Optical Burst Switching for Unbuffered Span-Constrained Networks

1. Optical Burst Switching for Unbuffered Span-Constrained Networks R. Rajaduray, D. J. Blumenthal Workshop on Optical Burst Switching Oct 3 2005 BroadNets Conference Optical Communications and Photonic Networks Department of Electrical and Computer Engineering University of California, Santa Barbara This work was funded by an Intel Grant

2. Acknowledgements • Technical assistance provided by: • Nicholas Burgan-Illig (part of the Research Internship in Science and Engineering program) • Dr Shlomo Ovadia and Dr Mario Paniccia at Intel Corporation

3. Outline • Introduction • LER Architecture • Predictive Bandwidth Reservation

4. Why consider all-optical networks • Graph shows traffic on all US backbones • Growth of 100% per year • Possible solution: All-optical networks • Likely that all-optical networks will be unbuffered • Cost, complexity • No buffering for congestion control or contention resolution Andrew Odlyzko, Crisis and mythology in the telecom world, CommsDaySummit, Sydney, Australia, Feb. 16, 2004.

5. Why OBS for Unbuffered Span-Constrained Networks? 1 • OBS: excellent choice for unbuffered all-optical networks • Delayed reservation1 feature improves performance • Lower processing overhead per unit data compared to OPS • More efficient bandwidth utilization compared to OCS • Unbuffered network performance degrades with hop count2 • Potential area of application: span-constrained networks • Span-constrained networks have rapidly grown in importance3 • Examples: Local Area Networks (LANs) and Storage Area Networks (SANs) • Hop count ≤ 4, Span distance ≤ 10 km 1Yoo et al SPIE Vol. 3230, pp. 79-90, Nov. 1997 2 M. Yoo et al OFC 1999 p. 177-79 3 S. Ovadia et al IEEE Communications Magazine vol 41, issue 11, Nov. 2003 pp. S24 - S32

6. OBS Unbuffered Span-Constrained Network Reference Model • 3 level hierarchy • Electronic terminals generate packets at lower bit rate • Concentrator multiplexes and aggregates electronic packets into higher bit rate optical bursts • Optical bursts switched through central subnetwork (core network) • Developed reference model based on hierarchy • Label Edge Router (LER) acts as concentrator and aggregator • Core network of unbuffered Photonic Burst Switches (PBSs) • PBSs forward bursts from ingress to egress edge router • Just Enough Time (JET)1 signaling used to set up path for bursts • Schedules using Latest Available Used Channel with Void Filling (LAUC-VF)2 1 Qiao et al JHSN vol 8 pp. 69-84 1999 2 Xiong et al IEEE JSAC vol 18 no 10 pp. 1838–51 Oct 2000

7. Outline of Presentation • Demonstrate LER architecture • Chose design parameters from representative set which led to lowest latency • Show that these parameters do not limit throughput • Compare this LER performance to similar for OPS system • Demonstrate contention avoidance scheme for core called Predictive Bandwidth Reservation (PBR) • PBR is designed to operate in parallel with LER • Show thatit is able to reduce loss in network

8. Outline • Introduction • LER Architecture • Predictive Bandwidth Reservation

9. Label Edge Router (LER) in OBS Unbuffered Network • Label Edge Router (LER) acts as aggregator and concentrator • Latency can be significant1 • Throughput may be limited due to LER • Designed LER architecture: • Chose a combination of parameters from a set of combinations which led to lowest latency • Ensured that choice did not limit throughput • Compared performance to LER for Optical Packet Switched (OPS) system • LER for OPS system had throughput limitation due to delayed reservation 1Rajaduray et al IEEE J Lightwave Tech pp. 2693-2705 vol 22 no 11

10. OBS LER Architecture Stage 2 Stage 3 Stage 4 Stage 1 (1 Gb/s) (10 Gb/s) 1 × 10 Gb/s Optical Output 1 1 7 10 Output TX Queue 7 Burst Queues 7 Burst Assembly Units • Stage 1 (Sorting Router): Packets from 10 input channels (1 Gb/s) sorted and sent to 1 of 7 output channels (10 Gb/s) feeding burst assembly units (one per destination) • iSLIP1 protocol used • Internal speed-up to 10 Gb/s from 1 Gb/s • Stage 2 (Burst Assembly): Packets are assembled into bursts within each assembly unit, and sent out • Stage 3 (Transmission Scheduling): Fully assembled bursts queued in burst queues and transmitted to output queue over switch fabric • Stage 4 (Output Transmission): Control label transmitted followed by burst an offset time after according to JET protocol. Assume processing time per-hop of 1 µs 1 N. McKeown, ”The iSLIP scheduling algorithm for input-queued switches”, IEEE/ACM Trans Networking April 1999 pp. 188–201

11. 0 OBS LER Burst Assembly Algorithm Incoming Packets BURST ASSEMBLY Outgoing Bursts T Fmax Fmin • Assume burst assembly starts at time 0 • Burst size, minimum; and maximum threshold burst sizes are normalized to max data receivable in time T • If before T, normalized burst size ≥ normalized max threshold, send out burst • Demonstrated in animation • Soft threshold: Keep last packet which pushed burstsize over thresholdx • Hard threshold: Start a new burst with last packet • If at T: • Normalized burst size≥normalized minimum threshold, send out burst • Elsecontinue aggregating until normalized burst size≥normalized minimum threshold • Choice of burst assembly parameters impacts LER latency

12. Choice of OBS LER Burst Assembly Parameters • Norm min threshold (Fmin) = 0.025, norm max threshold(Fmax) = 0.085 leads to lowest latency among set of design parameters (shown in graph) • Reduces burst assembly and transmission time between stages • Choice of T determines impact of self-similarity • Can affect variance of burst assembly or variance of burst size • T = 64 μs to negate impact of self-similarity

13. LER Design Guidelines • Design of Stage 2: • Burst assembly parameters have been chosen (Fmin = 0.025, Fmax = 0.085, T = 64) • Hard threshold preferred over soft threshold algorithm • Lower mean and standard deviation of inter-stage transmission time • Design of Stage 3: • Choice made from Longest Queue First (LQF), Oldest Burst First (OBF) and Random selection • OBF leads to lowest Stage 3 waiting time variance amongst chosen techniques

14. Comparison to Optical Packet Switch Label Edge Router (OPS LER) • Setting Fmin = 0.025; Fmax = 0.085; T = 64: no limit on OBS LER throughput • Compared OBS LER to 2-stage OPS LER • Latency of OPS LER lower (85 to 93%) than Optical Burst Switched (OBS) LER • Throughput of OPS LER limited by JET control channel overhead • For typical processing time of 1 μs; hop count and packet length distribution considered; throughput of OPS LER limited to 0.7

15. Conclusions for Label Edge Router (LER) • Designed an LER architecture for an OBS unbuffered span-constrained network • Made choices from set of parameters • Choices made led to lowest mean or variance of latency • Choices did not limit OBS LER throughput • Compared to Optical Packet Switched LER • Latency of OPS LER is lower than minimum latency of Optical Burst Switched LER • OPS LER throughput limited due to control signaling overhead

16. Outline • Introduction • LER Architecture • Predictive Bandwidth Reservation

17. LER2 LER3 4 LER1 PBS2 PBS1 LER4 4 4 4 PBS3 4 4 4 4 4 4 4 LER8 LER5 PBS4 PBS5 4 LER7 LER6 Motivation for Predictive Bandwidth Reservation (PBR) • Desire high bandwidth efficiency, low loss; and low latency in network core • Statistical multiplexing using BW reservation/queueing over upstream links of routes - can increase BW efficiency (orange links in route) • Dedicated wavelengths for downstream links to reduce loss (black links in route) • Contention over upstream links may lead to loss • Contention resolution – reactive solution to contention • Contention avoidance through bandwidth reservation - proactive solution • Introduced Predictive Bandwidth Reservation (PBR) • Bandwidth reservation in parallel with edge router operation • Uses predictions made based on past statistics after monitoring LER channels

18. DP Reserved ΔAC ΔLP 2ΔLP ΔAT ΔAT - Δoffset Basic PBR LER PBS Stage 1 Stage 2 Stage 3 Stage 4 T = 0 PBS PBR Processor Prediction using LER statistics • PBR request sent to PBS either when burst assembly starts (Stage 2) or ends (Stage 3) • Choice depends on which one minimizes latency (Stage 3 is shown) • Duration of reservation set to Fmax× T (Stage 2-initiated), or burst duration (Stage 3-initiated) • Requested start time of reservation set using predictions from past statistics after monitoring LER channels and can depend on propagation delay between LER and PBS • PBS PBR processor makes reservation in desired outgoing PBS channel at first avail time • Send confirmation to the LER • LER sets transmission deadline for burst transmission to make desired time • Control label precedes burst transmission by JET offset

19. A Need for improved PBR techniques Burst B misses reservation t5 - ΔLP t2 - ΔLP PBS Switch Fabric LER Output 1 A B t1 t2 • Bursts only allowed to make 1 reservation • If burst misses reservation, transmitted at next available time • May collide with other burst or reservation and be dropped • Major cause of burst drop is reservation overlap • Burst A makes a reservation on output channel 1 of PBS • Burst B makes reservation on output channel 2 which overlaps burst A reservation • Burst B is delayed, misses reservation and may be dropped • Basic PBR must be improved to deal with overlapping reservation problem Output 2 B B t3 t4 t5 PBS PBR Processor

20. Bandwidth Resource Allocation allowance Reserved T = 0 ΔLP T = 2ΔLP PBR-BRA LER PBS Stage 1 Stage 2 Stage 3 Stage 4 PBS PBR Processor ΔAC ΔAT Prediction using LER statistics ΔAT - Δoffset • Make Bandwidth Reservation Allocation (BRA) allowance for reservation overlap • Define normalized BRA duration as ΔBRN • Reservation duration after BRA allowance is (1 + ΔBRN) × (reservation duration) • Basic PBR is special case with ΔBRN = 0 • Burst loss reduced with ΔBRN, but reservation system becomes unstable • Arrival rate to reservation system exceeds service rate of reservation system • Can limit throughput of network • Need to maintain stability while reducing burst loss

21. A PBR-BRA with Locally Aware Reservation (PBR-BRA-LAR) LER B B • Set BRA allowance accordingly to not cause instability • Assume that start time of requested reservation = start time of potential transmission • Ensure potential transmission times do not overlap • Change if necessary • Example: • Potential transmission time of burst A at LER is recorded • Burst B intends to make reservation • Potential transmission overlaps potential transmission of burst A • Reservation time is changed • Can add extra backoff duration to new requested start time • Marginally improves loss, but can lead to reservation system instability t1 - ΔLP t3 - ΔLP t2 - ΔLP t4 - ΔLP t5 - ΔLP Initiated at LER

22. t3 t4 PBR-BRA with Core Allocation after Monitoring (PBR-BRA-CAM) PBS Switch Fabric LER Output 1 A t1 t2 • Core Allocates bandwidth after Monitoring (CAM) • PBS scans previous reservations for bursts from same LER • Ensures that requestedreservation time does not overlap previous reservation • Changes requested start of reservation time if necessary • Example: • Burst A makes a reservation for time [t1, t2] on output channel 1 • Burst B intends to make reservation • Reservation time checked • Time changed if overlap with burst A reservation time • Lowest loss performance, but limited by reservation system instability • Increased BRA allowance leads to instability at lower network utilization Output 2 B t2 t5 PBS PBR Processor Initiated at PBS

23. LER2 LER3 4 LER1 PBS2 PBS1 LER4 4 4 4 PBS3 4 4 4 4 4 4 4 LER8 LER5 PBS4 PBS5 4 LER7 LER6 Assumptions • Use burst assembly parameters from previous section: Fmin = 0.025; Fmax = 0.085; T = 64 • Reservation initiated from Stage 3 over 2nd link of route (Example of red link of route, route links ≥ 3) • Bursts can only make 1 reservation • If burst is late, transmit at next available time • If burst is delayed and collides with another reservation slot on same link, the burst is dropped

24. Comparison of Loss across Techniques • Graph shows comparison of no PBR, basic PBR and improved PBR techniques • Increasing BRA allowance improves performance (compare ΔBRN = 0 vs ΔBRN = 2) • Improvement limited by instability • Using LAR improves performance • Marginal improvement for backoff factor ΔGN > 0 • PBR-BRA-CAM offers burst loss ≤ 0.1% • Increased BRA allowance improves performance, but instability sets in earlier • For BRA allowance = 0, reservation system stable until region of ICU = 0.8 to 0.9 • PBR-BRA-CAM allows network to meet loss requirements for VoIP (req loss = 1%) and multimedia (req loss = 10%) at 80% utilization • Without PBR-BRA-CAM, utilization is limited to 4% for VoIP and 40% for multimedia

25. Comparison of Loss and Latency • For ICU = 0.4, possible to trade off latency for loss using PBR • For ICU = 0.8, trade-off is only possible for PBR-BRA-CAM • Overlapping reservation problem insufficiently handled by basic PBR • At ICU = 0.9, OBS without PBR has best throughput and latency performance

26. Conclusions from Predictive Bandwidth Reservation (PBR) Work • Demonstrated contention avoidance using bandwidth reservation (PBR) • Demonstrated improvements to overcome overlapping reservation problem • PBR-BRA-CAM can result in loss ≤ 0.1% up to 80% utilization • Enables network to meet loss requirements for VoIP and multimedia at 80% utilization • Increased loss comes at expense of latency • At low utilization, possible to trade of loss with latency using Basic PBR • At high utilization, tradeoff only possible with PBR-BRA-CAM

27. Overall Conclusions • Designed an LER architecture for an unbuffered network • Chose parameters from set which led to lowest latency • No throughput limitation for parameters • LER for OPS system had throughput limitation • Demonstrated contention avoidance using Predictive Bandwidth Reservation • Designed improvements to PBR as well • Using PBR-BRA-CAM, can result in low loss • Network can meet loss req for VoIP and multimedia at 80% utilization • Increased loss comes at expense of latency

28. THANK YOU