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@@ -2,12 +2,89 @@
 .. SPDX-License-Identifier: CC-BY-4.0
 
 
+O-DU-L2 Architecture
+======================
+
+
 O-DU implements the functional blocks of L2 layer of a 5G NR protocol stacks.
-These layers primarily include NR MAC and NR RLC layers.
-In order to manage these layers, DU_APP submodule has been introduced which can be comsidered as the 
-master module of O-DU.
+These layers primarily include NR MAC NR Scheduler and NR RLC layers.
 
+O-DU modules are developed as shown in the below diagram.
+
+.. image:: ODUArch.jpg
+  :width: 400
+  :alt: ODU Arch diagram
+
+O-DU Thread Architecture
+--------------------------
+
+As shown in Figure 1, there are multiple entities within O-DU. Modules sharing a
+given color belong to one thread. O-DU architecture can be defined at a thread
+level as follows:
+
+-	Thread 1: O-DU thread
+
+-	Thread 2: DU APP inclusive of Config Handler, DU Manager, UE Manager, EGTP Handler and ASN.1 Codecs
+
+-	Thread 3: 5G NR RLC DL and MAC (inclusive of 5G NR SCH and Lower MAC)
+
+-	Thread 4: 5G NR RLC UL
+
+-	Thread 5: SCTP Handler
+
+
+O-DU Modules
+--------------------------
+
+DU APP 
+^^^^^^^^^^^^^^^^^^
+This module configures and manages all the operations of O-DU.
+It interfaces with external entities as follows:
+
+-	OAM:  DU APP interacts with OAM on the O1 interface for configuration, alarms and performance management.
+
+-	O-CU: DU APP interacts with O-CU for RAN functionalities over the F1 interface which is built on SCTP. Control messages are exchanged on the F1-C interface and data messages on the F1-U interface.
+
+-	RIC: DU APP interacts with RIC on E2 interface over SCTP.
+
+
+DU App submodules are as follows:
+
+-	Config Handler manages the configurations received on O1 interfaces andstores them within DU APP context.
+
+-	DU Manager handles all cell operations at the DU APP.
+
+-	UE Manager handles UE contexts at the DU APP.
+
+-	SCTP handler is responsible for establishing SCTP connections with O-CU, RIC.
+
+-	EGTP handler is responsible for establishing EGTP connection with O-CU for data message exchange.
+
+-	ASN.1 Codecs contain ASN.1 encode/decode functions which are used for System information, F1AP and E2AP messages.
+
+5G NR RLC
+^^^^^^^^^^^^^^^^^^
+This module provides services for transferring the control and data messages
+between MAC layer and O-CU (via DU App).
+
+5G NR RLC UL and 5G NR RLC DL are the sub modules of this module that implement
+uplink and downlink functionality respectively. 
+
+5G NR MAC
+^^^^^^^^^^^^^^^^^^
+This module uses the services of the NR physical layer to send and receive data
+on the various logical channels.
+Functions of the 5G NR MAC module are as follows:
+
+-	5G NR MAC is responsible for multiplexing and de-multiplexing of the data on various logical channels.
+
+-	5G NR SCH schedules resources on UL and DL for cell and UE based procedures.
+
+-	Lower MAC interfaces between the MAC and the lower layers of the O-DU and implements all the messages of FAPI specification.
+
+O-DU Utility and Common Functions
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+These modules help in the working of O-DU and message exchanges between
+the O-DU modules.
 
 
-o-du-l2 Overview
-======================