diff --git a/src/core/src/serialization/ecal_serialize_common.cpp b/src/core/src/serialization/ecal_serialize_common.cpp
index 6862cce..992a0e6 100644
--- a/src/core/src/serialization/ecal_serialize_common.cpp
+++ b/src/core/src/serialization/ecal_serialize_common.cpp
@@ -83,7 +83,7 @@ namespace eCAL
     ///////////////////////////////////////////////
     // bytes
     ///////////////////////////////////////////////
-    bool encode_bytes_field(pb_ostream_t* stream, const pb_field_iter_t* field, void* const* arg)
+    bool encode_bytes_field_nano_bytes(pb_ostream_t* stream, const pb_field_iter_t* field, void* const* arg)
     {
       if (arg == nullptr)  return false;
       if (*arg == nullptr) return false;
@@ -99,10 +99,28 @@ namespace eCAL
     {
       if (nano_bytes.length == 0) return;
 
-      pb_callback.funcs.encode = &encode_bytes_field;
+      pb_callback.funcs.encode = &encode_bytes_field_nano_bytes;
       pb_callback.arg = (void*)(&nano_bytes);
     }
 
+    bool encode_bytes_field_vec(pb_ostream_t* stream, const pb_field_iter_t* field, void* const* arg)
+    {
+      if (arg == nullptr)  return false;
+      if (*arg == nullptr) return false;
+
+      if (!pb_encode_tag_for_field(stream, field))
+        return false;
+
+      auto* vec = (std::vector<char>*)(*arg);
+      return pb_encode_string(stream, (pb_byte_t*)vec->data(), vec->size());
+    }
+
+    void encode_bytes(pb_callback_t& pb_callback, const std::vector<char>& vec)
+    {
+      pb_callback.funcs.encode = &encode_bytes_field_vec;
+      pb_callback.arg = (void*)(&vec);
+    }
+
     bool decode_bytes_field(pb_istream_t* stream, const pb_field_iter_t* /*field*/, void** arg)
     {
       if (arg == nullptr)  return false;
diff --git a/src/core/src/serialization/ecal_serialize_common.h b/src/core/src/serialization/ecal_serialize_common.h
index 20b7fd3..634cc96 100644
--- a/src/core/src/serialization/ecal_serialize_common.h
+++ b/src/core/src/serialization/ecal_serialize_common.h
@@ -50,6 +50,7 @@ namespace eCAL
     void decode_string(pb_callback_t& pb_callback, std::string& str);
 
     void encode_bytes(pb_callback_t& pb_callback, const SNanoBytes& nano_bytes);
+    void encode_bytes(pb_callback_t& pb_callback, const std::vector<char>& vec);
     void decode_bytes(pb_callback_t& pb_callback, std::vector<char>& vec);
 
     void encode_map(pb_callback_t& pb_callback, const std::map<std::string, std::string>& str_map);
diff --git a/src/core/src/serialization/ecal_serialize_sample_payload.cpp b/src/core/src/serialization/ecal_serialize_sample_payload.cpp
index 5172431..64de574 100644
--- a/src/core/src/serialization/ecal_serialize_sample_payload.cpp
+++ b/src/core/src/serialization/ecal_serialize_sample_payload.cpp
@@ -81,15 +81,18 @@ namespace
 
     // topic content
     pb_sample_.has_content = true;
-    pb_sample_.content.id = payload_.content.id;
+    pb_sample_.content.id    = payload_.content.id;
     pb_sample_.content.clock = payload_.content.clock;
-    pb_sample_.content.time = payload_.content.time;
-    pb_sample_.content.hash = payload_.content.hash;
-    pb_sample_.content.size = payload_.content.size;
+    pb_sample_.content.time  = payload_.content.time;
+    pb_sample_.content.hash  = payload_.content.hash;
+    pb_sample_.content.size  = payload_.content.size;
 
     // topic content payload
     eCAL::nanopb::encode_bytes(pb_sample_.content.payload, nano_bytes_);
 
+    // padding
+    eCAL::nanopb::encode_bytes(pb_sample_.padding, payload_.padding);
+
     ///////////////////////////////////////////////
     // evaluate byte size
     ///////////////////////////////////////////////
@@ -154,6 +157,9 @@ namespace
     payload_.content.payload.type = eCAL::Payload::pl_vec;
     eCAL::nanopb::decode_bytes(pb_sample.content.payload, payload_.content.payload.vec);
 
+    // padding
+    eCAL::nanopb::decode_bytes(pb_sample.padding, payload_.padding);
+
     ///////////////////////////////////////////////
     // decode it
     ///////////////////////////////////////////////
diff --git a/src/core/src/serialization/ecal_struct_sample_payload.h b/src/core/src/serialization/ecal_struct_sample_payload.h
index 0279c8b..47b033a 100644
--- a/src/core/src/serialization/ecal_struct_sample_payload.h
+++ b/src/core/src/serialization/ecal_struct_sample_payload.h
@@ -77,6 +77,7 @@ namespace eCAL
       eCmdType                            cmd_type = bct_none;          // payload command type
       Topic                               topic;                        // topic information
       Content                             content;                      // topic content
+      std::vector<char>                   padding;                      // padding to artificially increase the size of the message. This is a workaround for TCP topics, to get the actual user-payload 8-byte-aligned. REMOVE ME IN ECAL6
     };
   }
 }
diff --git a/src/core/src/serialization/nanopb/ecal.pb.h b/src/core/src/serialization/nanopb/ecal.pb.h
index 60a5d6a..20c8437 100644
--- a/src/core/src/serialization/nanopb/ecal.pb.h
+++ b/src/core/src/serialization/nanopb/ecal.pb.h
@@ -35,7 +35,7 @@ typedef struct _eCAL_pb_Content {
     int64_t clock; /* internal used clock */
     int64_t time; /* time the content was updated */
     pb_callback_t payload; /* octet stream */
-    int32_t size; /* size (additional for none payload "header only samples") */
+    int32_t size; /* size (redundant for compatibility) */
     int64_t hash; /* unique hash for that sample */
 } eCAL_pb_Content;
 
diff --git a/src/core/src/serialization/nanopb/layer.pb.c b/src/core/src/serialization/nanopb/layer.pb.c
index e2dc733..876144d 100644
--- a/src/core/src/serialization/nanopb/layer.pb.c
+++ b/src/core/src/serialization/nanopb/layer.pb.c
@@ -12,9 +12,6 @@ PB_BIND(eCAL_pb_LayerParUdpMC, eCAL_pb_LayerParUdpMC, AUTO)
 PB_BIND(eCAL_pb_LayerParShm, eCAL_pb_LayerParShm, AUTO)
 
 
-PB_BIND(eCAL_pb_LayerParInproc, eCAL_pb_LayerParInproc, AUTO)
-
-
 PB_BIND(eCAL_pb_LayerParTcp, eCAL_pb_LayerParTcp, AUTO)
 
 
diff --git a/src/core/src/serialization/nanopb/layer.pb.h b/src/core/src/serialization/nanopb/layer.pb.h
index 2965be9..9abe83c 100644
--- a/src/core/src/serialization/nanopb/layer.pb.h
+++ b/src/core/src/serialization/nanopb/layer.pb.h
@@ -13,8 +13,11 @@
 typedef enum _eCAL_pb_eTLayerType {
     eCAL_pb_eTLayerType_tl_none = 0, /* undefined */
     eCAL_pb_eTLayerType_tl_ecal_udp_mc = 1, /* ecal udp multicast */
+    /* 2 = ecal udp unicast (not supported anymore)
+ 3 = ecal udp metal (not supported anymore) */
     eCAL_pb_eTLayerType_tl_ecal_shm = 4, /* ecal shared memory */
     eCAL_pb_eTLayerType_tl_ecal_tcp = 5, /* ecal tcp */
+    /* 42 = inproc (not supported anymore) */
     eCAL_pb_eTLayerType_tl_all = 255 /* all layer */
 } eCAL_pb_eTLayerType;
 
@@ -27,10 +30,6 @@ typedef struct _eCAL_pb_LayerParShm {
     pb_callback_t memory_file_list; /* list of memory file names */
 } eCAL_pb_LayerParShm;
 
-typedef struct _eCAL_pb_LayerParInproc {
-    char dummy_field;
-} eCAL_pb_LayerParInproc;
-
 typedef struct _eCAL_pb_LayerParTcp {
     int32_t port; /* tcp writers port number */
 } eCAL_pb_LayerParTcp;
@@ -40,6 +39,7 @@ typedef struct _eCAL_pb_ConnnectionPar {
     eCAL_pb_LayerParUdpMC layer_par_udpmc; /* parameter for ecal udp multicast */
     bool has_layer_par_shm;
     eCAL_pb_LayerParShm layer_par_shm; /* parameter for ecal shared memory */
+    /* 3 = parameter for ecal inner process */
     bool has_layer_par_tcp;
     eCAL_pb_LayerParTcp layer_par_tcp; /* parameter for ecal tcp */
 } eCAL_pb_ConnnectionPar;
@@ -66,20 +66,17 @@ extern "C" {
 
 
 
-
 #define eCAL_pb_TLayer_type_ENUMTYPE eCAL_pb_eTLayerType
 
 
 /* Initializer values for message structs */
 #define eCAL_pb_LayerParUdpMC_init_default       {0}
 #define eCAL_pb_LayerParShm_init_default         {{{NULL}, NULL}}
-#define eCAL_pb_LayerParInproc_init_default      {0}
 #define eCAL_pb_LayerParTcp_init_default         {0}
 #define eCAL_pb_ConnnectionPar_init_default      {false, eCAL_pb_LayerParUdpMC_init_default, false, eCAL_pb_LayerParShm_init_default, false, eCAL_pb_LayerParTcp_init_default}
 #define eCAL_pb_TLayer_init_default              {_eCAL_pb_eTLayerType_MIN, 0, 0, false, eCAL_pb_ConnnectionPar_init_default}
 #define eCAL_pb_LayerParUdpMC_init_zero          {0}
 #define eCAL_pb_LayerParShm_init_zero            {{{NULL}, NULL}}
-#define eCAL_pb_LayerParInproc_init_zero         {0}
 #define eCAL_pb_LayerParTcp_init_zero            {0}
 #define eCAL_pb_ConnnectionPar_init_zero         {false, eCAL_pb_LayerParUdpMC_init_zero, false, eCAL_pb_LayerParShm_init_zero, false, eCAL_pb_LayerParTcp_init_zero}
 #define eCAL_pb_TLayer_init_zero                 {_eCAL_pb_eTLayerType_MIN, 0, 0, false, eCAL_pb_ConnnectionPar_init_zero}
@@ -106,11 +103,6 @@ X(a, CALLBACK, REPEATED, STRING,   memory_file_list,   1)
 #define eCAL_pb_LayerParShm_CALLBACK pb_default_field_callback
 #define eCAL_pb_LayerParShm_DEFAULT NULL
 
-#define eCAL_pb_LayerParInproc_FIELDLIST(X, a) \
-
-#define eCAL_pb_LayerParInproc_CALLBACK NULL
-#define eCAL_pb_LayerParInproc_DEFAULT NULL
-
 #define eCAL_pb_LayerParTcp_FIELDLIST(X, a) \
 X(a, STATIC,   SINGULAR, INT32,    port,              1)
 #define eCAL_pb_LayerParTcp_CALLBACK NULL
@@ -137,7 +129,6 @@ X(a, STATIC,   OPTIONAL, MESSAGE,  par_layer,         5)
 
 extern const pb_msgdesc_t eCAL_pb_LayerParUdpMC_msg;
 extern const pb_msgdesc_t eCAL_pb_LayerParShm_msg;
-extern const pb_msgdesc_t eCAL_pb_LayerParInproc_msg;
 extern const pb_msgdesc_t eCAL_pb_LayerParTcp_msg;
 extern const pb_msgdesc_t eCAL_pb_ConnnectionPar_msg;
 extern const pb_msgdesc_t eCAL_pb_TLayer_msg;
@@ -145,7 +136,6 @@ extern const pb_msgdesc_t eCAL_pb_TLayer_msg;
 /* Defines for backwards compatibility with code written before nanopb-0.4.0 */
 #define eCAL_pb_LayerParUdpMC_fields &eCAL_pb_LayerParUdpMC_msg
 #define eCAL_pb_LayerParShm_fields &eCAL_pb_LayerParShm_msg
-#define eCAL_pb_LayerParInproc_fields &eCAL_pb_LayerParInproc_msg
 #define eCAL_pb_LayerParTcp_fields &eCAL_pb_LayerParTcp_msg
 #define eCAL_pb_ConnnectionPar_fields &eCAL_pb_ConnnectionPar_msg
 #define eCAL_pb_TLayer_fields &eCAL_pb_TLayer_msg
@@ -155,7 +145,6 @@ extern const pb_msgdesc_t eCAL_pb_TLayer_msg;
 /* eCAL_pb_ConnnectionPar_size depends on runtime parameters */
 /* eCAL_pb_TLayer_size depends on runtime parameters */
 #define ECAL_PB_LAYER_PB_H_MAX_SIZE              eCAL_pb_LayerParTcp_size
-#define eCAL_pb_LayerParInproc_size              0
 #define eCAL_pb_LayerParTcp_size                 11
 #define eCAL_pb_LayerParUdpMC_size               0
 
diff --git a/src/core/src/util/ecal_expmap.h b/src/core/src/util/ecal_expmap.h
index 229a0f5..b9a321b 100644
--- a/src/core/src/util/ecal_expmap.h
+++ b/src/core/src/util/ecal_expmap.h
@@ -66,9 +66,11 @@ namespace eCAL
         friend class const_iterator;
 
       public:
-        using value_type = std::pair<Key, T>;
-        using pointer    = std::pair<Key, T>*;
-        using reference  = std::pair<Key, T>&;
+        using iterator_category = std::bidirectional_iterator_tag;
+        using value_type        = std::pair<Key, T>;
+        using difference_type   = std::ptrdiff_t;
+        using pointer           = std::pair<Key, T>*;
+        using reference         = std::pair<Key, T>&;
 
         explicit iterator(const typename key_to_value_type::iterator _it)
           : it(_it)
@@ -102,9 +104,11 @@ namespace eCAL
       class const_iterator
       {
       public:
-        using value_type = std::pair<Key, T>;
-        using pointer    = std::pair<Key, T>*;
-        using reference  = std::pair<Key, T>&;
+        using iterator_category = std::bidirectional_iterator_tag;
+        using value_type        = std::pair<Key, T>;
+        using difference_type   = std::ptrdiff_t;
+        using pointer           = std::pair<Key, T>*;
+        using reference         = std::pair<Key, T>&;
 
         explicit const_iterator(const iterator& other)
           : it(other.it)
diff --git a/src/protobuf/ecal.proto b/src/protobuf/ecal.proto
index bf1ba16..8786162 100644
--- a/src/protobuf/ecal.proto
+++ b/src/protobuf/ecal.proto
@@ -31,9 +31,9 @@ message Content                                // topic content
   int64        id                    =  1;     // sample id
   int64        clock                 =  2;     // internal used clock
   int64        time                  =  3;     // time the content was updated
-  int64        hash                  =  7;     // unique hash for that sample
-  int32        size                  =  6;     // size (additional for none payload "header only samples")
   bytes        payload               =  4;     // octet stream
+  int32        size                  =  6;     // size (redundant for compatibility)
+  int64        hash                  =  7;     // unique hash for that sample
 }
 
 enum eCmdType                                  // command type
diff --git a/src/protobuf/layer.proto b/src/protobuf/layer.proto
index d6de62d..b6af045 100644
--- a/src/protobuf/layer.proto
+++ b/src/protobuf/layer.proto
@@ -30,10 +30,6 @@ message LayerParShm
   repeated string  memory_file_list   =   1;    // list of memory file names
 }
 
-message LayerParInproc
-{
-}
-
 message LayerParTcp
 {
   int32            port               =   1;    // tcp writers port number
@@ -43,6 +39,7 @@ message ConnnectionPar                          // connection parameter for read
 {
   LayerParUdpMC    layer_par_udpmc    =   1;    // parameter for ecal udp multicast
   LayerParShm      layer_par_shm      =   2;    // parameter for ecal shared memory
+                                                // 3 = parameter for ecal inner process
   LayerParTcp      layer_par_tcp      =   4;    // parameter for ecal tcp
 }
 
@@ -50,8 +47,11 @@ enum eTLayerType                                // transport layer
 {
   tl_none                             =   0;    // undefined
   tl_ecal_udp_mc                      =   1;    // ecal udp multicast
+                                                // 2 = ecal udp unicast (not supported anymore)
+                                                // 3 = ecal udp metal (not supported anymore)
   tl_ecal_shm                         =   4;    // ecal shared memory
   tl_ecal_tcp                         =   5;    // ecal tcp
+                                                // 42 = inproc (not supported anymore)
   tl_all                              = 255;    // all layer
 }
 
diff --git a/tests/serialization_test/src/common_generate.cpp b/tests/serialization_test/src/common_generate.cpp
index ab7eab7..a5cd9a7 100644
--- a/tests/serialization_test/src/common_generate.cpp
+++ b/tests/serialization_test/src/common_generate.cpp
@@ -19,6 +19,7 @@
 
 #include <cstdlib>
 #include <string>
+#include <vector>
 
 namespace eCAL
 {
@@ -36,4 +37,18 @@ namespace eCAL
 
     return result;
   }
+  
+  std::vector<char> GenerateRandomVector(size_t length)
+  {
+    std::vector<char> result;
+    result.reserve(length);
+
+    for (size_t i = 0; i < length; ++i)
+    {
+      char random_byte = rand() % 256; // Generates a random byte (0-255)
+      result.push_back(random_byte);
+    }
+
+    return result;
+  }
 }
diff --git a/tests/serialization_test/src/payload_compare.cpp b/tests/serialization_test/src/payload_compare.cpp
index 9be97ab..a4ae16b 100644
--- a/tests/serialization_test/src/payload_compare.cpp
+++ b/tests/serialization_test/src/payload_compare.cpp
@@ -75,6 +75,11 @@ namespace eCAL
         }
       }
 
+      // compare padding
+      if (sample1.padding != sample2.padding) {
+        return false;
+      }
+
       // all comparisons passed, samples are equal
       return true;
     }
diff --git a/tests/serialization_test/src/payload_generate.cpp b/tests/serialization_test/src/payload_generate.cpp
index 9ebf01f..6731adf 100644
--- a/tests/serialization_test/src/payload_generate.cpp
+++ b/tests/serialization_test/src/payload_generate.cpp
@@ -24,6 +24,7 @@
 namespace eCAL
 {
   std::string GenerateString(size_t length);
+  std::vector<char> GenerateRandomVector(size_t length);
 
   namespace Payload
   {
@@ -105,6 +106,7 @@ namespace eCAL
       sample.cmd_type = static_cast<eCmdType>(rand() % 17);  //  command type
       sample.topic    = GenerateTopic();
       sample.content  = GenerateContent(payload_vec);
+      sample.padding  = GenerateRandomVector(8);
 
       return sample;
     }