A novel switching paradigm for buffer-less WDM networks

1
A novel switching paradigm for buffer-less WDM
networks

• Myungsik Yoo and Chunming Qiao
• EE and CSE Departments
• University at Buffalo (SUNY)

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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

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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

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Comparison of three paradigms
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OBS based on Just-Enough-Time
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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 tbl (offset time at node i
  
• Efficient utilization of BW (as well as FDLs if
  any)

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BW Utilization vs Latency

• Comparing JET and NoDR

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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)

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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

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Extra Offset Time for Priority
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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

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QoS Performance Improvement

• Blocking probability after 6 hops (offered load
  0.8)

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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