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TTM1: Approaches to Optical Internet Packet Switching

TTM1: Approaches to Optical Internet Packet Switching. David K. Hunter and Ivan Andonovic. Abstract. Increased capcity demands  WDM Next evolution after WDM: Optical switching (OPS). Introduction.

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TTM1: Approaches to Optical Internet Packet Switching

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  1. TTM1:Approaches to Optical Internet Packet Switching David K. Hunter and Ivan Andonovic

  2. Abstract • Increased capcity demands  WDM • Next evolution after WDM: Optical switching (OPS)

  3. Introduction • There is a ”mismatch” between the capacity available through use of WDM and processing capacities of routers. • IP routers have the following tasks: • Routing: Build connectivity through establishing routing tables in a network. Different protocols used to spread information (e.g. OSPF, IS-IS) • Forwarding: Decide output port interface • Switching: Transport a packet to the correct output port • Buffering: If contention, store packet temporarily

  4. Optical Packet Switching • Transmission and switching in the optical domain, but forwarding and routing in the electronical domain. • The next step would be to process packet headers (forwarding) in the optical domain. Then only the actual routing is left for the elctronical domain.

  5. Optical Packet Switching • (At least) two alternative approaches to OPS: • Fixed Length Packets (FLP) • Variable Length Packets (VLP) • (But additionally one could distinguish between Asynchronous or Syncronous (Slotted) transport).

  6. The design of Optical Packet Switches • Three principal sub-blocks (Note: This is a slotted network): • Input interface: Alignment of packets i time. Why? • Switching core: Transports packets to the correct output port • Output interface: Header insertion

  7. The design of Optical Packet Switches • Packet format defined in the KEOPS project • Sync.pattern. Why? • Guard time. Why? • More sync: payload sync. Why? • More guard. Why?

  8. Wavelength in Contention Resolution Two possible multiplexing schemes: • Scattered Wavelength Path (SCWP) • Packets are spread on random (”scattered”) free wavelengths. • Shared Wavelength Path (SHWP) • Each path (=”virtual connection”) in the optical packet layer is assigned a particular wavelength. Wavelengths may be shared by many paths. (But packets belonging to a path will not change to another wavelength).

  9. Wavelength in Contention Resolution • Using SCWP there is one large buffer per fiber for all wavelengths. Buffer depth per wavelength is size of buffer divided by number of wavelengths. • Using SHWP there is one buffer per wavelength. Comparison of buffer depth for achieving PLR 10-9

  10. Wavelength in Contention Resolution • Broadcast and Select Switch (KEOPS) • Wavelength encoder. N wavelength converters, one for each input. Encoding each packet on a fixed wavelength with a unique wavelength for each input. • Buffer and broadcast section. Number of FDLs and a space switch stage. Electronically controlled selection (full signal?). • Wavelength selector block. N demultiplexers, followed by electronically controlled selection. • All packets available at all outputs => support multicast

  11. Wavelength in Contention Resolution WASPNET design: • No large splitting losses as in KEOPS B&S • Core components are Tuneable Wavelength Converters (TWCs), and 2N x 2N Arrayed Waveguide Grating (AWG). Pluss N*N space switch.

  12. Variable-Length Optical Packet Switching • S stages, D in/outputs in every stage except first (N inputs) and last (N outputs); and D FDLs. • Delay line granularity of each stage is N times that of the next stage. • Brute force algoritme controlling the switch is computationally intensive. Delay lines in units of packet granularity

  13. Conclusions • At the start of OPS (year 2000) Most OPS approaches assumed fixed length packets and synchronous operation of switches. • If the goal is to carry variable length packets (as in Ethernet) asynchronous operation may be necessary. • Use of wavelength dimension to resolve contention is also shown to be useful.

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