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Optically Switched Networking
Michael DalesMichael Dales
Intel Research CambridgeIntel Research Cambridge
www.intel.com/research
• Intel Research •
OverviewOverview
Part 1 – Technology overviewPart 1 – Technology overview
Optical fibre as a connection mediumOptical fibre as a connection medium
Optical switching fabricsOptical switching fabrics
Optical switchesOptical switches
Part 2 – Example networkPart 2 – Example network
SWIFT Architecture overviewSWIFT Architecture overview
Current workCurrent work
Research topicsResearch topics
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Recommended readingRecommended reading
If optical networks turn you on then the following text If optical networks turn you on then the following text book is worth seeking:book is worth seeking:
““Optical Networks, A Practical Perspective” by Rajiv Optical Networks, A Practical Perspective” by Rajiv Ramaswami and Kumar N. Sivarajan, Morgan KaufmanRamaswami and Kumar N. Sivarajan, Morgan Kaufman
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Optical fibre linksOptical fibre links
Optical fibre – yet another wireOptical fibre – yet another wire
Advantages:Advantages:
Capacity – long haul links of 160 Gbps over a single fibreCapacity – long haul links of 160 Gbps over a single fibre
Range – signal can travel further without regenerationRange – signal can travel further without regeneration
Noise immunity – does not suffer from EM interferenceNoise immunity – does not suffer from EM interference
Weight/space – a lot lighter/smaller than copperWeight/space – a lot lighter/smaller than copper
Power – …Power – …
Popular in the long haul networkPopular in the long haul network
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Optical fibre linksOptical fibre links
Not all good – some problems:Not all good – some problems:
Polarisation sensitivityPolarisation sensitivity
Chromatic dispersionChromatic dispersion
Non-linear behaviourNon-linear behaviour
Fibre more delicateFibre more delicate
Can’t be thrown around like copperCan’t be thrown around like copper
Minimum coil radiusMinimum coil radius
Coupling/splitting costsCoupling/splitting costs
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Optical fibre linksOptical fibre links
In copper we use TDM to multiplex multiple In copper we use TDM to multiplex multiple channels on a single linkchannels on a single link
In fibre can also use Wavelength Division In fibre can also use Wavelength Division Multiplexing (WDM)Multiplexing (WDM)
Each wavelength (lambda, Each wavelength (lambda, ) can carry a different ) can carry a different channelchannel
Free extra wires!Free extra wires!
Can TDM each wavelength tooCan TDM each wavelength too
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Switched optical networksSwitched optical networks
Optical links are common in high speed switched networks:Optical links are common in high speed switched networks:
ATM, Infiniband, Fibre-channelATM, Infiniband, Fibre-channel
But all these networks convert data back to electrons at the But all these networks convert data back to electrons at the switchswitch
PD
PD
PD
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Switched optical networksSwitched optical networks
O-E-O switch design makes it easy to design an O-E-O switch design makes it easy to design an optical network (just like copper ones!)optical network (just like copper ones!)
Disadvantages:Disadvantages:
Size/power – need to duplicate electronics for each Size/power – need to duplicate electronics for each lambdalambda
Latency – O-E-O conversion takes timeLatency – O-E-O conversion takes time
Bandwidth – for really high capacity, electronics can Bandwidth – for really high capacity, electronics can become the bottleneck(?)become the bottleneck(?)
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Optically switched networksOptically switched networks
A key focus of the optical network community is to A key focus of the optical network community is to find ways to make all optical networksfind ways to make all optical networks
Packets stay in photons from edge to edgePackets stay in photons from edge to edge
Techniques used depend on traffic type – circuit Techniques used depend on traffic type – circuit switching and packet switching have very different switching and packet switching have very different requirementsrequirements
Might want to move to different wavelength across Might want to move to different wavelength across switchswitch
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Optical switch fabricsOptical switch fabrics
Switch fabric design covered later in courseSwitch fabric design covered later in course
Here we look at switching elements for lightHere we look at switching elements for light
Need a way to switch light from one port to anotherNeed a way to switch light from one port to another
Many possible ways with varying loss, switching time, Many possible ways with varying loss, switching time, polarisation dependency, etc.polarisation dependency, etc.
Mechanical – moveable mirrors Mechanical – moveable mirrors
Can uses MEMS devices for compactness (e.g., glimmerglass)Can uses MEMS devices for compactness (e.g., glimmerglass)
Thermo-optical – heat it to change Thermo-optical – heat it to change
Electro-optical – control by current Electro-optical – control by current
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Buffering?Buffering?
In an electronic switch we use buffering to:In an electronic switch we use buffering to:
Delay packet whilst we decide what to do with itDelay packet whilst we decide what to do with it
Resolve contention when multiple packets want to go to Resolve contention when multiple packets want to go to the same place at the same timethe same place at the same time
There is no optical equivalent of random access There is no optical equivalent of random access memorymemory
Best we have are Fibre Delay LinesBest we have are Fibre Delay Lines
Use a long loop of fibre to delay the signal for a whileUse a long loop of fibre to delay the signal for a while
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Optical switchesOptical switches
The switching fabric is only half the story – how do The switching fabric is only half the story – how do we decide where to switch the packet?we decide where to switch the packet?
In electronic switch read header and then route In electronic switch read header and then route through fabric accordinglythrough fabric accordingly
In optical switches we have three options:In optical switches we have three options:
Convert the header to electrons and process electronicallyConvert the header to electrons and process electronically
Process the header optically using optical logicProcess the header optically using optical logic
Forget it all and use some form of reservationForget it all and use some form of reservation
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Optical switchesOptical switches
Use electronics to route packet:Use electronics to route packet:
Read header from photons and convert to electronsRead header from photons and convert to electrons
Use a FDL to buffer packet whilst switch makes decisionUse a FDL to buffer packet whilst switch makes decision
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Optical switchesOptical switches
Alternatively use reservation – signal ahead of time Alternatively use reservation – signal ahead of time that a packet is coming, typically on a reserved lthat a packet is coming, typically on a reserved l
One popular technique is Optical Burst SwitchingOne popular technique is Optical Burst Switching
Packets grouped into a burst at source to amortise Packets grouped into a burst at source to amortise overheadoverhead
Control packet fired into network ahead of time – passes Control packet fired into network ahead of time – passes through switches setting up a paththrough switches setting up a path
A fixed-delay time later the burst is sent through networkA fixed-delay time later the burst is sent through network
No guarantee that you’ll get throughNo guarantee that you’ll get through
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Optical switchesOptical switches
Alternatively use photonic devices to perform optical Alternatively use photonic devices to perform optical header readingheader reading
No need to convert to electronsNo need to convert to electrons
Still not a prime time technology – can only handle a Still not a prime time technology – can only handle a couple of addressing bitscouple of addressing bits
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SWIFT optical networkSWIFT optical network
SWIFT is a research project between Intel SWIFT is a research project between Intel Research, University of Cambridge, Essex Research, University of Cambridge, Essex University, and Intense PhotonicsUniversity, and Intense Photonics
Aim to built a short range, high capacity, wavelength Aim to built a short range, high capacity, wavelength striped, optically switched, packet switched networkstriped, optically switched, packet switched network
Aim for 100 Gbps and upAim for 100 Gbps and up
Use photonic devices under electronic controlUse photonic devices under electronic control
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SWIFT motivationSWIFT motivation
Optics traditionally used in long haul, but not in short Optics traditionally used in long haul, but not in short range, where copper dominates…range, where copper dominates…
……but copper will eventually run out (eventually…)but copper will eventually run out (eventually…)
SWIFT looks at applying optics to short range:SWIFT looks at applying optics to short range:
Device interconnects, Cluster/supercomputer Device interconnects, Cluster/supercomputer interconnects, Storage Area Networks, etc.interconnects, Storage Area Networks, etc.
Want have optical data-path, but still use electronics Want have optical data-path, but still use electronics for controlfor control
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Architecture overviewArchitecture overview
A short range packet switched network based upon:A short range packet switched network based upon:
WDM to increase bandwidth per linkWDM to increase bandwidth per link
An all optical data pathAn all optical data path
A single switch for simplicity (for now)A single switch for simplicity (for now)
An electronic control planeAn electronic control plane
Use WDM for Use WDM for striping – use all striping – use all s for one channels for one channel
Create a light busCreate a light bus
Reserve one channel for controlReserve one channel for control
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Switch designSwitch design
Optical data-path: packets remain optical Optical data-path: packets remain optical throughout the networkthroughout the network
Light-paths need to be constructed through the Light-paths need to be constructed through the switch before packets arriveswitch before packets arrive
Asynchronous control signalling used to request Asynchronous control signalling used to request switch configurationswitch configuration
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Switch fabricSwitch fabric Many light switching technologies, ranging from Many light switching technologies, ranging from
mechanical mirrors to semiconductor solutionsmechanical mirrors to semiconductor solutions
Switch response time is important for packet Switch response time is important for packet switchingswitching
We use Semiconductor Optical Amplifiers We use Semiconductor Optical Amplifiers (SOAs)(SOAs)
Turn light on or off based on an electrical inputTurn light on or off based on an electrical input
Have a switching time of a few nanosecondsHave a switching time of a few nanoseconds
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Switch fabricSwitch fabric Demonstrated Demonstrated
switching 10 * 10 Gbps switching 10 * 10 Gbps channels through an channels through an SOA SOA
55us/div – Packet is 94.72us data, 1.28 us guard band
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Host interfaceHost interface
Host interface has two main tasksHost interface has two main tasks
Taking packets and converting them to striped format Taking packets and converting them to striped format and vice versaand vice versa
Negotiating with the switch for accessNegotiating with the switch for access
When a node wishes to transmit it requests When a node wishes to transmit it requests permission over the control channel and waits for a permission over the control channel and waits for a light-path to be setuplight-path to be setup
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Wavelength stripingWavelength striping
To optical switch
To arbiter Request
From arbiter grant
Incoming packet
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DemonstratorDemonstrator Have built a test-bed networkHave built a test-bed network
Goal is to allow practical evaluation at many levels:Goal is to allow practical evaluation at many levels:
Photonics evaluationPhotonics evaluation
MAC layer testingMAC layer testing
Real application performanceReal application performance
Used to validate a simulation model for Used to validate a simulation model for investigation of network scalinginvestigation of network scaling
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Testbed overviewTestbed overview
Built a 3 node test-bedBuilt a 3 node test-bed
Two main components: host Two main components: host interfaces and switchinterfaces and switch
Control electronics on FPGAsControl electronics on FPGAs
2 data 2 data in 1500nm range in 1500nm range
1 control 1 control in 1300 nm range in 1300 nm range
Couplers/AWGs used to Couplers/AWGs used to combine/split combine/split ss
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Current demonstratorCurrent demonstrator
Current setup seen hereCurrent setup seen here
Three racks:Three racks:
1: switch1: switch
2: host interface board2: host interface board
3: host interface transceivers3: host interface transceivers
PCs off shotPCs off shot
Large due to using off the Large due to using off the shelf components!shelf components!
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StatusStatus Recently got first stage workingRecently got first stage working
Switches packets between nodesSwitches packets between nodes
Data striped over both wavelengthsData striped over both wavelengths
Can run TCP, UDP, ICMP, etc. end to endCan run TCP, UDP, ICMP, etc. end to end
Currently tuning performance for benchmarkingCurrently tuning performance for benchmarking
Have simulation model in NS2 ready to correlate Have simulation model in NS2 ready to correlate against testbedagainst testbed
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Future workFuture work Looking at several areas, includingLooking at several areas, including
Switch fabric designSwitch fabric design
Photonic device controlPhotonic device control
Current SOA configuration done manuallyCurrent SOA configuration done manually
Want to automate this process using electronicsWant to automate this process using electronics
Network scheduling and managementNetwork scheduling and management
Improve on request/grant protocolImprove on request/grant protocol