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

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

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

Comparison of three paradigms

OBS based on Just-Enough-Time

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 t b to t b +l (offset time at node i : Efficient utilization of BW (as well as FDLs if any)

BW Utilization vs Latency Comparing JET and NoDR

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)

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”

Extra Offset Time for Priority

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

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

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