1 Optical Packet Switching Techniques Walter Picco MS Thesis Defense December 2001 Fabio Neri, Marco Ajmone Marsan Telecommunication Networks Group

2 Overview Introduction and motivations Goals of the thesis State-of-the-art and enabling technologies SIMON: an optical network simulator Optical networks design Obtained results

3 The need of optics Future network requirements: High bandwidth capacity Flexibility, robustness Power supply and equipment footprint reduction Optics offers a good evolution perspective

4 Optical framework today Point to point communications Circuit switching with packet switching electronic control why ? Optical packet switching: –no optical memories –slow optical switches

5 Optical packet switching Bandwidth is not a problem Network cost is in the commutation New protocols and architectures needed New tools to measure performance New design techniques more

6 Overview Introduction and motivations Goals of the thesis State-of-the-art and enabling technologies SIMON: an optical network simulator Optical networks design Obtained results

7 Goals New optical network simulator TopologySimulationPerformance

8 Goals New analysis and design method for optical networks ResourcesAnalysisTopology

9 Overview Introduction and motivations Goals of the thesis State-of-the-art and enabling technologies SIMON: an optical network simulator Optical networks design Obtained results

10 Transmitting data Wavelength Division Multiplexing: the huge bandwidth of an optical fiber is divided in many channels (colors) Each channel occupies a different frequency slot

11 Storing data Optical RAM is not available yet Fiber Delay Lines (FDLs) are used instead FDLs Forward usageFeedback usage FDL

12 Processing data Electronics limits the speed in data forwarding Optical 3R regeneration (and wavelength conversion) is now possible Physical layer is not a matter of concern All-optical solutions are currently at the study 3R 1 2

13 Switching data Tomorrow (a possibility): Micro Electro Mechanical Systems Today: Semiconductor Optical Amplifiers

14 Overview Introduction and motivations Goals of the thesis State-of-the-art and enabling technologies SIMON: an optical network simulator Optical networks design Obtained results

15 Fixed routing implementation Not good for WDM The starting simulator: CLASS Simulator of ATM networks Topology independent Adaptable tool } fiber channel

16 CLASS modifications Dynamic routing strategy Each WDM channel must be listed in the network description file Maximum flexibility in the network description } fiber channel

17 SIMON node architecture

18 Time division Slotted network: t t t C 1 C 2 C 3 t 0 timeslot P 1 P 2 t 1

19 Overview Introduction and motivations Goals of the thesis State-of-the-art and enabling technologies SIMON: an optical network simulator Optical networks design Obtained results

20 Designing WDM networks Given: Network topology and the traffic matrix Find: Number of WDM channels on each link Optimizing: Network throughput Meeting a cost constraint: Network cost  commutation Fixed number of ports for all the switches

21 The optimization problem Mathematical statement: Find minimum (maximum) of a non-linear function in the discrete domain, meeting some constraints NP-complete problem Only heuristic solutions are possible

22 Proposed approach 1)Find: –P tot : packet loss probability of the whole network –n i : number of WDM channels on link i 2)Elaborate a heuristic solution to find the minimum of P tot

23 Link model Classical queueing theory: M/M/L/k queue server  WDM channel buffer slot  FDL k 1 2 L servers buffer more

24 Node model Input fibers Output fibers

25 FDLs can’t be modeled as a simple buffer –discrete storage time –noise addition at each recirculation All the FDLs of a node are shared among the different queues Model limitations channel FDL A B

26 Network model The packet loss probability ( P f ) of a flow is: The packet loss probability ( P tot ) of the whole network results: First step completed

27 Cost constraint: (channel ports + FDLs ports) = constant optimum balance  optimum solution Searching the minimum Network connectivity (number of channel ports) Storage capacity (number of FDLs) Level

28 Heuristic approach Starting topology: maximum connected Iteration steps: –the current topology is perturbed –if the perturbed topology has a lower P tot the topology is modified Highest possible level

29 Heuristic approach Topology perturbation: –all the links are analyzed –the link that modified gives the lower P tot is memorized cancelled added

30 Overview Introduction and motivations Goals of the thesis State-of-the-art and enabling technologies SIMON: an optical network simulator Optical networks design Obtained results

31 General backbone: topology Node User

32 General backbone: throughput Total network load [Gbps] Fraction of packets successfully transferred M/M/L/k (4 MR) M/M/L/k (  MR)

33 General backbone: delay Packets net delay M/M/L/k (4 MR) M/M/L/k (  MR) Total network load [Gbps]

34 USA backbone: topology

35 USA backbone: throughput M/M/L/k (4 MR) M/M/L/k (  MR) Total network load [Gbps] Fraction of packets successfully transferred more

36 Conclusions Two key elements: A new tool capable to simulate the next generation optical networks A new optimization target in the optical networks design giving good results more

37 E S

38 Optical Burst Switching Packets are assembled in the network edge, forming bursts Advantages: –More efficient exploitation of the bandwidth –Possibility to implement Service Differentiation Disadvantages: –More complicated network structure –More complicated forwarding process continue

39 Link model Packet loss probability P on the link: –  link capacity –  link traffic load – offered load [Erlangs], continue

40 Japan backbone: topology

41 Japan backbone: throughput M/M/L/k (4 MR) M/M/L/k (  MR) Total network load [Gbps] Fraction of packets successfully transferred continue

42 Future work Simulator: –Support for different architectures –FDLs of variable length Heuristic approach: –More detailed model for FDLs continue

43 End of presentation