diff --git a/osm_nbi/subscription_topics.py b/osm_nbi/subscription_topics.py
index a5c9c44..7a3d52e 100644
--- a/osm_nbi/subscription_topics.py
+++ b/osm_nbi/subscription_topics.py
@@ -15,42 +15,95 @@
 
 __author__ = "Preethika P,preethika.p@tataelxsi.co.in"
 
-
 import requests
 from osm_nbi.base_topic import BaseTopic, EngineException
 from osm_nbi.validation import subscription
+from http import HTTPStatus
 
 
 class CommonSubscriptions(BaseTopic):
     topic = "subscriptions"
     topic_msg = None
-    
+
+    def format_subscription(self, subs_data):
+        """
+        Brings lexicographical order for list items at any nested level. For subscriptions max level of nesting is 4.
+        :param subs_data: Subscription data to be ordered.
+        :return: None
+        """
+        if isinstance(subs_data, dict):
+            for key in subs_data.keys():
+                # Base case
+                if isinstance(subs_data[key], list):
+                    subs_data[key].sort()
+                    return
+                # Recursive case
+                self.format_subscription(subs_data[key])
+        return
+
+    def check_conflict_on_new(self, session, content):
+        """
+        Two subscriptions are equal if Auth username, CallbackUri and filter are same.
+        :param session: Session object.
+        :param content: Subscription data.
+        :return: None if no conflict otherwise, raises an exception.
+        """
+        # Get all subscriptions from db table subscriptions and compare.
+        self.format_subscription(content)
+        filter_dict = {"CallbackUri": content["CallbackUri"]}
+        if content.get("authentication"):
+            if content["authentication"].get("authType") == "basic":
+                filter_dict["authentication.authType"] = "basic"
+            # elif add other authTypes here
+        else:
+            filter_dict["authentication"] = None  # For Items without authentication
+        existing_subscriptions = self.db.get_list("subscriptions", q_filter=filter_dict)
+        new_sub_pwd = None
+        if content.get("authentication") and content["authentication"].get("authType") == "basic":
+            new_sub_pwd = content["authentication"]["paramsBasic"]["password"]
+            content["authentication"]["paramsBasic"].pop("password", None)
+        for existing_subscription in existing_subscriptions:
+            sub_id = existing_subscription.pop("_id", None)
+            existing_subscription.pop("_admin", None)
+            existing_subscription.pop("schema_version", None)
+            if existing_subscription.get("authentication") and \
+                    existing_subscription["authentication"].get("authType") == "basic":
+                existing_subscription["authentication"]["paramsBasic"].pop("password", None)
+            # self.logger.debug(existing_subscription)
+            if existing_subscription == content:
+                raise EngineException("Subscription already exists with id: {}".format(sub_id),
+                                      HTTPStatus.CONFLICT)
+        if new_sub_pwd:
+            content["authentication"]["paramsBasic"]["password"] = new_sub_pwd
+        return
+
     def format_on_new(self, content, project_id=None, make_public=False):
         super().format_on_new(content, project_id=project_id, make_public=make_public)
-        
+
         # TODO check how to release Engine.write_lock during the check
         def _check_endpoint(url, auth):
             """
             Checks if the notification endpoint is valid
             :param url: the notification end
-            :param auth: contains the aunthentication details with type basic
+            :param auth: contains the authentication details with type basic
             """
             try:
                 if auth is None:
                     response = requests.get(url, timeout=5)
-                    if response.status_code != 204:
+                    if response.status_code != HTTPStatus.NO_CONTENT:
                         raise EngineException("Cannot access to the notification URL '{}',received {}: {}"
                                               .format(url, response.status_code, response.content))
                 elif auth["authType"] == "basic":
                     username = auth["paramsBasic"].get("userName")
                     password = auth["paramsBasic"].get("password")
                     response = requests.get(url, auth=(username, password), timeout=5)
-                    if response.status_code != 204:
+                    if response.status_code != HTTPStatus.NO_CONTENT:
                         raise EngineException("Cannot access to the notification URL '{}',received {}: {}"
                                               .format(url, response.status_code, response.content))
             except requests.exceptions.RequestException as e:
                 error_text = type(e).__name__ + ": " + str(e)
                 raise EngineException("Cannot access to the notification URL '{}': {}".format(url, error_text))
+
         url = content["CallbackUri"]
         auth = content.get("authentication")
         _check_endpoint(url, auth)
@@ -58,7 +111,7 @@
         if auth is not None and auth["authType"] == "basic":
             if content["authentication"]["paramsBasic"].get("password"):
                 content["authentication"]["paramsBasic"]["password"] = \
-                    self.db.encrypt(content["authentication"]["paramsBasic"]["password"], 
+                    self.db.encrypt(content["authentication"]["paramsBasic"]["password"],
                                     schema_version=schema_version, salt=content["_id"])
         return None
 
@@ -78,8 +131,7 @@
         :param _id: subscription_id deleted
         """
         super().delete_extra(session, _id, db_content, not_send_msg)
-        filter_q = {}
-        filter_q["reference"] = _id
+        filter_q = {"reference": _id}
         self.db.del_list("mapped_subscriptions", filter_q)