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NEPHELE Report Summary

Project ID: 645212
Funded under: H2020-EU.

Periodic Reporting for period 1 - NEPHELE (eNd to End scalable and dynamically reconfigurable oPtical arcHitecture for application-awarE SDN cLoud datacentErs)

Reporting period: 2015-02-01 to 2016-07-31

Summary of the context and overall objectives of the project

The cloud is revolutionizing the internet with a whole new user experience. Cloud services are being rapidly deployed, causing traffic in datacenters to explode. To keep pace with this soaring demand, datacenters are growing in size, hosting tens of thousands of servers and consuming as much electricity as a small town. Scaling-out the datacenter is generating enormous connectivity requirements whereas the emerging concept of resource disaggregation is further raising the bar in network capacity and latency. Traditional datacentre network architectures scale super-linearly with the number of servers, imposing a ceiling on the maximum economically-viable datacenter dimensions. Content providers face the challenge of scaling their infrastructure in a cost-effective manner, in order to improve their services to the end-user. New networking solutions are urgently needed to sustain the booming growth in the cloud ecosystem.

NEPHELE is a European research project on network technologies, developing a dynamic optical network infrastructure for future scale-out, disaggregated datacenters. NEPHELE builds on the enormous capacity of optical links and leverages hybrid optical-electronic switching to attain the ideal combination of high bandwidth at reduced cost and power compared to current datacenter networks. In order to effectively integrate the new paradigm of optical switching into the datacenter networking ecosystem, NEPHELE follows an end-to-end approach extending from the datacenter architecture to the overlaying control plane and up to the interfaces with the application, in order to deliver a fully functional networking solution. Within the project’s workplan a manifold of recent developments and disciplines are leveraged in order to unleash the potential of optical switching in the datacenter:

• novel network architectures for optically switched data plane leveraging mature, off-the-shelf photonic technologies,
• Software-defined networking for network configuration and interaction with the data plane,
• Application-defined networking for interaction with the datacenter cloud management platform.

To blend these concepts into a fully functional end-to-end solution NEPHELE aligns its interdisciplinary approach with the end-user needs, as a means of bridging innovative research with near-market exploitation.

NEPHELE’s hybrid electronic-optical network architecture scales linearly with the number of datacenter hosts and consolidates compute and storage networks over a single, Ethernet optical TDMA network. Low latency, hardware-level dynamic re-configurability and quasi-deterministic Quality-of-Service (QoS) are supported in view of disaggregated datacenter deployment scenarios. A fully functional control plane overlay is being developed, comprising a Software-Defined Networking (SDN) controller along with its interfaces. The southbound interface abstracts physical layer infrastructure and allows dynamic hardware-level network reconfigurability. The northbound interface links the SDN controller with the application requirements through an Application Programming Interface. NEPHELE’s innovative control plane enables Application Defined Networking and merges hardware and software virtualization over the hybrid optical infrastructure. It also integrates SDN modules and functions for inter-datacenter connectivity, enabling dynamic bandwidth allocation based on the needs of migrating virtual machines (VMs), as well as on existing Service Level Agreements for transparent networking among telecom and datacenter operators’ domains.

NEPHELE is developing an end-to-end solution extending from the datacenter architecture and optical subsystem design, to the overlaying control plane and application interfaces. Driven by user needs, the project aims to bridge innovative research in datacenter networking with near-market exploitation, achieving transformational impact in energy consumption and cost that will allow datacenters to continue to scale. NEPHELE’s objectives address a vigorous multi-billion Euro market and the industrial partners of the consortium hold considerable market shares across the value chain. As a result, NEPHELE will strengthen Europe’s industrial position in the field of cloud datacenter technologies.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The main achievements during the first project period are summarized below:

WP1: Project Management [M01-M36] (leader: ICCS/NTUA)
All necessary documentation for consortium management was finalized and signed (Grant Agreement, Declarations of Honour, Consortium Agreement and Commission-initiated amendment). The first payment was distributed to the partners. Five plenary meetings, two review meetings and one smaller project meeting were organized and mechanisms were established for consortium communication. Project management instruments performed technical planning, risk management and innovation management. Quality assurance mechanisms were setup for project reporting and fourteen reports were generated and submitted to the Commission.

WP2: Optical cloud DC interconnect architecture [M01-M24] (leader: IRT)
Use cases were motivated by the industrial partners and were defined according to a common methodology. The requirements for management and control were collected and the main functions that need to be provided by the NEPHELE system were identified. The data plane specifications were also defined, as were the functionalities of the associated building blocks. Data- and control-plane requirements were linked with the planned implementation and demonstration, for each use case in NEPHELE. Dimensioning and performance analysis were carried out for different traffic patterns. At the control plane, the functional architecture of the NEPHELE system was defined and the information models used to abstract the different network nodes were specified. Interfaces and interactions among the different architectural components were consolidated both for the intra- and the inter-DC cases.

WP3: Hybrid ToR switch and network interfaces [M01-M28] (leader: MLNX)
The tunable transmitter for NEPHELE’s ToR switch was developed and fast wavelength tuning operation was demonstrated with tuning time well within NEPHELE’s specifications. The WSS subsystem was designed and its SPI control interface was developed; however evaluation was hampered by the defective SPI interface operation of the commercial module that was used. Debugging in liaison with the supplier (NISTICA) was ineffective and contingency actions were put in effect. First, an I2C control interface was setup and verified the optical routing functionality of the WSS with the switching time targeted in NEPHELE. However, the module’s reconfiguration rate was limited by the slow communication speed of the I2C interface and was therefore not suitable for the slotted NEPHELE dataplane. To overcome this obstacle, a WSS module was setup according to the “demultiplex, switch and multiplex” technique. The contingency WSS module was evaluated successfully and was applied in WP6 experiments. In the meantime, debugging of the NISTICA WSS is still in progress. The 1×2 fast switch subsystem was developed and tested. The optical power combiner was investigated with several approaches. Following simulations and consideration of potential implications to the overall system, the final approach was consolidated in liaison with WP2 and WP4. Four FPGA boards were specified for the NEPHELE data plane with their exact functionality, I/O requirements and compute/memory requirements. Design and evaluation has been completed for the majority of FPGA software components and interfaces.

WP4: Algorithms and protocol adaptations for efficient QoS provisioning inside and across DCs [M05-M28] (leader: UPAT)
The dynamic bandwidth allocation problem has been defined and formulated according to the WP2 architecture specifications. Two classes of algorithms were developed in a full suite; offline algorithms that schedule a static traffic matrix and incremental algorithms that are better suited to dynamic traffic scenarios. For each class, a set of algorithms was developed and evaluated in simulations, achieving different trade-offs between performance and running time. The effect of control plane overhead was evaluated for the NEPHELE network. In parallel, architecture requirements are studied towards supporting CSMA in NEPHELE and their performance is under investigation. Specifications for the TDMA OpenFlow agent were defined in collaboration with WP5. Finally, next generation data storage system link protocols within modified optically interconnected data storage platforms were evaluated for various interconnect link lengths.

WP5: SDN Control-plane and Interfacing with Cloud Management [M07-M32] (leader: GWDG)
The preferred solutions for NEPHELE’s SDN controller, SDN cloud management platform and protocol for southbound communication have been specified after analysis of the options (OpenDaylight, OpenStack and OpenFlow respectively). A preliminary prototype of the NEPHELE intra-DC SDN controller has been released and a user guide has been created. An OpenFlow Agent has been designed along with its communication (messaging and call flows) with the corresponding interfaces. Application-aware networking is investigated in collaboration with MikelAngelo and within this framework, traffic recording experiments have been conducted and analysed towards the identification of a viable approach in NEPHELE. For the inter-datacenter control plane, Julius has been selected as a framework for evaluating the use of elastic optical networks in conjunction with the SDN paradigm. OpenStack is identified as a candidate solution for the inter-DC scenarios at hand.

WP6: Testbed and demo [M04-M36] (leader: XRT)
The testing regime has been defined for the evaluation of the NEPHELE prototypes and testing procedures have been specified. A test plan has been consolidated with the definition of evaluation experiments, including tests on networking functionalities, innovative hardware and architecture and their interaction. The physical layer of the NEPHELE intra-DC network was validated in a set of system experiments. Both intra-pod and inter-pod routing were evaluated, concerning communication between racks within the same pod or between different pods respectively. Interaction with the FPGAs is being integrated in the testbed. The design of the converged optically enabled Ethernet data storage and switch platform, NephDem06.01, which comprises the innovation zone of the NEPHELE architecture has been successfully completed ahead of schedule. The first system prototype has been completely developed and is undergoing characterization. The NephDem06.01 platform is developed within the framework of the EU cross-project initiative PhoxLab and comprises a comprehensive suite of card assemblies, with controller module cards, mezzanine cards, an electro-optical mid-plane, storage and server end nodes, as well as the associated optical interface cards.

WP7: Exploitation, standardization and market planning [M01-M36] (leader: XRT)
The methodology for generating coherent and targeted exploitation plans has been established and the first exploitation report has been generated. The study includes a market analysis and competitive analysis on the areas relevant to NEPHELE, an overview of ongoing standardization activities, a list of dissemination actions and the detailed exploitation plans of the consortium members. NEPHELE has been very well disseminated through talks, publications and its website. In addition NEPHELE drew attention through a high profile joint exhibition at OFC 2016 with the Japanese PETRA consortium resulting in online articles referencing the project. More recently, a joint exhibition was organized with the PhoxTrot project at ECOC 2016, where prototypes of the NephDem06.01 platform were on display at the largest photonics communications event in Europe. Promotional material was generated and disseminated in relevant events. Communication with several European projects and initiatives was initiated and liaison activities were carried out. IPR in topics relevant to NEPHELE was tracked and evaluated, whereas two patents were filed.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

"The proliferation of the cloud application-, platform- and infrastructure-as-a-service models is motivating the construction of new and more powerful datacenters [1]. This is raising the bar in communication requirements not only among the cloud datacenters, but also within them. Today’s datacenters are typically designed with a fat-tree or oversubscribed fat-tree interconnection topology, which are plagued by scalability limitations, rigid allocation of resources and difficulty to adapt to the east-west traffic profiles of modern datacenters. Optical switching has been investigated for transferring aggregated traffic between racks or collections of racks, partly or entirely replacing the higher levels of the electronic tree networks [2],[3],[4]. Several optical switching technologies have been considered such as MEMS, wavelength switching, optical add-drop multiplexers and optical packet switching.
MEMS switches have long reconfiguration times that typically range in the order of tens to hundreds of milliseconds. Therefore, they are typically used in tandem with an electrical packet-switched network. MEMS-based hybrid electronic-optical networks have been reported in Helios [2], Calient [5], and REACToR [6]. One limitation of this approach is the delay introduced by the control plane that serves to classify traffic and handle the network reconfiguration [7], which can go up to the seconds’ timescale. Also, since the radix of MEMS switches is quite limited (up to 320 port switches are commercially available) and building higher-port switches out of smaller ones is complex (due to losses and synchronization issues), the hybrid solution based on MEMS exhibits scalability problems.

Wavelength-switching concepts have been investigated by virtue of the fast reconfiguration time of tunable lasers (in the ns regime), which can be configured to implement a non-blocking switch when interconnected with an Arrayed Waveguide Grating Router (AWGR). A number of initiatives have investigated this concept in different realizations, such as DOS [8], LIONS [9], Petabit [10] and IRIS [11],[12],[13]. On the downside, wavelength-switched concepts face significant scalability issues due to the limited number of wavelengths available in the optical communication C-band.

Optical add-drop multiplexing nodes based on Wavelength Selective Switches (WSSs) offer more flexibility as they combine space- and wavelength-switching. A prominent example is Mordia [14], which uses WSSs similar to NEPHELE’s achieving switching times in the order of 10 μs. However, the Mordia architecture is a flat ring that interconnects racks, which scales badly. In addition to the architecture and physical layer implementation, Mordia has also researched algorithms to ensure fast reconfiguration of the underlying network infrastructure. Although the proposed algorithms are 2-3 orders of magnitude faster than traditional approaches, they still rely on superlinear complexity algorithms. Such algorithms cannot scale to huge datacenters of thousands of racks for medium to high dynamic traffic, which is the case as measured in real datacenters [15]. The main limitations of Mordia remain its scalability and cost.

Optical packet switching is also investigated as an alternative to the hybrid electro-optical approach and in an attempt to shed the electrical switches completely from the datacenter. The Lightness project [15] is developing a hybrid datacenter network that combines optical packet switching (OPS) and optical circuit switching (OCS). The OPS switch provides WDM operation and is based on WSSs implemented with AWGs followed by large SOA arrays in order to perform the OPS between different ToR switches. This SOA-based switching concept has been well-investigated in the past in the context of OPS-telecom networks [16], however it still involves significant hurdles, such as the relatively high power consumption and power dissipation of the switches, as well as the lack of an established supply chain (switching components are not commercialized and validated in any operating environment). The OCS is realized through Architecture on Demand (AoD) nodes where an optical backplane of large port count MEMS is connected to several signal processing modules as well as to the input/outputs of the node. The AoD offers flexibility as the components are not hardwired but can be interconnected together in an arbitrary manner. The latter provides additional network services where required, but also results in redundant optical equipment thus increasing overall equipment cost and management overheads. Finally, since MEMS switches do not scale, scalability is also a huge problem in this AoD-OCS concept.

The research areas and topics related to the NEPHELE objectives, such as hybrid optical datacenter networks, optical switching and dynamic resource allocation e.g. by means of slotted operation remain in the frontline of research efforts. Numerous publications, workshops and invited talks in recent conferences such as the Optical Fiber communication (OFC) conference, the International Conference on Transparent Optical Networks (ICTON) and the European Conference on Optical Communication (ECOC) suggest that NEPHELE targets technologies that attract a great interest from the scientific community. Indicatively, publications in OFC targeted among others all-optical [17] or hybrid [18],[19] switching in datacenter networks and optical datacenter network architectures [20],[21],[22], while several invited talks addressed the topics of datacenter scalability and networking as well as quality of service and cloud services in datacenter networks . In the latest ICTON, a selection of relevant talks included topics such as optimal resource allocation of hybrid-switched datacenter networks [23], hybrid packet switching [24], and flexible datacenter network architectures [25]. In ECOC respectively, a symposium in optical interconnects in datacenters was carried out, and several talks addressed among others topics such optical switching for software–defined datacenter networks [26], as well as optical [27] and WDM [28] switching in intra-datacenter networking (including talks associated to NEPHELE). Finally, relevant works concerning scalable optically-switched datacenter architectures [29] and hybrid optical datacenter network architectures [30] are published in other conferences and journals.

From the above it is clear that the topics addressed by NEPHELE are attracting increasing attention worldwide, from industry and academia alike. It is worth noting though, that the objectives and approach of NEPHELE remain original and are not compromised by the latest publications, but hold strong potential for generating a significant impact in the field. NEPHELE is combining innovations across disciplines, spanning from hybrid-optical datacenter switching to software-defined networking and datacenter disaggregation in an end-to-end and multi-oriented state-of-the-art datacenter architecture (see next paragraph for more details). During the second project period when the integration and combined testing of the individual research strands will be carried out, it is expected that the project’s visibility will be further enhanced significantly.

More specifically, in the WP2 framework a survey on current state-of-the-art for DC networks has been conducted within task 2.1 and was reported in D2.1. The evolution towards the concept of disaggregated DC has been identified and analyzed in that context, driving the consortium at specifying the requirements of the NEPHELE data plane. So far, the WP2 activities have designed the hybrid electronic-optical NEPHELE architecture following the concepts of disaggregated DCN and advanced SDN technologies, targeting different advantages compared to the traditional DC architecture. These advantages are covered by the following items:

• Combination of WDM technologies and TDMA approach in a dynamic fashion
• SDN based control plane, with fine-granular control and highly dynamic resource allocation
• Hybrid electrical/optical network to scale beyond the current limitation of fat-tree networks
• Mechanisms and algorithms to operate the NEPHELE hybrid data plane applying TDMA
• Application awareness into the network control plane
• Design of the following elements:
o NEPHELE POD switch
o NEPHELE ToR switch

Several algorithmic solutions were examined for the NEPHELE scheduling (resource allocation) engine. We focused on a centralized scheduling architecture and developed algorithms that range from optimal to heuristics that tradeoff performance for execution time. To meet the strict time requirements of a medium-large size datacenter with thousands of racks, we proposed algorithms that update the allocation of resources according to traffic changes and exhibit linear execution time. Currently we are examining ways to parallelize the proposed algorithms so as to achieve even lower execution times, suitable for real time operation of the network even for highly dynamic traffic. Detailed simulations for large datacenters showed the efficiency of the NEPHELE resource allocation engine, thus proving the high scalability of the proposed architecture compared to the state of the art.

The main advancement in terms of SDN is related to the extensions of an open source SDN controller (i.e. OpenDaylight) implemented to support the operation of NEPHELE optical resources and the scheduling of the network resources. In particular, the project has proposed an extended YANG model to represent wavelength and time-slot concepts in the OpenFlow protocol data structures, enabling the dynamic configuration of optical cross-connections, per time slot, at the controller south-bound interface. Moreover, the project has also proposed new north-bound interfaces, based on the REST paradigm, to enable the interaction between a cloud orchestrator and an SDN controller for application-aware DCN resource allocation. The project has implemented a set of SDN applications that coordinates several application requests building the global DCN traffic matrix and dynamically computing an efficient solution for the resource allocation based on the scheduling concepts. This solution is automatically translated in extended OpenFlow rules and configured on the DC network using the OpenFlow protocol.

Socio-economic impact
Optical interconnects play a central role in cloud datacenters, operating in close liaison with the compute and storage infrastructure. According to Infonetics the overall data centre networking market alone will reach $21.85 billion by 2018 on an 11.8% growth rate. This burgeoning market is driving growth in optical interconnects, as they represent an integral part of its ecosystem (along with switches and network interface cards) and are gaining ground against their electrical counterparts. Lightcounting predicts that by 2018, the market for Ethernet optical interconnects (1/10/40/100 GbE) will reach an aggregate of approximately $2.2 billion.
The overall global data centre market was estimated to be worth ~$150bn in 2014, growing at 9-10% a year. Already there is over 1.8 billion square feet of data centre space in 8.6 million data centres worldwide. Although North America led the early deployment of data centre, the industry has globalised rapidly as shown by the global distribution of data centre space. Whilst North America is still significant, data centre area in China has grown rapidly while Europe represents 26% of the data centre area. The market for the equipment contained in those centres is worth ~$114bn in 2014/15 and forecast to grow by over 14% annually, driven by both replacement of existing equipment and new data centre build.
NEPHELE is well-positioned to claim a large share of this burgeoning market. The project is pursuing an end-to-end development path, extending from the datacenter architecture to the overlaying control plane and interface to the application, in order to deliver a fully functional networking solution and turn the theoretical benefits of optical switching into tangible assets. The project took considerable care to develop its approach on COTS photonic components, so as to avoid the often long maturation time of photonic technologies, that may hinder rapid exploitation of project outcomes. In addition, NEPHELE was designed to fit current industry standards and norms (e.g. compatibility with Ethernet hosts) so that it can be smoothly integrated in the existing optical networking ecosystem.

The NEPHELE consortium is industry-driven and includes players across the value chain, enabling commercialization of the technology with a Europe-centric supply chain. Most importantly, the consortium includes leading vendors in the fields of optical interconnects and datacenter storage (i.e. Mellanox and Seagate), providing a viable path to the market. Mellanox has proven consistent leadership in each new technology generation as it was the first to market end-to-end solutions for 25, 50 and 100 Gb/s. According to Crehan Research Group Mellanox is the fastest growing Ethernet Vendor, whereas the company is the leading vendor for Infiniband, which is dominating the HPC application space. With revenues of $196.8 million and over 2000 employees in Europe, Mellanox is a competent player with a considerable socio-economic impact in Europe. Seagate is the second largest supplier of HDDs in the world, achieving 39.38% market share in Q1 2016. The company is experiencing very strong demand from cloud service providers (CSPs). Although unit shipments of Seagate’s HDDs have dropped 15% over the past five fiscal years, exabyte shipments have increased 112% and average capacity per drive has soared 133%. This is attributed to the shift from client-server to mobile cloud architectures. In fiscal 2016, Seagate shipped 233 exabytes, including 70 exabytes for its “business-critical” product line – a 28% increase over the prior year. The company met or exceeded analysts’ expectations with $2.7 billion in revenue for its fiscal fourth quarter, largely driven by sales to cloud service providers. Thus, solutions for cloud datacenters are central within the company’s interests and roadmaps. Both Mellanox and Seagate see substantial value in the technologies developed within NEPHELE as key enablers for sustaining growth in their business, thus reinforcing Europe’s share in the global scene.

Wider societal implications
Today’s data-affluent society relies on datacenters to store and rapidly access massive amounts of information. The internet, as the means of accessing this information, has evolved into a key driver for economy, as well as into a means for social interaction and social inclusion. Reflecting its content-centric design, the entire internet is built around datacenters. Scaling internet performance and associated cloud services necessitates scaling of datacenter connectivity; mostly intra-datacenter connectivity, since more than 2/3 of datacenter traffic concerns east-west connections between hosts inside the datacenter. NEPHELE technology aims to provide a viable solution for gracefully scaling capacity in datacenters, and can therefore underpin the societal implications of enhanced datacenter connectivity. Prominent examples are outlined below:

Supporting the digital single market. Data centres are the enablers for all types of digital goods and services. From value-added services offered by the cloud to instant content delivery provided by edge computing, datacenter technologies offer unlimited opportunities affecting economic growth and access to knowledge. Optical interconnects are essential to remove current barriers in the access of online services and create an environment of equal opportunities, where digital networks and services can prosper.

Increase supercomputer achievements: Optical interconnects are essential in high-performance computing (HPC) systems. Scaling the performance of HPC is expected to have a significant impact in a broad variety of societal challenges, giving rise to breakthroughs in medicine, material design, climate modelling and more.

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