diff --git a/tempest/test.py b/tempest/test.py
index a81b5d7..fc846ff 100644
--- a/tempest/test.py
+++ b/tempest/test.py
@@ -63,7 +63,14 @@
         'compute': CONF.service_available.nova,
         'image': CONF.service_available.glance,
         'volume': CONF.service_available.cinder,
+        # NOTE(masayukig): We have two network services which are neutron and
+        # nova-network. And we have no way to know whether nova-network is
+        # available or not. After the pending removal of nova-network from
+        # nova, we can treat the network/neutron case in the same manner as
+        # the other services.
         'network': True,
+        # NOTE(masayukig): Tempest tests always require the identity service.
+        # So we should set this True here.
         'identity': True,
         'object_storage': CONF.service_available.swift,
     }