The War Between Mice and Elephants

The War Between The War Between Mice and ElephantsMice and Elephants

ByByLiang Guo (Graduate Student)Liang Guo (Graduate Student)

Ibrahim Matta (Professor)Ibrahim Matta (Professor)Boston UniversityBoston University

ICNP’2001ICNP’2001

Presented ByPresented ByPreeti PhadnisPreeti Phadnis

OutlineOutline IntroductionIntroductionAnalyzing Short TCP Flow PerformanceAnalyzing Short TCP Flow PerformanceArchitecture and Mechanism –RIO-PSArchitecture and Mechanism –RIO-PSSimulationsSimulationsDiscussionsDiscussionsConclusions and Future workConclusions and Future work

Mice vs ElephantsMice vs Elephants

Mice : Short TCP Mice : Short TCP flows e.g. Web Trafficflows e.g. Web Traffic

20% of internet traffic 20% of internet traffic is carried by large is carried by large number of micenumber of mice

Elephants : Long TCP Elephants : Long TCP flows e.g. FTPflows e.g. FTP

80% of internet traffic 80% of internet traffic is carried by small is carried by small number of elephantsnumber of elephants

Internet todayInternet todayWWW : ” World Wide Wait “ term coined WWW : ” World Wide Wait “ term coined

by R. Khare and I .Jacobsby R. Khare and I .JacobsUsers spend long time downloading a Users spend long time downloading a

plain text webpage plain text webpage Reason: The mice don’t get the fair share Reason: The mice don’t get the fair share

of the network resourcesof the network resources

Factors effecting the performance Factors effecting the performance of miceof mice

TCP tries to conservatively ramp up its TCP tries to conservatively ramp up its transmission rate to the maximum available transmission rate to the maximum available bandwidthbandwidth

For short connections, since congestion window For short connections, since congestion window is very small, packet loss always requires is very small, packet loss always requires timeout to detect.timeout to detect.

For the first few packets, since no sampling data For the first few packets, since no sampling data is available, TCP has to use a conservatively is available, TCP has to use a conservatively estimated ITO value as RTO. Short Connection estimated ITO value as RTO. Short Connection performance is degraded due to large timeout performance is degraded due to large timeout period.period.

Related workRelated workCrovella et al 2001 [16] and Bansal et al Crovella et al 2001 [16] and Bansal et al

2001 [17] comment that size aware job 2001 [17] comment that size aware job scheduling helps enhance the response scheduling helps enhance the response time of short jobs without hurting the time of short jobs without hurting the performance of long jobs.performance of long jobs.

D.D Clark and W.Fang 1998 [4] AQM D.D Clark and W.Fang 1998 [4] AQM scheme using RED with In and Out Policyscheme using RED with In and Out Policy


Sensitivity Analysis for Short and Sensitivity Analysis for Short and Long TCP FlowsLong TCP Flows

Sensitivity Analysis of Transmission Sensitivity Analysis of Transmission TimeTime

Factors Effecting VariabilityFactors Effecting Variability When Loss rate high TCP Congestion control is When Loss rate high TCP Congestion control is

more likely to enter exponential back off phase, more likely to enter exponential back off phase, which can cause significantly high variability in which can cause significantly high variability in transmission time of each individual packet of a transmission time of each individual packet of a flow. Short flows are effected more due to this flow. Short flows are effected more due to this reason.reason.

When loss rate low, TCP either in slow start or When loss rate low, TCP either in slow start or congestion avoidance phase. This dimension of congestion avoidance phase. This dimension of variability is more pronounced for long flows.variability is more pronounced for long flows.

Preferential Treatment to Short Preferential Treatment to Short TCP flowsTCP flows

Simulation using NS simulatorSimulation using NS simulator10 long(10000-packet) TCP-NewReno 10 long(10000-packet) TCP-NewReno

flows and 10 short(100-packet) TCP-flows and 10 short(100-packet) TCP-Newreno flows over 1.25Mbps link.Newreno flows over 1.25Mbps link.

Queue Management Policy – Drop Tail, Queue Management Policy – Drop Tail, RED ,RIO with preference to short flows.RED ,RIO with preference to short flows.

Link Utilization under Drop Tail, Link Utilization under Drop Tail, RED and RIO-PSRED and RIO-PS

Network Goodput Under Different SchemesNetwork Goodput Under Different Schemes


Proposed Architecture Proposed Architecture

Edge RouterEdge Router Determines packet coming from long or short Determines packet coming from long or short

flowflow Maintains a counter LMaintains a counter Ltt that tracks how many that tracks how many

packets have been observed so far for a flow. packets have been observed so far for a flow. LLtt is dynamicis dynamic

Per flow state information are softly maintained to Per flow state information are softly maintained to detect the termination of flow. The flow hash detect the termination of flow. The flow hash table is updated periodically every table is updated periodically every TTuu time units. time units.

It is configured with SLR (Short to Long ratio).It is configured with SLR (Short to Long ratio). It then periodically (every It then periodically (every TTcc time units) performs time units) performs

AIAD control over the threshold to achieve the AIAD control over the threshold to achieve the target SLRtarget SLR

Core RouterCore Router Gives preferential treatment to miceGives preferential treatment to mice RIO (Red In and Out) queuing policy is used[4] with RIO (Red In and Out) queuing policy is used[4] with

preferential treatment to short flows- RIO-PSpreferential treatment to short flows- RIO-PS RIO used twin RED algorithms for dropping packets one RIO used twin RED algorithms for dropping packets one

for ins and one for outs. for ins and one for outs. The probability of dropping “in” packets depends on the in The probability of dropping “in” packets depends on the in

average “in” packet queue and the probability of dropping average “in” packet queue and the probability of dropping “out” packets depend on the total average queue length.“out” packets depend on the total average queue length.

No packet reordering will happen in the FIFO queue with No packet reordering will happen in the FIFO queue with RIORIO

RIO inherits all features of REDRIO inherits all features of RED RIO performs soft prioritization, thus does not lose the RIO performs soft prioritization, thus does not lose the

benefit of statistical multiplexing. benefit of statistical multiplexing.

RIO Queue with preferential RIO Queue with preferential treatment to short flowstreatment to short flows


Simulation SetupSimulation Setup

Simulation ConfigurationSimulation Configuration

Experiment 1Experiment 1 4000 secs simulation time,2000 secs warm up time.4000 secs simulation time,2000 secs warm up time. Average response time relative to REDAverage response time relative to RED

Instantaneous Queue Size and Instantaneous Queue Size and Drop RateDrop Rate

Fairness of Transmission timeFairness of Transmission time

Transmission Time of foreground Transmission Time of foreground traffictraffic

Network goodputNetwork goodput

Experiment 2:Unbalanced RequestsExperiment 2:Unbalanced RequestsClient set 1 requests smaller objects ,Client set 2 requests larger objectsClient set 1 requests smaller objects ,Client set 2 requests larger objects

Experiment 2Experiment 2


DiscussionDiscussionSimulation ModelSimulation Model Dumbbell and Dancehall model used.Dumbbell and Dancehall model used. All TCP connections have similar end to end propagation All TCP connections have similar end to end propagation

delays, this is not common topology seen by internet delays, this is not common topology seen by internet usersusers

If reverse traffic present even better performanceIf reverse traffic present even better performanceQueue Management PolicyQueue Management Policy RIO neither provides absolute aggregate (class based) RIO neither provides absolute aggregate (class based)

nor relative flow based guarantees. nor relative flow based guarantees. Other AQM policies like PI controlled RED queue betterOther AQM policies like PI controlled RED queue better

DiscussionsDiscussionsDeployment IssuesDeployment Issues Edge devices need to perform per-flow state Edge devices need to perform per-flow state

maintenance and per packet processing but it does not maintenance and per packet processing but it does not effect performance.effect performance.

Not required to implement queue policies at each router, Not required to implement queue policies at each router, RIO-PS can be implemented at busy bottleneck links.RIO-PS can be implemented at busy bottleneck links.

Flow ClassificationFlow Classification Threshold based classification classifies the first few Threshold based classification classifies the first few

packets of all flows to be short but it helps enhance packets of all flows to be short but it helps enhance performance .performance .

DiscussionsDiscussionsController designController design The actual SLR depends on values of Tc and Tu, which The actual SLR depends on values of Tc and Tu, which

determines Lt. Smaller values of these increases determines Lt. Smaller values of these increases accuracy at the expense of increased overheadaccuracy at the expense of increased overhead

Malicious usersMalicious users Can break long transmissions into short flows but Can break long transmissions into short flows but

overhead of fragmentation and reassembly is very high.overhead of fragmentation and reassembly is very high.


Conclusions and Future WorkConclusions and Future WorkPerformance of mice is improvedPerformance of mice is improvedPerformance of few elephants is also Performance of few elephants is also

improvedimprovedOverall goodput of the system is also Overall goodput of the system is also

improvedimprovedThe proposed architecture is flexible in The proposed architecture is flexible in

that the functionality that defines this that the functionality that defines this scheme can be largely tuned at the edge scheme can be largely tuned at the edge routersrouters

Future workFuture work Integrate size aware traffic management at Integrate size aware traffic management at

both network and transport layersboth network and transport layers

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The War Between Mice and Elephants