Latency and Time to first Packet/Byte
This question has come up a few times from customers and researchers alike. How much latency do you add using an OpenFlow based networking stack.
The question has a few answers and I will try to cover them here.
The main answer is, the added latency normally only affects the first packet or two. In my setup I generally see between 20-30 ms RTT for the first packet, then 0.1-0.2 ms after that. This is an important factor to consider. If your OpenFlow based networking stack (i.e. a router, controller and any shims you have inserted such as RFProxy) is on a fast machine, you should see the TTFP/TTFB in about the same range. I’ve been sending 64 byte packets at line rate across 20+ interfaces and experiencing around 30 ms. Once the flow is programmed, all of the latency comes from the switch/router only. i.e. the OpenFlow controlled device.
So to properly gauge the impact you need to first determine what the latency/jitter/delay is of your device when doing OpenFlow based forwarding. Most switches are very fast, under 0.1 ms, in fact some switches are in even faster. This is a benefit of OpenFlow based forwarding. While in a normal network stack, you would send ALL packets through multiple devices, with OpenFlow you can program the first device to send the packet straight into the network.
Here is a text based diagram.
Packet -> OF Switch -> Controller -> Router -> Proxy -> Controller -> OF Switch -> End Device
Second to nth packet:
Packet -> OF Switch -> End Device
You can see just from the diagram how much is cut out of the path. In a normal network you would always be in the middle ground such as:
Packet -> Router -> Switch -> End Device
With OpenFlow you can cut out the Router at a minimum. Yes you take a hit on the TTFB, but after that, things go much faster. As technology improves, you will see pre-population of OpenFlow paths, better optimization, etc. In the end the OpenFlow (or just the Network API) world can be much better.
Being December 25th, I hope everyone has a wonderful day be it a normal day or a family centric day.