1. Pathload @ IBBT Johannes Deleu

2. Overview Setup @ IBBT How pathload works (by example) SmartBits clarified First results presented at the previous conf call Load generated by pathload Effects of burstiness on pathload

3. Setup @ IBBT

4. How pathload works Pathload estimates the available bandwidth by sending packet trains at different rates and measuring the one-way-delay. It looks for increasing trends as an indication for congestion. INCREASINGNO TRENDGREY

5. How pathload works (by example)

8. Clarifying SmartBits Burstsize 1 (on-time -> 12.30 usec off-time -> 8.21 usec) Burstsize 2 (on-time -> 24.60 usec off-time -> 16.42 usec) Burstsize 3 (on-time -> 36.90 usec off-time -> 24.63 usec) Packets of 1518 bytes @ 1 Gbps: 8*(12+8+1518) / 1000 Mbps = 12.304 usec Generating a load of 600 Mbps: 8*(12+8+1518) / 600 Mbps = 20.51 usec

9. First results Poor accuracy at low loads (or high available bitrates) –Max. clock granularity of traffic generator is 1 usec –Clock resolution is hard to achieve Tendency to get stuck in an ‘infinite’ loop –Derivation errors in internal variables –Wrong trend classification has big consequences This might be a big problem in real world situations where load conditions change. Question: what is the load generated by pathload ? Bad influence of bursty (on-off) cross traffic

10. 10 Mbps accuracy @ 1000 Mbps -> 100 nsec clock granularity

11. Load generated by Pathload tcpdumpiterations x packetsize x 12 x 100 tcp control connection

15. Bad influence of burstiness probe duration = 3000 usec Probe duration: Available bandwidth = 400 Mbps => interpacket interval = 8x1500/400Mbps = 30 usec 100 packets per probe => Total duration = 100x30 = 3000 usec

16. Bursts ‘seen’ per probe