Optically Switched Networking Michael Dales Intel Research Cambridge

Optically Switched Networking Michael Dales Intel Research Cambridge www. intel. com/research

• Intel Research • Overview Part 1 – Technology overview w Optical fibre as a connection medium w Optical switching fabrics w Optical switches Part 2 – Example network w SWIFT Architecture overview w Current work w Research topics www. intel. com/research

• Intel Research • Recommended reading If optical networks turn you on the following text book is worth seeking: w “Optical Networks, A Practical Perspective” by Rajiv Ramaswami and Kumar N. Sivarajan, Morgan Kaufman www. intel. com/research

Part 1 – Technology overview www. intel. com/research

• Intel Research • Optical fibre links Optical fibre – yet another wire Advantages: w Capacity – long haul links of 160 Gbps over a single fibre w Range – signal can travel further without regeneration w Noise immunity – does not suffer from EM interference w Weight/space – a lot lighter/smaller than copper w Power – … Popular in the long haul network www. intel. com/research

• Intel Research • Optical fibre links Not all good – some problems: w Polarisation sensitivity w Chromatic dispersion w Non-linear behaviour w Fibre more delicate § Can’t be thrown around like copper § Minimum coil radius w Coupling/splitting costs www. intel. com/research

• Intel Research • Optical fibre links In copper we use TDM to multiplex multiple channels on a single link In fibre can also use Wavelength Division Multiplexing (WDM) Each wavelength (lambda, l) can carry a different channel w Free extra wires! Can TDM each wavelength too www. intel. com/research

• Intel Research • Switched optical networks Optical links are common in high speed switched networks: w ATM, Infiniband, Fibre-channel But all these networks convert data back to electrons at the switch www. intel. com/research

• Intel Research • Switched optical networks O-E-O switch design makes it easy to design an optical network (just like copper ones!) Disadvantages: w Size/power – need to duplicate electronics for each lambda w Latency – O-E-O conversion takes time w Bandwidth – for really high capacity, electronics can become the bottleneck(? ) www. intel. com/research

• Intel Research • Optically switched networks A key focus of the optical network community is to find ways to make all optical networks Packets stay in photons from edge to edge Techniques used depend on traffic type – circuit switching and packet switching have very different requirements Might want to move to different wavelength across switch www. intel. com/research

• Intel Research • Optical switch fabrics Switch fabric design covered later in course w Here we look at switching elements for light Need a way to switch light from one port to another Many possible ways with varying loss, switching time, polarisation dependency, etc. w Mechanical – moveable mirrors § Can uses MEMS devices for compactness (e. g. , glimmerglass) w Thermo-optical – heat it to change w Electro-optical – control by current www. intel. com/research

• Intel Research • Buffering? In an electronic switch we use buffering to: w Delay packet whilst we decide what to do with it w Resolve contention when multiple packets want to go to the same place at the same time There is no optical equivalent of random access memory Best we have are Fibre Delay Lines w Use a long loop of fibre to delay the signal for a while www. intel. com/research

• Intel Research • Optical switches The switching fabric is only half the story – how do we decide where to switch the packet? In electronic switch read header and then route through fabric accordingly In optical switches we have three options: w Convert the header to electrons and process electronically w Process the header optically using optical logic w Forget it all and use some form of reservation www. intel. com/research

• Intel Research • Optical switches Use electronics to route packet: w Read header from photons and convert to electrons w Use a FDL to buffer packet whilst switch makes decision www. intel. com/research

• Intel Research • Optical switches Alternatively use reservation – signal ahead of time that a packet is coming, typically on a reserved l One popular technique is Optical Burst Switching w Packets grouped into a burst at source to amortise overhead w Control packet fired into network ahead of time – passes through switches setting up a path w A fixed-delay time later the burst is sent through network No guarantee that you’ll get through www. intel. com/research

• Intel Research • Optical switches Alternatively use photonic devices to perform optical header reading No need to convert to electrons Still not a prime technology – can only handle a couple of addressing bits www. intel. com/research

Part II - Example www. intel. com/research

• Intel Research • SWIFT optical network SWIFT is a research project between Intel Research, University of Cambridge, Essex University, and Intense Photonics Aim to built a short range, high capacity, wavelength striped, optically switched, packet switched network Aim for 100 Gbps and up Use photonic devices under electronic control www. intel. com/research

• Intel Research • SWIFT motivation Optics traditionally used in long haul, but not in short range, where copper dominates… …but copper will eventually run out (eventually…) SWIFT looks at applying optics to short range: w Device interconnects, Cluster/supercomputer interconnects, Storage Area Networks, etc. Want have optical data-path, but still use electronics for control www. intel. com/research

• Intel Research • Architecture overview A short range packet switched network based upon: w WDM to increase bandwidth per link w An all optical data path w A single switch for simplicity (for now) w An electronic control plane Use WDM for l striping – use all ls for one channel w Create a light bus w Reserve one channel for control www. intel. com/research

• Intel Research • Overview www. intel. com/research

• Intel Research • Switch design Optical data-path: packets remain optical throughout the network Light-paths need to be constructed through the switch before packets arrive Asynchronous control signalling used to request switch configuration www. intel. com/research

• Intel Research • Switch fabric Many light switching technologies, ranging from mechanical mirrors to semiconductor solutions Switch response time is important for packet switching We use Semiconductor Optical Amplifiers (SOAs) w Turn light on or off based on an electrical input w Have a switching time of a few nanoseconds www. intel. com/research

• Intel Research • Switch fabric Demonstrated switching 10 * 10 Gbps channels through an SOA 55 us/div – Packet is 94. 72 us data, 1. 28 us guard band www. intel. com/research

• Intel Research • Host interface has two main tasks w Taking packets and converting them to striped format and vice versa w Negotiating with the switch for access When a node wishes to transmit it requests permission over the control channel and waits for a light-path to be setup www. intel. com/research

• Intel Research • Wavelength striping From arbiter grant To arbiter Request Incoming packet To optical switch www. intel. com/research

• Intel Research • Demonstrator Have built a test-bed network Goal is to allow practical evaluation at many levels: w Photonics evaluation w MAC layer testing w Real application performance Used to validate a simulation model for investigation of network scaling www. intel. com/research

• Intel Research • Testbed overview Built a 3 node test-bed 2 data l in 1500 nm range Two main components: host interfaces and switch 1 control l in 1300 nm range Couplers/AWGs used to Control electronics on FPGAs combine/split ls www. intel. com/research

• Intel Research • Current demonstrator Current setup seen here Three racks: w 1: switch w 2: host interface board w 3: host interface transceivers PCs off shot Large due to using off the shelf components! www. intel. com/research

• Intel Research • Status Recently got first stage working w Switches packets between nodes w Data striped over both wavelengths w Can run TCP, UDP, ICMP, etc. end to end Currently tuning performance for benchmarking Have simulation model in NS 2 ready to correlate against testbed www. intel. com/research

• Intel Research • Future work Looking at several areas, including w Switch fabric design w Photonic device control §Current SOA configuration done manually §Want to automate this process using electronics w Network scheduling and management §Improve on request/grant protocol www. intel. com/research