Target
------

Target source code: master branch of March of 2016
Target feature: OFP-Li (OpenFlow Plugin Lithium design)
Target data: flow-node-inventory:table in the operational DS
Related OpenFlow message: FLOW_REMOVED

Problems
--------

With the OFP-Li, applications need to use operational DS (flow-node-inventory:table) to get information about flow entries installed in OpenFlow switches.

In my understanding, when statistics manager of the OPF-Li is installed, the flow entry information on the operational DS is updated only by the statistics manager.
And, the statistics manager does not use FLOW_REMOVED to update the flow entry information in the DS.

As a result, with the current implementation of the OFP-Li, applications face the following two problems to detect the removal of flow entries.

1. It takes so long time (several seconds) to detect the removal.
2. It is possible that applications fail to detect the removal.

First, when the statics manager is installed, the OFP-Li does not update the operational DS on the event of FLOW_REMOVED.
Instead, the statistics manager updates (removes the flow entry from) the operational DS only based on the statistics information which the statistics manager gets from switch.
However, by default, the statistics manager gets the statistics information from the switch at intervals of several seconds.
Therefore, it takes several seconds for applications which listen data change on the operational DS to detect the removal of a flow entry after the flow entry is actually removed from the switch.

Second, when an application installs a flow entry whose timeout is a few seconds, it is possible that the statistics manager could not be aware of the installation and removal of the flow entry.
That's because the statistics manager does not use the notification of FLOW_REMOVED to update the operational DS.
As a result, the application would fail to detect the removal of the flow entry.