diff --git a/libowlps/owlps.h b/libowlps/owlps.h
index 1c90790..285ad72 100644
--- a/libowlps/owlps.h
+++ b/libowlps/owlps.h
@@ -27,8 +27,10 @@ extern "C" {
 // Port on which aggregator and positioning server communicate:
 #define OWL_DEFAULT_AGGREGATION_PORT 9902
 // Port on which the aggregator listens for hello messages from the
-// listeners, and the listeners listen for orders from the aggregator:
-#define OWL_DEFAULT_AUTOCALIBRATION_PORT 9904
+// listeners:
+#define OWL_DEFAULT_AUTOCALIBRATION_HELLO_PORT 9903
+// Port on which the listeners listen for orders from the aggregator:
+#define OWL_DEFAULT_AUTOCALIBRATION_ORDER_PORT 9904
 // Port on which the mobile listens for its position:
 #define OWL_DEFAULT_RESULT_PORT 9910
 
diff --git a/owlps-aggregator/owlps-aggregator.h b/owlps-aggregator/owlps-aggregator.h
index 31639fa..55161e6 100644
--- a/owlps-aggregator/owlps-aggregator.h
+++ b/owlps-aggregator/owlps-aggregator.h
@@ -9,7 +9,7 @@
 
 
 /* Arguments & program configuration */
-#define OPTIONS "a:Ac:C:Df:hi:k:K:l:o:p:qt:vV" // getopt string
+#define OPTIONS "Ac:C:Df:hH:i:k:K:l:o:O:p:qt:vV" // getopt string
 #define DEFAULT_CONFIG_FILE "/usr/local/etc/owlps/owlps-aggregator.conf"
 #define DEFAULT_AGGREGATE_TIMEOUT 1500 // milliseconds
 #define DEFAULT_KEEP_TIMEOUT 3000 // milliseconds
diff --git a/owlps-aggregator/owlps-aggregatord.c b/owlps-aggregator/owlps-aggregatord.c
index 1c62dd5..d310512 100644
--- a/owlps-aggregator/owlps-aggregatord.c
+++ b/owlps-aggregator/owlps-aggregatord.c
@@ -229,9 +229,13 @@ int parse_config_file(int argc, char **argv)
 
       // Autocalibration activated?
       CFG_BOOL("autocalibration", cfg_false, CFGF_NONE),
-      // Port on which autocalibration data are exchanged:
-      CFG_INT("autocalibration_port", OWL_DEFAULT_AUTOCALIBRATION_PORT,
-              CFGF_NONE),
+      // Port on which autocalibration orders are sent to the listeners:
+      CFG_INT("autocalibration_order_port",
+              OWL_DEFAULT_AUTOCALIBRATION_ORDER_PORT, CFGF_NONE),
+      // Port on which autocalibration hello are received from the
+      // listeners:
+      CFG_INT("autocalibration_hello_port",
+              OWL_DEFAULT_AUTOCALIBRATION_HELLO_PORT, CFGF_NONE),
       // Time we keep APs in the list (in seconds):
       CFG_INT("ap_keep_timeout", DEFAULT_AP_KEEP_TIMEOUT, CFGF_NONE),
       // Time between two checks of the AP list (in milliseconds):
@@ -308,10 +312,6 @@ int parse_command_line(int argc, char **argv)
         case 'A' :
           cfg_setbool(cfg, "autocalibration", cfg_true) ;
           break ;
-        case 'a' :
-          cfg_setint(cfg, "autocalibration_port",
-                     strtol(optarg, NULL, 0)) ;
-          break ;
         case 'c' :
           cfg_setint(cfg, "check_interval", strtol(optarg, NULL, 0)) ;
           break ;
@@ -323,6 +323,10 @@ int parse_command_line(int argc, char **argv)
           break ;
         case 'f' : // Config file
           break ; // (already parsed)
+        case 'H' :
+          cfg_setint(cfg, "autocalibration_hello_port",
+                     strtol(optarg, NULL, 0)) ;
+          break ;
         case 'i' :
           cfg_setstr(cfg, "positioner_ip", optarg) ;
           break ;
@@ -338,6 +342,10 @@ int parse_command_line(int argc, char **argv)
         case 'o' :
           cfg_setstr(cfg, "output_file", optarg) ;
           break ;
+        case 'O' :
+          cfg_setint(cfg, "autocalibration_order_port",
+                     strtol(optarg, NULL, 0)) ;
+          break ;
         case 'p' :
           cfg_setint(cfg, "positioner_port", strtol(optarg, NULL, 0)) ;
           break ;
@@ -921,7 +929,7 @@ void* listen_for_aps(void *NULL_value)
 
   listen_sockfd =
     owl_create_udp_listening_socket(cfg_getint(cfg,
-                                               "autocalibration_port")) ;
+                                               "autocalibration_hello_port")) ;
   if (listen_sockfd < 0)
     {
       perror("Error! Cannot create UDP listening socket from the"
@@ -1191,7 +1199,8 @@ void order_send(ap_list *ap)
 
   sockfd =
     owl_create_udp_trx_socket(ap->ip_addr,
-                              cfg_getint(cfg, "autocalibration_port"),
+                              cfg_getint(cfg,
+                                         "autocalibration_order_port"),
                               &serv, &client) ;
 
   message.order = AUTOCALIBRATION_ORDER_SEND ;
@@ -1380,8 +1389,10 @@ void print_usage()
 
          "Autocalibration options:\n"
          "\t-A\t\t\tEnable autocalibration (default: disabled).\n"
-         "\t-a port\t\t\tPort on which autocalibration data"
-         " are exchanged\n\t\t\t\twith the listeners (default: %d).\n"
+         "\t-O port\t\t\tPort on which autocalibration orders are"
+         " sent to\n\t\t\t\tthe listeners (default: %d).\n"
+         "\t-H port\t\t\tPort on which autocalibration hello are"
+         " received\n\t\t\t\tfrom the listeners (default: %d).\n"
          "\t-K ap_keep_timeout\tInactive APs are kept during"
          " 'ap_keep_timeout'\n\t\t\t\tseconds (default: %d s).\n"
          "\t-C ap_check_interval\tTime (in milliseconds) between two"
@@ -1397,7 +1408,8 @@ void print_usage()
          DEFAULT_AGGREGATE_TIMEOUT,
          DEFAULT_KEEP_TIMEOUT,
          DEFAULT_CHECK_INTERVAL,
-         OWL_DEFAULT_AUTOCALIBRATION_PORT,
+         OWL_DEFAULT_AUTOCALIBRATION_ORDER_PORT,
+         OWL_DEFAULT_AUTOCALIBRATION_HELLO_PORT,
          DEFAULT_AP_KEEP_TIMEOUT,
          DEFAULT_AP_CHECK_INTERVAL
          ) ;
diff --git a/owlps-listener/owlps-listener.h b/owlps-listener/owlps-listener.h
index 84588a3..5505267 100644
--- a/owlps-listener/owlps-listener.h
+++ b/owlps-listener/owlps-listener.h
@@ -62,7 +62,7 @@
 
 
 /* Arguments & program configuration */
-#define OPTIONS "a:ADf:hH:i:I:Kl:m:n:p:P:qr:t:vVw:" // getopt string
+#define OPTIONS "ADf:hH:i:I:Kl:m:n:O:p:P:qr:t:T:vVw:" // getopt string
 #define DEFAULT_CONFIG_FILE "/usr/local/etc/owlps/owlps-listener.conf"
 enum {MODE_ACTIVE = 'a', MODE_PASSIVE = 'p', MODE_MIXED = 'm'} ;
 #define DEFAULT_AUTOCALIBRATION_HELLO_DELAY 120 // seconds
@@ -257,10 +257,14 @@ void print_version(void) ;
   (cfg_setint(cfg, "autocalibration_request_port", (PORT)))
 #define GET_AUTOCALIBRATION_REQUEST_PORT() \
   (cfg_getint(cfg, "autocalibration_request_port"))
-#define SET_AUTOCALIBRATION_PORT(PORT) \
-  (cfg_setint(cfg, "autocalibration_port", (PORT)))
-#define GET_AUTOCALIBRATION_PORT() \
-  (cfg_getint(cfg, "autocalibration_port"))
+#define SET_AUTOCALIBRATION_ORDER_PORT(PORT) \
+  (cfg_setint(cfg, "autocalibration_order_port", (PORT)))
+#define GET_AUTOCALIBRATION_ORDER_PORT() \
+  (cfg_getint(cfg, "autocalibration_order_port"))
+#define SET_AUTOCALIBRATION_HELLO_PORT(PORT) \
+  (cfg_setint(cfg, "autocalibration_hello_port", (PORT)))
+#define GET_AUTOCALIBRATION_HELLO_PORT() \
+  (cfg_getint(cfg, "autocalibration_hello_port"))
 #define SET_AUTOCALIBRATION_HELLO_DELAY(DELAY) \
   (cfg_setint(cfg, "autocalibration_hello_delay", (DELAY)))
 #define GET_AUTOCALIBRATION_HELLO_DELAY() \
@@ -348,10 +352,14 @@ void print_version(void) ;
   (options.autocalibration_request_port = (PORT))
 #define GET_AUTOCALIBRATION_REQUEST_PORT() \
   (options.autocalibration_request_port)
-#define SET_AUTOCALIBRATION_PORT(PORT) \
-  (options.autocalibration_port = (PORT))
-#define GET_AUTOCALIBRATION_PORT() \
-  (options.autocalibration_port)
+#define SET_AUTOCALIBRATION_ORDER_PORT(PORT) \
+  (options.autocalibration_order_port = (PORT))
+#define GET_AUTOCALIBRATION_ORDER_PORT() \
+  (options.autocalibration_order_port)
+#define SET_AUTOCALIBRATION_HELLO_PORT(PORT) \
+  (options.autocalibration_hello_port = (PORT))
+#define GET_AUTOCALIBRATION_HELLO_PORT() \
+  (options.autocalibration_hello_port)
 #define SET_AUTOCALIBRATION_HELLO_DELAY(DELAY) \
   (options.autocalibration_hello_delay = (DELAY))
 #define GET_AUTOCALIBRATION_HELLO_DELAY() \
diff --git a/owlps-listener/owlps-listenerd.c b/owlps-listener/owlps-listenerd.c
index 9bc2445..8a18504 100644
--- a/owlps-listener/owlps-listenerd.c
+++ b/owlps-listener/owlps-listenerd.c
@@ -74,7 +74,8 @@ struct {
   owl_bool autocalibration ;
   char autocalibration_ip[INET_ADDRSTRLEN] ;
   uint_fast16_t autocalibration_request_port ;
-  uint_fast16_t autocalibration_port ;
+  uint_fast16_t autocalibration_order_port ;
+  uint_fast16_t autocalibration_hello_port ;
   uint_fast32_t autocalibration_hello_delay ;
   uint_fast32_t autocalibration_delay ;
   uint_fast16_t autocalibration_nb_packets ;
@@ -99,7 +100,8 @@ struct {
   owl_false,
   "",
   0,
-  OWL_DEFAULT_AUTOCALIBRATION_PORT,
+  OWL_DEFAULT_AUTOCALIBRATION_ORDER_PORT,
+  OWL_DEFAULT_AUTOCALIBRATION_HELLO_PORT,
   DEFAULT_AUTOCALIBRATION_HELLO_DELAY,
   DEFAULT_AUTOCALIBRATION_DELAY,
   DEFAULT_AUTOCALIBRATION_NBPKT,
@@ -330,9 +332,12 @@ int parse_config_file(int argc, char **argv)
       // Port on which autocalibration requests are sent (default: 0,
       // but will be set to listening_port in the config check):
       CFG_INT("autocalibration_request_port", 0, CFGF_NONE),
-      // Port on which autocalibration data are exchanged:
-      CFG_INT("autocalibration_port", OWL_DEFAULT_AUTOCALIBRATION_PORT,
-              CFGF_NONE),
+      // Port on which autocalibration orders are received:
+      CFG_INT("autocalibration_order_port",
+              OWL_DEFAULT_AUTOCALIBRATION_ORDER_PORT, CFGF_NONE),
+      // Port on which autocalibration hello are sent:
+      CFG_INT("autocalibration_hello_port",
+              OWL_DEFAULT_AUTOCALIBRATION_HELLO_PORT, CFGF_NONE),
       // Delay between two hello messages:
       CFG_INT("autocalibration_hello_delay",
               DEFAULT_AUTOCALIBRATION_HELLO_DELAY,
@@ -461,11 +466,6 @@ int parse_main_options(int argc, char **argv)
                   " is not available and will be ignored. All other"
                   " autocalibration-related options will also be"
                   " ignored.\n") ;
-#endif // USE_PTHREAD
-          break ;
-        case 'a' :
-#ifdef USE_PTHREAD
-          SET_AUTOCALIBRATION_PORT(strtol(optarg, NULL, 0)) ;
 #endif // USE_PTHREAD
           break ;
         case 'D' :
@@ -475,7 +475,7 @@ int parse_main_options(int argc, char **argv)
           break ; // (already parsed)
         case 'H' :
 #ifdef USE_PTHREAD
-          SET_AUTOCALIBRATION_HELLO_DELAY(strtol(optarg, NULL, 0)) ;
+          SET_AUTOCALIBRATION_HELLO_PORT(strtol(optarg, NULL, 0)) ;
 #endif // USE_PTHREAD
           break ;
         case 'i' :
@@ -504,6 +504,11 @@ int parse_main_options(int argc, char **argv)
         case 'n' :
 #ifdef USE_PTHREAD
           SET_AUTOCALIBRATION_NBPKT(strtol(optarg, NULL, 0)) ;
+#endif // USE_PTHREAD
+          break ;
+        case 'O' :
+#ifdef USE_PTHREAD
+          SET_AUTOCALIBRATION_ORDER_PORT(strtol(optarg, NULL, 0)) ;
 #endif // USE_PTHREAD
           break ;
         case 'p' :
@@ -523,6 +528,11 @@ int parse_main_options(int argc, char **argv)
         case 't' :
 #ifdef USE_PTHREAD
           SET_AUTOCALIBRATION_DELAY(strtol(optarg, NULL, 0)) ;
+#endif // USE_PTHREAD
+          break ;
+        case 'T' :
+#ifdef USE_PTHREAD
+          SET_AUTOCALIBRATION_HELLO_DELAY(strtol(optarg, NULL, 0)) ;
 #endif // USE_PTHREAD
           break ;
         case 'v' :
@@ -652,13 +662,21 @@ int check_configuration()
                     " failing back to the default value.\n") ;
           SET_AUTOCALIBRATION_REQUEST_PORT(GET_LISTENING_PORT()) ;
         }
-      if (GET_AUTOCALIBRATION_PORT() < 1 ||
-          GET_AUTOCALIBRATION_PORT() > 65535)
+      if (GET_AUTOCALIBRATION_ORDER_PORT() < 1 ||
+          GET_AUTOCALIBRATION_ORDER_PORT() > 65535)
         {
           if (VERBOSE_WARNING)
-            fprintf(stderr, "Warning! Bad autocalibration_port:"
+            fprintf(stderr, "Warning! Bad autocalibration_order_port:"
                     " failing back to the default value.\n") ;
-          SET_AUTOCALIBRATION_PORT(OWL_DEFAULT_AUTOCALIBRATION_PORT) ;
+          SET_AUTOCALIBRATION_ORDER_PORT(OWL_DEFAULT_AUTOCALIBRATION_ORDER_PORT) ;
+        }
+      if (GET_AUTOCALIBRATION_HELLO_PORT() < 1 ||
+          GET_AUTOCALIBRATION_HELLO_PORT() > 65535)
+        {
+          if (VERBOSE_WARNING)
+            fprintf(stderr, "Warning! Bad autocalibration_hello_port:"
+                    " failing back to the default value.\n") ;
+          SET_AUTOCALIBRATION_HELLO_PORT(OWL_DEFAULT_AUTOCALIBRATION_HELLO_PORT) ;
         }
     }
 #endif // USE_PTHREAD
@@ -688,7 +706,8 @@ void print_configuration()
           "autocalibration = %s\n"
           "autocalibration_ip = \"%s\"\n"
           "autocalibration_request_port = %"PRIuFAST16"\n"
-          "autocalibration_port = %"PRIuFAST16"\n"
+          "autocalibration_order_port = %"PRIuFAST16"\n"
+          "autocalibration_hello_port = %"PRIuFAST16"\n"
           "autocalibration_hello_delay = %"PRIuFAST32"\n"
           "autocalibration_delay = %"PRIuFAST32"\n"
           "autocalibration_nb_packets = %"PRIuFAST16"\n"
@@ -712,7 +731,8 @@ void print_configuration()
           OWL_BOOL_TO_STRING(GET_AUTOCALIBRATION()),
           GET_AUTOCALIBRATION_IP(),
           GET_AUTOCALIBRATION_REQUEST_PORT(),
-          GET_AUTOCALIBRATION_PORT(),
+          GET_AUTOCALIBRATION_ORDER_PORT(),
+          GET_AUTOCALIBRATION_HELLO_PORT(),
           GET_AUTOCALIBRATION_HELLO_DELAY(),
           GET_AUTOCALIBRATION_DELAY(),
           GET_AUTOCALIBRATION_NBPKT(),
@@ -1291,7 +1311,8 @@ void* autocalibrate_hello(void *NULL_value)
 
   send_sockfd =
     owl_create_trx_socket(GET_AGGREGATION_IP(),
-                          GET_AUTOCALIBRATION_PORT(), &serv, NULL) ;
+                          GET_AUTOCALIBRATION_HELLO_PORT(),
+                          &serv, NULL) ;
   pthread_cleanup_push(&owl_close_fd, &send_sockfd) ;
 
   memcpy(&message.ap_mac_addr_bytes, my_mac_bytes, ETHER_ADDR_LEN) ;
@@ -1331,7 +1352,7 @@ void* autocalibrate(void *NULL_value)
 
   // Socket to receive orders from the aggregator
   listen_sockfd =
-    owl_create_udp_listening_socket(GET_AUTOCALIBRATION_PORT()) ;
+    owl_create_udp_listening_socket(GET_AUTOCALIBRATION_ORDER_PORT()) ;
   if (listen_sockfd < 0)
     {
       perror("Error! Cannot create UDP listening socket from the"
@@ -1530,10 +1551,12 @@ void print_usage()
          " requests\n\t\t\t\t(default: aggregation_ip).\n"
          "\t-P autocalib_req_port\tPort on which autocalibration"
          " requests are sent\n\t\t\t\t(default: listening_port).\n"
-         "\t-a autocalib_port\tPort on which autocalibration data (hello"
-         " &\n\t\t\t\torders) are exchanged with the aggregation"
-         "\n\t\t\t\tserver (default: %d).\n"
-         "\t-H hello_delay\t\tTime between each hello message sent to"
+         "\t-O order_port\t\tPort on which autocalibration orders are"
+         "\n\t\t\t\treceived from the aggregation server (default:"
+         "\n\t\t\t\t%d).\n"
+         "\t-H hello_port\t\tPort on which hello messages are sent to"
+         " the\n\t\t\t\taggregation server (default: %d).\n"
+         "\t-T hello_delay\t\tTime between each hello message sent to"
          " the\n\t\t\t\taggregation server, in seconds (default:"
          " %d s).\n"
          "\t-t delay\t\tTime between each autocalibration"
@@ -1556,7 +1579,8 @@ void print_usage()
          DEFAULT_CONFIG_FILE,
          OWL_DEFAULT_REQUEST_PORT,
          OWL_DEFAULT_LISTENER_PORT,
-         OWL_DEFAULT_AUTOCALIBRATION_PORT,
+         OWL_DEFAULT_AUTOCALIBRATION_ORDER_PORT,
+         OWL_DEFAULT_AUTOCALIBRATION_HELLO_PORT,
          DEFAULT_AUTOCALIBRATION_HELLO_DELAY,
          DEFAULT_AUTOCALIBRATION_DELAY,
          DEFAULT_AUTOCALIBRATION_NBPKT