Aggressiveness Protective Fair Queuing for Bursty Applications

transcript

APFQ - Nir Halachmi (IDC)

Nir Halachmi (IDC)

Joint work with

Dr. Anat Bremler Barr (IDC) and Prof. Hanoch Levy (TAU)

Background: Network planning

Link Capacity

• Network Designers use the traffic properties to plan the capacity of the network.

Background: Exploiters

Link Capacity

• Exploiters– Malicious: Denial of Service (DDOS)– Innocent: pre-fetching, massive users

Exploiter

Background: Solution- Fair Scheduling protection against Exploiters

Link Capacity

• Weighted Fair Queuing (WFQ) mechanisms provides that the resource is fairly (typically equally) divided among all

Exploiter

Our main contribution

• The user traffic is bursty. • WFQ cannot provide fair service to bursty

applications in the presence of aggressive users

• We propose WFQ-like mechanism called Aggressiveness Protective Fair Queuing (APFQ) that solves this problem.

Bursty Application

• Many application are bursty (model on/off ~ active/idle)– Http

on off

Bursty Traffic

• Network Designers use the traffic burstiness property to plan the capacity of the network.

Link Capacity

Aggressive Users

• Aggressive user use the idle time to get more BW

Link Capacity

WFQ defensives

• WFQ cannot provide good fairness in the presence of such aggressive users.

Link Capacity

The effect of aggressive user on polite users (WFQ)

100.0%

Link Capacity (Kb/s)

ackets

All Polite - Polite traffic avarege

Mixed users - Polite traffic avarege

Mixed users - Aggressive trafficavarege

Aggressiveness Protective Fair Queuing (APFQ)

We propose a new WFQ-like mechanism called Aggressiveness Protective Fair Queuing (APFQ) that solves this problem by dynamically decreasing the weight of the aggressive users.

Agenda

• Related Work.

• Solution Requirements.

• APFQ algorithm.

• APFQ analysis

• Simulation.

Related Work• Dynamic WFQ was proposed to handle the fact that

it is hard to assign static weight accurately [Shin and el.

2001][Makrakis and el. 2001]. – Fix the weight according to arrival rate or the queue

length.

– Does not address bursty traffic problem.

• Dynamic WFQ was proposed as part of a mechanism to handle DDOS [Thomas and el. 2003]

– Penalty mechanism to flows

– Does not deal with traffic burstiness and does not suggest or analyze the weight function mechanism

Solution Requirements

• Provide fairness to polite users.

• The limitation imposed on the users is a function of the system load.– Protect innocent users by negatively discriminating

aggressive users on an overloaded Network.

Link Capacity

• Dynamic weight function that reduces the weight assigned to aggressive users

• For every flow (user) the mechanism counts the amount of traffic that a source has generated in the near history

• It uses this amount to affect the weight given to the user.

Weight function

• BS – the assigned quota.• SM(t) – offered traffic during the last sliding.

window in time t.

• wo original fix weight.• α – punishment factor – configure by the system.

APFQ Illustrated• Polite user transmit data:

• Aggressive User Transmitted data under WFQ

• Aggressive User Transmitted data under APFQ

APFQ algorithm

Weight

KBytes

Analysis pre conditions

• Polite user transmits at rate R for Ton and idle for Toff. • Aggressive user transmits at constant peak rate R.• N concurrently active users.• K aggressive users , N-K polite users.• For each user original fix weight wo = 1• Packets that are not transmitted within a period of ∆ from

their arrival time are dropped.• B is the output link capacity. • ∆ = Ton + Toff = sliding window size.• ƒ = burst factor =

TonTon

ToffTon

• Offered Data

• Transmitted Data WFQ

• Transmitted Data APFQ

Polite User

politeT

onAPFQpoliteon T

• Offered Data

•Total offered Data

• Transmitted Data WFQ

Naive Aggressive User

•Transmitted Data APFQ

• For α =1

• For α=2

Naive Aggressive User

ononAPFQ

naiveTonon

ondtTT

naive )log1(on

Continuous Naive Aggressive • Continuous Naive Aggressive - an aggressive user that was active in the previous window size.

• I.e., offered traffic during the last sliding

• Hence the assigned weight is fixed

RtSM )(

Continuous Naive Aggressive

onAPFQ

naivecontT

onAPFQ

naivecontT

•Transmitted Data APFQ

•For α =1 Exactly as polite use under APFQ

• For α=2 Exactly as polite use under APFQf

Sophisticated Aggressive

• Sophisticated Aggressive user is assumed to know the function used by APFQ and optimizes its offered traffic in order to maximize the traffic APFQ will transmit for him.

• An approach for the sophisticated aggressive user is to offer the same amount of traffic as the mechanism allow her to transmit.

•Sophisticated Aggressive user is assumed to know the function used by APFQ and optimizes its offered traffic in order to maximize the traffic APFQ will transmit for him.

Sophisticated User Upper Bound

• Lemma: Under APFQ a sophisticated aggressive user cannot transmit in a period of duration ∆ more than (m+2)·BS traffic where m is derived from equation

BSfDAPFQ

tedsophistica 212

BSfDAPFQ

tedsophistica 2133

Sketch of proof

ion TTi1

Sophisticated User Lower Bound

• Lemma: There is a strategy where the sophisticated aggressive user can transmit during an interval of length ∆ under APFQ with α at least (m+1)·BS traffic where m is derived from equation

BSfDAPFQ

tedsophistica 112

BSfDAPFQ

tedsophistica 1133

Optimal Strategy for sophisticated aggressive

Analysis Summery

User TypeWFQ transmitted traffic

APFQ transmitted traffic (α=1)

APFQ transmitted traffic (α=2)

Polite user111

Naïve aggressive userƒ1 + log ƒ2

Continuous naïve aggressive user

Sophisticated userƒ

212 f 2)1(33 f

Simulation

• Simulated APFQ on NS2

• NS2 code implementing WFQ contributed by Paulo Losi

• APFQ was implemented as a software wrapper around WFQ.

Tests Set-upWorkstation 1

Workstation 2

Workstation 3

Workstation N

Server

Router

Link Capacity

Experiment 1

• Examine the percentage of packets transmitted per flow as a function of the link capacity.

• Scenario 1: 12 polite users

• Scenario 2: 10 polite users and 2 aggressive users.

Experiment 1 Results

100.0%

Link Capacity (Kb/s)

ackets

All polite- WFQ Polite traffic avarege

Mixed users - WFQ Polite trafficavaregeMixed users- WFQ Aggressive trafficavaregeMixed users- APFQ Polite trafficavaregeMixed users- APFQ Aggressive trafficavarege

Experiment 2

• Examine how many aggressive users a given network can handle without negatively affecting the polite users.

• Test APFQ robustness to large networks.

Experiment 2

• 300 users with a variable number of aggressive users out of them.

• The number of aggressive users was increased in each round.

• The Link-capacity was set to 9000Kb/sec.

100.0%

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49

Number Of Aggressive Users

WFQ Polite traffic avarege

WFQ Aggressive traffic avarege

APFQ polite traffic avarege

APFQ Aggressive trafficavarege

Experiment 2 Results

Implementation consideration

• APFQ can use a regular WFQ.

• Experiments revealed that Dynamic WFQ, in some scenarios, can causes disorder.

• The cause of the problem is that the WFQ implementation implicitly assumed the weight of the queues is constant (i.e. static weight).

Conclusion

• Aggressive users use the idle time to get more bandwidth.

• WFQ has a fairness problems in the presence of aggressive users.

• APFQ is a mechanism that provide fairness in such cases, using a dynamic weight function.

Questions?

Thank You

Problem demonstration

0.25P4F=4

8 7 6 5 4 3 2

1P3F=3

6 6 5 4 3 2 1

1P2F=2

6 5 4 3 2 1 0

V_t =0

V_t =1

V_t =2

P8F=13

8 7 6 5 4 3 2

P8F=13

8 7 6 5 4 3 2

0.25p6F=9

P8F=13

8 7 6 5 4 3 2

V_t =9.2

V_t =10

V_t =8.4

0.25p6

P8F=13

8 7 6 5 4 3 2

0.25p6

P8F=13

8 7 6 5 4 3 2

P7F=6 P1

The new flow packet should have been transmitted by now

0.25p6F=9

P8F=13

The new flow arrive and it’s finish time is set by the virtual time and not by the real round time (it finish time should have been 3)

V_t =7.6

V_t =6.8

V_t =6

Sketch of proof

Aggressiveness Protective Fair Queuing for Bursty Applications

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