pathload @ ibbt johannes deleu. overview setup @ ibbt how pathload works (by example) smartbits...
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Pathload @ IBBT
Johannes Deleu
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
Setup @ IBBT
Click router Click router
Pathload_snd Pathload_rcv
Traffic generator(SmartBits or Linux)
Traffic receiver(SmartBits or Linux)
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.
INCREASING NO TREND GREY
How pathload works (by example)
666,67
342,86
500
600571,43 561,14
437,04
480 476,8
0
100
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500
600
700
800
0 1 2 3 4 5 6 7 8 9 10
Iteration
Rat
e (i
n M
bp
s)
available bandw idth
Rmin
Rmax
R
Gmin
Gmax
packetsize=1518 burstsize=1
0
200
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1600
0 200 400 600 800 1000 1200
cross traffic (in Mbps)
av
ail
ab
le b
an
dw
ith
(in
Mb
ps
)
available bandwidth
min
max
iperf
packetsize=1518 burtsize=100
0
200
400
600
800
1000
1200
1400
1600
0 200 400 600 800 1000 1200
cross traffic (in Mbps)
avail
ab
le b
an
dw
idth
(in
Mb
ps)
available bandwithd
min
max
iperf
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
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
Maximum resolution (current implementation of pathload)
0
200
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600
800
1000
1200
10 15 20 25 30 35 40 45
Interpacket interval (in usec)
Str
eam
rat
e (i
n M
bp
s)
0
10
20
30
40
50
60
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80
90
100
probe rate
maximum accuracy
10 Mbps accuracy @ 1000 Mbps -> 100 nsec clock granularity
Load generated by Pathloadbytes captured iterations packetsize rough bytes predicted difference
12732270 7 1486 12482400 24987012783866 7 1486 12482400 30146612783998 7 1486 12482400 301598
tcpdump iterations x packetsize x 12 x 100
tcp controlconnection
Probe duration
0
500
1000
1500
2000
2500
3000
3500
4000
4500
200 400 600 800 1000 1200 1400
Probe rate (in Mbps)
Pro
be
du
rati
on
(in
use
c)
Accuracy (load 600 Mbps, packetsize 1518)
0
100
200
300
400
500
600
700
0 20 40 60 80 100 120 140
Burstsize
Rate
(in
Mbps
) Rmin
Rmax
Accuracy (load 600Mbps, packetsize 1024)
0
100
200
300
400
500
600
700
0 20 40 60 80 100 120 140
Burstsize
Rate
(in
Mbps
) Rmin
Rmax
Accuracy (load 600 Mbps, packetsize 512)
0
200
400
600
800
1000
1200
1400
0 50 100 150 200 250
Burstsize
Rate
(in
Mbps
) Rmin
Rmax
Bad influence of burstiness
probe duration = 3000 usec
probe duration = 3000 usec
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
burstsize probe duration packetsize period bursts per probe packetsize period bursts per probe packetsize period bursts per probe1 3000 1538 20,50666667 146,2938882 1044 13,92 215,5172414 532 7,093333 422,93233082 3000 1538 41,01333333 73,14694408 1044 27,84 107,7586207 532 14,18667 211,46616544 3000 1538 82,02666667 36,57347204 1044 55,68 53,87931034 532 28,37333 105,73308278 3000 1538 164,0533333 18,28673602 1044 111,36 26,93965517 532 56,74667 52,86654135
16 3000 1538 328,1066667 9,14336801 1044 222,72 13,46982759 532 113,4933 26,4332706832 3000 1538 656,2133333 4,571684005 1044 445,44 6,734913793 532 226,9867 13,2166353440 3000 1538 820,2666667 3,657347204 1044 556,8 5,387931034 532 283,7333 10,5733082748 3000 1538 984,32 3,047789337 1044 668,16 4,489942529 532 340,48 8,81109022664 3000 1538 1312,426667 2,285842003 1044 890,88 3,367456897 532 453,9733 6,60831766972 3000 1538 1476,48 2,031859558 1044 1002,24 2,993295019 532 510,72 5,87406015
128 3000 1538 2624,853333 1,142921001 1044 1781,76 1,683728448 532 907,9467 3,304158835192 3000 1538 3937,28 0,761947334 1044 2672,64 1,122485632 532 1361,92 2,202772556256 3000 1538 5249,706667 0,571460501 1044 3563,52 0,841864224 532 1815,893 1,652079417512 3000 1538 10499,41333 0,28573025 1044 7127,04 0,420932112 532 3631,787 0,826039709