optically switched networking

www.intel.com/research

Optically Switched Networking

Michael DalesMichael Dales

Intel Research CambridgeIntel Research Cambridge


• Intel Research •

Overview 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



Recommended 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


Part 1 – Technology overview



Optical 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



Optical 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



Optical 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



Switched 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



Switched 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(?)



Optically 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



Optical 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



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



Optical 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



Optical 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



Optical 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



Optical 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


Part II - Example



SWIFT 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



SWIFT 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



Architecture 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



Overview



Switch 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



Switch 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 (SOAs)We use Semiconductor Optical Amplifiers (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



Switch 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



Host 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



Wavelength striping

To optical switch

To arbiter Request

From arbiter grant

Incoming packet



Demonstrator 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 investigation Used to validate a simulation model for investigation of network scalingof network scaling



Testbed 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



Current 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!



Status 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 against Have simulation model in NS2 ready to correlate against testbedtestbed



Future 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

optically switched networking

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