diff --git a/src/hfp.c b/src/hfp.c
index 4d33ca07a..8e01c6347 100644
--- a/src/hfp.c
+++ b/src/hfp.c
@@ -623,6 +623,11 @@ static void process_command(hfp_connection_t * context){
     context->command = HFP_CMD_NONE;
     int offset = 0;
     int isHandsFree = 1;
+    
+    if (strncmp((char *)context->line_buffer+offset, HFP_CALL_ANSWERED, strlen(HFP_CALL_ANSWERED)) == 0){
+        context->command = HFP_CMD_CALL_ANSWERED;
+        return;
+    }
 
     if (strncmp((char *)context->line_buffer, "AT", 2) == 0){
         offset = 2;
@@ -745,7 +750,6 @@ static void process_command(hfp_connection_t * context){
         }
         return;
     } 
-
     
     if (strncmp((char *)context->line_buffer+offset, "AT+", 3) == 0){
         context->command = HFP_CMD_UNKNOWN;
diff --git a/src/hfp.h b/src/hfp.h
index dcd7f1705..8c78cb3d5 100644
--- a/src/hfp.h
+++ b/src/hfp.h
@@ -89,6 +89,7 @@ extern "C" {
 */
 #define HFP_AGSF_THREE_WAY_CALLING  0
 #define HFP_AGSF_EC_NR_FUNCTION     1
+#define HFP_AGSF_IN_BAND_RING_TONE  3
 #define HFP_AGSF_CODEC_NEGOTIATION  9
 #define HFP_AGSF_HF_INDICATORS      10
 #define HFP_AGSF_ESCO               11
@@ -114,6 +115,7 @@ extern "C" {
 #define HFP_EXTENDED_AUDIO_GATEWAY_ERROR "+CME ERROR"
 #define HFP_TRIGGER_CODEC_CONNECTION_SETUP "+BCC"
 #define HFP_CONFIRM_COMMON_CODEC "+BCS"
+#define HFP_CALL_ANSWERED "ATA"
 
 #define HFP_OK "OK"
 #define HFP_ERROR "ERROR"
@@ -143,8 +145,8 @@ typedef enum {
     HFP_CMD_EXTENDED_AUDIO_GATEWAY_ERROR,
     HFP_CMD_TRIGGER_CODEC_CONNECTION_SETUP,
     HFP_CMD_AG_SUGGESTED_CODEC,
-    HFP_CMD_HF_CONFIRMED_CODEC
-    
+    HFP_CMD_HF_CONFIRMED_CODEC,
+    HFP_CMD_CALL_ANSWERED
 } hfp_command_t;
 
 typedef enum {
@@ -253,7 +255,9 @@ typedef enum {
     HFP_W4_SCO_CONNECTED,
     
     HFP_AUDIO_CONNECTION_ESTABLISHED,
-    
+    HFP_RING_ALERT,
+    HFP_CALL_ACTIVE,
+
     HFP_W2_DISCONNECT_SCO,
     HFP_W4_SCO_DISCONNECTED, // 30
 
@@ -374,7 +378,9 @@ typedef struct hfp_connection {
     uint8_t start_call;
     uint8_t terminate_call;
     uint8_t start_ringing;
-    uint8_t stop_ringing;
+    uint8_t update_call_status;
+    uint8_t update_callsetup_status;
+    
 } hfp_connection_t;
 
 // UTILS_START : TODO move to utils
diff --git a/src/hfp_ag.c b/src/hfp_ag.c
index b93192d63..17ca69ff9 100644
--- a/src/hfp_ag.c
+++ b/src/hfp_ag.c
@@ -684,6 +684,42 @@ static int hfp_ag_run_for_context_codecs_connection(hfp_connection_t * context){
                 done = 1;
                 return done;
             }
+            if (context->start_ringing){
+                context->start_ringing = 0;
+                context->state = HFP_RING_ALERT;
+                hfp_emit_event(hfp_callback, HFP_SUBEVENT_START_RINGINIG, 0);
+            }
+            break;
+        
+        case HFP_RING_ALERT:
+            // check if ATA
+            if (context->command == HFP_CMD_CALL_ANSWERED){
+                context->state = HFP_CALL_ACTIVE;
+                context->update_call_status = 1;
+                hfp_emit_event(hfp_callback, HFP_SUBEVENT_STOP_RINGINIG, 0);
+                hfp_ag_ok(context->rfcomm_cid);
+                done = 1;
+                return done;
+            }
+            break;
+        case HFP_CALL_ACTIVE:
+            if (context->update_call_status){
+                context->update_call_status = 0;
+                context->update_callsetup_status = 1;
+                hfp_ag_indicator_t * indicator = get_ag_indicator_for_name(context, "call");
+                indicator->status = HFP_CALL_STATUS_ACTIVE_OR_HELD_CALL_IS_PRESENT;
+                hfp_ag_transfer_ag_indicators_status_cmd(context->rfcomm_cid, indicator);
+                done = 1;
+                return done;
+            }
+            if (context->update_callsetup_status){
+                context->update_callsetup_status = 0;
+                hfp_ag_indicator_t * indicator = get_ag_indicator_for_name(context, "callsetup");
+                indicator->status = HFP_HELDCALL_STATUS_NO_CALLS_HELD;
+                hfp_ag_transfer_ag_indicators_status_cmd(context->rfcomm_cid, indicator);
+                done = 1;
+                return done;   
+            }
             break;
         default:
             break;
@@ -714,16 +750,6 @@ static int hfp_ag_run_for_context_codecs_connection(hfp_connection_t * context){
         return done;
     }
     
-    if (context->start_ringing){
-        context->start_ringing = 0;
-        hfp_emit_event(hfp_callback, HFP_SUBEVENT_START_RINGINIG, 0);
-    }
-
-    if (context->stop_ringing){
-        context->stop_ringing = 0;
-        hfp_emit_event(hfp_callback, HFP_SUBEVENT_STOP_RINGINIG, 0);
-    }
-
     return done;
 }
 
@@ -936,6 +962,7 @@ void hfp_ag_call(bd_addr_t bd_addr){
     hfp_run_for_context(connection);
 }
 
+
 /**
  * @brief 
  */
diff --git a/src/hfp_ag.h b/src/hfp_ag.h
index eb8231baa..003b5ba8d 100644
--- a/src/hfp_ag.h
+++ b/src/hfp_ag.h
@@ -167,6 +167,7 @@ void hfp_ag_release_audio_connection(bd_addr_t bd_addr);
  */
 void hfp_ag_call(bd_addr_t bd_addr);
 
+
 /**
  * @brief 
  */
diff --git a/test/hfp/Makefile b/test/hfp/Makefile
index 5609d6696..83e729edd 100644
--- a/test/hfp/Makefile
+++ b/test/hfp/Makefile
@@ -43,8 +43,8 @@ COMMON_OBJ  = $(COMMON:.c=.o)
 MOCK_OBJ  = $(MOCK:.c=.o)
 
 # CC = gcc-fsf-4.9
-CFLAGS  = -g -Wall -I. -I../ -I${BTSTACK_ROOT}/src -I${BTSTACK_ROOT}/include
-# CFLAGS += -Werror
+CFLAGS  = -g -Wall -Wmissing-prototype -I. -I../ -I${BTSTACK_ROOT}/src -I${BTSTACK_ROOT}/include
+CFLAGS += -Werror
 
 VPATH += ${BTSTACK_ROOT}/src
 VPATH += ${BTSTACK_ROOT}/ble
diff --git a/test/hfp/hfp_ag_client_test.c b/test/hfp/hfp_ag_client_test.c
index bedfdcdbd..7e4da399b 100644
--- a/test/hfp/hfp_ag_client_test.c
+++ b/test/hfp/hfp_ag_client_test.c
@@ -98,7 +98,7 @@ static uint8_t service_level_connection_established = 0;
 static uint8_t codecs_connection_established = 0;
 static uint8_t audio_connection_established = 0;
 static uint8_t start_ringing = 0;
-
+static uint8_t stop_ringing = 0;
 
 int expected_rfcomm_command(const char * expected_cmd){
     char * ag_cmd = (char *)get_rfcomm_payload();
@@ -171,6 +171,7 @@ void packet_handler(uint8_t * event, uint16_t event_size){
             break;
         case HFP_SUBEVENT_STOP_RINGINIG:
             printf("\n** Stop ringing **\n\n"); 
+            stop_ringing = 1;
             start_ringing = 0;
             break;
         default:
@@ -221,7 +222,7 @@ TEST(HFPClient, HFAnswerIncomingCallWithInBandRingTone){
     CHECK_EQUAL(audio_connection_established, 1);
 
     simulate_test_sequence(alert_ic_setup(), alert_ic_setup_size());
-    CHECK_EQUAL(start_ringing, 1);
+    CHECK_EQUAL(stop_ringing, 1);
 }
 
 
diff --git a/test/hfp/test_sequences.c b/test/hfp/test_sequences.c
index 0a84087f5..4cf4cd033 100644
--- a/test/hfp/test_sequences.c
+++ b/test/hfp/test_sequences.c
@@ -155,23 +155,12 @@ const char * ic_test1[] = {
 
 const char * ic_alert_test1[] = {
     "NOP",
-    // //"RING",
-    // "NOP",
-    // "+CLIP:\"1234\",128",
-    // "NOP",
-    // "InBandRingTone",
-    // "NOP",
-    // "RING",
-    // "NOP",
-    // "+CLIP:\"1234\",128", // 128-143, 144-159, 160-175
-    // "NOP",
-    // "InBandRingTone",
-    // "ATA",
-    // "OK",
-    // "NOP",
-    // "+CIEV:2,1", // call = 1
-    // "NOP",
-    // "+CIEV:3,0"
+    "ATA",
+    "OK",
+    "NOP",
+    "+CIEV:2,1", // call = 1
+    "NOP",
+    "+CIEV:3,0"    
 };
 
 hfp_test_item_t ic_tests[] = {