Scheduling Proposals Scheduling Group Giulio Galante Wensheng Hua

Scheduling Proposals Scheduling Group Giulio Galante, Wensheng Hua, Sundar Iyer, Isaac Keslassy, Pablo Molinero, Gireesh Shrimali, Rui Zhang

Round-Robin Non-Round-Robin Two-Stage Switch (I) Two-Stage Switch (II) Longer Packets

Input-Queued Packet Switch Scheduler 1, 1 i, j N, N Crossbar inputs 1. . N 1 outputs. . N

Round-Robin Scheduling

Round-Robin: main properties • Simple to implement • 100% throughput with uniform traffic Bad throughput with non-uniform traffic

Non-Round-Robin Scheduling Too complex with a 100 Tbps router Up to 100% throughput • Computation complexity: • Cell time = 64 B /160 Gbps = 3. 2 ns = one clock cycle (today, 50 ns ; MWM: N 3) • Ports: 625 (today, 32) • Communication complexity • Number of bidirectional links: 625 (today, 170) • Information flow rate: 0. 3 Gcells/s x 20 b/cell = 6 Gbps (today, 2. 5 Gbps)

Round-Robin Simple | No 100% throughput Non-Round-Robin 100% throughput | Complex Two-Stage Switch (I) Two-Stage Switch (II) Longer Packets

Two-Stage Switch (I) External Inputs Internal Inputs External Outputs 1 1 1 N N N First Round-Robin Second Round-Robin [C. S. Chang et al. : http: //www. ee. nthu. edu. tw/~cschang/Part. I. pdf]

Two-Stage Switch (I): main properties • Simple to implement • 100% throughput • Possibility of using two sides of same mirrors Mis-sequencing!

Two-Stage Switch (II) New N 3 instead of N 2 [Paper under review: http: //klamath. stanford. edu/~keslassy/tmp/two-stage. pdf]

Two-Stage Switch (II): main properties • No missequencing • 100% throughput • Low average delay (within a bound from “optimal” outputqueued switch) Idea not thoroughly studied: difficult implementation?

Round-Robin Simple | No 100% throughput Non-Round-Robin 100% throughput | Complex Two-Stage Switch (I) 100% throughput, simple | Missequencing Two-Stage Switch (II) 100% throughput, no missequencing | Implementation? Longer Packets

Longer packets Variable-size packets [Tassiulas et al. : http: //www. glue. umd. edu/~koushik/hoti 00 -kkar. ps. gz]

Round-Robin Simple | No 100% throughput Non-Round-Robin 100% throughput | Complex Two-Stage Switch (I) 100% throughput, simple | Missequencing Two-Stage Switch (II) Longer Packets 100% throughput, more time between computations | Implementation? 100% throughput, no missequencing | Implementation?

1. Crossbar

2. Multistage Networks Banyan Network (2 x 2) 2 Layers of kxk switches (100 x 100)