diff --git a/owlps-aggregator/owlps-aggregatord.c b/owlps-aggregator/owlps-aggregatord.c
index 8a63773..575ad95 100644
--- a/owlps-aggregator/owlps-aggregatord.c
+++ b/owlps-aggregator/owlps-aggregatord.c
@@ -860,6 +860,13 @@ void* monitor_requests(void *const NULL_value)
   if (VERBOSE_WARNING)
     fprintf(stderr, "Monitor requests thread launched.\n") ;
 
+  /* Open the socket to the positioning server
+   * We don't need to check wether or not the socket was opened
+   * successfuly because the network transmission is not mandatory
+   * (aggregated data will be written to the output file
+   * anyway). owl_close_fd() and the rest of the code here handle
+   * negative file descriptors.
+   */
   sockfd =
     owl_create_udp_trx_socket(cfg_getstr(cfg, "positioner_host"),
                               cfg_getint(cfg, "positioner_port"),
@@ -1020,7 +1027,8 @@ void flush_request_list(FILE *const stream,
  * Parameters:
  * - request_ptr: the request to print
  * - stream: the stream to print to
- * - sockfd: the file descriptor of the socket to send to
+ * - sockfd: the file descriptor of the socket to send to (can be
+ *   negative, in which case no transmission will be attempted)
  * - serv: the server's information
  */
 void output_request(request_list *const request_ptr,
@@ -1082,7 +1090,13 @@ void output_request(request_list *const request_ptr,
     }
   request.nb_info = htons(request.nb_info) ;
   // Send the request's main data:
-  sendto(sockfd, &request, sizeof(request), 0, serv, serv_len) ;
+  if (sockfd >= 0)
+    {
+      ssize_t n;
+      n = sendto(sockfd, &request, sizeof(request), 0, serv, serv_len);
+      if (n != sizeof(request))
+        perror("Couldn't send the request's main data");
+    }
 
   // Send request's per-CP information to the server and delete it
   // from the request
@@ -1096,7 +1110,13 @@ void output_request(request_list *const request_ptr,
       info.capture_time = request_info_ptr->capture_time ;
       owl_hton_timestamp(&info.capture_time) ;
       info.ss_dbm = request_info_ptr->ss_dbm ;
-      sendto(sockfd, &info, sizeof(info), 0, serv, serv_len) ;
+      if (sockfd >= 0)
+        {
+          ssize_t n;
+          n = sendto(sockfd, &info, sizeof(info), 0, serv, serv_len);
+          if (n != sizeof(info))
+            perror("Couldn't send the CP information");
+        }
 
       // Print CP info to the output file
       owl_mac_bytes_to_string_r(request_info_ptr->cp_mac_addr_bytes,
@@ -1497,6 +1517,11 @@ void order_send(const cp_list *const cp)
                               cfg_getint(cfg,
                                          "autocalibration_order_port"),
                               &serv) ;
+  if (sockfd < 0)
+    {
+      fprintf(stderr, "Can't transmit autocalibration order.\n");
+      return;
+    }
 
   message.order = AUTOCALIBRATION_ORDER_SEND ;
   nsent = sendto(sockfd, &message, sizeof(message), 0, &serv, serv_len) ;