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Scaling Internet Routers Using Optics Isaac Keslassy, et al. Proceedings of SIGCOMM 2003. Slides: http://tiny-tera.stanford.edu/~nickm/talks/Sigcomm_2003.ppt Do we need faster routers? Traffic still growing 2x every year Router capacity growing 2x every 18 months

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scaling internet routers using optics

Scaling Internet Routers Using Optics

Isaac Keslassy, et al.

Proceedings of SIGCOMM 2003.

Slides: http://tiny-tera.stanford.edu/~nickm/talks/Sigcomm_2003.ppt

applied research laboratory

do we need faster routers
Do we need faster routers?
  • Traffic still growing 2x every year
  • Router capacity growing 2x every 18 months
  • By 2015, there will be a 16x disparity
    • 16 times the number of routers
    • 16 times the space
    • 256 times the power
    • 100 times the cost
  • => Necessity for faster, cost effective, space and power efficient routers.

Source: Dr. Nick McKeown’s SIGCOMM talk

applied research laboratory

current router juniper t640
Current router : Juniper T640
  • T640: Half-rack
    • 37.45 x 17.43 x 31 in (H x W x D)
    • 95.12 x 44.27 x 78.74 cms (area ≈ 3 m2)
    • 32 interface card slots
    • 640 Gbps front side switching capacity
    • 6500 W power dissipation
    • Black body radiation = T4 W/m2
    • at 350 F, Power radiated = 2325 W/m2
    • Operating temp. = 32 to 104 F = 0 to 40 C
  •  = Stefan Boltzmann constant = 5.670 * 10-8 W / m2 K4
  • References:
    • http://www.alcatel.com/products/productCollateralList.jhtml?productRepID=/x/opgproduct/Alcatel_7670_RSP.jhtml
    • http://www.juniper.net/products/ip_infrastructure/t_series/100051.html#03
    • http://www.cisco.com/en/US/products/hw/routers/ps167/products_data_sheet09186a0080092041.html

applied research laboratory

multi rack routers
Multi-rack routers
  • Switch fabric and linecards on separate racks
  • Problem: Switch fabric power density is limiting
    • Limit = 2.5 Tbps (scheduler, opto-electronic conversion, other electronics)
  • Switch fabric can be single stage or multi stage
    • Single stage: complexity of arbitration algorithms
    • Multi-stage: unpredictable performance (unknown throughput guarantees)

Switch fabric

Linecards

applied research laboratory

optical switch fabric
Optical switch fabric
  • Pluses
    • huge capacity
    • bit rate independent
    • low power
  • Minuses
    • slow to configure (MEMS ≈ 10 ms)
    • fast switching fabrics based on tunable lasers are expensive
  • Reference:
    • http://www.lightreading.com/document.asp?doc_id=2254&site=lightreading

applied research laboratory

goals
Goals
  • Identify architectures with predictable throughput and scalable capacity
    • Use the load balanced switch described by C-S. Chang
    • Find practical solutions to the problems with the switch when used in a realistic setting
  • Use optics with negligible power consumption to build higher capacity single rack switch fabrics (100 Tbps)
  • Design a practical 100 Tbps switch with 640 linecards each supporting 160 Gbps

applied research laboratory

load balanced switch
Load balanced switch
  • 100 % throughput for a broad class of traffic
  • No scheduler => scalable

VOQ

VOQ

VOQ

applied research laboratory

problems with load balanced switch
Problems with load-balanced switch
  • Packets can be mis-sequenced
  • Pathological traffic patterns can make throughput arbitrarily small
  • Does not work when some of the linecards are not present or are have failed
  • Requires two crossbars that are difficult or expensive to implement using optical switches

applied research laboratory

linecard block diagram
Linecard block diagram
  • Both input and output blocks in one linecard
  • Intermediate input block for the second stage in the load balanced switch

applied research laboratory

switch reconfigurations
Switch reconfigurations
  • The crossbars in the load balanced switch can be replaced with a fixed mesh of N2 links each of rate R/N
  • The two meshes can be replaced with a single mesh carrying twice the capacity (with packets traversing the fabric twice)

R

R

R

R/N

R/N

R

2R/N

applied research laboratory

optical switch fabric with awgrs
Optical switch fabric with AWGRs
  • AWGR: data-rate independent passive optical device that consumes no power
  • Each wavelength operates at rate 2R/N
  • Reduces the amount of fiber required in the mesh (N2)
  • N = 64 is feasible but N = 640 is not

AWGR = Arrayed Wavelength Grating Router

applied research laboratory

decomposing the mesh
Decomposing the mesh

2R/8

1

1

2

2

3

3

4

4

5

5

6

6

7

7

8

8

Source: Dr. Nick McKeown’s SIGCOMM slides

applied research laboratory

decomposing the mesh13

WDM

TDM

Decomposing the mesh

1

2R/8

2R/8

1

2R/4

2R/8

2R/8

2

2

3

3

4

4

5

5

6

6

7

7

8

8

Source: Dr. Nick McKeown’s SIGCOMM slides

applied research laboratory

full ordered frames first foff
Full Ordered Frames First (FOFF)
  • Every N time slots
    • Select a queue to serve in round robin order that holds more than N packets
    • If no queue has N packets, pick a non-empty queue in round robin order
    • Serve this queue for the next N time slots

N FIFO queues

(one per output)

To intermediate input block

input

applied research laboratory

foff properties
FOFF properties
  • No Mis-sequencing
    • Bounds the amount of mis-sequencing inside the switch
    • Resequencing buffer at most N2 + 1 packets
  • FOFF guarantees 100 % throughput for any traffic pattern
  • Practical to implement
    • Each stage has N queues, first and last stages hold N2+1 packets/linecard
    • Decentralized and does not need complex scheduling
  • Priorities are easy to implement using kN queues at each linecard to support k priority levels

applied research laboratory

flexible linecard placement
Flexible linecard placement
  • When second linecard fails, links between first and second linecards have to support a rate of 2R/2
  • Switch fabric must be able to interconnect linecards over a range of rates from 2R/N to R => Not practical

2R/3

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partitioned switch
Partitioned switch
  • Theorems:
  • M = L+G-1, each path supporting a rate of 2R
  • Polynomial time reconfiguration when new linecards are added or removed.

M input/output channels for each linecard

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m l g 1 illustration
M = L + G -1 illustration
  • Total traffic going out or coming in at Group 1 = LR
  • Total number of linecards = L + G -1
  • Number of extra paths needed to/from first group = L -1

Group 1

Group 1

LC 1

LC 1

LC 2

LC 2

LC L

LC L

Group 2

Group 2

LC 1

LC 1

Group G

Group G

LC 1

LC 1

applied research laboratory

hybrid electro optical switch
Hybrid electro-optical switch

applied research laboratory

optical switch
Optical Switch

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100tb s load balanced router

40 x 40

MEMS

Linecard Rack 1

Linecard Rack G = 40

Switch Rack < 100W

L = 16

160Gb/s

linecards

L = 16

160Gb/s

linecards

1

2

55

56

100Tb/s Load-Balanced Router

L = 16

160Gb/s

linecards

Source: Dr. Nick McKeown’s SIGCOMM slides

applied research laboratory