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Value of Supporting Class-of-Service in IP Backbones

Murat Yuksel (University of Nevada – Reno) yuksem@cse.unr.edu

K. K. Ramakrishnan (AT&T Labs Research) kkrama@research.att.com

Shiv Kalyanaraman (Rensselaer Polytechnic Institute) shivkuma@ecse.rpi.edu

Joseph D. Houle (AT&T) jdhoule@att.com

Rita Sadhvani (AT&T) rsadhvani@att.com

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Motivation: Thick (Over-provisioned) or Thin (Engineered) Pipes ?

Thin: How to deal with bursts/overload?And meet premium SLAs… !

Thick: Cost of overprovisioning?Can this commodity model break even?

0 40000 80000

10000

0

rate

time

[Jim Roberts et al.]

Media-rich applications require performance guarantees:

e.g.: VoIP requires <300ms round-trip delay, <1% loss

How to respond to these application needs?

CoS approach: provide priority (i.e. higher class) to premium traffic

Classless (best-effort) service approach: over-provision the capacity

Question: How much extra capacity does the classless service require to match the performance of the higher class (premium) service in the CoS approach?

0 40000 80000

10000

0

rate

time

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Two Service Types: CoS vs. Classless

Premium

BE

D

CoS Link (differentiated)

D

Prem= gD

BE=(1-g)D

D

GIVEN: D, D and a performance target (i.e. ttarget or ptarget)

FIND: What is the minimum N that gives the same performance as in the premium class of the CoS case?

N=?

Classless Link (neutral)

BE

Sch

edulin

g(e

.g.

pri

ori

ty)

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REC: Required Extra Capacity

REC = <required neutral link capacity> - <CoS link capacity>= N - D (rate)

= 100(N/D – 1) (%)

How to quantify REC?

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Link Model: Poisson traffic Assume:

Poisson traffic, Exponential packet lengths for traffic in each class i.e.

Premium class traffic is Poisson with g D

Best-effort class traffic is Poisson with (1-g) D

The aggregate traffic for the neutral link is also Poisson with rate D

conservative: the superposition would be more bursty

Delay: M/M/1N = 1/ttarget + D

Loss: M/M/1/KKDNp2target

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More Bursty Traffic: MMPP MMPP = Markov-Modulated

Poisson Process Easy to do the math… Simplest MMPP is of two states.

MMPP traffic with mean D

Traffic w/ equivalent rate to the neutral case, but w/ more burstiness.

1 2

aar

aaar

ar

1

1

2

1

Higher r means more bursty traffic.

7Simulated Link Model: DelayMMPP/M/1 model

a=0.5, r=8

a=0.5, r=4

If packet size is 1KB and the CoS link is D = 10Gb/s:5,000packets of delay = 4.1 ms

REC can be quite high even for very small g and medium utilization.

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a=0.5, r=4, K=15Simulated Link Model: LossMMPP/M/1/K model

a=0.5, r=4, K=6

For a 1Gb/s link carrying 1KB packets:

K = ~6pkts 0.1ms buffer time

K = ~15pkts 0.25ms buffer time

K = ~60pkts 1ms buffer time

a=0.5, r=4, K=60

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Network Model Steps to calculate REC for a network:

Step 1: Construct the routing matrix RFxL based on shortest path

Run Dijkstra’s algorithm on the topology matrices ANxN and WNxN

Step 2: Form the traffic vector Fx1 from TNxN Step 3: Calculate the traffic load on each link: RT

= Q Step 4: Check the feasibility of the traffic load and

routing For any link

If link capacity is less than the traffic load (e.g. C < Q) then update T accordingly and go to Step 2.

Step 5: Calculate the required per-link REC (i.e. N - D) by using QI as the traffic rate D for Ith link, and the performance goal ptarget or ttarget.

Used Rocketfuel

topologies for ANxN and WNxN.

Used gravity model for

TNxN.

Made a look-up to the simulated link model

results.

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Network Model: Delay

Conservative MMPP: a=0.5, r=4

Abovenet

Sprintlink

Queuing delay range for legacy applications such as

VoIP.

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Network Model: LossConservative MMPP:

a=0.5, r=4

Sprintlink

Abovenet

Reasonable buffer: K=60 pkts

Loss probability range for typical ISP

practices.

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Summary A framework to study REC for delay or loss being the

performance target. Link model

REC grows when: traffic becomes more bursty the utilization of the CoS link becomes higher the performance target becomes tighter the fraction g of the Premium class traffic becomes smaller

With conservative burstiness assumptions of MMPP traffic, REC ranges up to 100% even when g is 0.2 and the CoS link utilization is 40%.

Network model: For legacy g2g performance targets, REC ranges from 50% to over

100% as g reduces below 0.5 and the CoS link utilization goes up to 60%.

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Thank you!

THE END