Structural Design And Performance Investigation Of Nonblocking Ring Based Networks For Data Center

Data center construction is forcast to boom over the next few years as the growing demand of data center operations,including big data explosion,is expected to push more data center facilities for prompt upgrades.However,the bottleneck can occur naturally,during high network use in terms of costs,maintenance,power consumption,cooling and space constraints.To address this issue,several research institutes have resorted to optical networking to lower the cost,power,and network complexity while achieving high bandwidth and network flexibility in DCNs.Whereas,an optical network that scales to a large number of ports,that provides nonblocking point-to-point interconnection among distributed nodes and that is easy in cabling does not exist yet.Among numerous DCN solutions,the ROADM ring is considered as one of the most promising candidates due to it capability of providing the advantages as following: 1)it is logically equivalent to an optical switch by using add,drop ports of ROADM to allow any wavelength to be switched at any node;2)it is a combination of switching and transmission,which means the coverage could be extended by easily stretching ROADM rings to address distributed nodes at large;3)it is easy in cabling because thousands of servers can be connected to single ROADM ring by short-reach fibers nearby the ring,thus cutting the cost and reducing the number of long fibers.Our thesis focues on the researches of the structural design of ROADM rings to achieve nonblocking scalability,and easy cabling at the same time,and the details are discussed as follows:1.Research on three-stage Clos network with ROADM ring on one stageTo build a nonblocking Clos based network,we firstly introduced conventional “Fattree” network,i.e.the folded Clos network: a typical way to cascade small-scaled switches into a large switch based on three-stage Clos network theory.Then,three structures are considered to use ROADM-ring based switches to replace switching modules on three different stages.The main contributed work includes:1)We notice that wavelength constraints of ROADM-ring based switches have various effects on input stage,middle stage and output stage of Clos network.To guarantee nonblocking property,the impact includes three aspects,one is in software requirement such as strategy or routing algorithm,the other is in hardware requirement.2)An implementation is presented to carry out the MRM topology,which means the input and output stage are MEMS switches whereas the middle stage uses ROADM rings.Due to the symmtry of the MRM structure,the transmitter side could use fixed lasers to cut cost with the reduction of long cables by a factor of t.2.Research on three-stage Clos network with bidirectional rings on central stageFor the limited cascading stages problem caused by the coexistence of many same wavelength channels in each stage,we introduced the wavelength conversion capability into three stage Clos network.In particular,we introduced the wavelength converters into WSS based ROADM.Thus,it is possible to build large scale networks by cascading more than three stages of ROADM rings.The main contributed work includes:1)The three-stage Clos network features ROADM rings on each stage is proposed that wavelength contention might reduce the throughput of network.To prevent wavelength contention,it requires wavelength converters in the middle stage in addition to tunable lasers and recervers in the input and output stages.The existing three wavelength conversion methods are reviewed and compared in advantages,disadvantages and application scenarios.2)A novel structure is proposed by combining WSSs and wavelength converters,which can realize all three wavelength conversion methods as a whole.Analytic results is verified and compared with simulation results.The blocking probability turned out to be acceptable with flexible wavelength conversion capability.3.Research on nonblocking networks with ROADM ring on two or multiple stagesMRM structure is symmetry in structure but insymmetry in wavelength routing.As a result,a significant number of fibers are used to address such insymmetry.To further simplify cabling in ROADM ring based network,we introduced the system architecture and wavelength constraint issue in three-stage Clos networks,and analyzed the effects of two stages of ROADM rings on the network.To guarantee nonblocking property,the impact includes three aspects,other is in hardware requirement,the one is in software requirement such as strategy or routing algorithm,the other is in hardware requirement.The main contributed work includes:1)We propose three structures with ROADM rings placed in input and output stages to construct a RMR network.To guarantee nonblocking property,it requires hardware upgrade in this structure.Results showed that the software requirement,including strategy and routing algorithm are also important in addition to Clos requirement.Arbitrary strategy would cause wavelength contention even though the hardware requirement is satisfied.2)Compared with MRM structure,RMR topology tends to be the most promising solution due to its nonblocking scalability,symmetry in structure and wavelength,reduced long cablings and simplified routing algorithm owing to corresponding strategy.3)Furthermore,to further reduce the number of short cables,we propose another RWR structure that replace the huge number of MEMSs in middle stage with several WSSs.Results showed that the novel RWR structure could further lower the hardware requirement but the same nonblocking scalability could be maintained.4)Lastly,a novel two layer structure is proposed to enlarge the capacity while combining the advantage of ROADM rings and TWC based OXCs.Nonblocking conditions are given along with the implementation scenarios.Its consistency of hardware provides another solution for optical networking in the future mega data centers.