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.