1. High-Performance Networking Group Isaac Keslassy, Nick McKeown
Two-Stage Switch
High-Performance Networking Group
Isaac Keslassy, Nick McKeown

2. Input-Queued Packet Switch
Scheduler
inputs
outputs
Crossbar 1 . N 1 N

3. Round-Robin Scheduling
Uniform & non-bursty traffic => 100% throughput
Problem: traffic is non-uniform & bursty

4. Two-Stage Switch (I) External Inputs Internal Inputs External Outputs1 N 1 N 1 N
First Round-Robin
Second Round-Robin
[C.S.Chang et al.:

5. Two-Stage Switch (I) External Inputs Internal Inputs External Outputs
Load Balancing 1 N 1 N 1 N
First Round-Robin
Second Round-Robin
[C.S.Chang et al.:

6. Two-Stage Switch (I) No scheduling Problem: unbounded mis-sequencing
External Inputs
Internal Inputs
External Outputs 1 N 1 N 1 N
First Round-Robin
Second Round-Robin
No scheduling
Problem: unbounded mis-sequencing

7. Two-Stage Switch (II) New N3 instead of N2
[Infocom’02 paper:

8. Current Work Practical implementation of this scheme
Statistical bounds on mis-sequencing
Queue length distributions
TCP properties

10. An optical two-stage switch
Phase 1 1
Phase 2 2 3