WDM/TDM over Passive Optical Networks with Cascaded-AWGRs for Data Centers

Data centers based on Passive Optical Networks (PONs) can provide high capacity, low cost, scalability, elasticity and high energy-efficiency. This paper introduces the use of WDM-TDM multiple access in a PON-based data center that offers multipath routing via two-tier cascaded Arrayed Waveguide Grating Routers (AWGRs) to improve the utilization of resources. A Mixed Integer Linear Programming (MILP) model is developed to optimize resource allocation while considering multipath routing. The results show that all-to-all connectivity is achieved in the architecture through the use of two different wavelength within different time slots for the communication between racks in the same or different cells, as well as with the OLT switches

Experimental Evaluation of Server Centric Passive Optical Network Based Data Centre Architecture

Passive optical networks (PON) technology has recently been proposed as a solution for scalability, energy efficiency, high capacity, low cost, flexibility and oversubscription issues in data centres. This paper experimentally demonstrates and discusses the implementation of a server centric PON based data centre architecture with high speed and reliability. The architecture is set up using a set of servers grouped into racks directly connected together and to the Optical Line Terminal (OLT) through gateway servers. The switching and routing functionalities have been embedded into servers using 4x10GE Xilinx NetFPGA. Flow continuity has been observed through live video streaming using IP cameras transmitting over up to 110 km optical connections through WDM nodes and the PON network

Future PON Data Centre Networks

Significant research efforts have been devoted over the last decade to design efficient data centre networks. However, major concerns are still raised about the power consumption of data centres and its impact on global warming in the first place and on the electricity bill of data centres in the second place. Passive Optical Network (PON) technology with its proven performance in residential access networks can provide energy efficient, high capacity, low cost, scalable, and highly elastic solutions to support connectivity inside modern data centres. Here, we focus on introducing PONs in the architecture of data centres to resolve many issues in current data centre designs such as high cost and high power consumption resulting from the large number of access and aggregation switches needed to interconnect hundreds of thousands of servers. PONs can also overcome the problems of switch oversubscription and unbalanced traffic in data centres where PON architectures and protocols have historically been optimised to deal with these problems and handle bursty traffic efficiently. In this thesis, five novel PON data centre designs are proposed and compared to facilitate intra and inter rack communications. In addition to maximising the use of only passive optical devices, other challenges have to be addressed by these designs including off-loading the inter-rack traffic from the Optical Line Terminal (OLT) switch to avoid undesired power consumption and delays, facilitating multi-path routing, and reducing or eliminating the need for expensive tuneable lasers. The Scalability of the proposed architectures in terms of efficiently accommodating hundreds of thousands of servers is discussed. CAPEX and energy consumption of the proposed architectures are also investigated and savings compared to conventional architectures, such as the Fat-Tree and BCube, are demonstrated. The Routing and Wavelength Assignment (RWA) in intra and inter rack communication and the resource provisioning needed to cater for different applications that can be hosted in data centre are optimised using Mixed Integer Linear Programming (MILP) models to minimise the PON designs power consumption. Furthermore, real-time energy-efficient routing and resource provisioning algorithms are developed. In addition to optimising the power consumption, delay is also considered for the delay sensitive applications that can be hosted in the proposed data centre architectures. To further reduce power consumption and overcome issues related to link oversubscription and multi-path routing, Software Defined Network (SDN) based design is proposed

MONet: Heterogeneous Memory over Optical Network for Large-Scale Data Centre Resource Disaggregation

Memory over Optical Network (MONet) system is a disaggregated data center architecture where serial (HMC) / parallel (DDR4) memory resources can be accessed over optically switched interconnects within and between racks. An FPGA/ASIC-based custom hardware IP (ReMAT) supports heterogeneous memory pools, accommodates optical-to-electrical conversion for remote access, performs the required serial/parallel conversion and hosts the necessary local memory controller. Optically interconnected HMC-based (serial I/O type) memory card is accessed by a memory controller embedded in the compute card, simplifying the hardware near the memory modules. This substantially reduces overheads on latency, cost, power consumption and space. We characterize CPU-memory performance, by experimentally demonstrating the impact of distance, number of switching hops, transceivers, channel bonding and bit-rate per transceiver on bit-error rate, power consumption, additional latency, sustained remote memory bandwidth/throughput (using industry standard benchmark STREAMS) and cloud workload performance (such as operations per second, average added latency and retired instructions per second on memcached with YCSB cloud workloads). MONet pushes the CPU-memory operational limit from a few centimetres to 10s of metres, yet applications can experience as low as 10% performance penalty (at 36m) compared to a direct-attached equivalent. Using the proposed parallel topology, a system can support up to 100,000 disaggregated cards