Your Data Center Is a Router: The Case for Reconfigurable Optical Circuit Switched Paths - PowerPoint PPT Presentation

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Your Data Center Is a Router: The Case for Reconfigurable Optical Circuit Switched Paths. Core Switch. End of Row Switch. Top of Rack Switch. Data Center Network. Today’s Data Center Network. Picture from: James Hamilton, Architecture for Modular Data Centers .

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Your Data Center Is a Router: The Case for Reconfigurable Optical Circuit Switched Paths

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Your Data Center Is a Router:

The Case for Reconfigurable Optical Circuit Switched Paths


Data center network l.jpg

Core

Switch

End of Row

Switch

Top of Rack Switch

Data Center Network

  • Today’s Data Center Network

Picture from: James Hamilton, Architecture for Modular Data Centers

  • Data intensive applications are experiencing bandwidth bottleneck in the tree structure data center networks.

    • E.g. Video data processing, MapReduce …


Full bisection bandwidth solutions l.jpg

Tree

FatTree

BCube

Picture from: Ken Hall, Green Data Centers

Full bisection bandwidth solutions

  • Re-structure data center network to provide full bisection bandwidth among all the servers.

  • Complicated network structure, hard to construct and expand.


Full bisection bandwidth may not be necessary l.jpg

Full bisection bandwidth may not be necessary

  • Temporal Traffic Locality

    • Applications might hit CPU, disk IO or Sync bounds.

    • e.g. MapReduce

  • Spatial Traffic Locality

    • Nodes only communicate with a small number of partners.

    • e.g. Earthquake simulation

  • Many measurement studies have suggested evidence of traffic locality.

    • [SC05][WREN09][IMC09][HotNets09]

Full bisection bandwidth solutions provide too much with high costs.


An alternative design hybrid data center network l.jpg

A

B

C

D

E

F

An alternative design: hybrid data center network

  • Hybrid network may give us best of both worlds:

    • Optical circuit-switched paths for data intensive transfer.

    • Electrical packet-switched paths for timely delivery.

Electrical packet-switched network

Optical circuit-switched network


Optical circuit switching l.jpg

Optical Circuit Switching

  • MEMS Optical Switching Module

Picture from: http://www.ntt.co.jp/milab/en/project/pr05_3Dmems.html

Switching at whatever rate

modulated on input/output ports

Up to tens of ms physical

reconfiguration time


Optical channels l.jpg

40G, 100Gbps technology

has been developed.

15.5Tbps over a single fiber!

Price data from: Joe Berthold, Hot Interconnects’09

Optical Channels

  • Ultra-high bandwidth

  • Dropping prices


Optical circuits in datacenters l.jpg

  • Advantage:

    • Simple and flexible: easy to construct, expand and manage

    • Ultra-high bandwidth

    • Low power

  • Disadvantage:

    • Fat pipes are not all-to-all.

    • Reconfiguration overhead

Optical circuits in datacenters

A

B

C

D

E

F

A - E, B - D, C - F

A - D, B - E, C - F

A - F, B - E, C - D


Research questions l.jpg

Research questions

  • Enough traffic locality in data centers to leverage optical path?

  • Reconfigure optical paths fast enough to meet dynamic traffic?

  • How to integrate optical circuits into data centers at low costs?

  • How to manage and leverage optical paths?

  • How do applications behave over the hybrid network?


Is there enough traffic locality l.jpg

10 sec TM

10s

10s

10s

Time

Is there enough traffic locality?

  • Analyzing production data center traffic trace:

    • 7 racks, 155 servers, 1060 cores

    • One week NetFlow traces collected at all servers

    • Configure 3 optical paths out of total 21 cross-rack paths with maximum optical traffic, reconfigure every 10s.

Traffic locality: a few optical paths have the potential to

offload significant amount of traffic from electrical networks.


Can optical paths be reconfigured fast enough optical path configuration algorithm l.jpg

Graph G: (V, E)

R1

R2

R3

R4

R5

R6

R7

R8

wxy= vol(Rx, Ry) + vol(Ry, Rx)

R1

R2

w12

R1

R2

w27

w14

R4

w43

R3

R3

Optical path configuration is a maximum weight perfect matching on graph G.

R5

w35

w38

w47

R4

R8

w36

w68

R5

R6

R7

R6

Solved by polynomial time Edmonds’ algorithm[1]!

R7

R8

[1] J. Edmonds, Paths, trees and flowers, Canadian J. of Mathematics, pp 449-467, 1965

Can optical paths be reconfigured fast enough? - Optical Path Configuration Algorithm


Can optical paths be reconfigured fast enough optical path configuration time l.jpg

Can optical paths be reconfigured fast enough? - Optical Path Configuration Time

  • Several time factors

    • Computation time

      • 640ms for a 1000-rack data center using Edmonds’ algorithm.

    • Signaling time

      • < 1ms in data centers

    • Physical reconfiguration time

      • Up to tens ms for MEMS optical switches

Even in very large data centers, optical paths can

still be reconfigured at small time scales (< 1 sec).


How to manage optical paths in data centers l.jpg

How to manage optical paths in data centers?

  • Routing over dynamicdual-path (electrical/optical) network:

  • Ethernet Spanning Tree?

    • NO, dual paths will be blocked

  • Link State Routing?

    • NO, long routing convergence time after reconfiguration


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VLAN1: Electrical

VLAN2: Optical

How to manage optical paths in data centers?

  • VLAN based dual-path routing:

  • Advantages:

    • Leverage both electrical and optical paths by tagging packets

    • No route convergence delay after optical reconfiguration

    • No need to modify switches


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Servers

  • Extensive buffering at servers

    • Traffic demands measurement

    • Aggregate traffic and batch for optical transfer

  • Per-rack virtual output queuing:

    • Avoid head-of-line blocking

User

Apps

Kernel

Per-rack Virtual Output Queue

Scheduler

Network Interface

How to manage optical paths in data centers?

  • How to measure application traffic demand?


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Stats

  • Configurable virtual output queue scheduler to control traffic to optical paths.

  • A centralized manager to control the optical path configuration.

Config

Config

Stats

Per-rack Virtual Output Queue

Config

Scheduler

How to manage optical paths in data centers?

  • How to configure optical paths and schedule traffic to them?

Servers

User

Apps

Daemon

Configuration Manager

Kernel

A

B

C

D

Switches with VLAN settings

Traffic

Network Interface


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Challenges

  • TCP/IP reacting to optical path reconfiguration.

  • Potential long delays caused by extensive queuing at servers.

  • Collecting traffic demand from a million servers.

  • Choosing the right buffer sizes and reconfiguration intervals.


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Summary

  • Adding optical circuit switched paths into data centers.

  • Potential benefits:

  • A simpler and flexible data center network design.

  • Relieving data intensive applications from network bottlenecks.


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