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Designing a Predictable Backbone Network with Valiant Load Balancing. Nick McKeown Stanford University All the hard stuff was done by: Rui Zhang-Shen. Clean Slate Design for the Internet http://cleanslate.stanford.edu. NSF 100 x 100 Clean Slate Program http://100x100network.org. 2. 1. 3.

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designing a predictable backbone network with valiant load balancing

Designing a Predictable Backbone Network with Valiant Load Balancing

Nick McKeown

Stanford University

All the hard stuff was done by: Rui Zhang-Shen

Clean Slate Design for the Internet

http://cleanslate.stanford.edu

NSF 100 x 100 Clean Slate Program

http://100x100network.org

backbone network

2

1

3

5

4

Backbone network

Backbone network design using VLB

us backbone networks observations
US Backbone Networks: Observations
  • ~50 nodes interconnected by long-haul optical links
  • Increasingly rich mesh topology
    • Built over mesh of WDM or TDM circuits and switches
    • Reduce hop count and delay
    • Fault tolerance
    • Load balancing
  • Low utilization—links over-provisioned
    • Uncertainty in traffic matrix the network is designed for
    • Headroom for future growth
    • Prepare to take over when links or routers fail
    • Minimize congestion and delay variation

Backbone network design using VLB

traffic matrices

Back-bone

2

1

Regional

Node i

3

ri

5

ri

4

ri is easier to predict

and has to be predicted anyway

Traffic Matrices

To

From

Traffic matrix is hard to predict

Backbone network design using VLB

what fraction of traffic matrices can they support

80% utilization: 0.0003%

67% utilization: 1.1%

80% utilization: 0.026%

67% utilization: 0.66%

80% utilization: 0.00008%

67% utilization: 0.09%

80% utilization: 0.0009%

67% utilization: 0.026%

What fraction of traffic matrices can they support?

Verio

Abilene

Sprint

AT&T

Verio, AT&T, and Sprint topologies courtesy of RocketFuel

Backbone network design using VLB

desired characteristics
Desired Characteristics
  • Dependable
    • Continues to operate when traffic patterns change in the short and long term
    • Continues to operate under failure
    • Recovers quickly
  • Efficient
    • And at no extra cost

Backbone network design using VLB

why is this hard

r

r

r

r

r

Why is this hard?

r

r

1

2

r

3

N

r

4

r

r

Backbone network design using VLB

why is this hard8

r

r

r

r

r

Nr

Why is this hard?

r

r

1

2

r

3

N

r

4

r

r

Backbone network design using VLB

our approach
Our Approach
  • The operator already estimates ri
    • Requires only local knowledge of users and market estimates
  • Use Valiant Load Balancing (VLB)
    • Supports all traffic matrices
  • History
    • L. G. Valiant, G. Brebner, 1981-82
      • Parallel communication
      • Statistical delay guarantee
    • C.-S. Chang, etc.; I. Keslassy etc., 2001-05
      • Switch scheduling
      • Throughput guarantee
      • Optimality

Backbone network design using VLB

valiant load balancing
Valiant Load-Balancing

r

r

1

2

r

3

N

r

4

r

r

Backbone network design using VLB

valiant load balancing11

1

2

3

N

4

Valiant Load-Balancing

2r/N

r

r

r

r

4

2

  • In practice:
  • The mesh could be a mesh of lambdas or TDM circuits
  • Send on direct path, and only spread when network is congested.

r

r

Backbone network design using VLB

aside routers based on vlb
Aside: Routers based on VLB

Can you build a router switched backplane based on VLB?

Appealing possibilities

100% throughput for any arrival pattern

No per-packet arbitration and scheduling

Passive switch fabric consumes almost zero power

Switch Rack < 100W

Linecards

Linecards

Linecards

40 x 40

MEMS

1

2

55

56

“Scaling Routers using Optics” Sigcomm 2003

Backbone network design using VLB

failures

1

2

3

N

4

Failures
  • Node failures
    • Takes away corresponding links and traffic
    • Still a full mesh network
  • Links failures
    • Asymmetric network
    • Many scenarios

Backbone network design using VLB

fault tolerance
Fault Tolerance
  • Load balance traffic over available paths
  • To tolerate any k link or router failures, sufficient to increase the capacity each link by
  • Example: A 50 node network requires 11% more capacity to withstand any 5 failures.

Backbone network design using VLB

heterogeneous network

1

2

3

N

cij rirj

4

Heterogeneous Network

R= iri

r2

r1

Homogeneous:

c = 2r/N

rN

r3

cij = 2rirj /R

r4

ri

Gravity Configuration

Backbone network design using VLB

heterogeneous network16
Heterogeneous Network
  • As before, the total capacity we need with VLB is twice what we’d need if we knew the traffic matrix (and it was static).
  • With oblivious routing we need an extra

capacity.

Backbone network design using VLB

is vlb efficient
Is VLB efficient?
  • Not knowing the traffic matrix means we need a total capacity 2-times larger than if we did.
  • But we never know the traffic matrix, and it changes. So the cost is surprisingly small.
  • Anecdotally, a network that can support all traffic matrices and behaves predictably on failure requires less capacity than existing networks.

Backbone network design using VLB

interconnecting backbones

Rp

q2

q3

2

1

2

1

q4

N

3

N

3

4

4

Interconnecting Backbones
  • Peering parameters:
    • Rp is maximum peering traffic
    • qi¸0 for peering nodes, qi=0 for non-peering nodes, iqi=1
  • Peering link capacity: Rpqi

Backbone network design using VLB

within a vlb network
Within a VLB Network
  • Assume peering condition is fixed
    • Given: Rp ; qi
    • Variables: pi
  • Spread traffic over the peering links

Backbone network design using VLB

spread over peering links

1

2

2

1

3

N

N

3

4

4

Spread over peering links

1

1

1

cij = ri pj + rj pi

+ min(ri,Rp)(max(pj,qj)-pj) + min(rj,Rp)(max(pi,qi)-pi)

  • If Rp >ri, optimal solution: pi = qi ;cij = ri qj + rj qi
  • Efficient use of peering links
  • Supports all traffic matrices as before

Backbone network design using VLB

other questions
Other questions
  • Delay-sensitive applications
    • How much does it matter?
    • It may matter for interactive voice, video, gaming
    • Dealing with it: “Express paths” ,Adaptive load-balancing

Backbone network design using VLB