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IBBT Johannes Deleu. Overview IBBT How pathload works (by example) SmartBits clarified First results presented at the previous conf.

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Presentation on theme: "IBBT Johannes Deleu. Overview IBBT How pathload works (by example) SmartBits clarified First results presented at the previous conf."— Presentation transcript:

1 IBBT Johannes Deleu

2 Overview 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 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)

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8 Clarifying SmartBits Burstsize 1 (on-time -> usec off-time -> 8.21 usec) Burstsize 2 (on-time -> usec off-time -> usec) Burstsize 3 (on-time -> usec off-time -> usec) Packets of Gbps: 8*( ) / 1000 Mbps = usec Generating a load of 600 Mbps: 8*( ) / 600 Mbps = 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 1000 Mbps -> 100 nsec clock granularity

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

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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


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