Added specification
Also did a minor adjustment on intro and architecture
Change-Id: I047ec1c1ee4ef5b421e98ecd242c96d55692fdb9
diff --git a/architecture.rst b/architecture.rst
index c4d6a1f..7a1f8a6 100644
--- a/architecture.rst
+++ b/architecture.rst
@@ -1,6 +1,28 @@
Architecture and Design
***********************
+Overview
+--------
+
+.. image:: images/arch-overview.png
+ :width: 1000px
+
+Trellis operates as a **hybrid L2/L3 fabric**.
+
+As a **pure (or classic) SDN** solution, Trellis **does not use any of the traditional control protocols** typically found in networking, a non-exhaustive list of which includes:
+STP, MSTP, RSTP, LACP, MLAG, PIM, IGMP, OSPF, IS-IS, Trill, RSVP, LDP and BGP.
+
+Instead, Trellis **uses an SDN Controller (ONOS) decoupled from the data-plane hardware to directly program ASIC forwarding tables using OpenFlow and with OF-DPA**,
+an open-API from Broadcom running on the switches.
+
+In this design, a set of applications running on ONOS implement all the fabric functionality and features,
+such as **Ethernet switching**, **IP routing**, **multicast**, **DHCP Relay**, **pseudowires** and more.
+
+.. note::
+ You can learn more about Trellis features and design concepts by visiting the `Project Website <https://opennetworking.org/trellis>`_ and
+ reading the `Platform Brief <https://www.opennetworking.org/wp-content/uploads/2019/09/TrellisPlatformBrief.pdf>`_.
+
+
Introduction to OF-DPA Pipeline
-------------------------------