2002-10-22 Yang Chen (Lander)1Optical Burst Switching (OBS): The Dawn of A New Era in Optical NetworkingPresented by Yang Chen (LANDER)Yang Chen (Lander)22002-10-22Outline Historical Review Burst reservation Burst assembly OBS node Towards the Optical Internet ConclusionYang Chen (Lander)32002-10-22Burst switching--Historical Review Electronic Domain Design for competition with ATM, etc. “Burst switching—An update”, Amstutz 1989 Optical Domain Based on optical TDMA system, centralized control Highball projects, U. of Delaware 1990 Common Issue Centralized transmission arrangement/schedulingYang Chen (Lander)42002-10-22Burst switching--Historical Review ATM wins? Compared with primitive Burst switching, ATM is more cost effective Research on burst transmission protocols went on. In ATM network, I. Widjaja 1996 Tell and Go (TAG)/Tell and Wait  In Optical Network, G. Hudek and D. Muder 1995  Connect/Confirmation (CC), TAG, Reservation/Scheduling with Just-in-Time (JIT) SwitchingYang Chen (Lander)52002-10-22WDM!! Huge bandwidth provisioning. How to use this bandwidth efficiently? Wavelength Routed Network Static connection, inefficient bandwidth allocation Optical Packet Switching (OPS) High processing speed requirement, big overhead, no practical optical buffer and control unit Opaque WDM network O/E/O conversion is required at each node for traffic groomingYang Chen (Lander)62002-10-22Optical Burst Switching ---- A Reborn of Burst Switching  What is OBS? Separation of transmission and control Offset time between control packet and data burst Out of band signaling  Intermediate transmission granularity Advantages of OBS More flexible and efficient compared with wavelength routed network. More scalable and cost effective compared with OEO approaches Smaller overhead and more practical compared with OPS.Yang Chen (Lander)72002-10-22OBS—A General IdeaYang Chen (Lander)82002-10-22OBS NetworkYang Chen (Lander)92002-10-22Compared with O/E/O approachesYang Chen (Lander)102002-10-22Outline Historical Review Burst reservation Burst assembly OBS node Towards the Optical Internet ConclusionYang Chen (Lander)112002-10-22Burst Reservation----Overview Two way reservation Forward reservation Backward reservation Example: WR-OBS  One way reservation With/ Without offset time With/ Without burst length info Examples: TAG, JIT, JET.Yang Chen (Lander)122002-10-22Two Way Reservation ---- WR-OBS End-to-End connection setup Fast-circuit like switching Pro Guaranteed transmission Con Longer delay and inefficient bandwidth utilizationYang Chen (Lander)132002-10-22Yang Chen (Lander)142002-10-22One Way Reservation ---- TAG BW reserved right after control packet is processed No burst length information, BW released with: an explicit release packet (problematic if lost) or frequent refresh with time-out (overhead) T = 0 (or negligible) , otherwise wastes BW FDLs per node > max{proc. + switch time} Later evolved to adopt JET’s featuresYang Chen (Lander)152002-10-22Yang Chen (Lander)162002-10-22One Way Reservation ---- JIT Based on Tell-And-Wait (TAW)  Just-In-Time (JIT) with centralized control Sends a request, and the centralized scheduler decides the time to transmit, and informs the sender. JIT with distributed reservation (RIT)  A scheduler on every switch, globally synchronized JIT with two-way hop-by-hop reservation  Similar to fast circuit-switching under distributed control. Differ from RIT in that there is no burst length info. Based on TAG and JET  Uses offset time to avoid FDLs, and burst length info for reservation as in JET but no delayed reservation.Yang Chen (Lander)172002-10-22Yang Chen (Lander)182002-10-22Just Enough Time (JET) signaling Proposed in 1997 by Yoo and Qiao. Basic ideas Carrying information about the burst length in the control head to increase the bandwidth utilization Cut through switching configuration using an offset time to reduce end-to-end delayYang Chen (Lander)192002-10-22Yang Chen (Lander)202002-10-22JET signaling Compared with TAG JET does not require FDL set to compensate for the configuration delay; shorter delay Compared with JIT,  JET uses the bandwidth more efficiently due to possible Delayed Reservation (DR),  However, it has stricter synchronization requirement It is well adopted by researchersYang Chen (Lander)212002-10-22Delayed ReservationYang Chen (Lander)222002-10-22One way? Or two way? Performance parameter Throughput Burst delay Bandwidth requirement Determining factors End-to-end propagation delay Optical Device configuration time Burst transmission time Tradeoff has to be made regarding to network dimension, burst size, transmission speed, etcYang Chen (Lander)232002-10-22Routing and Wavelength Assignment Routing Determine a path from source to destination Wavelength assignment Determine which wavelength is used for data transmission Wavelength conversion Two way reservation has central routing and wavelength assignment. Less burst loss when no wavelength converter provided, (Tradeoff: central control, extra delay)  One way reservations generally assume full wavelength conversion. Otherwise, multiple wavelength reservations or priority-based wavelength assignment will be considered in order to reduce burst loss.Yang Chen (Lander)242002-10-22Priority based Wavelength AssignmentYang Chen (Lander)252002-10-22Outline Historical Review Burst reservation Burst assembly OBS node Towards the Optical Internet ConclusionYang Chen (Lander)262002-10-22Burst AssemblyYang Chen (Lander)272002-10-22Burst Assembly (cont.)Yang Chen (Lander)282002-10-22Characteristic of Assembled Traffic Recent studies showed that  The assembly traffic follows Gaussian distribution. X. Yu and K. Laevens, Opticomm 2002 Long range dependence still exists with traffic smoothing effect The smoothing effect on the traffic will enhance the performance of OBS network compared with OPS in a scenario with/without FDL setYang Chen (Lander)292002-10-22Burst assembly does take effect Why the burst assembly is so important? Simply changing the burst length will affect the whole network’s performance was recently reported Although inter-arrival time