IBBT Johannes Deleu

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

IBBT

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

How pathload works (by example)

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

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 Mbps 1000 Mbps -> 100 nsec clock granularity

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

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

Bursts ‘seen’ per probe