The data reported here are from our OSDI publication
An instance of nse simulated 2Mb constant bit rate UDP flows between pairs of nodes on 2Mb links with 50ms latencies. To measure nse's ability to keep pace with real time, and thus with live traffic, a similar link was instantiated inside the same nse simulation, to forward live TCP traffic between two physical Emulab nodes, again at a rate of 2Mb. On an 850MHz PC, we were able to scale the number of simulated flows up to 150 simulated links and 300 simulated nodes, while maintaining the full throughput of the live TCP connection. With additional simulated links, the throughput dropped precipitously. We also measured nse's TCP model on the simulated links: the performance dropped after 80 simulated links due to a higher event rate from the acknowledgment traffic in the return path.
As a capacity test, we generated streams of UDP round-trip traffic between two nodes, with an interposed 850 Mhz PC running nse on a FreeBSD 4.5 1000HZ kernel. A maximum stable packet rate of 4000 packets per second was determined over a range of packet rates and link delays using 64-byte and 1518-byte packets. Since these are round trip measurements, the packet rates are actually twice the numbers reported. With this capacity, we performed experiments to measure the delay, bandwidth and loss rates for representative values. The results are summarized in Tables 1, 2 and 3
Emulab's integration of nse is much less mature than its support for dummynet based emulation. This is reflected in the large percentage error values in bandwidth and loss rates. Integrating nse has already uncovered a number of problems that have since been solved; as we continue to gain experience with nse, we expect the situation to improve.
delay (ms) |
packet size (bytes) |
observed | adjusted | |||
---|---|---|---|---|---|---|
RTT (ms) | stddev | %err | RTT (ms) | %err | ||
0 | 64 | 0.238 | 0.004 | N/A | N/A | N/A |
1518 | 1.544 | 0.025 | N/A | N/A | N/A | |
5 | 64 | 10.251 | 0.295 | 2.51 | 10.013 | 0.13 |
1518 | 11.586 | 0.067 | 15.86 | 10.032 | 0.32 | |
10 | 64 | 20.255 | 0.014 | 1.28 | 20.017 | 0.09 |
1518 | 21.675 | 0.093 | 8.38 | 20.121 | 0.61 | |
50 | 64 | 100.474 | 0.029 | 0.47 | 100.236 | 0.24 |
1518 | 102.394 | 3.440 | 2.39 | 100.840 | 0.84 | |
300 | 64 | 601.690 | 0.546 | 0.28 | 601.452 | 0.24 |
1518 | 602.999 | 0.093 | 0.49 | 601.445 | 0.24 |