Performance comparison of scheduling algorithms for IPTV traffic over Polymorphous OBS routers Jos´ e Alberto Hern´ andez V´ ıctor L´ opez, Jos´ e Luis Garc´ ıa Dorado and Javier Aracil Networking Research Group Universidad Aut´ onoma de Madrid, Spain email: [Jose.Hernandez]@uam.es ICTON-MW’07 December, 2007 J. A. Hern´ andez et al Scheduling algorithms for IPTV in POBS
Contents ◮ Introduction to OBS and to POBS ◮ IPTV traffic and its characteristics ◮ Scheduling algorithms for combining best-effort traffic with synchronous reservations for IPTV traffic: FF, RR, SRR, SSRR ◮ Scenario definition and experiments ◮ Conclusions J. A. Hern´ andez et al Scheduling algorithms for IPTV in POBS
Optical Burst Switching review In OBS networks: ◮ Edge nodes aggregate incoming traffic into optical data bursts (1 optical burst contains many packets). ◮ Core nodes switch data bursts all-optically (no O/E/O conversion) accross the DWDM physical layer. J. A. Hern´ andez et al Scheduling algorithms for IPTV in POBS
Burst-assembly process In an edge OBS node: ◮ For each data burst, a Burst-Control Packet (BCP) is generated and transmitted after the data burst is assembled. ◮ Typically, the BCP contains the size of the data burst and expected arriving time at the intermediate nodes. It reserves resources for the forthcoming data burst. ◮ The time difference between the BCP and its associated data burst is known as offset time . J. A. Hern´ andez et al Scheduling algorithms for IPTV in POBS
Polymorphous OBS ◮ In the Polymorphous OBS architecture, a BCP (with extended attributes) may reserve: ◮ A full wavelength (1) ◮ Synchronous fixed-size time slots (2) ◮ Asynchronous best-effort capacity (3) Control Unit Control Plane BCPs 1 2 2 2 3 3 �� 1 T 2 2 2 3 3 �� 2 1 3 3 3 3 �� 3 Full wavelength reservation TDM circuit reservation OXC ◮ The synchronous reservations may be used by services which require periodic capacity, but do not need a full wavelength (for instance, IP TeleVision). Goal Find the best way to combine IPTV reservations with asynchronous best-effort traffic that brings best performance (less blocking probability). J. A. Hern´ andez et al Scheduling algorithms for IPTV in POBS
IPTV Traffic characteristics ◮ Observed characteristics of IPTV service from a Spanish IPTV service provider: ◮ MPEG-2 encoding ◮ 4.16 Mbps per TV channel ◮ Constant Bit Rate stream with packet interarrival times of 2 , 5 ms ◮ This configuration belongs to Standard Definition TV J. A. Hern´ andez et al Scheduling algorithms for IPTV in POBS
Scheduling algorithms for combining IPTV traffic together with best-effort ◮ First fit (FF): All TV channels are inserted together over the same wavelength. ◮ Round Robin (RR): TV channels are grouped together and allocated over different wavelengths following a Round Robin fashion. T on = N ch x T 1ch T on = N ch x T 1ch D D D D D �� 1 �� 1 T on +T off = 2.5ms T on +T off = 2.5ms D D D D �� 2 �� 2 ... ... D D D D D D �� M �� M First Fit Round Robin J. A. Hern´ andez et al Scheduling algorithms for IPTV in POBS
Scheduling algorithms for IPTV traffic together with best-effort (2) ◮ Synchronous Round Robin (SRR): Channels are splitted into different wavelengths, and transmitted at the same time in each lambda. ◮ Synchronous Shifted Round Robin (SSRR): Same as SRR but the time is shifted for different lambdas. T on +T off = 2.5ms T on +T off = 2.5ms D D D D D D D ... ... �� 1 �� 1 T on = N ch x T 1ch / M D D �� 2 D D D D D ... ... ... T on = N ch x T 1ch / M �� 2 ... D D D D D D ... ... �� M �� M Synchronous Round Robin Synchronous Shifted Round Robin J. A. Hern´ andez et al Scheduling algorithms for IPTV in POBS
Analytical approximations ◮ Using the Erlang-B formula, ignoring the retroblocking effect of OBS (which arises when offset times are highly variable): P block = P block | off P ( off ) + P block | on P ( on ) ◮ First Fit: T on + D E B ( I , M − 1) + T off − D P block = E B ( I , M ) T off + T on T off + T on ◮ Synchronous Round Robin: T on + D + T off − D P block = E B ( I , M ) T off + T on T off + T on ◮ D = burst size, M = Number of wavelengths, I = Offered traffic J. A. Hern´ andez et al Scheduling algorithms for IPTV in POBS
Experiments: Scenario definition ◮ We have considered 192 channels transmitted over the POBS network. 192 × 4 , 16 Mbps = 799 Mbps over a M = 8-wavelength with capacity 10 Gbps per wavelength. ◮ T on + T off = 2 , 5 ms as measured, T off = 2 , 3 ms for FF and RR, and T off = 2 , 475 ms for SRR and SSRR. ◮ T on = N ch × B ch = 192 × 4 , 16 Mbps = 8 % × 2 , 5 ms FF, RR C 10 Gbps ◮ T on = N ch × B ch = 192 × 4 , 16 Mbps = 1 % × 2 , 5 ms SRR, SSRR M × C 8 × 10 Gbps ◮ Load: ρ = λ D M , where D ∈ { 0 , 025 , 0 , 125 , 0 , 25 , 0 , 5 ms } For instance, D = 150 packets × 1024 · 8 = 0 , 125 ms 10 Gbps J. A. Hern´ andez et al Scheduling algorithms for IPTV in POBS
Simulations and results (1) D=0.025 ms D=0.125 ms 1 1 0.1 0.1 Blocking Probability Blocking Probability 0.01 0.01 0.001 0.001 1e-04 FF 1e-04 FF RR RR 1e-05 1e-05 SRR SRR SSRR SSRR 1e-06 1e-06 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 ρ ρ D=0.25 ms D=0.5 ms 1 1 0.1 0.1 Blocking Probability Blocking Probability 0.01 0.01 0.001 0.001 1e-04 1e-04 FF FF RR RR 1e-05 SRR 1e-05 SRR SSRR SSRR 1e-06 1e-06 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 ρ ρ ◮ FF and RR shows best performance, especially for large D . ◮ Hence, it is better to merge TV channel transmition than split them over different wavelengths. J. A. Hern´ andez et al Scheduling algorithms for IPTV in POBS
Simulations and results (2) ρ =0.5 1 FF RR SRR SSRR Blocking Probability 0.1 0.01 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 D (ms) ◮ FF and RR shows best performance, and same behaviour regardless of burst size D . J. A. Hern´ andez et al Scheduling algorithms for IPTV in POBS
Simulations and results (3) D=0.025 ms D=0.125 ms 1 1 p s p s p t p t 0.1 0.1 Blocking Probability Blocking Probability 0.01 0.01 0.001 0.001 1e-04 1e-04 1e-05 1e-05 1e-06 1e-06 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 ρ ρ D=0.25 ms D=0.5 ms 1 1 p s p s p t p t 0.1 0.1 Blocking Probability Blocking Probability 0.01 0.01 0.001 0.001 1e-04 1e-04 1e-05 1e-05 1e-06 1e-06 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 ρ ρ J. A. Hern´ andez et al Scheduling algorithms for IPTV in POBS
Simulations and results (4) D=0.025 ms D=0.125 ms 1 1 p s p s p t p t Blocking Probability Blocking Probability 0.1 0.1 0.01 0.01 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 ρ ρ D=0.25 ms D=0.5 ms 1 1 p s p s p t p t Blocking Probability Blocking Probability 0.1 0.1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 ρ ρ J. A. Hern´ andez et al Scheduling algorithms for IPTV in POBS
Summary and conclusions ◮ Main conclusions: ◮ FF and RR show similar performance results and are the best strategies among the four scheduling algorithms studied. ◮ It is better to group all channels and transmit them at once than splitting them over different wavelengths, especially when D is comparable to T off . ◮ The analytical approximations for FF and SRR are shown to be accurate. J. A. Hern´ andez et al Scheduling algorithms for IPTV in POBS
Questions Thank you!! J. A. Hern´ andez et al Scheduling algorithms for IPTV in POBS
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