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A Survey of Optical Burst Switching in the Next-Generation Optical Internet

A Survey of Optical Burst Switching in the Next-Generation Optical Internet. Outline. Introduction Switching Techniques Optical Burst Switching QoS Support in All-Optical Networks Performance Issues Conclusions. . Introduction. Introduction IP runs over all-optical WDM layer

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A Survey of Optical Burst Switching in the Next-Generation Optical Internet

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  1. A Survey of Optical Burst Switching in the Next-Generation Optical Internet

  2. Outline • Introduction • Switching Techniques • Optical Burst Switching • QoS Support in All-Optical Networks • Performance Issues • Conclusions 

  3. Introduction • Introduction • IP runs over all-optical WDM layer • Challenging issues • How to support QoS?

  4. Introduction • New optical switches/routers (hardware) are being built for the next-generation optical Internet. • The huge bandwidth of fiber optic networks • Due to DWDM (dense wavelength-division multiplexing ) technique • Data transmitted optically has to be slowed down at each node if it is to be switched electronically.

  5. Introduction • IP over WDM • Transport IP packets directly over the optical layer without any O/E/O conversion. • No optical form of RAM available today • Novel protocols (software) running on top of optical switches/routers are needed.

  6. Introduction • Challenging issues • The current lack of optical random access memory • The requirement for synchronization • How to provide basic QoS support?

  7. Introduction

  8. Switching Techniques • Switching Technique • Wavelength routing • Optical packet switching • Optical burst switching

  9. Switching Techniques • Wavelength routing • Two-way reservation is needed to setup lightpaths • Advantages: • No optical buffer or O/E/O conversion of data is needed. • Limitations: • Low bandwidth utilization • There are not enough wavelengths in the fiber to enable full mesh connectivity • Setting up and tearing down a lightpath would take at least several tens of milliseconds

  10. Switching Techniques • Optical packet/cell switching • The payload(data) is sent along with its header without setting up a path • Each packet needs to be buffered • Due to the tight coupling in time between the payload and header, store-and-forward nature • The size of the payload is too small given the high channel bandwidth of optical networks, resulting in relatively high control overhead.

  11. Switching Techniques • Optical burst switching • Combines the best of circuit and packet switching while avoiding their shortcomings. • One-way reservation. (a data burst follows a corresponding control packet without waiting for an acknowledgment) • Control can be performed electronically, but data can be switched optically. • A burst will cut through intermediate nodes without being buffered.

  12. Switching Techniques

  13. OBS • Optical Burst Switching • Open-ended • TAG ( tell-and-go ) • IBT ( in-band-terminator ) • Close-ended • JET ( just-enough-time ) • Differ mainly in the way that bandwidth release is triggered 

  14. OBS • TAG (tell-and-go) • The source node sends a release packet • IBT (in-band-terminator) • A burst contains an IBT (e.g., silence in a voice circuit), and bandwidth is released as soon as the IBT is detected.

  15. OBS • JET (just-enough-time) T(i) = T - Σδ(h)

  16. OBS • JET • Offset Time • Delayed Reservation (DR)

  17. QoS Support • QoS Support in All-Optical Networks • Without FDLs • With FDLs ( FDL : fiber delay line )

  18. QoS Support • QoS scheme • Critical data can be transported at the WDM layer more reliably than noncritical data. • Intraclass contentions and interclass contentions

  19. Without FDLs t01 > l0

  20. With FDLs

  21. Multiple Classes • tdiff : the difference in the offset times assigned to class i and class (i-1) • R : The lower bound of the isolation degree

  22. Performance Issues • Performance Issues • Blocking probability • Queuing delay and end-to-end latency

  23. Performance Issues

  24. Performance Issues

  25. Performance Issues • The impact of the extra offset time, depends on the number of classes, and the offset time difference (tdiff)used. The mean burst size : 15 kbytes 10 Gb/s => L = 12 μs Service classes (n) : 4 tdiff = 3L (at least 95% class isolation) • Maximum additional delay = 108 μs (n -1) * tdiff

  26. Conclusions • The integration of IP and WDM • Overview of Optical Burst Switching • Achieving a balance between wavelength routing and optical packet switching • Without requiring buffering at the WDM layer • Support QoS in optical networks • An OBS protocol : JET • The use of offset time and DR

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