implementation issues in the optical router project

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

Implementation Issuesin the Optical Router Project

Isaac Keslassy, Da Chuang,Nick McKeown

High Performance Networking Group

klamath.stanford.edu

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Switch fabric design

Design a switch fabric using a two-stage switch architecture 625 linecards of 160Gbps

Features: Low power Reliability Arbitrary addition and deletion of linecards (due to

upgrades/failures) Scalability

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Given the set of features:

System Constraints

Maximize Total Capacity Cs.t. Rack Power: P < 5kW Rack Volume: V < 2m3

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Racks of linecards

Optical links

SwitchFabric

100Tb/s Router

5

Two-stage reminder: spreading

R/N

Passive mesh

1

23

1

23

R/NR/N123

123

Cyclic Shift Cyclic Shift

R R

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Possible Optical Components

Our bag of tricks: WGRs (wavelength determines routing) Tunable Lasers (transmitters) Tunable Filters (receivers) Star Couplers (broadcast-and-select) Traditional MEMs (mirrors)

Ideally, use a passive component: Less power Reliable

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WGR : A Passive Optical Component

Wavelength i on input port j goes to output port (i+j) mod N

Can shuffle information from different inputs

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WGR Based Solution (N=64)

1,

2

…N

1,

2

…N

1,

2

…N

NxN WGR

Laser/Modulator

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N

Linecard 1

Linecard 2

Linecard N

Detector

Linecard 1

Linecard 2

Linecard N

1,

2

…N

1,

2

…N

1,

2

…N

12

N

12

N

12

N

12

N

12

N

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Problem 1: Missing Linecards

R/N R/NIngress

Linecard 1

IngressLinecard 2

IngressLinecard N

MidstageLinecard 1

MidstageLinecard 2

MidstageLinecard N

EgressLinecard 1

EgressLinecard 2

EgressLinecard NR/N R/N

R

R

R

R

R

R

R/2 R/2

R/2 R/2

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WGR

Features: Low power Reliability Arbitrary addition and deletion of

linecards (due to upgrades/failures)

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Solutions to Problem 1

Change data rate per lambda

WGRs of binary sizes with static MEMs

New device: programmable WGR e.g. if only 2 linecards,

• odd wavelengths -> port 0• even wavelengths -> port 1

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Problem 2: Scalability to 640 Linecards

Linecard 1

Linecard 2

Linecard W

WxW WGR

Linecard 1

Linecard 2

Linecard W

Group M

WxW WGR

Linecard 1

Linecard 2

Linecard W

Group 2

WxW WGR

Linecard 1

Linecard 2

Linecard W

Group 1

MxM

MxM

MxM

Linecard 1

Linecard 2

Linecard W

Linecard 1

Linecard 2

Linecard W

Group 1

Group 2

Group M

MEMS

MEMS

Additional spreading stage with MEMS

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WGR and MEMS

Features: Low power Reliability Arbitrary addition and deletion of

linecards (due to upgrades/failures) Scalability: N=640 linecards

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Possible Optical Components

Our bag of tricks: WGRs (wavelength determines routing) Tunable Lasers (transmitters) Tunable Filters (receivers) Star Couplers (broadcast-and-select) Traditional MEMs (mirrors)

Ideally, use a passive component: Less power Reliable

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Star Coupler: Another Passive Optical Component

Broadcast and Select Device all wavelengths on all input ports are broadcast to all output ports

Need tunable filter to select correct data

Collision can occur if two input ports use the same wavelength

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Star Coupler3x3

Star coupler

3x3Star coupler

3x3Star coupler

3x3Star coupler

Linecard 1

Linecard 2

Linecard 3

Linecard 4

Linecard 5

Linecard 6

(1, 1, 1)

(1, 1, 2)

(1, 2, 1)

(1, 2, 2)

(2, 1, 1)

(2, 1, 2)

(2, 2, 1)

(2, 2, 2)

(3, 1, 1)

(3, 1, 2)

(3, 2, 1)

(3, 2, 2)

Group 1

Group 2

Group 3

(1, 1, 1)

(1, 1, 2)

(1, 1, 3)

(1, 2, 1)

(1, 2, 2)

(1, 2, 3)

(2, 2, 1)

(2, 2, 2)

(2, 2, 3)

(2, 1, 1)

(2, 1, 2)

(2, 1, 3)

Linecard 1

Linecard 2

Linecard 3

Linecard 4

Linecard 5

Linecard 6

Group 1

Group 2

Group 3

(1, 1, 1)

(1, 1, 2)

(1, 1, 3)

(1, 2, 1)

(1, 2, 2)

(1, 2, 3)

(2, 2, 1)

(2, 2, 2)

(2, 2, 3)

(2, 1, 1)

(2, 1, 2)

(2, 1, 3)

(1, 1, 1)

(1, 1, 2)

(1, 2, 1)

(1, 2, 2)

(2, 1, 1)

(2, 1, 2)

(2, 2, 1)

(2, 2, 2)

(3, 1, 1)

(3, 1, 2)

(3, 2, 1)

(3, 2, 2)

Two spreading stages: space and wavelength

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Star Coupler

Features: Low power Reliability Arbitrary addition and deletion of

linecards (due to upgrades/failures) Scalability: N=640 linecards

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A Complete Solution3x3

Star coupler

3x3Star coupler

3x3Star coupler

3x3Star coupler

2x2

2x2

2x2

2x2

2x2

2x2

2x2

2x2

2x2

2x2

2x2

2x2

Linecard 1

Linecard 2

Linecard 3

Linecard 4

Linecard 5

Linecard 6

Group 1

Group 2

Group 3

Linecard 1

Linecard 2

Linecard 3

Linecard 4

Linecard 5

Linecard 6

Group 1

Group 2

Group 3

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A Complete Solution

Features: Low power Reliability Arbitrary addition and deletion of

linecards (due to upgrades/failures) Scalability: N=640 linecards

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Conclusion

WGR based solution is practical but not flexible

Star coupler based solution meets all requirements but is cumbersome

New optical components may help