diff --git a/openwisp_monitoring/check/classes/iperf.py b/openwisp_monitoring/check/classes/iperf.py
index 59e5505f0..acfecfed3 100644
--- a/openwisp_monitoring/check/classes/iperf.py
+++ b/openwisp_monitoring/check/classes/iperf.py
@@ -24,7 +24,7 @@ def check(self, store=True):
         device_connection = self._get_device_connection(device)
         if not device_connection:
             logger.warning(
-                f'"DeviceConnection is not properly set for "{device}", iperf check skipped!'
+                f'DeviceConnection is not properly set for "{device}", iperf check skipped!'
             )
             return
         device_connection.connect()
diff --git a/openwisp_monitoring/db/backends/influxdb/queries.py b/openwisp_monitoring/db/backends/influxdb/queries.py
index 7352cf4c3..ec4a575db 100644
--- a/openwisp_monitoring/db/backends/influxdb/queries.py
+++ b/openwisp_monitoring/db/backends/influxdb/queries.py
@@ -110,8 +110,9 @@
     },
     'transfer': {
         'influxdb': (
-            "SELECT MEAN(sent_bytes) AS sent, "
-            "MEAN(received_bytes) AS received FROM {key} WHERE "
+            "SELECT SUM(received_bytes) AS received, "
+            "SUM(sent_bytes) AS sent,"
+            "SUM(sent_bytes) + SUM(received_bytes) AS total FROM {key} WHERE "
             "time >= '{time}' AND content_type = '{content_type}' AND "
             "object_id = '{object_id}' GROUP BY time(1d)"
         )
diff --git a/openwisp_monitoring/monitoring/configuration.py b/openwisp_monitoring/monitoring/configuration.py
index b15282705..aabd5870c 100644
--- a/openwisp_monitoring/monitoring/configuration.py
+++ b/openwisp_monitoring/monitoring/configuration.py
@@ -574,17 +574,24 @@ def _get_access_tech():
                 'colors': [DEFAULT_COLORS[5], DEFAULT_COLORS[9]],
             },
             'transfer': {
-                'type': 'stackedbar',
+                'type': 'stackedbar+lines',
                 'title': _('Transfer'),
+                'trace_type': {
+                    'received': 'stackedbar',
+                    'sent': 'stackedbar',
+                    'total': 'lines',
+                },
+                'trace_order': ['total', 'received', 'sent'],
                 'description': _('Total transfer during Iperf3 test in TCP mode.'),
                 'summary_labels': [
-                    _('Sent bytes'),
                     _('Received bytes'),
+                    _('Sent bytes'),
+                    _('Total upload traffic'),
                 ],
                 'unit': _(' GB'),
                 'order': 290,
                 'query': chart_query['transfer'],
-                'colors': [DEFAULT_COLORS[2], DEFAULT_COLORS[4]],
+                'colors': [DEFAULT_COLORS[7], DEFAULT_COLORS[2], DEFAULT_COLORS[4]],
             },
             'retransmits': {
                 'type': 'bar',