Things You Can Do in Budapest During Summer Time Aleksandar Kuzmanovic Rice University & Ericsson...

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


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


My Goals

• Modeling and reality?


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


Background

• Precise measurement infrastructureO

ne w

ay d

ela

y (

sec)

->

Packet departure time (sec) ->


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


Theory

• Lindley’s equation

• CT information imbedded in delay• Ideal case: minimally backlogging condition

[QK99]

)( 11 iiii txww


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)

->


Probing schemeS e nde r R e c e ive r

U D P

T C P

T im e

One

way

del

ay


Aside…

• Experiments on LAN• Time-sharing in Linux

Time (sec) ->

Inte

r-arr

ival ti

me (

sec)

->


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


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)

->


Wide Area vs. Metropolitan Area Network


Cross Traffic EstimationSample Path

• Differentiate delay, know C

• Cross traffic: from: Budapest to: NY iperf - 1 TCP

• Probing traffic from: Budapest to: Melbourne


Cross Traffic EstimationMoving Average


Signs

• Delay difference

• => two queues

• => two casesQ 1 Q 2


Wide Area Network revisited

• Differentiation btw. primary (256K) & secondary (transatlantic) bottlenecks

• Secondary traffic underestimated for Csec./256K


Primary & Secondary Bottlenecks

• LAN traffic controllable

• Separation between primary (256K)& secondary (LAN) cross traffic


TCP Cross Traffic

• Iperf (number of TCP connections >=3)

• => delay decreases yet we see clusters of packet losses (queue size ~ delay~pck. loss?)


Role of packet sizes

• => change packet size


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


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


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


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


Ongoing work

• Short and long lived TCP connections• Heterogeneous TCP traffic…


C ro s s tra ffic : E ric s s o n - T e c h . U n iv .


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


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…)


The End


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