1 Advances in Optical Switching Mohammad Ilyas, PhD College of Engineering & Computer Science Florida Atlantic University Boca Raton, Florida USA

2 Outline Introduction Switching techniques Challenges in optical switching Future directions Summary

3 Introduction All communication networks have links and switching nodes Not all nodes are connected to all other nodes Switching nodes route information from links to links Switching techniques have changed significantly as the link capacities have increased

4 D S A typical communication network Introduction (continued)

5 Switching nodes switch information from incoming links to outgoing links Routing, flow control, and congestion control are some of the important aspects Traditional wide area networks are primarily for one type of service

6 Introduction (continued) Resource - primarily transmission capacity and buffering capacity Supply and demand concept Resource sharing - pre-allocations versus dynamic allocations Dynamic Pre-allocation Time

7 Functional diagram of a switch Switching matrix Input Output Info header Routingalgorithm New header Info Introduction (continued)

8 Switching Techniques Two broad categories of switching: space division switch and time division switch A space division switch has multiple inputs and multiple outputs A time division switch has a single multiplexed input and the time slots are interchanged to switch the information

9 Switching Techniques (continued) Space switch         Input Output

10 Switching Techniques (continued) Time division switch Logic for time slot interchange Input Output        

11 Switching Techniques (continued) Performance aspects –Connectivity - set of pairs that can be simultaneously connected through a switch –Delay - the amount of time the switch takes to route the incoming information to an appropriate output –Throughput - the amount of information that can be successfully handled by the switch / unit time

12 Switching Techniques (continued) Switch architectures –Crossbar switch (also called matrix type or single-stage space division switch) –Multi-stage space division switch –bus type –ring type –Optical switches

13 Switching Techniques (continued) Crossbar switch Input Output

14 Switching Techniques (continued) Switch architectures (continued) –Multistage switches have a variety of configurations –These switches are modular and are usually made up of 2 x 2 switching modules and may have input or output buffers Input Output

15 Switching Techniques (continued) Omega Input Output Tag = = down For output 110, the routing tag is 011 Tag = 01 1 = down Tag = 0 0 = up

16 Switching Techniques (continued) Impact of input buffers –If we add buffers, then less packets are discarded and the throughput increases –At the same time, the addition of buffers adds to the queueing delay and the overall switching delay increases –Larger the number of buffers, better is the throughput –May cause HOL blocking

17 Switching Techniques (continued) InputBuffers Switch Outputs Inputs

18 Optical Switching Optical switching mostly needs optical-to- electronic and electronic-to-optical conversion This slows down the process and increases delay Pure optical switching has its own challenges: –Can we buffer in optical domain –Utilization –Error recovery –others

19 Optical Switching (continued) Switching information in optical domain can reduce the delay Optical switching requires capability to direct the light beam to a desired output based on the address Storage of information is not possible in optical domain Real time processing (possibly optical computing) is needed

20 Optical Switching (continued) Once the address of a packet has been identified, it can be used to direct the trailing information properly the delay (if needed) is introduced by looping the information (in optical domain) for some time The technology is being developed for an eventual goal of building large optical switches

21 Optical Switching (continued) Demand on communication network is increasing and is expected to continue Need for pushing more and more information through networks Many approaches: –WDM optical switching – Lamda switching –Optical burst switching –Several variations are possible

22 Optical Switching (continued) The term “burst switching“ means taking several packets together and transmitting them together and no buffering In case of conflict for an output port, one of the incoming bursts would be dropped. At a switching speed of 1 μs, one could switch bursts of 10 μs length (typically containing many packets) Possible use of optical buffers Optical burst switching allows betters sharing of bandwidth

23 Optical Switching (continued) Optical burst switching: –Increasing data rate versus utilization –A packet of 10,000 bits on an optical link, occupies only 1 micro second of transmission –A link of 1 Kilometer introduces 5 microseconds of propagation delay –If information is transmitted one packet at a time, it results in very poor transmission efficiency –This cannot be ignored in designing optical switching

24 Optical Switching (continued) Optical burst switching (continued): –Increasing data rate versus utilization –A packet of 10,000 bits on an optical link, occupies only 1 micro second of transmission –A link of 1 Kilometer introduces 5 microseconds of propagation delay –If information is transmitted one packet at a time, it results in very poor transmission efficiency –This cannot be ignored in designing optical switching

25 Future directions Switching in optical domain is almost a necessity Innovative approaches such as optical burst switching are needed to better share the resources New materials may help with buffering in optical domain Optical computing needed for reading packets on the go

26 Conclusions Optical networks are rapidly emerging Several challenging research problems Utilization versus throughput and delay Some wastage is unavoidable

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