High PerformanceSwitching and RoutingTelecom Center Workshop: Sept 4, 1997.

Two-Stage Switch

High-Performance Networking Group

Isaac Keslassy, Nick McKeown

Input-Queued Packet Switch

Crossbar

Scheduler

inputs

outputs

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Round-Robin Scheduling

• Uniform & non-bursty traffic => 100% throughput

• Problem: traffic is non-uniform & bursty

Two-Stage Switch (I)

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N

1

N

1

N

External Outputs

Internal Inputs

External Inputs

First Round-Robin Second Round-Robin

[C.S.Chang et al.: http://www.ee.nthu.edu.tw/~cschang/PartI.pdf]

Two-Stage Switch (I)

1

N

1

N

1

N

External Outputs

Internal Inputs

External Inputs

First Round-Robin Second Round-Robin

Load Balancing

[C.S.Chang et al.: http://www.ee.nthu.edu.tw/~cschang/PartI.pdf]

Two-Stage Switch (I)

1

N

1

N

1

N

External Outputs

Internal Inputs

External Inputs

First Round-Robin Second Round-Robin

• No scheduling• Problem: unbounded mis-sequencing

Two-Stage Switch (II)

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FlowSplitter

LoadBalancer VOQs First-Stage Round-Robin Second-Stage Round-RobinVOQs

External inputs Internal outputs Internal inputs External outputs

1 1 1

N N N

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[Infocom’02 paper: http://klamath.stanford.edu/~keslassy/tmp/two-stage.pdf]

New

N3 instead of N2

Current Work

• Practical implementation of this scheme

• Statistical bounds on mis-sequencing• Queue length distributions• TCP properties

An optical two-stage switch

1

2

3

Phase 2

Phase 1