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+..
+   SPDX-FileCopyrightText: © 2020 Open Networking Foundation <support@opennetworking.org>
+   SPDX-License-Identifier: Apache-2.0
+
+.. _design_smf:
+
+SMF Design Overview
+===================
+
+.. image:: ../_static/images/CN-SMF.png
+  :width: 500px
+
+UPF-Adapter
+-----------
+
+As UPF may not support connections from multiple SMF instances with same Node-Id,
+UPF-Adapter layer has been introduced.
+
+* UPF-Adapter acts like Mux-Demux for PFCP messages between multiple SMF instances and UPF.
+
+* SMF sends custom PFCP msg to UPF-Adapter if UPF-Adapter is deployed.
+
+* The UPF-Adapter intercepts and modifies certain fields before sending PFCP msg to actual UPF.
+
+* Similar handling is done for the response from UPF towards SMF.
+