Implementation Issues in the Optical Router Project

Implementation Issues in the Optical Router Project Isaac Keslassy, Da Chuang, Nick McKeown High Performance Networking Group klamath.stanford.edu

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

System Constraints • Given the set of features: Maximize Total Capacity C s.t. Rack Power: P < 5kW Rack Volume: V < 2m3

Switch Fabric 100Tb/s Router Optical links Racks of linecards

R R 1 1 1 1 2 2 2 2 Cyclic Shift Cyclic Shift R/N R/N R/N 3 3 3 3 Passive mesh Two-stage reminder: spreading

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

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

Detector Laser/Modulator l l 1 1 1 N 1 1 l l l l , , l l 1 2 1 2 Linecard 1 Linecard 1 2 2 2 1 l l … … N N l l N N l l 1 1 2 1 l l 2 2 , l l , l l Linecard 2 Linecard 2 1 2 1 2 2 2 3 l 2 … l … NxN WGR N N l l N N l l 1 1 N N-1 N N l l l l , , l l 1 2 1 2 Linecard N Linecard N 2 2 1 N l l … … N N l l N N WGR Based Solution (N=64)

 R/2  R/2  R/2  R/2 R/N R/N Ingress Linecard 1 Midstage Linecard 1 Egress Linecard 1 R R R R R R Ingress Linecard 2 Midstage Linecard 2 Egress Linecard 2 Ingress Linecard N Midstage Linecard N Egress Linecard N R/N R/N Problem 1: Missing Linecards

WGR • Features: • Low power • Reliability • Arbitrary addition and deletion of linecards (due to upgrades/failures)

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

Additional spreading stage with MEMS Problem 2: Scalability to 640 Linecards

WGR and MEMS • Features: • Low power • Reliability • Arbitrary addition and deletion of linecards (due to upgrades/failures) • Scalability: N=640 linecards

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

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

Star Coupler • Two spreading stages: space and wavelength

Star Coupler • Features: • Low power • Reliability • Arbitrary addition and deletion of linecards (due to upgrades/failures) • Scalability: N=640 linecards

A Complete Solution

A Complete Solution • Features: • Low power • Reliability • Arbitrary addition and deletion of linecards (due to upgrades/failures) • Scalability: N=640 linecards

Conclusion • WGR based solution is practical but not flexible • Star coupler based solution meets all requirements but is cumbersome • New optical components may help

Implementation Issues in the Optical Router Project