Journal of Emerging Technologies in Web Intelligence Contents

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142 JOURNAL OF EMERGING TECHNOLOGIES IN WEB INTELLIGENCE, VOL. 2, NO. 2, MAY 2010Multistage Interconnection Networks: ATransition from Electronic to OpticalRinkle Rani AggarwalDepartment of Computer Science & Engineering,Thapar University, Patiala –147004 (India)raggarwal@thapar.eduDr. Lakhwinder Kaur, Dr. Himanshu AggarwalDepartment of Computer Engineering,Punjabi University, Patiala–147002 (India)mahal2k8@yahoo.com, himanshu@pbi.ac.inAbstract—Optical communication are necessary forachieving reliable, fast and flexible communication.Advances in electro-optic technologies have made opticalcommunication a reliable networking choice to meet theincreasing demands for high bandwidth and lowcommunication latency of high-performancecomputing/communication applications. So optical networksgives high performance as well as low latency. Althoughoptical MINs hold great promise and have advantages overtheir electronic networks, they also hold their ownchallenges. This paper compares electronic and OpticalMINs. The design issues and solution approaches availablefor optical MINs are also explained and analyzed.Index Terms— Multistage Interconnection Networks (MIN),Optical networks, Crosstalk, Window methods.I. INTRODUCTIONTo meet the increasing demands of high performancecomputing applications for high channel bandwidth andlow communication latency, traditional metal-basedcommunication technology used in parallel computingsystems is becoming a potential bottleneck. Now, theneed arise either for some significant progress in thetraditional interconnects or for some new interconnecttechnology be introduced in parallel computing systems.Electro-optic technologies have made opticalcommunication a promising network choice to meet theincreasing demands with its advancement in thetechnology. Fiber optic communications offer acombination of high bandwidth, low error probability andgigabit transmission capacity.Multistage interconnection networks have beenextensively accepted as an interconnecting scheme forparallel computing systems. As optical technologyadvances, there is considerable interest in using opticaltechnology to implement interconnection network andswitches. A multistage interconnection network iscomposed of several stages of switch elements by whichany input port can be connected to any output port in thenetwork. Optical MIN represents a very important classof interconnecting schemes used for constructing Opticalinterconnections for communication networks andmultiprocessor systems. This network consists of Ninputs, N outputs and n stages (n=log 2 N). Each stage hasN/2 switching elements each SE has two inputs and twooutputs connected in a certain pattern. The most widelyused MINs are the electronic MINs. In electronic MINs,electricity is used, since in optical MINs, light is used totransmit the messages. Although electronic MINs andoptical MINs have many similarities but there are somefundamental differences between them. Available opticalMINs were built mainly on banyan or its equivalent (e.g.baseline, omega) networks because they are fast in switchsetting (self-routing) and also have a small number ofswitches between an input-output pair. Banyan networkshave a unique path between an input-output pair, and thismakes them blocking networks. Non-blocking networkscan be constructed by either appending some extra stagesto the back of a regular banyan network. Crosstalk inoptical networks is one of the major shortcomings inoptical switching networks, and avoiding crosstalk is animportant for making optical communication properly. Toavoid a crosstalk, many approaches have been used suchas time domain and space domain approaches. Becausethe messages should be partitioned into several groups tosend to the network, some methods are used to findconflicts between the messages.II. MULTISTAGE INTERCONNECTIONNETWORKSMultistage interconnection networks (MINs) consistof more than one stage of small interconnection elementscalled switching elements and links interconnecting them.Multistage interconnection networks (MINs) are used inmultiprocessing systems to provide cost-effective, highbandwidthcommunication between processors and/ormemory modules. A MIN normally connects N inputs toN outputs and is referred as an N × N MIN [9,10]. Theparameter N is called the size of the network. There areseveral different multistage interconnection networks© 2010 ACADEMY PUBLISHERdoi:10.4304/jetwi.2.2.142-147
JOURNAL OF EMERGING TECHNOLOGIES IN WEB INTELLIGENCE, VOL. 2, NO. 2, MAY 2010 143proposed and studied in the literature. Figure 1 illustratesa structure of multistage interconnection network, whichare representatives of a general class of networks. Thisfigure shows the connection between p inputs and boutputs, and connection between these is via number ofstages. Multistage interconnection network is actually acompromise between crossbar and shared bus networksof various types of multiprocessor interconnectionsnetworks [1]. Multistage interconnection networksattempt to reduce cost and decrease the path lengthspeed mismatch occur due to the high speed of opticalsignals. The second approach is all-optical switching.This has removed the problem that occurred with thehybrid approach but, such systems will not becomepractical in the future and hence only hybrid opticalMINs are considered. In hybrid optical MINs, theelectronically controlled optical switches, such as lithiumniobate directional couplers, can have switching speedsfrom hundreds of picoseconds to tens of nanoseconds.A. Switching in optical networksIn optical networks, circuit switching is used. Packetswitching is not possible with Optical MultistageInterconnection Networks. If packet switching is used,the address information in each packet must be decodedin order to determine the switch state. In a hybrid MIN, itmeans it require conversions from optical signals toelectronic ones, which could be very costly [4]. For thisreason, circuit switching is usually preferred in opticalMINs.Figure 1: A MultistageNetworkMINsTABLE IPROPERTIES OF DIFFERENT INTERCONNECTIONTECHNIQUESOPTICALELECTRONICProperty Bus Crossbar MultistageSpeed Low High HighCost Low High ModerateReliability Low High HighConfigurability High Low ModerateComplexity Low High ModerateHYBRIDGUIDEDWAVEALL OPTICSSPACEOPTICSIII. OPTICAL MULTISTAGE INTERCONNECTIONNETWORKSAn optical MIN can be implemented with either freespaceoptics or guided wave technology. It uses the TimeDivision Multiplexing. To exploit the huge opticalbandwidth of fiber, the Wavelength DivisionMultiplexing (WDM) technique can also be used. WithWDM, the optical spectrum is divided into manydifferent logical channels, and each channel correspondsto a unique wavelength. Optical switching, involves theswitching of optical signals, rather than electronic signalsas in conventional electronic systems. Two types ofguided wave optical switching systems can be used [5].The first is a hybrid approach in which optical signals areswitched, but the switches are electronically controlled.With this approach, the use of electronic control signalsmeans that the routing will be carried out electronically.As such, the speed of the electronic switch control signalscan be much less than the bit rate of the optical signalsbeing switched. So, with this approach there is a bigFigure 2: Types of Multistage NetworksB. Comparison of Electronic and Optical NetworksThere are lots of benefits of optical networks overthe electronic ones. The main benefit of the opticalnetworks over the electronic network is the high speed ofthe Optical signals. In the optical networks light istransmitted which has a very good speed but in theelectronic Multistage interconnection networks electricityis used which has very slow speed. The second advantageis the Bandwidth. Now a day’s applications incommunication require high bandwidth, the opticalnetworks gives combination of very high bandwidth andlow latency. Therefore, they have been used in theparallel processing applications. Optical MINs are alsoused in wide area networks, which require less errorprobability and very high bandwidth. Fiber optic© 2010 ACADEMY PUBLISHER
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