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A novel switching paradigm for buffer-less WDM networks

This paper highlights the emergence of Optical Burst Switching (OBS) as a novel paradigm for Next Generation Optical Internet, offering insights into its benefits over traditional optical switching methods. The study proposes a buffer-less WDM layer capable of supporting basic Quality of Service (QoS), showcasing improved efficiency and reduced latency. By utilizing a Just-Enough-Time mechanism and delayed reservation of bandwidth, OBS optimizes bandwidth utilization while maintaining low latency, making it suitable for bursty traffic and short-lived sessions. The paper also discusses the implementation of Class 0 and Class 1 burst priority schemes to enhance QoS performance without the need for buffering. Overall, OBS is positioned as a promising solution for future optical network architectures.

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A novel switching paradigm for buffer-less WDM networks

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  1. A novel switching paradigm for buffer-less WDM networks Myungsik Yoo and Chunming Qiao EE and CSE Departments University at Buffalo (SUNY)

  2. Why WDM Optical Internet ? • Explosion of the Internet traffic • Advances in DWDM networking technology • Emergence of Terabit routers with OC-48 line speed • Reduced capital equipment and operating costs • Current incarnation: IP routers over WDM links • Envisioned Next Generation Optical Internet: • IP over an all-optical WDM layer

  3. Existing switching paradigm • Optical circuit switching • set-up delay = round-trip time • a limited number of wavelengths and thus limited connectivity • not suitable for bursty traffic and short-lived sessions • Optical packet/cell switching • a payload and its header are sent together (tightly coupled) • need to buffer the payload while processing the header • high control overhead due to small packet/cell size • Optical Burst Switching (OBS) • combines the best of the two while avoiding their shortcomings

  4. Comparison of three paradigms

  5. OBS based on Just-Enough-Time

  6. Unique Features • Loosely coupled bursts and their control packets • uses an offset time + out-of-band control • Offset time : , where H is number of hops to go • A burst is buffered only at the source node • Delayed Reservation (DR) of BW at node i • reserved from tb to tb+l (offset time at node i : • Efficient utilization of BW (as well as FDLs if any)

  7. BW Utilization vs Latency • Comparing JET and NoDR

  8. OBS for IP over WDM • Run IP on top of WDM switches • Use a dedicated control wavelength between the IP entities • for routing control packets • To send data, a control packet first sets up a connection • one-way reservation based on offset time and DR • Then, the data burst cuts through intermediate IP entities • reduces latency & processing load at IP routers • Similar to multi-protocol label switching (MPLS)

  9. Support QoS at the WDM Layer • IP provides only best-effort services • A WDM layer supporting basic QoS is useful • E.g. to let Class 1 have a higher priority than Class 0 • Existing approaches (e.g. Fair Queueing) require buffer • Challenge: support priority in a buffer-less WDM layer • Solution: assign Class 1 bursts an extra offset time • Class 1 bursts can reserve BW much in advance • Class 0 bursts can only “buy tickets at door”

  10. Extra Offset Time for Priority

  11. Differentiated Services • Assume: the length of Class 0 bursts is exponentially distributed with an average of L • L may be a few Kbits or a few microseconds at OC-48 • At least 95% of Class 0 bursts are shorter than 3L • and at least 99% of them are shorter than 5L • So, if the extra offset time = 3L, at least 95% of Class 0 bursts will not block a Class 1 burst • Blocking probability of Class 1 bursts will be reduced • average blocking probability (over all bursts) unchanged

  12. QoS Performance Improvement • Blocking probability after 6 hops (offered load = 0.8)

  13. Conclusion • Optical Burst Switching (OBS) is a novel switching paradigm for the Next Generation Optical Internet • A buffer-less WDM layer can support basic QoS • Future work on supporting multiple classes • Also to interwork with other approaches to achieve absolute vs. relative QoS guarantee

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