backendId computation backend identifier.
          * @see Backend
          */
-        virtual bool supportBackend(int backendId);
+        virtual bool supportBackend(int backendId);  // FIXIT const
 
         /**
          * @brief Returns Halide backend node.
@@ -495,18 +495,29 @@ CV__DNN_INLINE_NS_BEGIN
         /** @brief Converts string name of the layer to the integer identifier.
          *  @returns id of the layer, or -1 if the layer wasn't found.
          */
-        CV_WRAP int getLayerId(const String &layer);
+        CV_WRAP int getLayerId(const String &layer) const;
 
         CV_WRAP std::vector<String> getLayerNames() const;
 
-        /** @brief Container for strings and integers. */
+        /** @brief Container for strings and integers.
+         *
+         * @deprecated Use getLayerId() with int result.
+         */
         typedef DictValue LayerId;
 
         /** @brief Returns pointer to layer with specified id or name which the network use. */
-        CV_WRAP Ptr<Layer> getLayer(LayerId layerId);
+        CV_WRAP Ptr<Layer> getLayer(int layerId) const;
+        /** @overload
+         *  @deprecated Use int getLayerId(const String &layer)
+         */
+        CV_WRAP inline Ptr<Layer> getLayer(const String& layerName) const { return getLayer(getLayerId(layerName)); }
+        /** @overload
+         *  @deprecated to be removed
+         */
+        CV_WRAP Ptr<Layer> getLayer(const LayerId& layerId) const;
 
         /** @brief Returns pointers to input layers of specific layer. */
-        std::vector<Ptr<Layer> > getLayerInputs(LayerId layerId); // FIXIT: CV_WRAP
+        std::vector<Ptr<Layer> > getLayerInputs(int layerId) const; // FIXIT: CV_WRAP
 
         /** @brief Connects output of the first layer to input of the second layer.
          *  @param outPin descriptor of the first layer output.
@@ -662,14 +673,16 @@ CV__DNN_INLINE_NS_BEGIN
          *  @note If shape of the new blob differs from the previous shape,
          *  then the following forward pass may fail.
         */
-        CV_WRAP void setParam(LayerId layer, int numParam, const Mat &blob);
+        CV_WRAP void setParam(int layer, int numParam, const Mat &blob);
+        CV_WRAP inline void setParam(const String& layerName, int numParam, const Mat &blob) { return setParam(getLayerId(layerName), numParam, blob); }
 
         /** @brief Returns parameter blob of the layer.
          *  @param layer name or id of the layer.
          *  @param numParam index of the layer parameter in the Layer::blobs array.
          *  @see Layer::blobs
          */
-        CV_WRAP Mat getParam(LayerId layer, int numParam = 0);
+        CV_WRAP Mat getParam(int layer, int numParam = 0) const;
+        CV_WRAP inline Mat getParam(const String& layerName, int numParam = 0) const { return getParam(getLayerId(layerName), numParam); }
 
         /** @brief Returns indexes of layers with unconnected outputs.
          */
diff --git a/modules/dnn/misc/objc/gen_dict.json b/modules/dnn/misc/objc/gen_dict.json
index e6d561fba0256f87896bed56e1e403c5c85679ee..6072bdfc01d8fe669edab642fcbda5f7079102f8 100644
--- a/modules/dnn/misc/objc/gen_dict.json
+++ b/modules/dnn/misc/objc/gen_dict.json
@@ -18,8 +18,12 @@
             "(long)getFLOPS:(NSArray<IntVector*>*)netInputShapes" : { "getFLOPS" : {"name" : "getFLOPSWithNetInputShapes"} },
             "(long)getFLOPS:(int)layerId netInputShape:(IntVector*)netInputShape" : { "getFLOPS" : {"name" : "getFLOPSWithLayerId"} },
             "(long)getFLOPS:(int)layerId netInputShapes:(NSArray<IntVector*>*)netInputShapes" : { "getFLOPS" : {"name" : "getFLOPSWithLayerId"} },
+            "(Layer*)getLayer:(NSString*)layerName" : { "getLayer" : {"name" : "getLayerByName"} },
+            "(Layer*)getLayer:(DictValue*)layerId" : { "getLayer" : {"name" : "getLayerByDictValue"} },
             "(void)getLayersShapes:(IntVector*)netInputShape layersIds:(IntVector*)layersIds inLayersShapes:(NSMutableArray<NSMutableArray<IntVector*>*>*)inLayersShapes outLayersShapes:(NSMutableArray<NSMutableArray<IntVector*>*>*)outLayersShapes" : { "getLayersShapes" : {"name" : "getLayersShapesWithNetInputShape"} },
-            "(void)getLayersShapes:(NSArray<IntVector*>*)netInputShapes layersIds:(IntVector*)layersIds inLayersShapes:(NSMutableArray<NSMutableArray<IntVector*>*>*)inLayersShapes outLayersShapes:(NSMutableArray<NSMutableArray<IntVector*>*>*)outLayersShapes" : { "getLayersShapes" : {"name" : "getLayersShapesWithNetInputShapes"} }
+            "(void)getLayersShapes:(NSArray<IntVector*>*)netInputShapes layersIds:(IntVector*)layersIds inLayersShapes:(NSMutableArray<NSMutableArray<IntVector*>*>*)inLayersShapes outLayersShapes:(NSMutableArray<NSMutableArray<IntVector*>*>*)outLayersShapes" : { "getLayersShapes" : {"name" : "getLayersShapesWithNetInputShapes"} },
+            "(Mat*)getParam:(NSString*)layerName numParam:(int)numParam" : { "getParam" : {"name" : "getParamByName"} },
+            "(void)setParam:(NSString*)layerName numParam:(int)numParam blob:(Mat*)blob" : { "setParam" : {"name" : "setParamByName"} }
         }
     },
     "type_dict": {
diff --git a/modules/dnn/src/dnn.cpp b/modules/dnn/src/dnn.cpp
index 67312dba7831cb64f20cf2eb711b67b8c451947b..ab2442c9523098459663b4688227987c681ae779 100644
--- a/modules/dnn/src/dnn.cpp
+++ b/modules/dnn/src/dnn.cpp
@@ -895,11 +895,11 @@ public:
     // layer blob.
     int numReferences(const LayerPin& lp)
     {
-        std::map<LayerPin, LayerPin>::iterator mapIt = reuseMap.find(lp);
+        std::map<LayerPin, LayerPin>::const_iterator mapIt = reuseMap.find(lp);
         CV_Assert(mapIt != reuseMap.end());
         LayerPin memHost = mapIt->second;
 
-        std::map<LayerPin, int>::iterator refIt = refCounter.find(memHost);
+        std::map<LayerPin, int>::const_iterator refIt = refCounter.find(memHost);
         CV_Assert(refIt != refCounter.end());
         return refIt->second;
     }
@@ -927,7 +927,7 @@ public:
     // Decrease references counter to allocated memory inside specific blob.
     void releaseReference(const LayerPin& lp)
     {
-        std::map<LayerPin, LayerPin>::iterator mapIt = reuseMap.find(lp);
+        std::map<LayerPin, LayerPin>::const_iterator mapIt = reuseMap.find(lp);
         CV_Assert(mapIt != reuseMap.end());
 
         std::map<LayerPin, int>::iterator refIt = refCounter.find(mapIt->second);
@@ -951,8 +951,8 @@ public:
             Mat bestBlob;
             LayerPin bestBlobPin;
 
-            std::map<LayerPin, Mat>::iterator hostIt;
-            std::map<LayerPin, int>::iterator refIt;
+            std::map<LayerPin, Mat>::const_iterator hostIt;
+            std::map<LayerPin, int>::const_iterator refIt;
 
             const int targetTotal = total(shape);
             int bestBlobTotal = INT_MAX;
@@ -964,7 +964,7 @@ public:
                 // it might be used as output.
                 if (refIt != refCounter.end() && refIt->second == 0)
                 {
-                    Mat& unusedBlob = hostIt->second;
+                    const Mat& unusedBlob = hostIt->second;
                     if (unusedBlob.total() >= targetTotal &&
                         unusedBlob.total() < bestBlobTotal &&
                         unusedBlob.type() == dtype)
@@ -1177,7 +1177,7 @@ detail::NetImplBase::NetImplBase()
     // nothing
 }
 
-std::string detail::NetImplBase::getDumpFileNameBase()
+std::string detail::NetImplBase::getDumpFileNameBase() const
 {
     std::string dumpFileNameBase = cv::format("ocv_dnn_net_%05d_%02d", networkId, networkDumpCounter++);
     return dumpFileNameBase;
@@ -1230,7 +1230,6 @@ struct Net::Impl : public detail::NetImplBase
     bool fusion;
     bool isAsync;
     std::vector<int64> layersTimings;
-    Mat output_blob;
 
 #ifdef HAVE_CUDA
     struct CudaInfo_t
@@ -1329,7 +1328,7 @@ struct Net::Impl : public detail::NetImplBase
         std::vector< std::reference_wrapper<LayerData> > compileList; compileList.reserve(64);
         for (MapIdToLayerData::iterator it = layers.begin(); it != layers.end(); ++it)
         {
-            LayerData &ld = it->second;
+            LayerData& ld = it->second;
             Ptr<Layer> layer = ld.layerInstance;
             if (layer->supportBackend(DNN_BACKEND_HALIDE) && !ld.skip)
             {
@@ -1522,19 +1521,19 @@ struct Net::Impl : public detail::NetImplBase
         }
     }
 
-    int getLayerId(const String &layerName)
+    int getLayerId(const String &layerName) const
     {
-        std::map<String, int>::iterator it = layerNameToId.find(layerName);
+        std::map<String, int>::const_iterator it = layerNameToId.find(layerName);
         return (it != layerNameToId.end()) ? it->second : -1;
     }
 
-    int getLayerId(int id)
+    int getLayerId(int id) const
     {
-        MapIdToLayerData::iterator it = layers.find(id);
+        MapIdToLayerData::const_iterator it = layers.find(id);
         return (it != layers.end()) ? id : -1;
     }
 
-    int getLayerId(DictValue &layerDesc)
+    int getLayerId(DictValue &layerDesc) const
     {
         if (layerDesc.isInt())
             return getLayerId(layerDesc.get<int>());
@@ -1545,23 +1544,23 @@ struct Net::Impl : public detail::NetImplBase
         return -1;
     }
 
-    String getLayerName(int id)
+    String getLayerName(int id) const
     {
-        MapIdToLayerData::iterator it = layers.find(id);
+        MapIdToLayerData::const_iterator it = layers.find(id);
         return (it != layers.end()) ? it->second.name : "(unknown layer)";
     }
 
-    LayerData& getLayerData(int id)
+    LayerData& getLayerData(int id) const
     {
-        MapIdToLayerData::iterator it = layers.find(id);
+        MapIdToLayerData::const_iterator it = layers.find(id);
 
         if (it == layers.end())
             CV_Error(Error::StsObjectNotFound, format("Layer with requested id=%d not found", id));
 
-        return it->second;
+        return const_cast<LayerData&>(it->second);
     }
 
-    LayerData& getLayerData(const String &layerName)
+    LayerData& getLayerData(const String &layerName) const
     {
         int id = getLayerId(layerName);
 
@@ -1571,7 +1570,7 @@ struct Net::Impl : public detail::NetImplBase
         return getLayerData(id);
     }
 
-    LayerData& getLayerData(const DictValue &layerDesc)
+    LayerData& getLayerData(const DictValue &layerDesc) const
     {
         CV_Assert(layerDesc.isInt() || layerDesc.isString());
         if (layerDesc.isInt())
@@ -1597,14 +1596,14 @@ struct Net::Impl : public detail::NetImplBase
         ld.inputBlobsId[inNum] = from;
     }
 
-    int resolvePinOutputName(LayerData &ld, const String &outName)
+    int resolvePinOutputName(LayerData &ld, const String &outName) const
     {
         if (outName.empty())
             return 0;
         return ld.getLayerInstance()->outputNameToIndex(outName);
     }
 
-    LayerPin getPinByAlias(const String &layerName)
+    LayerPin getPinByAlias(const String &layerName) const
     {
         LayerPin pin;
         pin.lid = (layerName.empty()) ? 0 : getLayerId(layerName);
@@ -1615,13 +1614,17 @@ struct Net::Impl : public detail::NetImplBase
         return pin;
     }
 
-    std::vector<LayerPin> getLayerOutPins(const String &layerName)
+    std::vector<LayerPin> getLayerOutPins(const String &layerName) const
     {
         int lid = (layerName.empty()) ? 0 : getLayerId(layerName);
 
-        std::vector<LayerPin> pins;
+        MapIdToLayerData::const_iterator it = layers.find(lid);
+        if (it == layers.end())
+            CV_Error_(Error::StsOutOfRange, ("Layer #%d is not valid", lid));
+        const size_t nOutputs = it->second.outputBlobs.size();
 
-        for (int i = 0; i < layers[lid].outputBlobs.size(); i++)
+        std::vector<LayerPin> pins;
+        for (int i = 0; i < nOutputs; i++)
         {
             pins.push_back(LayerPin(lid, i));
         }
@@ -2087,12 +2090,11 @@ struct Net::Impl : public detail::NetImplBase
         CV_TRACE_FUNCTION();
         CV_Assert_N(preferableBackend == DNN_BACKEND_INFERENCE_ENGINE_NGRAPH, haveInfEngine());
 
-        MapIdToLayerData::iterator it;
         Ptr<InfEngineNgraphNet> net;
 
-        for (it = layers.begin(); it != layers.end(); ++it)
+        for (MapIdToLayerData::const_iterator it = layers.begin(); it != layers.end(); ++it)
         {
-            LayerData &ld = it->second;
+            const LayerData& ld = it->second;
             if (ld.id == 0)
             {
                 CV_Assert((netInputLayer->outNames.empty() && ld.outputBlobsWrappers.size() == 1) ||
@@ -2128,9 +2130,9 @@ struct Net::Impl : public detail::NetImplBase
             InfEngineNgraphNet& ienet = *ieNode->net;
             ienet.reset();
 
-            for (it = layers.begin(); it != layers.end(); ++it)
+            for (MapIdToLayerData::iterator it = layers.begin(); it != layers.end(); ++it)
             {
-                LayerData &ld = it->second;
+                LayerData& ld = it->second;
                 if (ld.id == 0)
                 {
                     for (int i = 0; i < ld.inputBlobsWrappers.size(); ++i)
@@ -2172,9 +2174,9 @@ struct Net::Impl : public detail::NetImplBase
         // Build Inference Engine networks from sets of layers that support this
         // backend. Split a whole model on several Inference Engine networks if
         // some of layers are not implemented.
-        for (it = layers.begin(); it != layers.end(); ++it)
+        for (MapIdToLayerData::iterator it = layers.begin(); it != layers.end(); ++it)
         {
-            LayerData &ld = it->second;
+            LayerData& ld = it->second;
 
             if (ld.id == 0 && ld.skip)
                 continue;
@@ -2430,10 +2432,9 @@ struct Net::Impl : public detail::NetImplBase
         CV_TRACE_FUNCTION();
         CV_Assert_N(preferableBackend == DNN_BACKEND_WEBNN, haveWebnn());
 
-        MapIdToLayerData::iterator it;
         Ptr<WebnnNet> net;
 
-        for (it = layers.begin(); it != layers.end(); ++it)
+        for (MapIdToLayerData::iterator it = layers.begin(); it != layers.end(); ++it)
         {
             LayerData &ld = it->second;
             if (ld.id == 0)
@@ -2462,7 +2463,7 @@ struct Net::Impl : public detail::NetImplBase
         // Build WebNN networks from sets of layers that support this
         // backend. Split a whole model on several WebNN networks if
         // some of layers are not implemented.
-        for (it = layers.begin(); it != layers.end(); ++it)
+        for (MapIdToLayerData::iterator it = layers.begin(); it != layers.end(); ++it)
         {
             LayerData &ld = it->second;
 
@@ -2662,8 +2663,7 @@ struct Net::Impl : public detail::NetImplBase
         if (!haveVulkan())
             return;
 
-        MapIdToLayerData::iterator it = layers.begin();
-        for (; it != layers.end(); it++)
+        for (MapIdToLayerData::iterator it = layers.begin(); it != layers.end(); it++)
         {
             LayerData &ld = it->second;
             Ptr<Layer> layer = ld.layerInstance;
@@ -2812,7 +2812,7 @@ struct Net::Impl : public detail::NetImplBase
             ld.inputLayersId.insert(ld.inputBlobsId[i].lid);
 
         //allocate parents
-        for (set<int>::iterator i = ld.inputLayersId.begin(); i != ld.inputLayersId.end(); i++)
+        for (set<int>::const_iterator i = ld.inputLayersId.begin(); i != ld.inputLayersId.end(); i++)
             allocateLayer(*i, layersShapes);
 
         //bind inputs
@@ -2902,8 +2902,7 @@ struct Net::Impl : public detail::NetImplBase
         // we try to embed this activation into the convolution and disable separate execution of the activation
         std::set<LayerPin> pinsToKeep(blobsToKeep_.begin(),
                                       blobsToKeep_.end());
-        MapIdToLayerData::iterator it;
-        for (it = layers.begin(); it != layers.end(); it++)
+        for (MapIdToLayerData::const_iterator it = layers.begin(); it != layers.end(); it++)
         {
             int lid = it->first;
             LayerData& ld = layers[lid];
@@ -3450,8 +3449,7 @@ struct Net::Impl : public detail::NetImplBase
     {
         CV_TRACE_FUNCTION();
 
-        MapIdToLayerData::iterator it;
-        for (it = layers.begin(); it != layers.end(); it++)
+        for (MapIdToLayerData::iterator it = layers.begin(); it != layers.end(); it++)
             it->second.flag = 0;
 
         CV_Assert(!layers[0].outputBlobs.empty());
@@ -3485,7 +3483,7 @@ struct Net::Impl : public detail::NetImplBase
         // Fake references to input blobs.
         for (int i = 0; i < layers[0].outputBlobs.size(); ++i)
             blobManager.addReference(LayerPin(0, i));
-        for (it = layers.begin(); it != layers.end(); ++it)
+        for (MapIdToLayerData::const_iterator it = layers.begin(); it != layers.end(); ++it)
         {
             const LayerData& ld = it->second;
             blobManager.addReferences(ld.inputBlobsId);
@@ -3496,7 +3494,7 @@ struct Net::Impl : public detail::NetImplBase
             blobManager.addReference(blobsToKeep_[i]);
         }
 
-        for (it = layers.begin(); it != layers.end(); it++)
+        for (MapIdToLayerData::const_iterator it = layers.begin(); it != layers.end(); it++)
         {
             int lid = it->first;
             allocateLayer(lid, layersShapes);
@@ -3517,7 +3515,11 @@ struct Net::Impl : public detail::NetImplBase
             TickMeter tm;
             tm.start();
 
+#ifndef HAVE_VULKAN
+            std::map<int, Ptr<BackendNode> >::const_iterator it = ld.backendNodes.find(preferableBackend);
+#else
             std::map<int, Ptr<BackendNode> >::iterator it = ld.backendNodes.find(preferableBackend);
+#endif
             if (preferableBackend == DNN_BACKEND_OPENCV || it == ld.backendNodes.end() || it->second.empty())
             {
                 if (isAsync)
@@ -3711,6 +3713,7 @@ struct Net::Impl : public detail::NetImplBase
                 {
                     forwardWebnn(ld.outputBlobsWrappers, node, isAsync);
                 }
+#ifdef HAVE_VULKAN
                 else if (preferableBackend == DNN_BACKEND_VKCOM)
                 {
                     try
@@ -3724,6 +3727,7 @@ struct Net::Impl : public detail::NetImplBase
                         forwardLayer(ld);
                     }
                 }
+#endif
                 else
                 {
                     CV_Error(Error::StsNotImplemented, "Unknown backend identifier");
@@ -3748,8 +3752,7 @@ struct Net::Impl : public detail::NetImplBase
 
         if (clearFlags)
         {
-            MapIdToLayerData::iterator it;
-            for (it = layers.begin(); it != layers.end(); it++)
+            for (MapIdToLayerData::iterator it = layers.begin(); it != layers.end(); it++)
                 it->second.flag = 0;
         }
 
@@ -3758,8 +3761,7 @@ struct Net::Impl : public detail::NetImplBase
             return;
 
         //forward parents
-        MapIdToLayerData::iterator it;
-        for (it = layers.begin(); it != layers.end() && (it->second.id < ld.id); ++it)
+        for (MapIdToLayerData::iterator it = layers.begin(); it != layers.end() && (it->second.id < ld.id); ++it)
         {
             LayerData &ld = it->second;
             if (ld.flag)
@@ -3845,7 +3847,7 @@ struct Net::Impl : public detail::NetImplBase
             for(int i = 0; i < inputLayerIds.size(); i++)
             {
                 int layerId = inputLayerIds[i].lid;
-                LayersShapesMap::iterator it =
+                LayersShapesMap::const_iterator it =
                         inOutShapes.find(layerId);
                 if(it == inOutShapes.end() ||
                         it->second.out.empty())
@@ -3928,7 +3930,7 @@ struct Net::Impl : public detail::NetImplBase
         inOutShapes.clear();
 
         inOutShapes[0].in = netInputShapes; //insert shape for first input layer
-        for (MapIdToLayerData::iterator it = layers.begin();
+        for (MapIdToLayerData::const_iterator it = layers.begin();
              it != layers.end(); it++)
         {
             getLayerShapesRecursively(it->first, inOutShapes);
@@ -3969,12 +3971,11 @@ struct Net::Impl : public detail::NetImplBase
         CV_LOG_DEBUG(NULL, toString(inputShapes, "Network input shapes"));
         LayersShapesMap layersShapes;
         layersShapes[0].in = inputShapes;
-        for (MapIdToLayerData::iterator it = layers.begin();
-             it != layers.end(); it++)
+        for (MapIdToLayerData::iterator it = layers.begin(); it != layers.end(); it++)
         {
             int layerId = it->first;
             LayerData& layerData = it->second;
-            std::vector<LayerPin>& inputLayerIds = layerData.inputBlobsId;
+            const std::vector<LayerPin>& inputLayerIds = layerData.inputBlobsId;
             LayerShapes& layerShapes = layersShapes[layerId];
             CV_LOG_DEBUG(NULL, "layer " << layerId << ": [" << layerData.type << "]:(" << layerData.name << ") with inputs.size=" << inputLayerIds.size());
             if (layerShapes.in.empty())
@@ -3984,7 +3985,7 @@ struct Net::Impl : public detail::NetImplBase
                     const LayerPin& inputPin = inputLayerIds[i];
                     int inputLayerId = inputPin.lid;
                     CV_LOG_DEBUG(NULL, "    input[" << i << "] " << inputLayerId << ":" << inputPin.oid << " as [" << layers[inputLayerId].type << "]:(" << layers[inputLayerId].name << ")");
-                    LayersShapesMap::iterator inputIt = layersShapes.find(inputLayerId);
+                    LayersShapesMap::const_iterator inputIt = layersShapes.find(inputLayerId);
                     if (inputIt == layersShapes.end() || inputIt->second.out.empty())
                     {
                         getLayerShapesRecursively(inputLayerId, layersShapes);
@@ -4001,19 +4002,23 @@ struct Net::Impl : public detail::NetImplBase
         CV_LOG_DEBUG(NULL, "updateLayersShapes() - DONE");
     }
 
-    LayerPin getLatestLayerPin(const std::vector<LayerPin>& pins)
+    LayerPin getLatestLayerPin(const std::vector<LayerPin>& pins) const
     {
         return *std::max_element(pins.begin(), pins.end());
     }
 
-    Mat getBlob(const LayerPin& pin)
+    Mat getBlob(const LayerPin& pin) const
     {
         CV_TRACE_FUNCTION();
 
         if (!pin.valid())
             CV_Error(Error::StsObjectNotFound, "Requested blob not found");
 
-        LayerData &ld = layers[pin.lid];
+        MapIdToLayerData::const_iterator it = layers.find(pin.lid);
+        if (it == layers.end())
+            CV_Error_(Error::StsOutOfRange, ("Layer #%d is not valid (output #%d requested)", pin.lid, pin.oid));
+
+        const LayerData &ld = it->second;
         if ((size_t)pin.oid >= ld.outputBlobs.size())
         {
             CV_Error(Error::StsOutOfRange, format("Layer \"%s\" produce only %zu outputs, "
@@ -4029,6 +4034,7 @@ struct Net::Impl : public detail::NetImplBase
 
         if (ld.outputBlobs[pin.oid].depth() == CV_16S)
         {
+            Mat output_blob;
             convertFp16(ld.outputBlobs[pin.oid], output_blob);
             return output_blob;
         }
@@ -4036,7 +4042,7 @@ struct Net::Impl : public detail::NetImplBase
             return ld.outputBlobs[pin.oid];
     }
 
-    Mat getBlob(String outputName)
+    Mat getBlob(String outputName) const
     {
         return getBlob(getPinByAlias(outputName));
     }
@@ -4096,9 +4102,9 @@ struct Net::Impl : public detail::NetImplBase
     Net createNetworkFromModelOptimizer(InferenceEngine::CNNNetwork& ieNet);
 #endif
 
-    string dump();
+    string dump() const;
 
-    void dumpNetworkToFile()
+    void dumpNetworkToFile() const
     {
 #ifndef OPENCV_DNN_DISABLE_NETWORK_AUTO_DUMP
         string dumpFileNameBase = getDumpFileNameBase();
@@ -5059,7 +5065,7 @@ void Net::setInput(InputArray blob, const String& name, double scalefactor, cons
     impl->netWasAllocated = impl->netWasAllocated && oldShape;
 }
 
-Mat Net::getParam(LayerId layer, int numParam)
+Mat Net::getParam(int layer, int numParam) const
 {
     LayerData &ld = impl->getLayerData(layer);
     std::vector<Mat> &layerBlobs = ld.getLayerInstance()->blobs;
@@ -5067,7 +5073,7 @@ Mat Net::getParam(LayerId layer, int numParam)
     return layerBlobs[numParam];
 }
 
-void Net::setParam(LayerId layer, int numParam, const Mat &blob)
+void Net::setParam(int layer, int numParam, const Mat &blob)
 {
     LayerData &ld = impl->getLayerData(layer);
 
@@ -5077,7 +5083,7 @@ void Net::setParam(LayerId layer, int numParam, const Mat &blob)
     layerBlobs[numParam] = blob;
 }
 
-int Net::getLayerId(const String &layer)
+int Net::getLayerId(const String &layer) const
 {
     return impl->getLayerId(layer);
 }
@@ -5120,7 +5126,7 @@ String Net::dump()
     return impl->dump();
 }
 
-string Net::Impl::dump()
+string Net::Impl::dump() const
 {
     bool hasInput = !netInputLayer->inputsData.empty();
 
@@ -5388,13 +5394,18 @@ void Net::dumpToFile(const String& path) {
     file.close();
 }
 
-Ptr<Layer> Net::getLayer(LayerId layerId)
+Ptr<Layer> Net::getLayer(int layerId) const
+{
+    LayerData &ld = impl->getLayerData(layerId);
+    return ld.getLayerInstance();
+}
+Ptr<Layer> Net::getLayer(const LayerId& layerId) const
 {
     LayerData &ld = impl->getLayerData(layerId);
     return ld.getLayerInstance();
 }
 
-std::vector<Ptr<Layer> > Net::getLayerInputs(LayerId layerId)
+std::vector<Ptr<Layer> > Net::getLayerInputs(int layerId) const
 {
     LayerData &ld = impl->getLayerData(layerId);
 
@@ -5413,7 +5424,7 @@ std::vector<String> Net::getLayerNames() const
     std::vector<String> res;
     res.reserve(impl->layers.size());
 
-    Impl::MapIdToLayerData::iterator it;
+    Impl::MapIdToLayerData::const_iterator it;
     for (it = impl->layers.begin(); it != impl->layers.end(); it++)
     {
         if (it->second.id) //skip Data layer
@@ -5432,11 +5443,11 @@ std::vector<int> Net::getUnconnectedOutLayers() const
 {
     std::vector<int> layersIds;
 
-    Impl::MapIdToLayerData::iterator it;
+    Impl::MapIdToLayerData::const_iterator it;
     for (it = impl->layers.begin(); it != impl->layers.end(); it++)
     {
         int lid = it->first;
-        LayerData &ld = it->second;
+        const LayerData &ld = it->second;
 
         if (ld.requiredOutputs.size() == 0)
             layersIds.push_back(lid);
@@ -5536,13 +5547,13 @@ int64 Net::getFLOPS(const MatShape& netInputShape) const
 int64 Net::getFLOPS(const int layerId,
               const std::vector<MatShape>& netInputShapes) const
 {
-    Impl::MapIdToLayerData::iterator layer = impl->layers.find(layerId);
+    Impl::MapIdToLayerData::const_iterator layer = impl->layers.find(layerId);
     CV_Assert(layer != impl->layers.end());
 
     LayerShapes shapes;
     impl->getLayerShapes(netInputShapes, layerId, shapes);
 
-    return layer->second.getLayerInstance()->getFLOPS(shapes.in, shapes.out);
+    return const_cast<LayerData&>(layer->second).getLayerInstance()->getFLOPS(shapes.in, shapes.out);
 }
 
 int64 Net::getFLOPS(const int layerId,
@@ -5556,7 +5567,7 @@ void Net::getLayerTypes(std::vector<String>& layersTypes) const
     layersTypes.clear();
 
     std::map<String, int> layers;
-    for (Impl::MapIdToLayerData::iterator it = impl->layers.begin();
+    for (Impl::MapIdToLayerData::const_iterator it = impl->layers.begin();
          it != impl->layers.end(); it++)
     {
         if (layers.find(it->second.type) == layers.end())
@@ -5564,7 +5575,7 @@ void Net::getLayerTypes(std::vector<String>& layersTypes) const
         layers[it->second.type]++;
     }
 
-    for (std::map<String, int>::iterator it = layers.begin();
+    for (std::map<String, int>::const_iterator it = layers.begin();
          it != layers.end(); it++)
     {
         layersTypes.push_back(it->first);
@@ -5574,7 +5585,7 @@ void Net::getLayerTypes(std::vector<String>& layersTypes) const
 int Net::getLayersCount(const String& layerType) const
 {
     int count = 0;
-    for (Impl::MapIdToLayerData::iterator it = impl->layers.begin();
+    for (Impl::MapIdToLayerData::const_iterator it = impl->layers.begin();
          it != impl->layers.end(); it++)
     {
         if (it->second.type == layerType)
@@ -5589,7 +5600,7 @@ void Net::getMemoryConsumption(const int layerId,
 {
     CV_TRACE_FUNCTION();
 
-    Impl::MapIdToLayerData::iterator layer = impl->layers.find(layerId);
+    Impl::MapIdToLayerData::const_iterator layer = impl->layers.find(layerId);
     CV_Assert(layer != impl->layers.end());
 
     weights = blobs = 0;
@@ -5658,7 +5669,7 @@ void Net::getMemoryConsumption(const std::vector<MatShape>& netInputShapes,
     for(int i = 0; i < layerIds.size(); i++)
     {
         int w = 0, b = 0;
-        Impl::MapIdToLayerData::iterator layer = impl->layers.find(layerIds[i]);
+        Impl::MapIdToLayerData::const_iterator layer = impl->layers.find(layerIds[i]);
         CV_Assert(layer != impl->layers.end());
 
         for(int j = 0; j < layer->second.params.blobs.size(); j++)
diff --git a/modules/dnn/src/dnn_common.hpp b/modules/dnn/src/dnn_common.hpp
index ffeb3bfda1adb375ccebe0882d6716e1a8237eb8..c7108e51434c23b79cbe238661f3ce59b0a475e1 100644
--- a/modules/dnn/src/dnn_common.hpp
+++ b/modules/dnn/src/dnn_common.hpp
@@ -71,12 +71,12 @@ private:
 struct NetImplBase
 {
     const int networkId;  // network global identifier
-    int networkDumpCounter;  // dump counter
+    mutable int networkDumpCounter;  // dump counter
     int dumpLevel;  // level of information dumps (initialized through OPENCV_DNN_NETWORK_DUMP parameter)
 
     NetImplBase();
 
-    std::string getDumpFileNameBase();
+    std::string getDumpFileNameBase() const;
 };
 
 }  // namespace detail
diff --git a/modules/dnn/src/layers/recurrent_layers.cpp b/modules/dnn/src/layers/recurrent_layers.cpp
index 14210becb4a0b880476876c423fa4ca242a0372b..dbb3e2700ae5a3ec47eae36efa4f257a38ff14b0 100644
--- a/modules/dnn/src/layers/recurrent_layers.cpp
+++ b/modules/dnn/src/layers/recurrent_layers.cpp
@@ -184,7 +184,7 @@ public:
         CV_Assert(!reverse || !bidirectional);
 
         // read activations
-        DictValue activations = params.get<DictValue>("activations", "");
+        DictValue activations = params.get<DictValue>("activations", DictValue(String()));
         if (activations.size() == 1) // if activations wasn't specified use default
         {
             f_activation = sigmoid;