| 128 | | - '''start''': is the function that will be called when the OpenFlow Controller is started. Here in our case, we read the file /tmp/portmap and figures out which OpenFlow port points to which path |
| 129 | | - '''switch_ready''': is the function that will be called each time a switch connects to the OpenFlow Controller. Here in our case, we allow all non-TCP flows to pass (including ARP and ICMP packets) and ask new inbound TCP flow to go to the controller. |
| 130 | | - '''packet_in''': is the function that will be called each time a packet arrives at the controller. Here in our case, we send out a flow_stats_request to get the current statistics about each flow. Then waits for the latest TCP flow stats. Here we create another thread to wait for the stats reply so that the controller is not blocked. It calls "decide_path()" to get path decisions. |
| 131 | | - '''stats_reply''': is the function that will be called when the OpenFlow Controller receives a flow_stats_reply message from the OpenFlow Switch. Here in our case, we update the flow statistics then signal the thread created in "packet_in" to continue. |
| | 128 | - '''start()''': is the function that will be called when the OpenFlow Controller is started. Here in our case, we read the file /tmp/portmap and figures out which OpenFlow port points to which path |
| | 129 | - '''switch_ready()''': is the function that will be called each time a switch connects to the OpenFlow Controller. Here in our case, we allow all non-TCP flows to pass (including ARP and ICMP packets) and ask new inbound TCP flow to go to the controller. We also starts a "timer" function that calls "query_stats()" once every 2 seconds. |
| | 130 | - '''query_stats()''': is the function that sends out a flow_stats_request to get the current statistics about each flow. |
| | 131 | - '''packet_in()''': is the function that will be called each time a packet arrives at the controller. Here in our case, we call "decide_path()" to get path decisions, then send flow entry back to the OpenFlow Switch to instruct the switch which path to take for this new TCP flow. |
| | 132 | - '''stats_reply()''': is the function that will be called when the OpenFlow Controller receives a flow_stats_reply message from the OpenFlow Switch. Here in our case, we update the flow statistics so that "decide_path()" can make the right decision. |
| 134 | | - '''The Whole Process: ''' Upon the arrival of a new TCP flow, the OpenFlow controller sends out a "FlowStatsRequest" message to the OpenFlow switch. The OpenFlow switch will reply with statistics information about all flows in its flow table. |
| 135 | | This flow statistics message will be fetched by the "stats_reply" function in the OpenFlow controller implemented by the user on node "Switch". Based on the statistics, experimenters can apply their own policy on which path to choose in different situations. |
| | 135 | - '''The Whole Process: ''' |
| | 136 | - When the OpenFlow switch is ready, our controller starts a function that asks for flow stats once every 2 seconds. |
| | 137 | - The OpenFlow switch will reply with statistics information about all flows in its flow table. |
| | 138 | - This flow statistics message will be fetched by the "stats_reply" function in the OpenFlow controller implemented by the user on node "Switch". |
| | 139 | - As a result, our controller updates its knowledge about both left and right path once every 2 seconds. |
| | 140 | - Upon the arrival of a new TCP flow, the OpenFlow controller decides which path to send the new flow to, based on the updated flow statistics. |
| | 141 | |
