First Demonstration of All-Optical Programmable SDM/TDM
Intra Data Centre and WDM Inter-DCN Communication
S.Y an(1),E.Hugues-Salas(1),V.J.F.Ranca˜no(2),Y.Shu(1),G.Saridis(1),B.R.Rofoee(1),Y.Y an(1),A.Peters(1) S.Jain(2),T.C.May-Smith(2),P.Petropoulos(2),D.J.Richardson(2),G.Zervas(1),D.Simeonidou(1)
(1)High Performance Networks Group,University of Bristol,UK(Shuangyi.Y an@bristol.ac.uk)
(2)Optoelectronics Research Centre,University of Southampton,UK(vjfr1u10@orc.soton.ac.uk)
Abstract We successfully demonstrate aflat-structured DCN powered by large-port-countfibre-switch-
based OCS,PLZT-switch enabled TDM and MEFs supported SDM.The inter-DCN T oR-to-T oR direct optical connections are setup through metro/core networks using all-optical SDM/WDM converters.
Introduction
Optical interconnection is the most promis-ing technology to provide power-efficient,high-bandwidth connections in large scale data centre networks(DCN).Large-port-countfi-bre switches(LPFS)enableflat-structured low-latency DCNs1,2.In such DCNs,a large quan-tity of links need to be setup between the Top-of-Racks(ToRs)and the centralized opti-cal switches to realize an optical circuit switch-ing(OCS)network.One approach is to explore DWDM technologies.However,ubiquitous con-nections between ToRs require frequent wave-length reconfiguration and switching.Thus,a DWDM-based OCS wouldfirst have to demulti-plex and switch individual wavelength channels. Thanks to recent advances infibre technologies, space division multiplexing(SDM)is now possi-ble,employing multicorefibres(MCF)or multi-elementfibres(MEF)which provide as many as 19parallel links in dimensions similar to those of a typical SMF3,4.Furthermore,VCSEL/PD arrays can potentially be matched to MCF/MEF,to pro-vide increased capacity with small footprints and low power-consumption5.The characteristics of SDM make it suitable for DCN applications.
In this paper,we demonstrate for thefirst time an all-optical OCS-based DCN,combining the benefits of both SDM and TDM technologies for intra-DCN communications using MEFs.A beam-steering192×192LPFS interconnects a)T oRs via MEF links,b)optical functional , PLZT
TDM switch,SDM/WDM converter and c) inter-DCN links.The LPFS can realize differ-ent connection ,a single hop OCS, to serve the long-lived dataflows for intra-DCN communications.The TDM switches,incorpo-rating OCS/TDM reconfigurable transceivers on ToRs,serve low-capacity,highly-connected data flows from100Mbit/s to5Gbit/s for intra-cluster communications.Bandwidth variable transmit-ters(BVTs)on T oRs provide inter-cluster links of up to320Gbit/s.In addition,by introduc-ing the architecture-on-demand(AoD)concept6 in DCN,network function programmability(NFP) is enabled to support variable traffic patterns as well as broadcasting and aggregation.
We also demonstrate cross-DCN T oR-to-T oR all-optical connections through the metro/core networks,using reversible SDM/WDM converters. Three SDM signals(up to320Gbit/s/channel) on the same-λ,originating from one or multiple T oRs,are converted optically to WDM signals to be transferred through the core networks.The direct optical T oR-to-T oR cross-DCN connections enable the remote distributed DCNs to appear as one big data centre,which could enhance scala-bility and reduce latency and cost.
Intra-and Inter-DCN Communications
Fig.1shows the proposed solutions for both intra-and inter-DCN communications.Each DCN con-sists of clusters with tens/hundreds of racks net-worked together and each rack isfilled up with tens of servers.Servers are interconnected to T oRs via10GE optical links.In our design,T oRs play a pivotal role in both inter-and intra-DCN communications.Fig.2shows the design of the proposed FPGA-based T oR.The T oR,imple-mented using FPGA optoelectronics(HTG Xilinx V6board),parsed the input traffic from servers and sent them out through different transmitters according to their destination.Programmable slotted-TDM/Ethernet over SDM signals are sent out through two SFP+transceivers for intra-cluster communication.Another four transmitters feed the traffic to a BVT to provide a link of up to320Gbit/s for high-capacity inter-cluster and inter-DCN communications.All the transmitters
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Fig.1:Proposed solution for intra-DCN communication (SDM+TDM)and inter-DCN communication (SDM+WDM)
use fixed wavelength lasers to avoid expensive temperature control.Then all the transceivers on the ToRs are connected to a LPFS with MEFs.The clusters are networked by interconnecting the centrali
zed LPFS in each cluster using SMFs or MEFs to form a mesh network.The inter-DCN communication is realized by transferring SDM signals through the metro/core networks with SD-M/WDM all-optical
converters.
鹀属Fig.2:FPGA-based T oR provide slotted-TDM/Ethernet signals for intra-DCN and BVT up to 320Gbit/s for inter-DCN
For the experimental setups,three 3-element MEFs of different lengths connect all the trans-mitters a
nd receivers in two T oRs to a 192×192fibre switch.The 4×4PLZT TDM switch,SD-M/WDM converter,WSS,EDFAs,couplers and splitters are all ready connected to the fibre switch for function programmability.A 100km SMF link is setup for metro/core transmission.
a)DWDM-based Inter-DCN communications Directed cross-DCN T oR-to-T oR connections are setup through the metro/core network using an all-optical SDM/WDM converter.The experimen-tal setup of the SDM/WDM converter is shown in Fig.1(c).The converter is a fibre-based dual-pump four-wave-mixing device 7,and uses a shared-pump bi-directional configuration that allows conversion of two SDM channels at the same time.It provides polarisation-,rate-and modulation format-independent operation.Using this converter,contiguous 3-carrier superchan-nel signals are obtained from three same-λSDM signals (either PM-QPSK or PM-16QAM signals were used in our experiments),which are sub-sequently launched into the metro/core networks.Then the superchannel signal is dropped at the edge node and sent to another DCN.By adopt-ing optical demultiplexing,each carrier is sent to different T oRs.The tested inter-DCN sce-nario is shown in Fig.1(d).The inter-DCN link adopts either PM-16QAM or PM-QPSK signals at 40Gbaud to trade off capacity against trans-mission distance.16QAM/QPSK constellations of the CH1signals are shown in Fig.1(a)for back-to-back and (b)after 100km
transmission.
延胡索酸
Fig.3:OSNR vs.BER for 40Gbaud PM-QPSK signals for
头版头条inter-DCN communication
For the 40Gbaud QPSK signal,we analyse the performance of the setup by measuring the BER to OSNR curve.The results are shown in Fig.3.The SDM/WDM converter introduces an OSNR penalty of about 1.61dB and 2.53dB at 1e-3for the two converted channels:CH1and CH3.Another SDM signal without wavelength conver-sion is put in the CH2wavelength slot.After 100km transmission,the CH1signals are transferred back to the T oR in another DCN.The penalty of the T oR-to-T oR connection is about 3.28dB.
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b)TDM/SDM Intra-DCN
communications
Fig.4:Experimental Setup of intra-cluster network
For intra-cluster communication,OCS-based SDM (Ethernet)and TDM technologies are used to provide a range of connections of bandwidth and capacity services.Fig.4shows the demon-stration setup.The single-hop SDM with an ele-ment capacity of 10Gbit/s is realized by reconfig-uring the interconnection of the LPFS to supports high throughput Ethernet ,the domi-nant traffic in DCNs.A synchronized (4×4)PLZT TDM switch is connected to the LPFS to realize TDM connections with variable capacity from 100Mbit/s to 5Gbit/s.Optical components,such as couplers and splitters are connected to the LPFS,and can be programmed to support aggregation,broadcasting and other network functionalities,as in the examples shown in the inset of Fig.4.
To test the performance of intra-cluster net-works,an Ethernet Traffic Analyser is used to generate Ethernet traffic between servers and ToR.In scenario (a),the latency of the P-P trans-mission is measured to be about 70µs,where the FPGA-based T oR contributes about 4.2µs (5%of the link latency).Fig.5presents the results for both SDM-Ethernet network in scenarios (a,b)and TDM network in scenarios (c,d,e).The max-imum Ethernet capacity/port is about 9.8Gbps.In the OCS-based SDM network,the broadcast op-eration introduces a power penalty of about 1.3dB at 1e-9due to the noise introduced by the EDFA used to compensate the loss of the splitter.In scenario (e),two ti
吸式挖泥船me-slot data flows (2.5Gbit/s)from two ToRs are aggregated to 5Gbit/s and fur-ther broadcast to three other T oRs.The PLZT TDM switch introduces a power penalty of about 2.1dB at 1e-9due to its cross talk (20dB).The re-ceived TDM capacity for different received optical power after broadcasting is also shown in Fig.5.SDM signals are used for inter-cluster commu-nication.The BVTs on T oRs generate 10Gbit/s OOK,40Gbaud PM-QPSK (160Gbit/s)or PM-
Fig.5:Experimental results of intra-cluster network
16QAM (320Gbit/s)signals to setup bandwidth-variable links between clusters.
Conclusions
An all-optical multi-dimensional and pro-grammable solution for both intra-and inter-DCN communications is proposed and successfully demonstrated .The MEF-based SDM technol-ogy provides low-loss and easy to handle links between T oRs and cluster LPFS.SDM and TDM technologies are used in an OCS manner to realize intra-DCN communications.The inter-DCN communication is realized by converting SDM signals to WDM signals using a multi-λSDM/WDM converter,and then transferring them to another DCN.The NFP enables the DCN to realize different network functions.
Acknowledgements
This work is supported by the EPSRC grant EP/I01196X The Photonics Hyperhighway,and the ECFP7grant no.619572,COSIGN.References
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