Resource utilization of modern data centers is significantly limited by the mismatch between the diversity of the resources required by running applications and the fixed amount of hardwired resources (e.g., number of central processing unit CPU cores, size of memory) in the server blades. In this regard, the concept of function disaggregation is introduced, where the integrated server blades containing all types of resources are replaced by the resource blades including only one specific function. Therefore, disaggregated data centers can offer high flexibility for resource allocation and hence their resource utilization can be largely improved. In addition, introducing function disaggregation simplifies the system upgrade, allowing for a quick adoption of new generation components in data centers. However, the communication between different resources faces severe problems in terms of latency and transmission bandwidth required. In particular, the CPU-memory interconnects in fully disaggregated data centers require ultra-low latency and ultrahigh transmission bandwidth in order to prevent performance degradation for running applications. Optical fiber communication is a promising technique to offer high capacity and low latency, but it is still very challenging for the state-of-the-art optical transmission technologies to meet the requirements of the fully disaggregated data centers. In this paper, different levels of function disaggregation are investigated. For the fully disaggregated data centers, two architectural options are presented, where optical interconnects are necessary for CPU-memory communications. We review the state-of-the-art optical transmission technologies and carry out performance assessment when employing them to support function disaggregation in data centers. The results reveal that function disaggregation does improve the efficiency of resource usage in the data centers, although the bandwidth provided by the state-of-the-art optical transmission technologies is not always sufficient for the fully disaggregated data centers. It calls for research in optical transmission to fully utilize the advantages of function disaggregation in data centers. I. INTRODUCTION Cloud computing is one of the major services provided by modern data centers (DCs), where users are able to freely choose resources and operating systems (OSs) for running their applications without considering the underlying
Even if Passive Optical Networks (PONs) have proven to be more energy-efficient that other access solutions, energy consumption minimization is becoming an important research target also in PON. In particular, to sustain the increased bandwidth demand of emerging applications in the access section of the network, new hybrid PON solutions employing WDM/TDM are being investigated. Compared with classics PON, the architecture of WDM/TDM-PONs requires more transceivers/receivers, hence they are expected to be more energy hungry than classical PONs. In this paper, we focus on the power consumption minimization in WDM/TDM-PONs and we propose an energy-efficient mechanism based on Dynamic Bandwidth and Wavelength Allocation whose objective is to switch off, whenever possible, the unnecessary receivers for upstream traffic at the Optical Line Terminal (OLT). Our proposed energy saving mechanism is able to decrease energy consumption at the OLT of about 30%, while maintaining the penalty introduced in terms of channel utilization and packet delay within an acceptable range. Detailed implementation of the proposed algorithm is presented, and simulation results are reported to quantify energy savings and effects on network performance on different network scenarios.
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