diff --git a/examples/server_example_substitution/server_example_substitution.c b/examples/server_example_substitution/server_example_substitution.c
index 0050f04f..2f41d892 100644
--- a/examples/server_example_substitution/server_example_substitution.c
+++ b/examples/server_example_substitution/server_example_substitution.c
@@ -2,7 +2,8 @@
  *  server_example_substitution.c
  *
  *  - How to use the IEC 61850 substitution service
- *  - Two data objects can be substituted:
+ *  - How to use the blocking service
+ *  - Two data objects can be substituted and/or blocked:
  *  -- GGIO1.AnIn1
  *  -- GGIO1.Ind1
  */
@@ -24,6 +25,8 @@ static IedServer iedServer = NULL;
 
 static bool subsAnIn1 = false;
 static bool subsInd1 = false;
+static bool blkEnaAnIn1 = false;
+static bool blkEnaInd1 = false;
 
 static float an1 = 0.f;
 static uint64_t timestamp = 0;
@@ -35,7 +38,6 @@ sigint_handler(int signalId)
     running = 0;
 }
 
-
 static void
 connectionHandler (IedServer self, ClientConnection connection, bool connected, void* parameter)
 {
@@ -54,13 +56,13 @@ updateProcessValues()
     Timestamp_setTimeInMilliseconds(&iecTimestamp, timestamp);
     Timestamp_setLeapSecondKnown(&iecTimestamp, true);
 
-    if (subsAnIn1 == false) {
+    if ((subsAnIn1 == false) && (blkEnaAnIn1 == false)) {
         IedServer_updateTimestampAttributeValue(iedServer, IEDMODEL_LD1_GGIO1_AnIn1_t, &iecTimestamp);
         IedServer_updateQuality(iedServer, IEDMODEL_LD1_GGIO1_AnIn1_q, QUALITY_VALIDITY_GOOD);
         IedServer_updateFloatAttributeValue(iedServer, IEDMODEL_LD1_GGIO1_AnIn1_mag_f, an1);
     }
 
-    if (subsInd1 == false) {
+    if ((subsInd1 == false) && (blkEnaInd1 == false)) {
         IedServer_updateTimestampAttributeValue(iedServer, IEDMODEL_LD1_GGIO1_Ind1_t, &iecTimestamp);
         IedServer_updateQuality(iedServer, IEDMODEL_LD1_GGIO1_Ind1_q, QUALITY_VALIDITY_GOOD);
         IedServer_updateBooleanAttributeValue(iedServer, IEDMODEL_LD1_GGIO1_Ind1_stVal, ind1);
@@ -116,6 +118,23 @@ writeAccessHandler (DataAttribute* dataAttribute, MmsValue* value, ClientConnect
         }
 
     }
+    else if (dataAttribute == IEDMODEL_LD1_GGIO1_AnIn1_blkEna) {
+        printf("Received GGIO1.AnIn1.blkEna: %i\n", MmsValue_getBoolean(value));
+
+        blkEnaAnIn1 = MmsValue_getBoolean(value);
+
+        /* Update quality flags */
+
+        Quality quality =
+                Quality_fromMmsValue(IedServer_getAttributeValue(iedServer, IEDMODEL_LD1_GGIO1_AnIn1_q));
+
+        if (blkEnaAnIn1)
+            Quality_setFlag(&quality, QUALITY_OPERATOR_BLOCKED);
+        else
+            Quality_unsetFlag(&quality, QUALITY_OPERATOR_BLOCKED);
+
+        IedServer_updateQuality(iedServer, IEDMODEL_LD1_GGIO1_AnIn1_q, quality);
+    }
     else if (dataAttribute == IEDMODEL_LD1_GGIO1_Ind1_subEna) {
         printf("Received GGIO1.Ind1.subEna: %i\n", MmsValue_getBoolean(value));
 
@@ -160,6 +179,23 @@ writeAccessHandler (DataAttribute* dataAttribute, MmsValue* value, ClientConnect
         }
 
     }
+    else if (dataAttribute == IEDMODEL_LD1_GGIO1_Ind1_blkEna) {
+        printf("Received GGIO1.Ind1.blkEna: %i\n", MmsValue_getBoolean(value));
+
+        blkEnaInd1 = MmsValue_getBoolean(value);
+
+        /* Update quality flags */
+
+        Quality quality =
+                Quality_fromMmsValue(IedServer_getAttributeValue(iedServer, IEDMODEL_LD1_GGIO1_Ind1_q));
+
+        if (blkEnaAnIn1)
+            Quality_setFlag(&quality, QUALITY_OPERATOR_BLOCKED);
+        else
+            Quality_unsetFlag(&quality, QUALITY_OPERATOR_BLOCKED);
+
+        IedServer_updateQuality(iedServer, IEDMODEL_LD1_GGIO1_Ind1_q, quality);
+    }
 
     return DATA_ACCESS_ERROR_SUCCESS;
 }
@@ -179,10 +215,12 @@ main(int argc, char** argv)
     IedServer_handleWriteAccess(iedServer, IEDMODEL_LD1_GGIO1_AnIn1_subEna, writeAccessHandler, NULL);
     IedServer_handleWriteAccess(iedServer, IEDMODEL_LD1_GGIO1_AnIn1_subMag_f, writeAccessHandler, NULL);
     IedServer_handleWriteAccess(iedServer, IEDMODEL_LD1_GGIO1_AnIn1_subQ, writeAccessHandler, NULL);
+    IedServer_handleWriteAccess(iedServer, IEDMODEL_LD1_GGIO1_AnIn1_blkEna, writeAccessHandler, NULL);
 
     IedServer_handleWriteAccess(iedServer, IEDMODEL_LD1_GGIO1_Ind1_subEna, writeAccessHandler, NULL);
     IedServer_handleWriteAccess(iedServer, IEDMODEL_LD1_GGIO1_Ind1_subVal, writeAccessHandler, NULL);
     IedServer_handleWriteAccess(iedServer, IEDMODEL_LD1_GGIO1_Ind1_subQ, writeAccessHandler, NULL);
+    IedServer_handleWriteAccess(iedServer, IEDMODEL_LD1_GGIO1_Ind1_blkEna, writeAccessHandler, NULL);
 
     /* MMS server will be instructed to start listening for client connections. */
     IedServer_start(iedServer, 102);
@@ -225,6 +263,6 @@ main(int argc, char** argv)
 
     /* Cleanup - free all resources */
     IedServer_destroy(iedServer);
-    return 0;
 
+    return 0;
 } /* main() */
diff --git a/examples/server_example_substitution/static_model.c b/examples/server_example_substitution/static_model.c
index 0f8bff5d..c59ba0df 100644
--- a/examples/server_example_substitution/static_model.c
+++ b/examples/server_example_substitution/static_model.c
@@ -1,7 +1,7 @@
 /*
  * static_model.c
  *
- * automatically generated from substitution_example.icd
+ * automatically generated from substitution_example.cid
  */
 #include "static_model.h"
 
@@ -242,7 +242,7 @@ DataAttribute iedModel_LD1_LPHD1_Proxy_subID = {
     DataAttributeModelType,
     "subID",
     (ModelNode*) &iedModel_LD1_LPHD1_Proxy,
-    NULL,
+    (ModelNode*) &iedModel_LD1_LPHD1_Proxy_blkEna,
     NULL,
     0,
     IEC61850_FC_SV,
@@ -251,6 +251,19 @@ DataAttribute iedModel_LD1_LPHD1_Proxy_subID = {
     NULL,
     0};
 
+DataAttribute iedModel_LD1_LPHD1_Proxy_blkEna = {
+    DataAttributeModelType,
+    "blkEna",
+    (ModelNode*) &iedModel_LD1_LPHD1_Proxy,
+    NULL,
+    NULL,
+    0,
+    IEC61850_FC_BL,
+    IEC61850_BOOLEAN,
+    0,
+    NULL,
+    0};
+
 LogicalNode iedModel_LD1_MMDC1 = {
     LogicalNodeModelType,
     "MMDC1",
@@ -424,7 +437,7 @@ DataAttribute iedModel_LD1_MMDC1_Watt_subID = {
     DataAttributeModelType,
     "subID",
     (ModelNode*) &iedModel_LD1_MMDC1_Watt,
-    NULL,
+    (ModelNode*) &iedModel_LD1_MMDC1_Watt_blkEna,
     NULL,
     0,
     IEC61850_FC_SV,
@@ -433,6 +446,19 @@ DataAttribute iedModel_LD1_MMDC1_Watt_subID = {
     NULL,
     0};
 
+DataAttribute iedModel_LD1_MMDC1_Watt_blkEna = {
+    DataAttributeModelType,
+    "blkEna",
+    (ModelNode*) &iedModel_LD1_MMDC1_Watt,
+    NULL,
+    NULL,
+    0,
+    IEC61850_FC_BL,
+    IEC61850_BOOLEAN,
+    0,
+    NULL,
+    0};
+
 DataObject iedModel_LD1_MMDC1_Amp = {
     DataObjectModelType,
     "Amp",
@@ -550,7 +576,7 @@ DataAttribute iedModel_LD1_MMDC1_Amp_subID = {
     DataAttributeModelType,
     "subID",
     (ModelNode*) &iedModel_LD1_MMDC1_Amp,
-    NULL,
+    (ModelNode*) &iedModel_LD1_MMDC1_Amp_blkEna,
     NULL,
     0,
     IEC61850_FC_SV,
@@ -559,6 +585,19 @@ DataAttribute iedModel_LD1_MMDC1_Amp_subID = {
     NULL,
     0};
 
+DataAttribute iedModel_LD1_MMDC1_Amp_blkEna = {
+    DataAttributeModelType,
+    "blkEna",
+    (ModelNode*) &iedModel_LD1_MMDC1_Amp,
+    NULL,
+    NULL,
+    0,
+    IEC61850_FC_BL,
+    IEC61850_BOOLEAN,
+    0,
+    NULL,
+    0};
+
 DataObject iedModel_LD1_MMDC1_Vol = {
     DataObjectModelType,
     "Vol",
@@ -676,7 +715,7 @@ DataAttribute iedModel_LD1_MMDC1_Vol_subID = {
     DataAttributeModelType,
     "subID",
     (ModelNode*) &iedModel_LD1_MMDC1_Vol,
-    NULL,
+    (ModelNode*) &iedModel_LD1_MMDC1_Vol_blkEna,
     NULL,
     0,
     IEC61850_FC_SV,
@@ -685,6 +724,19 @@ DataAttribute iedModel_LD1_MMDC1_Vol_subID = {
     NULL,
     0};
 
+DataAttribute iedModel_LD1_MMDC1_Vol_blkEna = {
+    DataAttributeModelType,
+    "blkEna",
+    (ModelNode*) &iedModel_LD1_MMDC1_Vol,
+    NULL,
+    NULL,
+    0,
+    IEC61850_FC_BL,
+    IEC61850_BOOLEAN,
+    0,
+    NULL,
+    0};
+
 LogicalNode iedModel_LD1_GGIO1 = {
     LogicalNodeModelType,
     "GGIO1",
@@ -832,7 +884,7 @@ DataAttribute iedModel_LD1_GGIO1_Ind1_subID = {
     DataAttributeModelType,
     "subID",
     (ModelNode*) &iedModel_LD1_GGIO1_Ind1,
-    NULL,
+    (ModelNode*) &iedModel_LD1_GGIO1_Ind1_blkEna,
     NULL,
     0,
     IEC61850_FC_SV,
@@ -841,6 +893,19 @@ DataAttribute iedModel_LD1_GGIO1_Ind1_subID = {
     NULL,
     0};
 
+DataAttribute iedModel_LD1_GGIO1_Ind1_blkEna = {
+    DataAttributeModelType,
+    "blkEna",
+    (ModelNode*) &iedModel_LD1_GGIO1_Ind1,
+    NULL,
+    NULL,
+    0,
+    IEC61850_FC_BL,
+    IEC61850_BOOLEAN,
+    0,
+    NULL,
+    0};
+
 DataObject iedModel_LD1_GGIO1_AnIn1 = {
     DataObjectModelType,
     "AnIn1",
@@ -958,7 +1023,7 @@ DataAttribute iedModel_LD1_GGIO1_AnIn1_subID = {
     DataAttributeModelType,
     "subID",
     (ModelNode*) &iedModel_LD1_GGIO1_AnIn1,
-    NULL,
+    (ModelNode*) &iedModel_LD1_GGIO1_AnIn1_blkEna,
     NULL,
     0,
     IEC61850_FC_SV,
@@ -967,6 +1032,19 @@ DataAttribute iedModel_LD1_GGIO1_AnIn1_subID = {
     NULL,
     0};
 
+DataAttribute iedModel_LD1_GGIO1_AnIn1_blkEna = {
+    DataAttributeModelType,
+    "blkEna",
+    (ModelNode*) &iedModel_LD1_GGIO1_AnIn1,
+    NULL,
+    NULL,
+    0,
+    IEC61850_FC_BL,
+    IEC61850_BOOLEAN,
+    0,
+    NULL,
+    0};
+
 extern ReportControlBlock iedModel_LD1_LLN0_report0;
 extern ReportControlBlock iedModel_LD1_LLN0_report1;
 
diff --git a/examples/server_example_substitution/static_model.h b/examples/server_example_substitution/static_model.h
index 1ad6a5e4..55fc628a 100644
--- a/examples/server_example_substitution/static_model.h
+++ b/examples/server_example_substitution/static_model.h
@@ -1,7 +1,7 @@
 /*
  * static_model.h
  *
- * automatically generated from substitution_example.icd
+ * automatically generated from substitution_example.cid
  */
 
 #ifndef STATIC_MODEL_H_
@@ -32,6 +32,7 @@ extern DataAttribute iedModel_LD1_LPHD1_Proxy_subEna;
 extern DataAttribute iedModel_LD1_LPHD1_Proxy_subVal;
 extern DataAttribute iedModel_LD1_LPHD1_Proxy_subQ;
 extern DataAttribute iedModel_LD1_LPHD1_Proxy_subID;
+extern DataAttribute iedModel_LD1_LPHD1_Proxy_blkEna;
 extern LogicalNode   iedModel_LD1_MMDC1;
 extern DataObject    iedModel_LD1_MMDC1_Beh;
 extern DataAttribute iedModel_LD1_MMDC1_Beh_stVal;
@@ -47,6 +48,7 @@ extern DataAttribute iedModel_LD1_MMDC1_Watt_subMag;
 extern DataAttribute iedModel_LD1_MMDC1_Watt_subMag_f;
 extern DataAttribute iedModel_LD1_MMDC1_Watt_subQ;
 extern DataAttribute iedModel_LD1_MMDC1_Watt_subID;
+extern DataAttribute iedModel_LD1_MMDC1_Watt_blkEna;
 extern DataObject    iedModel_LD1_MMDC1_Amp;
 extern DataAttribute iedModel_LD1_MMDC1_Amp_mag;
 extern DataAttribute iedModel_LD1_MMDC1_Amp_mag_f;
@@ -57,6 +59,7 @@ extern DataAttribute iedModel_LD1_MMDC1_Amp_subMag;
 extern DataAttribute iedModel_LD1_MMDC1_Amp_subMag_f;
 extern DataAttribute iedModel_LD1_MMDC1_Amp_subQ;
 extern DataAttribute iedModel_LD1_MMDC1_Amp_subID;
+extern DataAttribute iedModel_LD1_MMDC1_Amp_blkEna;
 extern DataObject    iedModel_LD1_MMDC1_Vol;
 extern DataAttribute iedModel_LD1_MMDC1_Vol_mag;
 extern DataAttribute iedModel_LD1_MMDC1_Vol_mag_f;
@@ -67,6 +70,7 @@ extern DataAttribute iedModel_LD1_MMDC1_Vol_subMag;
 extern DataAttribute iedModel_LD1_MMDC1_Vol_subMag_f;
 extern DataAttribute iedModel_LD1_MMDC1_Vol_subQ;
 extern DataAttribute iedModel_LD1_MMDC1_Vol_subID;
+extern DataAttribute iedModel_LD1_MMDC1_Vol_blkEna;
 extern LogicalNode   iedModel_LD1_GGIO1;
 extern DataObject    iedModel_LD1_GGIO1_Beh;
 extern DataAttribute iedModel_LD1_GGIO1_Beh_stVal;
@@ -80,6 +84,7 @@ extern DataAttribute iedModel_LD1_GGIO1_Ind1_subEna;
 extern DataAttribute iedModel_LD1_GGIO1_Ind1_subVal;
 extern DataAttribute iedModel_LD1_GGIO1_Ind1_subQ;
 extern DataAttribute iedModel_LD1_GGIO1_Ind1_subID;
+extern DataAttribute iedModel_LD1_GGIO1_Ind1_blkEna;
 extern DataObject    iedModel_LD1_GGIO1_AnIn1;
 extern DataAttribute iedModel_LD1_GGIO1_AnIn1_mag;
 extern DataAttribute iedModel_LD1_GGIO1_AnIn1_mag_f;
@@ -90,6 +95,7 @@ extern DataAttribute iedModel_LD1_GGIO1_AnIn1_subMag;
 extern DataAttribute iedModel_LD1_GGIO1_AnIn1_subMag_f;
 extern DataAttribute iedModel_LD1_GGIO1_AnIn1_subQ;
 extern DataAttribute iedModel_LD1_GGIO1_AnIn1_subID;
+extern DataAttribute iedModel_LD1_GGIO1_AnIn1_blkEna;
 
 
 
@@ -114,6 +120,7 @@ extern DataAttribute iedModel_LD1_GGIO1_AnIn1_subID;
 #define IEDMODEL_LD1_LPHD1_Proxy_subVal (&iedModel_LD1_LPHD1_Proxy_subVal)
 #define IEDMODEL_LD1_LPHD1_Proxy_subQ (&iedModel_LD1_LPHD1_Proxy_subQ)
 #define IEDMODEL_LD1_LPHD1_Proxy_subID (&iedModel_LD1_LPHD1_Proxy_subID)
+#define IEDMODEL_LD1_LPHD1_Proxy_blkEna (&iedModel_LD1_LPHD1_Proxy_blkEna)
 #define IEDMODEL_LD1_MMDC1 (&iedModel_LD1_MMDC1)
 #define IEDMODEL_LD1_MMDC1_Beh (&iedModel_LD1_MMDC1_Beh)
 #define IEDMODEL_LD1_MMDC1_Beh_stVal (&iedModel_LD1_MMDC1_Beh_stVal)
@@ -129,6 +136,7 @@ extern DataAttribute iedModel_LD1_GGIO1_AnIn1_subID;
 #define IEDMODEL_LD1_MMDC1_Watt_subMag_f (&iedModel_LD1_MMDC1_Watt_subMag_f)
 #define IEDMODEL_LD1_MMDC1_Watt_subQ (&iedModel_LD1_MMDC1_Watt_subQ)
 #define IEDMODEL_LD1_MMDC1_Watt_subID (&iedModel_LD1_MMDC1_Watt_subID)
+#define IEDMODEL_LD1_MMDC1_Watt_blkEna (&iedModel_LD1_MMDC1_Watt_blkEna)
 #define IEDMODEL_LD1_MMDC1_Amp (&iedModel_LD1_MMDC1_Amp)
 #define IEDMODEL_LD1_MMDC1_Amp_mag (&iedModel_LD1_MMDC1_Amp_mag)
 #define IEDMODEL_LD1_MMDC1_Amp_mag_f (&iedModel_LD1_MMDC1_Amp_mag_f)
@@ -139,6 +147,7 @@ extern DataAttribute iedModel_LD1_GGIO1_AnIn1_subID;
 #define IEDMODEL_LD1_MMDC1_Amp_subMag_f (&iedModel_LD1_MMDC1_Amp_subMag_f)
 #define IEDMODEL_LD1_MMDC1_Amp_subQ (&iedModel_LD1_MMDC1_Amp_subQ)
 #define IEDMODEL_LD1_MMDC1_Amp_subID (&iedModel_LD1_MMDC1_Amp_subID)
+#define IEDMODEL_LD1_MMDC1_Amp_blkEna (&iedModel_LD1_MMDC1_Amp_blkEna)
 #define IEDMODEL_LD1_MMDC1_Vol (&iedModel_LD1_MMDC1_Vol)
 #define IEDMODEL_LD1_MMDC1_Vol_mag (&iedModel_LD1_MMDC1_Vol_mag)
 #define IEDMODEL_LD1_MMDC1_Vol_mag_f (&iedModel_LD1_MMDC1_Vol_mag_f)
@@ -149,6 +158,7 @@ extern DataAttribute iedModel_LD1_GGIO1_AnIn1_subID;
 #define IEDMODEL_LD1_MMDC1_Vol_subMag_f (&iedModel_LD1_MMDC1_Vol_subMag_f)
 #define IEDMODEL_LD1_MMDC1_Vol_subQ (&iedModel_LD1_MMDC1_Vol_subQ)
 #define IEDMODEL_LD1_MMDC1_Vol_subID (&iedModel_LD1_MMDC1_Vol_subID)
+#define IEDMODEL_LD1_MMDC1_Vol_blkEna (&iedModel_LD1_MMDC1_Vol_blkEna)
 #define IEDMODEL_LD1_GGIO1 (&iedModel_LD1_GGIO1)
 #define IEDMODEL_LD1_GGIO1_Beh (&iedModel_LD1_GGIO1_Beh)
 #define IEDMODEL_LD1_GGIO1_Beh_stVal (&iedModel_LD1_GGIO1_Beh_stVal)
@@ -162,6 +172,7 @@ extern DataAttribute iedModel_LD1_GGIO1_AnIn1_subID;
 #define IEDMODEL_LD1_GGIO1_Ind1_subVal (&iedModel_LD1_GGIO1_Ind1_subVal)
 #define IEDMODEL_LD1_GGIO1_Ind1_subQ (&iedModel_LD1_GGIO1_Ind1_subQ)
 #define IEDMODEL_LD1_GGIO1_Ind1_subID (&iedModel_LD1_GGIO1_Ind1_subID)
+#define IEDMODEL_LD1_GGIO1_Ind1_blkEna (&iedModel_LD1_GGIO1_Ind1_blkEna)
 #define IEDMODEL_LD1_GGIO1_AnIn1 (&iedModel_LD1_GGIO1_AnIn1)
 #define IEDMODEL_LD1_GGIO1_AnIn1_mag (&iedModel_LD1_GGIO1_AnIn1_mag)
 #define IEDMODEL_LD1_GGIO1_AnIn1_mag_f (&iedModel_LD1_GGIO1_AnIn1_mag_f)
@@ -172,6 +183,7 @@ extern DataAttribute iedModel_LD1_GGIO1_AnIn1_subID;
 #define IEDMODEL_LD1_GGIO1_AnIn1_subMag_f (&iedModel_LD1_GGIO1_AnIn1_subMag_f)
 #define IEDMODEL_LD1_GGIO1_AnIn1_subQ (&iedModel_LD1_GGIO1_AnIn1_subQ)
 #define IEDMODEL_LD1_GGIO1_AnIn1_subID (&iedModel_LD1_GGIO1_AnIn1_subID)
+#define IEDMODEL_LD1_GGIO1_AnIn1_blkEna (&iedModel_LD1_GGIO1_AnIn1_blkEna)
 
 #endif /* STATIC_MODEL_H_ */
 
diff --git a/examples/server_example_substitution/substitution_example.cid b/examples/server_example_substitution/substitution_example.cid
index 32d62c33..30ac3635 100644
--- a/examples/server_example_substitution/substitution_example.cid
+++ b/examples/server_example_substitution/substitution_example.cid
@@ -99,6 +99,7 @@
       <DA bType="BOOLEAN" fc="SV" name="subVal"/>
       <DA bType="Quality" fc="SV" name="subQ"/>
       <DA bType="VisString64" fc="SV" name="subID"/>
+      <DA bType="BOOLEAN" fc="BL" name="blkEna"/>
     </DOType>
     <DOType cdc="MV" id="MV">
       <DA bType="Struct" dchg="true" dupd="false" fc="MX" name="mag" type="AnalogueValue"/>
@@ -108,6 +109,7 @@
       <DA bType="Struct" fc="SV" name="subMag" type="AnalogueValue"/>
       <DA bType="Quality" fc="SV" name="subQ"/>
       <DA bType="VisString64" fc="SV" name="subID"/>
+       <DA bType="BOOLEAN" fc="BL" name="blkEna"/>
     </DOType>
     <DAType id="AnalogueValue">
       <BDA bType="FLOAT32" name="f"/>
diff --git a/hal/inc/hal_socket.h b/hal/inc/hal_socket.h
index e52defb5..414a1a7e 100644
--- a/hal/inc/hal_socket.h
+++ b/hal/inc/hal_socket.h
@@ -151,8 +151,19 @@ UdpSocket_bind(UdpSocket self, const char* address, int port);
 PAL_API bool
 UdpSocket_sendTo(UdpSocket self, const char* address, int port, uint8_t* msg, int msgSize);
 
+/**
+ * \brief Receive data from UDP socket (store data and (optionally) the IP address of the sender
+ *
+ * \param self UDP socket instance
+ * \param address (optional) buffer to store the IP address as string
+ * \param maxAddrSize (optional) size of the provided buffer to store the IP address
+ * \param msg buffer to store the UDP message data
+ * \param msgSize the maximum size of the message to receive
+ *
+ * \return number of received bytes or -1 in case of an error
+ */
 PAL_API int
-UdpSocket_receiveFrom(UdpSocket self, char** address, int maxAddrSize, uint8_t* msg, int msgSize);
+UdpSocket_receiveFrom(UdpSocket self, char* address, int maxAddrSize, uint8_t* msg, int msgSize);
 
 
 PAL_API void
diff --git a/hal/socket/linux/socket_linux.c b/hal/socket/linux/socket_linux.c
index dc9bbaeb..3c3b284c 100644
--- a/hal/socket/linux/socket_linux.c
+++ b/hal/socket/linux/socket_linux.c
@@ -753,16 +753,43 @@ UdpSocket_sendTo(UdpSocket self, const char* address, int port, uint8_t* msg, in
 }
 
 int
-UdpSocket_receiveFrom(UdpSocket self, char** address, int maxAddrSize, uint8_t* msg, int msgSize)
+UdpSocket_receiveFrom(UdpSocket self, char* address, int maxAddrSize, uint8_t* msg, int msgSize)
 {
-    struct sockaddr_in remoteAddress;
+    struct sockaddr_storage remoteAddress;
+    socklen_t structSize = sizeof(struct sockaddr_storage);
 
-    int result = recvfrom(self->fd, msg, msgSize, MSG_DONTWAIT, NULL, NULL);
+    int result = recvfrom(self->fd, msg, msgSize, MSG_DONTWAIT, (struct sockaddr*)&remoteAddress, &structSize);
 
     if (result == -1) {
         if (DEBUG_SOCKET)
             printf("SOCKET: failed to receive UDP message (errno=%i)\n", errno);
     }
 
+    if (address) {
+        bool isIPv6;
+        char addrString[INET6_ADDRSTRLEN + 7];
+        int port;
+
+        if (remoteAddress.ss_family == AF_INET) {
+            struct sockaddr_in* ipv4Addr = (struct sockaddr_in*) &remoteAddress;
+            port = ntohs(ipv4Addr->sin_port);
+            inet_ntop(AF_INET, &(ipv4Addr->sin_addr), addrString, INET_ADDRSTRLEN);
+            isIPv6 = false;
+        }
+        else if (remoteAddress.ss_family == AF_INET6) {
+            struct sockaddr_in6* ipv6Addr = (struct sockaddr_in6*) &remoteAddress;
+            port = ntohs(ipv6Addr->sin6_port);
+            inet_ntop(AF_INET6, &(ipv6Addr->sin6_addr), addrString, INET6_ADDRSTRLEN);
+            isIPv6 = true;
+        }
+        else
+            return result ;
+
+        if (isIPv6)
+            snprintf(address, maxAddrSize, "[%s]:%i", addrString, port);
+        else
+            snprintf(address, maxAddrSize, "%s:%i", addrString, port);
+    }
+
     return result;
 }
diff --git a/hal/time/unix/time.c b/hal/time/unix/time.c
index 6565da33..5c1bffe7 100644
--- a/hal/time/unix/time.c
+++ b/hal/time/unix/time.c
@@ -1,7 +1,7 @@
 /*
  *  time.c
  *
- *  Copyright 2013, 2014 Michael Zillgith
+ *  Copyright 2013-2021 Michael Zillgith
  *
  *  This file is part of libIEC61850.
  *
diff --git a/src/iec61850/client/client_control.c b/src/iec61850/client/client_control.c
index 12b5669f..ad31648d 100644
--- a/src/iec61850/client/client_control.c
+++ b/src/iec61850/client/client_control.c
@@ -523,14 +523,15 @@ ControlObjectClient_operate(ControlObjectClient self, MmsValue* ctlVal, uint64_t
 
     MmsValue_update(self->ctlVal, ctlVal);
 
-    if (self->analogValue)
-        MmsValue_setElement(self->analogValue, 0, NULL);
-
     self->opertime = operTime;
 
     success = true;
 
 exit_function:
+
+    if (self->analogValue)
+        MmsValue_setElement(self->analogValue, 0, NULL);
+
     return success;
 }
 
@@ -624,13 +625,14 @@ ControlObjectClient_operateAsync(ControlObjectClient self, IedClientError* err,
     else {
         MmsValue_update(self->ctlVal, ctlVal);
 
-        if (self->analogValue)
-            MmsValue_setElement(self->analogValue, 0, NULL);
-
         self->opertime = operTime;
     }
 
 exit_function:
+
+    if (self->analogValue)
+        MmsValue_setElement(self->analogValue, 0, NULL);
+
     return invokeId;
 }
 
@@ -703,6 +705,8 @@ prepareSBOwParameters(ControlObjectClient self, MmsValue* ctlVal)
 bool
 ControlObjectClient_selectWithValue(ControlObjectClient self, MmsValue* ctlVal)
 {
+    bool retVal = true;
+
     resetLastApplError(self);
 
     char domainId[65];
@@ -741,22 +745,30 @@ ControlObjectClient_selectWithValue(ControlObjectClient self, MmsValue* ctlVal)
     if (mmsError != MMS_ERROR_NONE) {
         if (DEBUG_IED_CLIENT)
             printf("IED_CLIENT: select-with-value failed!\n");
-        return false;
+
+        retVal = false;
+
+        goto exit_function;
     }
     else {
         if (writeResult != DATA_ACCESS_ERROR_SUCCESS) {
             if (DEBUG_IED_CLIENT)
                 printf("IED_CLIENT: select-with-value failed!\n");
-            return false;
+
+            retVal = false;
+
+            goto exit_function;
         }
     }
 
     MmsValue_update(self->ctlVal, ctlVal);
 
+exit_function:
+
     if (self->analogValue)
         MmsValue_setElement(self->analogValue, 0, NULL);
 
-    return true;
+    return retVal;
 }
 
 static void
@@ -857,12 +869,13 @@ ControlObjectClient_selectWithValueAsync(ControlObjectClient self, IedClientErro
     }
     else {
         MmsValue_update(self->ctlVal, ctlVal);
-
-        if (self->analogValue)
-            MmsValue_setElement(self->analogValue, 0, NULL);
     }
 
 exit_function:
+
+    if (self->analogValue)
+        MmsValue_setElement(self->analogValue, 0, NULL);
+
     return invokeId;
 }
 
diff --git a/src/iec61850/client/ied_connection.c b/src/iec61850/client/ied_connection.c
index a055e7af..0e2da178 100644
--- a/src/iec61850/client/ied_connection.c
+++ b/src/iec61850/client/ied_connection.c
@@ -473,8 +473,12 @@ handleLastApplErrorMessage(IedConnection self, MmsValue* lastApplError)
     self->lastApplError.ctlNum = MmsValue_toUint32(ctlNum);
     self->lastApplError.addCause = (ControlAddCause) MmsValue_toInt32(addCause);
     self->lastApplError.error = (ControlLastApplError) MmsValue_toInt32(error);
+
+    Semaphore_wait(self->clientControlsLock);
+
     LinkedList control = LinkedList_getNext(self->clientControls);
-    while (control != NULL) {
+
+    while (control) {
         ControlObjectClient object = (ControlObjectClient) control->data;
 
         const char* objectRef = ControlObjectClient_getObjectReference(object);
@@ -485,6 +489,8 @@ handleLastApplErrorMessage(IedConnection self, MmsValue* lastApplError)
 
         control = LinkedList_getNext(control);
     }
+
+    Semaphore_post(self->clientControlsLock);
 }
 
 static void
@@ -515,9 +521,11 @@ informationReportHandler(void* parameter, char* domainName,
             if (DEBUG_IED_CLIENT)
                 printf("IED_CLIENT: RCVD CommandTermination for %s/%s\n", domainName, variableListName);
 
+            Semaphore_wait(self->clientControlsLock);
+
             LinkedList control = LinkedList_getNext(self->clientControls);
 
-            while (control != NULL) {
+            while (control) {
                ControlObjectClient object = (ControlObjectClient) control->data;
 
                const char* objectRef = ControlObjectClient_getObjectReference(object);
@@ -527,6 +535,8 @@ informationReportHandler(void* parameter, char* domainName,
 
                control = LinkedList_getNext(control);
             }
+
+            Semaphore_post(self->clientControlsLock);
         }
 
         MmsValue_delete(value);
@@ -587,6 +597,7 @@ createNewConnectionObject(TLSConfiguration tlsConfig, bool useThreads)
     if (self) {
         self->enabledReports = LinkedList_create();
         self->logicalDevices = NULL;
+        self->clientControlsLock = Semaphore_create(1);
         self->clientControls = LinkedList_create();
 
 
@@ -812,6 +823,7 @@ IedConnection_destroy(IedConnection self)
 
     LinkedList_destroyStatic(self->clientControls);
 
+    Semaphore_destroy(self->clientControlsLock);
     Semaphore_destroy(self->outstandingCallsLock);
     Semaphore_destroy(self->stateMutex);
     Semaphore_destroy(self->reportHandlerMutex);
@@ -3805,13 +3817,21 @@ IedConnection_getLastApplError(IedConnection self)
 void
 iedConnection_addControlClient(IedConnection self, ControlObjectClient control)
 {
+    Semaphore_wait(self->clientControlsLock);
+
     LinkedList_add(self->clientControls, control);
+
+    Semaphore_post(self->clientControlsLock);
 }
 
 void
 iedConnection_removeControlClient(IedConnection self, ControlObjectClient control)
 {
+    Semaphore_wait(self->clientControlsLock);
+
     LinkedList_remove(self->clientControls, control);
+
+    Semaphore_post(self->clientControlsLock);
 }
 
 FileDirectoryEntry
diff --git a/src/iec61850/inc/iec61850_client.h b/src/iec61850/inc/iec61850_client.h
index bdc55a03..c5c51818 100644
--- a/src/iec61850/inc/iec61850_client.h
+++ b/src/iec61850/inc/iec61850_client.h
@@ -1957,14 +1957,32 @@ ControlObjectClient_createEx(const char* objectReference, IedConnection connecti
 LIB61850_API void
 ControlObjectClient_destroy(ControlObjectClient self);
 
+/**
+ * Cause of the \ref ControlObjectClient_ControlActionHandler invocation
+ */
 typedef enum
 {
-    CONTROL_ACTION_TYPE_SELECT = 0,
-    CONTROL_ACTION_TYPE_OPERATE = 1,
-    CONTROL_ACTION_TYPE_CANCEL = 2
+    CONTROL_ACTION_TYPE_SELECT = 0, /** < callback was invoked because of a select command */
+    CONTROL_ACTION_TYPE_OPERATE = 1,  /** < callback was invoked because of an operate command */
+    CONTROL_ACTION_TYPE_CANCEL = 2 /** < callback was invoked because of a cancel command */
 } ControlActionType;
 
-
+/**
+ * \brief A callback handler that is invoked when a command termination message is received.
+ *
+ * This callback is invoked whenever a CommandTermination+ or CommandTermination- message is received.
+ * To distinguish between a CommandTermination+ and CommandTermination- please use the
+ * ControlObjectClient_getLastApplError function.
+ *
+ * NOTE: Do not call \ref ControlObjectClient_destroy inside of this callback! Doing so will cause a dead-lock.
+ *
+ * \param invokeId invoke ID of the command sent by the client
+ * \param parameter the user parameter that is passed to the callback function
+ * \param err the error code when an error occurred, or IED_ERROR_OK
+ * \param type control action type that caused the callback
+ * \param success true, when the command was successful, false otherwise
+ *
+ */
 typedef void
 (*ControlObjectClient_ControlActionHandler) (uint32_t invokeId, void* parameter, IedClientError err, ControlActionType type, bool success);
 
@@ -2196,7 +2214,7 @@ ControlObjectClient_setOrigin(ControlObjectClient self, const char* orIdent, int
  * NOTE: Some non-standard compliant servers may require this to accept oper/cancel requests
  *
  * \param self the ControlObjectClient instance
- * \param useContantT enable this behaviour with true, disable with false
+ * \param useContantT enable this behavior with true, disable with false
  */
 LIB61850_API void
 ControlObjectClient_useConstantT(ControlObjectClient self, bool useConstantT);
@@ -2233,13 +2251,15 @@ ControlObjectClient_setSynchroCheck(ControlObjectClient self, bool value);
 
 
 /**
- * \brief Private a callback handler that is invoked when a command termination message is received.
+ * \brief A callback handler that is invoked when a command termination message is received.
  *
  * This callback is invoked whenever a CommandTermination+ or CommandTermination- message is received.
  * To distinguish between a CommandTermination+ and CommandTermination- please use the
  * ControlObjectClient_getLastApplError function.
  *
- * \param parameter the user paramter that is passed to the callback function
+ * NOTE: Do not call \ref ControlObjectClient_destroy inside of this callback! Doing so will cause a dead-lock.
+ *
+ * \param parameter the user parameter that is passed to the callback function
  * \param controlClient the ControlObjectClient instance
  */
 typedef void (*CommandTerminationHandler) (void* parameter, ControlObjectClient controlClient);
diff --git a/src/iec61850/inc_private/ied_connection_private.h b/src/iec61850/inc_private/ied_connection_private.h
index 3b061b5b..5b7200ed 100644
--- a/src/iec61850/inc_private/ied_connection_private.h
+++ b/src/iec61850/inc_private/ied_connection_private.h
@@ -56,7 +56,10 @@ struct sIedConnection
     IedConnectionState state;
     LinkedList enabledReports;
     LinkedList logicalDevices;
+
+    Semaphore clientControlsLock;
     LinkedList clientControls;
+
     LastApplError lastApplError;
 
     Semaphore stateMutex;
diff --git a/src/iec61850/inc_private/ied_server_private.h b/src/iec61850/inc_private/ied_server_private.h
index 3d6aa3fd..6b1aad8a 100644
--- a/src/iec61850/inc_private/ied_server_private.h
+++ b/src/iec61850/inc_private/ied_server_private.h
@@ -32,6 +32,7 @@
 #define ALLOW_WRITE_ACCESS_SP 4
 #define ALLOW_WRITE_ACCESS_SV 8
 #define ALLOW_WRITE_ACCESS_SE 16
+#define ALLOW_WRITE_ACCESS_BL 32
 
 struct sIedServer
 {
diff --git a/src/iec61850/inc_private/reporting.h b/src/iec61850/inc_private/reporting.h
index b6d0bb75..f57abdf1 100644
--- a/src/iec61850/inc_private/reporting.h
+++ b/src/iec61850/inc_private/reporting.h
@@ -106,6 +106,8 @@ typedef struct {
     ReportBuffer* reportBuffer;
     MmsValue* timeOfEntry;
 
+    ReportControlBlock* rcb;
+
     IedServer server;
 } ReportControl;
 
diff --git a/src/iec61850/server/mms_mapping/mms_mapping.c b/src/iec61850/server/mms_mapping/mms_mapping.c
index 86497ccf..7f74d3fc 100644
--- a/src/iec61850/server/mms_mapping/mms_mapping.c
+++ b/src/iec61850/server/mms_mapping/mms_mapping.c
@@ -64,7 +64,7 @@ typedef struct
     EditSettingGroupConfirmationHandler editSgConfirmedHandler;
     void* editSgConfirmedHandlerParameter;
 
-    ClientConnection editingClient;
+    MmsServerConnection editingClient;
     uint64_t reservationTimeout;
 } SettingGroup;
 
@@ -587,7 +587,7 @@ unselectAllSettingGroups(MmsMapping* self, MmsServerConnection serverCon)
     while (settingGroupElement != NULL) {
         SettingGroup* settingGroup = (SettingGroup*) LinkedList_getData(settingGroupElement);
 
-        if (settingGroup->editingClient == (ClientConnection) serverCon)
+        if (settingGroup->editingClient == serverCon)
             unselectEditSettingGroup(settingGroup);
 
         settingGroupElement = LinkedList_getNext(settingGroupElement);
@@ -2100,45 +2100,9 @@ isReportControlBlock(char* separator)
 #endif /* (CONFIG_IEC61850_REPORT_SERVICE == 1) */
 
 static bool
-isFunctionalConstraintCF(char* separator)
+isFunctionalConstraint(const char* fcStr, char* separator)
 {
-    if (strncmp(separator + 1, "CF", 2) == 0)
-        return true;
-    else
-        return false;
-}
-
-static bool
-isFunctionalConstraintDC(char* separator)
-{
-    if (strncmp(separator + 1, "DC", 2) == 0)
-        return true;
-    else
-        return false;
-}
-
-static bool
-isFunctionalConstraintSP(char* separator)
-{
-    if (strncmp(separator + 1, "SP", 2) == 0)
-        return true;
-    else
-        return false;
-}
-
-static bool
-isFunctionalConstraintSV(char* separator)
-{
-    if (strncmp(separator + 1, "SV", 2) == 0)
-        return true;
-    else
-        return false;
-}
-
-static bool
-isFunctionalConstraintSE(char* separator)
-{
-    if (strncmp(separator + 1, "SE", 2) == 0)
+    if (strncmp(separator + 1, fcStr, 2) == 0)
         return true;
     else
         return false;
@@ -2445,16 +2409,18 @@ checkIfValueBelongsToModelNode(DataAttribute* dataAttribute, MmsValue* value, Mm
 static FunctionalConstraint
 getFunctionalConstraintForWritableNode(char* separator)
 {
-    if (isFunctionalConstraintCF(separator))
+    if (isFunctionalConstraint("CF", separator))
         return IEC61850_FC_CF;
-    if (isFunctionalConstraintDC(separator))
+    if (isFunctionalConstraint("DC", separator))
         return IEC61850_FC_DC;
-    if (isFunctionalConstraintSP(separator))
+    if (isFunctionalConstraint("SP", separator))
         return IEC61850_FC_SP;
-    if (isFunctionalConstraintSV(separator))
+    if (isFunctionalConstraint("SV", separator))
         return IEC61850_FC_SV;
-    if (isFunctionalConstraintSE(separator))
+    if (isFunctionalConstraint("SE", separator))
         return IEC61850_FC_SE;
+    if (isFunctionalConstraint("BL", separator))
+        return IEC61850_FC_BL;
 
     return IEC61850_FC_NONE;
 }
@@ -2497,6 +2463,13 @@ getAccessPolicyForFC(MmsMapping* self, FunctionalConstraint fc)
             return ACCESS_POLICY_DENY;
     }
 
+    if (fc == IEC61850_FC_BL) {
+        if (self->iedServer->writeAccessPolicies & ALLOW_WRITE_ACCESS_BL)
+            return ACCESS_POLICY_ALLOW;
+        else
+            return ACCESS_POLICY_DENY;
+    }
+
     return ACCESS_POLICY_DENY;
 }
 
@@ -2622,9 +2595,12 @@ mmsWriteHandler(void* parameter, MmsDomain* domain,
                     if ((val > 0) && (val <= sg->sgcb->numOfSGs)) {
                         if (val != sg->sgcb->actSG) {
 
-                            if (sg->actSgChangedHandler != NULL) {
+                            if (sg->actSgChangedHandler) {
+
+                                ClientConnection clientConnection = private_IedServer_getClientConnectionByHandle(self->iedServer, connection);
+
                                 if (sg->actSgChangedHandler(sg->actSgChangedHandlerParameter, sg->sgcb,
-                                        (uint8_t) val, (ClientConnection) connection))
+                                        (uint8_t) val, clientConnection))
                                 {
                                     sg->sgcb->actSG = val;
 
@@ -2634,7 +2610,6 @@ mmsWriteHandler(void* parameter, MmsDomain* domain,
                                     MmsValue_setUint8(actSg, sg->sgcb->actSG);
                                     MmsValue_setUtcTimeMs(lActTm, Hal_getTimeInMs());
                                 }
-
                                 else
                                     retVal = DATA_ACCESS_ERROR_OBJECT_ACCESS_DENIED;
                             }
@@ -2661,7 +2636,7 @@ mmsWriteHandler(void* parameter, MmsDomain* domain,
                     if (sg != NULL) {
                         uint32_t val = MmsValue_toUint32(value);
 
-                        if ((sg->editingClient != NULL) && ( sg->editingClient != (ClientConnection) connection)) {
+                        if ((sg->editingClient != NULL) && ( sg->editingClient != connection)) {
                             /* Edit SG was set by other client */
                             retVal = DATA_ACCESS_ERROR_TEMPORARILY_UNAVAILABLE;
                         }
@@ -2674,13 +2649,15 @@ mmsWriteHandler(void* parameter, MmsDomain* domain,
 
                                 if ((val > 0) && (val <= sg->sgcb->numOfSGs)) {
 
-                                    if (sg->editSgChangedHandler != NULL) {
+                                    if (sg->editSgChangedHandler) {
+
+                                        ClientConnection clientConnection = private_IedServer_getClientConnectionByHandle(self->iedServer, connection);
 
                                         if (sg->editSgChangedHandler(sg->editSgChangedHandlerParameter, sg->sgcb,
-                                                (uint8_t) val, (ClientConnection) connection))
+                                                (uint8_t) val, clientConnection))
                                         {
                                             sg->sgcb->editSG = val;
-                                            sg->editingClient = (ClientConnection) connection;
+                                            sg->editingClient = connection;
 
                                             sg->reservationTimeout = Hal_getTimeInMs() + (sg->sgcb->resvTms * 1000);
 
@@ -2736,8 +2713,8 @@ mmsWriteHandler(void* parameter, MmsDomain* domain,
 
                         if (val == true) {
                             if (sg->sgcb->editSG != 0) {
-                                if (sg->editingClient == (ClientConnection) connection) {
-                                    if (sg->editSgConfirmedHandler != NULL) {
+                                if (sg->editingClient == connection) {
+                                    if (sg->editSgConfirmedHandler) {
                                         sg->editSgConfirmedHandler(sg->editSgConfirmedHandlerParameter, sg->sgcb,
                                                 sg->sgcb->editSG);
 
@@ -2784,7 +2761,7 @@ mmsWriteHandler(void* parameter, MmsDomain* domain,
          SettingGroup* sg = getSettingGroupByMmsDomain(self, domain);
 
          if (sg != NULL) {
-             if (sg->editingClient != (ClientConnection) connection)
+             if (sg->editingClient != connection)
                  return DATA_ACCESS_ERROR_TEMPORARILY_UNAVAILABLE;
          }
          else
@@ -2811,7 +2788,7 @@ mmsWriteHandler(void* parameter, MmsDomain* domain,
                 printf("IED_SERVER: write to %s policy:%i\n", variableId, nodeAccessPolicy);
 
 #if (CONFIG_IEC61850_SETTING_GROUPS == 1)
-            if (isFunctionalConstraintSE(separator)) {
+            if (isFunctionalConstraint("SE", separator)) {
                 SettingGroup* sg = getSettingGroupByMmsDomain(self, domain);
 
                 if (sg != NULL) {
@@ -3189,7 +3166,7 @@ mmsReadAccessHandler (void* parameter, MmsDomain* domain, char* variableId, MmsS
 #if (CONFIG_IEC61850_SETTING_GROUPS == 1)
 
     if (separator) {
-        if (isFunctionalConstraintSE(separator)) {
+        if (isFunctionalConstraint("SE", separator)) {
             SettingGroup* sg = getSettingGroupByMmsDomain(self, domain);
 
             if (sg != NULL) {
diff --git a/src/iec61850/server/mms_mapping/reporting.c b/src/iec61850/server/mms_mapping/reporting.c
index 74398794..637f0503 100644
--- a/src/iec61850/server/mms_mapping/reporting.c
+++ b/src/iec61850/server/mms_mapping/reporting.c
@@ -40,7 +40,7 @@
 #include <string.h>
 
 /* if not explicitly set by client "ResvTms" will be set to this value */
-#define RESV_TMS_IMPLICIT_VALUE 30
+#define RESV_TMS_IMPLICIT_VALUE 10
 
 #ifndef DEBUG_IED_SERVER
 #define DEBUG_IED_SERVER 0
@@ -1345,6 +1345,8 @@ Reporting_createMmsBufferedRCBs(MmsMapping* self, MmsDomain* domain,
         rc->name = StringUtils_createString(3, logicalNode->name, "$BR$",
                 reportControlBlock->name);
 
+        rc->rcb = reportControlBlock;
+
         namedVariable->typeSpec.structure.elements[currentReport] =
                 createBufferedReportControlBlock(reportControlBlock, rc);
 
@@ -1385,6 +1387,8 @@ Reporting_createMmsUnbufferedRCBs(MmsMapping* self, MmsDomain* domain,
         rc->name = StringUtils_createString(3, logicalNode->name, "$RP$",
                 reportControlBlock->name);
 
+        rc->rcb = reportControlBlock;
+
         namedVariable->typeSpec.structure.elements[currentReport] =
                 createUnbufferedReportControlBlock(reportControlBlock, rc);
 
@@ -1472,8 +1476,19 @@ updateOwner(ReportControl* rc, MmsServerConnection connection)
                 }
             }
             else {
-                uint8_t emptyAddr[1];
-                MmsValue_setOctetString(owner, emptyAddr, 0);
+                if (rc->resvTms != -1) {
+                    uint8_t emptyAddr[1];
+                    MmsValue_setOctetString(owner, emptyAddr, 0);
+                }
+                else {
+                    /* Set to pre-configured owner */
+                    if (rc->rcb->clientReservation[0] == 4) {
+                        MmsValue_setOctetString(owner, rc->rcb->clientReservation + 1, 4);
+                    }
+                    else if (rc->rcb->clientReservation[0] == 6) {
+                        MmsValue_setOctetString(owner, rc->rcb->clientReservation + 1, 16);
+                    }
+                }
             }
         }
     }
@@ -1539,9 +1554,14 @@ static void
 checkReservationTimeout(MmsMapping* self, ReportControl* rc)
 {
     if (rc->enabled == false) {
-        if (rc->resvTms > 0) {
+        if (rc->reservationTimeout > 0) {
             if (Hal_getTimeInMs() > rc->reservationTimeout) {
-                rc->resvTms = 0;
+
+                if (rc->resvTms != -1)
+                    rc->resvTms = 0;
+
+                if (DEBUG_IED_SERVER)
+                    printf("IED_SERVER: reservation timeout expired for %s.%s\n", rc->parentLN->name, rc->name);
 
 #if (CONFIG_IEC61850_BRCB_WITH_RESVTMS == 1)
                 MmsValue* resvTmsVal = ReportControl_getRCBValue(rc, "ResvTms");
@@ -1646,6 +1666,10 @@ Reporting_RCBWriteAccessHandler(MmsMapping* self, ReportControl* rc, char* eleme
                     rc->reserved = true;
                     rc->clientConnection = connection;
                 }
+                else {
+                    if (DEBUG_IED_SERVER)
+                        printf("IED_SERVER: client IP not matching with pre-assigned owner\n");
+                }
 #else
                 rc->reserved = true;
                 rc->clientConnection = connection;
@@ -1681,6 +1705,18 @@ Reporting_RCBWriteAccessHandler(MmsMapping* self, ReportControl* rc, char* eleme
         goto exit_function;
     }
 
+#if (CONFIG_IEC61850_RCB_ALLOW_ONLY_PRECONFIGURED_CLIENT == 1)
+    if (isIpAddressMatchingWithOwner(rc, MmsServerConnection_getClientAddress(connection)) == false) {
+        retVal = DATA_ACCESS_ERROR_OBJECT_ACCESS_DENIED;
+
+        if (DEBUG_IED_SERVER)
+            printf("IED_SERVER: client IP not matching with pre-assigned owner --> write access denied!\n");
+
+        goto exit_function;
+    }
+#endif
+
+
     if (strcmp(elementName, "RptEna") == 0) {
 
         if (value->value.boolean == true) {
@@ -1696,8 +1732,7 @@ Reporting_RCBWriteAccessHandler(MmsMapping* self, ReportControl* rc, char* eleme
 
             if (updateReportDataset(self, rc, NULL, connection)) {
 
-                if (rc->resvTms != -1)
-                    updateOwner(rc, connection);
+                updateOwner(rc, connection);
 
                 MmsValue* rptEna = ReportControl_getRCBValue(rc, "RptEna");
 
@@ -1998,6 +2033,9 @@ exit_function:
 
             reserveRcb(rc, connection);
         }
+        else if (rc->resvTms == -1) {
+            reserveRcb(rc, connection);
+        }
     }
 
 #if (CONFIG_IEC61850_SERVICE_TRACKING == 1)
diff --git a/src/sampled_values/sv_subscriber.c b/src/sampled_values/sv_subscriber.c
index 950e803e..106430e0 100644
--- a/src/sampled_values/sv_subscriber.c
+++ b/src/sampled_values/sv_subscriber.c
@@ -156,17 +156,30 @@ static void*
 svReceiverLoop(void* threadParameter)
 {
     SVReceiver self = (SVReceiver) threadParameter;
+    EthernetHandleSet handleSet = EthernetHandleSet_new();
+    EthernetHandleSet_addSocket(handleSet, self->ethSocket);
 
     self->stopped = false;
 
     while (self->running) {
+            switch (EthernetHandleSet_waitReady(handleSet, 100))
+            {
+            case -1:
+                if (DEBUG_SV_SUBSCRIBER)
+                    printf("SV_SUBSCRIBER: EhtnernetHandleSet_waitReady() failure\n");
+                break;
+            case 0:
+                break;
+            default:
+                SVReceiver_tick(self);
+            }
 
-        if (SVReceiver_tick(self) == false)
-            Thread_sleep(1);
     }
 
     self->stopped = true;
 
+    EthernetHandleSet_destroy(handleSet);
+
     return NULL;
 }