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Raimena Veisllari
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  1. Optical Packet/Burst Switchingbased on : “Optical Packet and Burst Switching Technologies for the Future Photonic Internet” S.J. Ben Yoo Raimena Veisllari

  2. Content • Short Introduction • Optical Burst Switching (reservation, contention resolution) • Optical Switches Fabrics/Technologies • Optical Header Processing • Optical Packet Synchronization/Time Switch • Optical Packet Switches • Optical Label Switching • Testbed demonstration of edge/core OLR • Summary

  3. Optical Networks evolution • WDM ptp first-generation • The true benefit of optical networking may rise from avoiding electronics in the data plane • All-optical second generation • Format and protocol transparency • Simplifies hardware requirements in the data plane? • ROADM and OXC • OPS/OBS • True IP over WDM • Statistically Multiplexing

  4. Optical Networks Evolution Wei et. al.“High-Performance Hybrid-Switching Optical Router for IP over WDM Integration”

  5. OBS principles • Quickly transport large amount of data without provisioning long-lasting circuits. • Burst Header Cell (BHC) or BCP • Depends on the reservation scheme (one-way or two-way signalling), Usually Hdr info + burst length • If no resources available->contention resolution based on local node

  6. OBS Control Protocols • Based on the reservatio/contention resolution schemes employed. Differentiate between: • Setting the switching matrix : Sending the control packet in advance/not in advance (Toffset) • Releasing the switching matrix: Giving the payload length in advance/use release packet after the burst • One-way reservation (no ACK) or two-way reservation • Compare the low latency of one-way and the guaranteed delivery of two-way • TAG-based OBS (No ACK out-of-band) to achieve both datagram and VC switching • JET signalling (No FDL) • Built-in-offset Toffset=0 (FDL) • Other schemes available like fixed or limited duration and two-way signalling schemes based on RWA algorithms with practical limitation on number of nodes (not discussed).

  7. Just Enough Time (JET)

  8. OBS (2) • Requires a careful precomputation of T to avoid possible burst loss by compensating the total latency experienced by BHC. • Research on varying the QoS (CoS) by varying the offset time T. • Limitation: The burst blocking probability related to the number of wavelegths and the traffic load. • The built-in TAG-OBS uses OPS schemes • The built-in optical buffer (FDL) allows the burst to be «queued» for the time it takes to process BHC and set the switching matrix • Usually a low offset time + FDLs are employed throughout the network! (OPS-like OBS)

  9. OBS Contention Resolution • Contention: Burst requiring the same output, same wavelength at the same time in one node -> use alternative forwarding path • Wavelength domain • The most effective solution because it does not require additional latency while maintaining the shortest path or minimum hop. • Time domain • FDL (FIFO) and all inherited problems of such queueing and FDL size • Space domain • Hot-potato, forward to another output and let the network itself be a buffer. • Out-of-order sequencing • Delay/jitter

  10. Optical Switching Fabrics (1) • OBS vs. OPS • Subwavelength granularity • Fast switching speeds (us, ms) vs. nanoseconds in OPS • Other considerations? • Optical Switching fabrics carachteristics • Signal Quality Issues : Crosstalk, Jitter, Chirp, attenuation, OSNR • Configuration Issues: Scalability, blocking/nonblocking, promptness, switching domain, optical transparency, practical implementation • Performance issues: Switching speed, PLD, Insertion loss, level of transparency

  11. Optical Switching Fabrics (2) Optical switching technologies for OCS, OBS, and OPS

  12. OPS Technologies (1) • Categorizing based on the combination of: • Synchronous/Asynchronous pkt switching • Fixed/Variable packet length • Store and forward vs cut-through pkt switching • WDM, TDM and Optical CDM (difficulties in developing multiplexing devices for TDM and CDM) Synchronous fixed length Asynchronous Variable length

  13. Optical Hdr Processing

  14. Optical Hdr Techniques

  15. Optical Packet Synchronizer/Time Switch • In a system with N time granularity, K ports and W wavelengths there are needed NxKxW modules (Scalability? Complexity compared with the OPS itself?) • One possible solution is shared or loopback buffering.

  16. OPS for packet switching (1) • Guard time : longer than the longest transition time but short for efficient switching • Space Switching (KEOPS example Broadcast and select or NxN OXS with SOA)

  17. OPS for packet switching (2) • Optical Phase Array • Like a phased-array radar, the OPA components select wavelength paths across a 64 × 64 cross-point switch via an optical interference mechanism that operates by changing the waveguides’ refractive indices. 64 non-blocking 1x64 switches, the switching time 30ns. • Wavelength Routing Switching Fabric • KW x KW AWGRs with F shared recirculating FDLs; Switching in time, space and wavelength

  18. OPS for packet switching (3) • Store and Forward OPS and Optical Buffers • The lack of the optical buffer is the main problem in the OPS research so far mainly because of this switching paradigm. • TCP congestion control algorithm determines the size of the buffer • RTT x (data rate of the link) -> For OPS 25Mb for 10Gbps link • PLR vs systems scalability • Pipelined router architecture • TDM and CDM OPS • Research is less active due to the difficulties of producing ultrafast mux/dmux in optical TDM and optical CDM technologies • OPS using CMOS/RAM • Switch with high speed OE converters parallel to serial -> CMOS RAM -> serial to parallel (Is it still OPS all-optical?)

  19. Optical Label Switching (OLS) • DARPA proposal and patent (optical-tag switching) interoperable with MPLambdaS through GMPLS extension. It facilitates interoperability between OCS, OBS and OPS. • Discarding Store-and-forward, • 4 classes of labels 40 bits long: • Class A label dst oriented similar to IP hdr ( dst, src, QoS, CoS, optical TTL, exp bits) • Class B = Class A plus TE in the exp bits • Class C for label based forwarding similar to MPLS • Class D for Circuit Switching • Use a unified and pipelined contention resolution scheme in the wavelength, time and space domains • Error-free 101 hop-cascaded OLS router operations have been demonstrated with rapid clock recovery 1ns and guard time 2-3ns

  20. Optical Label Switching (OLS)

  21. Summary • OPS and OBS research on the combination of the vast optical bandwidth and subwavelength granularity by switching/routing packets and burst in the optical layer. • OBS offers BE with one-way signalling with milli to microseconds switching time • OPS needs faster switching times up to nanoseconds to be effective • Optical Label (Hdr) Processing and switching in times, space and wavelength domains provide the nanosecond speeds. • OLS facilitates the interoperability between OCS, OPS and OBS with less power requirement and reduced complexity??