MSc
SDN Performance Analysis
Two software-defined network topologies differing by one link, measured across 303 traffic loads: the added link doubles the load before saturation and removes a 33% latency penalty.
Four hosts, three switches, and one question: what does adding a single link do? Both topologies are emulated in Mininet under a Ryu shortest-path controller and driven with UDP flows at increasing rates until they break.
- Setup
- 4 hosts, 3 switches, every link 20 Mbps / 20 ms
- Difference
- One added link, s1–s3
- Measurements
- 303 runs, all raw traces committed
- Repository
- VincenzoImp/sdn-performance-analysis
What it was
Four unidirectional UDP flows with Poisson arrivals, swept across a hundred load levels on the first topology and two hundred on the second, measuring link utilisation from the controller’s port counters and end-to-end delay and packet loss from the traffic generator.
The report predicts the results before measuring them, from flow counts alone. In the first topology, one link carries all four flows while every other link carries two, so it should saturate at half the load, and one host’s packets should take a third longer than the other’s because they cross an extra hop.
Both predictions hold exactly. The bottleneck saturates at half the offered load of everything else; the disadvantaged host measures 80.6 ms against 60.4 ms, a ratio of 1.333. Adding the one link equalises every path to 60.3 ms, spreads the load evenly, and pushes the onset of sustained packet loss from a rate of 108 to 244, more than double.
What I took from it
Predicting the shape of the result before running the experiment is what makes the experiment worth running. Counting flows per link gave the utilisation ratio and the latency penalty on paper, and the measurement’s job was to confirm or refute that rather than to discover it.
The second topology also leaves one link carrying almost nothing: 0.4% utilisation. It is the cost of the fix, and the report does not call it one.