Space-Division Multiplexing in Data Center Networks: On Multi-Core Fiber Solutions and Crosstalk-Suppressed Resource Allocation

The rapid growth of traffic inside data centers caused by the increasing adoption of cloud services necessitates a scalable and cost-efficient networking infrastructure. Space-division multiplexing (SDM) is considered as a promising solution to overcome the optical network capacity crunch and support cost-effective network capacity scaling. Multi-core fiber (MCF) is regarded as the most feasible and efficient way to realize SDM networks, and its deployment inside data centers seems very likely as the issue of inter-core crosstalk (XT) is not severe over short link spans (<1  km ) compared to that in long-haul transmission. However, XT can still have a considerable effect in MCF over short distances, which can limit the transmission reach and in turn the data center’s size. XT can be further reduced by bi-directional transmission of optical signals in adjacent MCF cores. This paper evaluates the benefits of MCF-based SDM solutions in terms of maximizing the capacity and spatial efficiency of data center networks. To this end, we present an analytical model for XT in bi-directional normal step-index and trench-assisted MCFs and propose corresponding XT-aware core prioritization schemes. We further develop XT-aware spectrum resource allocation strategies aimed at relieving the complexity of online XT computation. These strategies divide the available spectrum into disjoint bands and incrementally add them to the pool of accessible resources based on the network conditions. Several combinations of core mapping and spectrum resource allocation algorithms are investigated for eight types of homogeneous MCFs comprising 7–61 cores, three different multiplexing schemes, and three data center network topologies with two traffic scenarios. Extensive simulation results show that combining bi-directional transmission in dense core fibers with tailored resource allocation schemes significantly increases the network capacity. Moreover, a multiplexing scheme that combines SDM and WDM can achieve up to 33 times higher link spatial efficiency and up to 300 times greater capacity compared to a WDM solution

Disaggregated optical data center in a box network using parallel OCS topologies

Two parallel OCS topologies are proposed that deliver 95 nsec round-trip latency on disaggregated optical data center in a box system. They offer 40% cost and 68% power consumption efficiency at maximum IT resource utilization

Optically Disaggregated Data Centers With Minimal Remote Memory Latency: Technologies, Architectures, and Resource Allocation

Disaggregated rack-scale data centers have been proposed as the only promising avenue to break the barrier of the fixed CPU-to-memory proportionality caused by main-tray direct-attached conventional/traditional server-centric systems. However, memory disaggregation has stringent network requirements in terms of latency, energy efficiency, bandwidth, and bandwidth density. This paper identifies all the requirements and key performance indicators of a network to disaggregate IT resources while summarizing the progress and importance of optical interconnects. Crucially, it proposes a rack-and-cluster scale architecture, which supports the disaggregation of CPU, memory, storage, and/or accelerator blocks. Optical circuit switching forms the core of this architecture, whereas the end-points (IT resources) are equipped with on-chip programmable hybrid electrical packet/circuit switches. This architecture offers dynamically reconfigurable physical topology to form virtual ones, each embedded with a set of functions. It analyzes the latency overhead of disaggregated DDR4 (parallel) and the proposed hybrid memory cube (serial) memory elements on the conventional and the proposed architecture. A set of resource allocation algorithms are introduced to (1) optimally select disaggregated IT resources with the lowest possible latency, (2) pool them together by means of a virtual network interconnect, and (3) compose virtual disaggregated servers. Simulation findings show up to a 34% resource utilization increase over traditional data centers while highlighting the importance of the placement and locality among compute, memory, and storage resources. In particular, the network-aware locality-based resource allocation algorithm achieves as low as 15 ns, 95 ns, and 315 ns memory transaction round-trip latency on 63%, 22%, and 15% of the allocated virtual machines (VMs) accordingly while utilizing 100% of the CPU resources. Furthermore, a formulation to parameterize and evaluate the additional financial costs endured by disaggregation is reported. It is shown that the more diverse the VM requests are, the higher the net financial gain is. Finally, an experiment was carried out using silicon photonic midboard optics and an optical circuit switch, which demonstrates forward error correction free 10−1210−12 bit error rate performance on up to five-tier scale-out networks

dReDBox: Materializing a full-stack rack-scale system prototype of a next-generation disaggregated datacenter

Current datacenters are based on server machines, whose mainboard and hardware components form the baseline, monolithic building block that the rest of the system software, middleware and application stack are built upon. This leads to the following limitations: (a) resource proportionality of a multi-tray system is bounded by the basic building block (mainboard), (b) resource allocation to processes or virtual machines (VMs) is bounded by the available resources within the boundary of the mainboard, leading to spare resource fragmentation and inefficiencies, and (c) upgrades must be applied to each and every server even when only a specific component needs to be upgraded. The dRedBox project (Disaggregated Recursive Datacentre-in-a-Box) addresses the above limitations, and proposes the next generation, low-power, across form-factor datacenters, departing from the paradigm of the mainboard-as-a-unit and enabling the creation of function-block-as-a-unit. Hardware-level disaggregation and software-defined wiring of resources is supported by a full-fledged Type-1 hypervisor that can execute commodity virtual machines, which communicate over a low-latency and high-throughput software-defined optical network. To evaluate its novel approach, dRedBox will demonstrate application execution in the domains of network functions virtualization, infrastructure analytics, and real-time video surveillance.This work has been supported in part by EU H2020 ICTproject dRedBox, contract #687632.Peer ReviewedPostprint (author's final draft

dRedDbox: Demonstrating disaggregated memory in an optical Data Centre

This paper showcases the first experimental demonstration of disaggregated memory using the dRedDbox optical Data Centre architecture. Experimental results demonstrate the 4-tier network scalability and performance of the system at the physical and application layer

MCF-SMF Hybrid Low-Latency Circuit-Switched Optical Network for Disaggregated Data Centers

This paper proposes and experimentally evaluates a fully developed novel architecture with purpose built low latency communication protocols for next generation disaggregated data centers (DDCs). In order to accommodate for capacity and latency needs of disaggregated IT elements (i.e. CPU, memory), this architecture makes use of a low latency and high capacity circuit switched optical network for interconnecting various endpoints, that are equipped with multi-channel Silicon photonic based integrated transceivers. In a move to further decrease the perceived latency between various disaggregated IT elements, this paper proposes a) a novel network topology, which cuts down the latency over the optical network by 34% while enhancing system scalability and b) channel bonding over multicore fiber (MCF) switched links to reduce head to tail latency and in turn increase sustained memory bandwidth for disaggregated remote memory. Furthermore, to reduce power consumption and enhance space efficiency, the integration of novel multi core fiber (MCF) based transceivers, fibers and optical switches are proposed and experimentally validated at the physical layer for this topology. It is shown that the integration of MCF based subsystems in this topology can bring about an improvement in energy efficiency of the optical switching layer which is above 60%. Finally, the performance of this proposed architecture and topology is evaluated experimentally at the application layer where the perceived memory throughput for accessing remote and local resources is measured and compared using electrical circuit and packet switching. The results also highlight a multi fold increase in application perceived memory throughput over the proposed DDC topology by utilization and bonding of multiple optical channels to interconnect disaggregated IT elements that can be carried over MCF links

Demonstration of NFV for mobile edge computing on an optically disaggregated datacentre in a box

This demonstrator showcases the hardware and software integration achieved by the dReDBox project [1] towards realization of a novel architecture using dynamically-reconfigurable optical interconnects to create a flexible, scalable and efficient disaggregated datacentre infrastructure

Comparison of SDM-WDM based Data Center Networks with equal/unequal core pitch Multi-Core Fibers

A wavelength-dependent crosstalk calculation formula for bi-directional MCF with unequal core pitches is derived. SDM-WDM based DCN simulations indicate that MCF core density and layout play a significant role on optimizing various scales of DCNs

Genetic Algorithm Optimization of Multi Core Fibre Transmission Links based on Silicon Photonic Transceivers

We demonstrate a genetic algorithm based system that can optimize optical interconnects using silicon photonic multi-core fibre coupled transceiver. The GA selects 48 parameters to deliver a minimum 6.9×10−16 BER on channels with diverse losses