1 Practical Optical Packet Routers Masataka Ohta Graduate School of Information Science and Engineering Tokyo Institute of Technology

2 Why Optical Computers are Impractical? Must compute optically –Logical AND/OR operations are non-linear –Optical devices have little non-linearity –Long interaction of highly concentrated light is necessary Not very fast Must memorize optically –Light can not stop

Why Optical Routers are Practical May not control optically –As long as payload is switched optically No one complains if optical routers are controlled electrically with electric header processing May not memorize optically –Buffers are to avoid packet collisions at output ports Delaying with FDLs (fiber delay lines) is enough 3

4 Timing Considerations 1Tbps is fast enough –to make fiber delay lines short 1500B packet is 12ns long or 3.6m long in vacuum 1Tbp is slow enough –to allow for electric control FPGA 2ns, external SERDES enables finer control SRAM for L3 route look up 3.3ns –to allow for optical switching Optical switches works within 100ps

5 Many Wavelengths enables Wideband 1Tbps Packets To Encode a Packet at 1Tbps –Simultaneously modulate 100 Wavelengths each at 10Gbps Single Wavelength Packets Many Wavelength Packets time Wavelength time

6 Optical Packet Format of Many Wavelength Packets for (Almost-all) Optical Switches Payload Header Time Wavelength Wavelengths to be processed, updated & switched electrically Wavelengths to be switched optically

7 Control Logic Routing Table Electric Optical Modified Header Original Header ADM Structure of an Optical Packet Switch with Many-Wavelength Packets Buffer

8 Very Small Amount of Buffer is Required at the Backbone Backbone Traffic is Poisson, if –backbone speed is much faster than access 1Tbps backbone is much faster than most, if not all, access –Paced TCP is used Exceptional hosts with exceptionally fast access should use paced TCP An Optical Buffer with 15 or 31 Fiber Delay Lines is Enough

Experiments on Many Wavelength Packets at NICT Buffering with 31 FDLs –S. Shinada, H. Furukawa, and N. Wada, "Investigation of Optical Buffer Capacity using Large-scale Fiber Delay Lines for Variable- length Optical Packet Switching," ECOC2013, Th. 1.A.1, Sep km transmission of 12.8Tbps packet –S. Shinada, J. M. D. Mendinueta, S. L. Ruben, and N. Wada, "Operation of a 12.8 Tbit/s DWDM Polarization Division Multiplexing 16-QAM Optical Packet Switching Node after 50-km of Fiber Transmission," ECOC2014, p. We.3.5.4, Sep Stable daily operation at 10Gbps*10wavelengths with 2FDLs 9

Estimated Power Consumption 1Tbps*4port optical routers with 15 FDLs can be constructed, for example, with –476 2:2 optical switches (2.5dB loss) Each consumes 10mW –128 10dB EDFAs (2.4mW optical output) Each consumes 40mW –About 10W of power 100Gbps*36port infiniband chip: 83W 10