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Things You Can Do in Budapest During Summer Time
Aleksandar Kuzmanovic
Rice University & Ericsson Traffic LabOctober 2001
Rice University & Ericsson Traffic Lab
Budapest
• Buda-Pest– History– Architecture– Decadency…
• Ericsson Traffic Lab– Unix– Young people– Security
Rice University & Ericsson Traffic Lab
People
• Ericsson Traffic Lab, Budapest– Andras Veres
• EMULab, The University of Melbourne– Attila Pasztor, Darryl Veitch
• Budapest University, Department of Physics– Gabor Simon, Gabor Vattay
Rice University & Ericsson Traffic Lab
Active Probing
Internal network inaccessible
• Poor understanding of origins of complex network dynamics
• Statistics is like the bikini…
Goal: Estimate the sample path of cross-traffic
Rice University & Ericsson Traffic Lab
Background
• Precise measurement infrastructureO
ne w
ay d
ela
y (
sec)
->
Packet departure time (sec) ->
Rice University & Ericsson Traffic Lab
Probing Uncertainty Principle
• Should not allow queue to empty between probe packets
• Small T for accurate measurements– but probe traffic would disturb
cross-traffic (and overflow bottleneck buffer!)
• Larger T leads to measurement uncertainties– queue could empty between probes
Rice University & Ericsson Traffic Lab
Theory
• Lindley’s equation
• CT information imbedded in delay• Ideal case: minimally backlogging condition
[QK99]
)( 11 iiii txww
Rice University & Ericsson Traffic Lab
Design Space
• No time synchronization between end points $ 2.000.000.000
• Delay difference
• Non-intrusiveness
• Stability
Time (sec) ->
On
e w
ay d
ela
y (
sec)
->
Rice University & Ericsson Traffic Lab
Probing schemeS e nde r R e c e ive r
U D P
T C P
T im e
One
way
del
ay
Rice University & Ericsson Traffic Lab
Aside…
• Experiments on LAN• Time-sharing in Linux
Time (sec) ->
Inte
r-arr
ival ti
me (
sec)
->
Rice University & Ericsson Traffic Lab
Traffic Lab – Experiment Setup
• Tcpdump, iperf (HTTP, TCP), sender, receiver…
e thr1 (1 9 5 .2 2 8 .1 3 9 .6 5 )
m o d e m p o o l
256 K b p s
Rice University & Ericsson Traffic Lab
Routes
• Tech. University Budapest6 nec2.ttt.bme.hu (152.66.247.2) 14.980 ms 14.212 ms 14.252 ms
• Columbia University, NY16 bongo.comet.columbia.edu (128.59. 64.210) 150.725 ms * 127.967 ms
• University of Melbourne23 potoroo.ee.mu.OZ.AU (128.250.76.186) 384.271 ms 383.408 ms 382.977 ms
• Houston, we have a problem… ->Time (sec) ->
On
e w
ay d
ela
y (
sec)
->
Rice University & Ericsson Traffic Lab
Cross Traffic EstimationSample Path
• Differentiate delay, know C
• Cross traffic: from: Budapest to: NY iperf - 1 TCP
• Probing traffic from: Budapest to: Melbourne
Rice University & Ericsson Traffic Lab
Signs
• Delay difference
• => two queues
• => two casesQ 1 Q 2
Rice University & Ericsson Traffic Lab
Wide Area Network revisited
• Differentiation btw. primary (256K) & secondary (transatlantic) bottlenecks
• Secondary traffic underestimated for Csec./256K
Rice University & Ericsson Traffic Lab
Primary & Secondary Bottlenecks
• LAN traffic controllable
• Separation between primary (256K)& secondary (LAN) cross traffic
Rice University & Ericsson Traffic Lab
TCP Cross Traffic
• Iperf (number of TCP connections >=3)
• => delay decreases yet we see clusters of packet losses (queue size ~ delay~pck. loss?)
Rice University & Ericsson Traffic Lab
Bit/sec. vs. Packet/sec.
• Up: 540 Bytes• Down: 60 Bytes• 540/60 = 9
– 256Kbps*9= 2.3Mbps
• UDP: 1500/30=50– 256K*50=
12.8Mbps - 1.5M*50= 75Mbps
Rice University & Ericsson Traffic Lab
Secondary Bottleneck
• Difference of CT estimate and tcpdump CT followed by clusters of packet losses
P ro b e s : E ric s s o n -A u s tra lia
C ro s s tra ffic : E ric s s o n - N Y (tc p d u m p )C ro s s tra ffic e s tim a te
Rice University & Ericsson Traffic Lab
Role of TCP
• Secondary CT (necessary for losses*) picks up the periodicity of probe traffic!
– Through losses– Through delay
• When phases match– Long burst of small packets causes losses on secondary bottleneck
P ro b e s : E ric s s o n -A u s tra lia
C ro s s tra ffic : E ric s s o n - N YS e c o n d a ry c ro s s tra ffic
Rice University & Ericsson Traffic Lab
Ongoing work
• Short and long lived TCP connections• Heterogeneous TCP traffic…
P ro b e s : E ric s s o n -A u s tra lia
C ro s s tra ffic : E ric s s o n - T e c h . U n iv .
P ro b e s : E ric s s o n -A u s tra lia
C ro s s tra ffic 1 : E ric s s o n - N YC ro s s tra ffic 2 : E ric s s o n - B u d a p e s t
Rice University & Ericsson Traffic Lab
Conclusions
• Scalable, edge-based tool for on-line network analysis, modeling, and measurement
• Scheme for estimating sample path of adaptive cross-traffic
• Differentiation between primary and secondary bottlenecks: two queue model
• Role of TCP (delay variation) and variable packet sizes– Low bit rate denial of service attack?– QoS in access networks (xDSL…)