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Optical Burst Switching CSIT 560 Internet Infrastructure: Switches and Router Prepared By Eric Lo Date: 6 Dec 2005 Agenda Introduction – – OBS Concept – – – – – – Basic Motivation Burst Assembly Just Enough Time (JET) Scheduling Content Resolution QoS Potential problem Other research – – – – R&D activities in Japan Dual header OBS Synchronized OBS Layered Architecture Introduction Circuit Switching – – – Bandwidth inefficient of bursty data (internet traffic). Frequent long circuit setup Waste bandwidth during off/low-traffic periods Packet Switching – – – A packet contains a header (e.g., addresses) and the payload (variable or fixed length). Each node needs to buffer, process the header, and send it to the next hop. Statistic sharing of link BW among packets with different source/destination (Statistical multiplexing) Introduction (Bursty traffic) Left: – – Poisson traffic (voice) smooth at large time scales and mux degrees Right: – – data (IP) traffic, bursty at all time scales and large mux degrees circuit-switching not efficient (max >> avg) Motivation Problems: – – – – Explosive traffic growth and bursty Traffic pattern Lack of optical buffer (RAM) for packet switching. Fiber delay lines (FDLs) are bulky and provide only limited & deterministic delays Need fast processing power of header and payload Solution: – – – Find a method between circuit switching and packet switching. To increase the Bandwidth efficiency. That’s Optical Burst Switching comes into the picture. Agenda Introduction – – OBS Concept – – – – – – Basic Motivation Burst Assembly Just Enough Time (JET) Scheduling Content Resolution QoS Potential problem Other research – – – – R&D activities in Japan Dual header OBS Synchronized OBS Layered Architecture OBS Concept Burst Assembly (and Disassembly) at Edge – Burst Switching/Reservation Protocol – – – client data (e.g., IP packets) assembled into bursts Control packet (CP) sent an offset time t ahead of burst Dedicated control channel (out-of-band signaling) for CP No fiber delay lines (FDLs) nor O/E/O conversions for burst at any intermediate (core) nodes Photonic Burst Switching Fabric inside Core – Leverages the best of optics (for burst switching) and electronics (for CP processing and fabric control) Packet (a) and OBS(b) switching Header recognition, processing, and generation Payload C Header A Setup Synchronizer 1 2 A New headers (a) Control wavelengths Control packets D C 2 2 O/E/O 1 Control packet processing (setup/bandwidth reservation) Offset time 2 B 2 FDL’s 1 Data wavelengths 1 2 Fixed-length (but unaligned) B Switch 1 Incoming fibers 2 Switch 1 1 Data bursts (b) D Optical Burst Switching Node • Multiple data channels share one control channel. Data bursts remain in optical domain while CPs go through O/E/O conversions Burst Assembly – Step 1 Time or length threshold is reached Control channel Assembly queues for different egress nodes ATM Cell IP Packet SONET Frame Data channel Burst Assembly Node Burst Assembly – Step 2 A CP is generated and sent out Control channel Assembly queues for different egress nodes ATM Cell IP Packet SONET Frame Data channel Burst Assembly Node Burst Assembly – Step 3 Control channel Assembly queues for different egress nodes ATM Cell IP Packet SONET Frame Data channel Burst Assembly Node Just-Enough-Time (JET) An offset time between Control packet(CP) and burst – No fiber delay line (FDL) required to delay the burst when CP is processed and switch fabric is configured. CP carries the burst length information – Facilitates delayed reservation (DR) for intelligent, efficient allocation of BW and FDL (if any), including look-ahead scheduling. JET – Step 1 Offset = T CP arrives the OEO node at time t1 OEO OEO OOO OOO JET – Step 2 CP goes through O/E conversion and configure switch fabric OEO OEO OOO OOO JET – Step 3 CP goes through E/O conversion and leaves O/E/O node at time t1+ OEO OEO OOO OOO JET – Step 4 When burst arrives at the intermediate node, the switch fabric is already configured OEO OEO OOO OOO JET – Step 5 Offset = T- OEO OEO OOO OOO Without any delay, the burst goes through the optical switch fabric JET – Offset time Control packet can leave right after = D s (s is the switch setting time) Delayed Reservation (DR) DR leads to efficient allocation of BW and any available FDLs (though not shown). Without DR, 2nd burst will be dropped in both cases (and FDLs will be wasted in Case 2). Burst Scheduling In general approach, it is to schedule incoming bursts in the order of the CP arrivals. It leaves several free time intervals between the scheduled reservations called void. – – Without void filling (only use open interval such as LAUC). With void filling (Can minimize starting and ending void such as LAUC-VF) Burst Scheduling Burst Scheduling – New approach Ordered Scheduling is to schedule bursts in the order of the burst arrivals instead of header arrivals. It places incoming reservations in a buffer and defers the scheduling until just before the actual burst arrives. Able to remove the negative effect of header arrival dynamics. Ordered Scheduling Content Resolution (1) When multiple bursts compete for the same output channel, how to avoid/reduce burst loss? Three major strategies – – – Deflection in space, time and wavelength Preemption of an existing reservation Segmentation of a burst into smaller pieces Content Resolution (2) Deflection – – – Space domain: applying deflection routing Wavelength domain: use a different wavelength via wavelength conversion Time domain: wait using a fiber delay line Segmentation – Drops, deflects or preempts one or more segments instead of an entire burst QoS Different offset time is assigned to different service classes over JET OBS networks so as to provide differentiated services in terms of burst loss probability for classes of different priorities. Difficult to maintain the same offset time in all routers. May starve lower priority bursts because higher priority bursts always have more opportunities to make wavelength reservation It may be unfair to long bursts of low priority because it is hard to find a long gap to serve a long burst of low priority in an almost full schedule table. QoS – New approach (PWRP) Preemptive Wavelength Reservation Protocol (PWRP) – Each class is associated with a predefined usage limit. Each switch maintains a usage profile for a class per output link and monitors the current usage of each class. QoS - PWRP Potential Problem Tends to have a high blocking probability May require an uneconomically large increase in network transmission capacity. Agenda Introduction – – OBS Concept – – – – – – Basic Motivation Burst Assembly Just Enough Time (JET) Scheduling Content Resolution QoS Potential problem Other research – – – – R&D activities in Japan Dual header OBS Synchronized OBS Layered Architecture Other Research R&D activities in Japan Other Research Dual header optical burst switching (DOBS) Other Research Synchronous Optical Burst Switching (SOBS) Other Research A Layered Architecture for Supporting Optical Burst Switching References OBS Forum tutorial slides by Chunming Qiao R. Parthiban, C. Leckie, A.Zalesky, AV.Tran*, Does Optical Burst Switching have a role in Core Network ? Farid, Vinod, Joel, A Layered Architecture for Supporting Optical Burst Switching Sami Sheeshia, Chun Qiao, Synchronous Optical Burst Switching Neil Barakat and Edward H Sargent, Dual Header Optical Burst Switching: A New Architecture for WDM Burst-Switched Networks Ken, etal., Photonic Network R&D Activities in Japan Wanjiun Liao, Chi-Hong Loi, Providing Service Differentiation for Optical-Burst-Switched Networks Thank you!