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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 - PowerPoint PPT Presentation
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applied research laboratory1
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 laboratory2
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 laboratory3
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.ht
ml
applied research laboratory4
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 laboratory5
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
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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
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Load balanced switch
• 100 % throughput for a broad class of traffic• No scheduler => scalable
VOQ
VOQ
VOQ
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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
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Linecard block diagram
• Both input and output blocks in one linecard• Intermediate input block for the second stage in the
load balanced switch
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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/N R/N R R 2R/N R
applied research laboratory11
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 laboratory12
Decomposing the mesh2R/81
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Source: Dr. Nick McKeown’s SIGCOMM slides
applied research laboratory13
Decomposing the mesh2R/4
2R/8
2R/8
2R/8
2R/8
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
TDMWDM
Source: Dr. Nick McKeown’s SIGCOMM slides
applied research laboratory14
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)
input To intermediate input block
applied research laboratory15
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 laboratory16
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
applied research laboratory17
Partitioned switch
M input/output channels for each linecard
Theorems:1) M = L+G-1, each path supporting
a rate of 2R2) Polynomial time reconfiguration
when new linecards are added or removed.
applied research laboratory18
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
LC 1LC 2
LC L
Group 1
LC 1
LC 1
Group 2
Group G
LC 1LC 2
LC L
Group 1
LC 1
LC 1
Group 2
Group G
applied research laboratory19
Hybrid electro-optical switch
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Optical Switch
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100Tb/s Load-Balanced Router
L = 16160Gb/s linecards
Linecard Rack G = 40
L = 16160Gb/s linecards
Linecard Rack 1
L = 16160Gb/s linecards
55 56
1 2
40 x 40MEMS
Switch Rack < 100W
Source: Dr. Nick McKeown’s SIGCOMM slides