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Value of Supporting Class-of-Service in IP Backbones
Murat Yuksel (University of Nevada – Reno) [email protected]
K. K. Ramakrishnan (AT&T Labs Research) [email protected]
Shiv Kalyanaraman (Rensselaer Polytechnic Institute) [email protected]
Joseph D. Houle (AT&T) [email protected]
Rita Sadhvani (AT&T) [email protected]
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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?
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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?
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rate
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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
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