AETHER-3049 add metering documentation
Change-Id: I26d8fc60a0e30f7f484f6f0ffe2c5bb581486f1b
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+..
+ SPDX-FileCopyrightText: © 2020 Open Networking Foundation <support@opennetworking.org>
+ SPDX-License-Identifier: Apache-2.0
+
+QoS Metering
+============
+
+Recommendations
+---------------
+
+Metering is fully supported, though it is recommended that changes to metering
+be avoided unless necessary to meet a specific need. Metering can sometimes lead
+to counterintuitive behavior, such as unexpected limitations in network performance.
+
+Description
+-----------
+
+Aether Supports three levels of QoS metering:
+
+* Per-Device-Per-Application. These meters apply to specific flows between devices
+ and applications. As a device may connect to many applications, it may have many
+ flows, and therefore many different meters may be specified. These meters are
+ configured in the Application page of the GUI.
+
+* Per-Device. These meters apply to the aggregate of all flows from a device,
+ regardless of the application the device is connecting to. These meters are
+ configured in the Device-Group page of the GUI.
+
+* Per-Slice. These meters apply to the aggregate of all flows from all devices to
+ all applications within the slice. These meters are configured in the Slice page of the GUI.
+
+These three levels of metering are depicted below:
+
+.. image:: images/qos-metering.svg
+