SDN controller path installation

Question

How the POX controller install the end-to-end paths flow entries (rules)? Is it in parallel or sequential ??

POX

Answer 1

Basically it depends on the switch. The Open vSwitch implements

nonblocking multiple-reader, single-writer flow tables

Basically what you can do, is setup multiple readers to read faster from a single switch, which is something that comes in handy cause you will have to fetch not only table flow mods currently installed but also statistics on several type of packets and more. When it comes to writing flow mods, even thought you can program your functions concurrently (use recoco basically for scheduling and repeating, but threads will work just fine as well), they will end up in a queue of a single writer in the switch.

The basic problem that you will have is that since your are writing from different threads you do not have control over the order each flow mod will arrive and be written on the switch. Taking this into consideration you could have flow mods overlapping each other, resulting in undesired network functionality. You can sure use OFPT_BARRIER_REQUEST to control some of the issues but in my opinion it will lead you in too much unnecessary code.

In the case you need to write to several different switches in parallel this can be accomplished as well and you should definitely use a multi-threading approach with recoco or your preferred library-module.