Synergistic Switch Control Enabled Optical Data Center Networks

We demonstrate the implementation and performance of optical burst switching in data centers. We propose the use of hybrid burst assembly algorithm and compare both the first-fit and horizon scheduling algorithms in a fat-tree topology.

The explosive growth of data center (DC) traffic imposes unprecedented challenges on the current electrical switch-based data center networks (DCNs) with the bottleneck of limited bandwidth and high latency. Benefitting from transparency to the data rate and format, optical switching with theoretically infinite bandwidth could overcome the bandwidth bottleneck of electrical switching DCNs. However, DCNs normally deploy multitenant applications with a variety of DC traffic. It is hard to reconfigure the optical interconnections in real-time to provide adaptable bandwidth to the traffic with heterogeneous characteristics. Moreover, to improve the bandwidth utilization, statistical multiplexing is generally deployed in optical DCNs to forward the traffic flow in a time slot, which requires the network time to be precisely synchronized to all network nodes. For fast optical switches with a nanosecond switching configuration time, overall end node times must be synchronized at subnanosecond magnitude. In this paper, we propose and experimentally investigate a reconfigurable and picosecond-synchronized optical DCN (ReSAW) based on an arrayed waveguide grating router (AWGR) and the White Rabbit (WR) protocol. A scheduler based on a distributed field-programmable gate array is implemented in the proposed ReSAW to realize flexible wavelength configuration by controlling the fast laser array based on semiconductor optical amplifiers (SOAs) according to time slot and traffic priority. Moreover, the WR protocol is implemented in optical DCNs for what we believe is the first time to synchronize the time of the distributed top of racks (ToRs). The experimental demonstration validates that ReSAW achieves an average end-to-end latency of 317.44 ns and a precise synchronized time with an average 386 ps skew. When the load is 0.4, the packet loss after ReSAW reconfiguration is less than 1.83 × 10 − 6 , and the network latency is less than 1.73 µs. Based on the experimental parameters and results, the OMNeT++ simulation model is built to further verify the reconfigurability and scalability of the ReSAW network. Results show that the packet loss rate and latency performance increase 8.24% and 12.47%, respectively, at a load of 0.6 as the ReSAW network scales from 2560 to 40,960 servers compared to before the reconfiguration.

We investigate the performance of a novel flat data center network (DCN) architecture based on distributed buffer-less optical switches and fast flow control. Scalability of the novel DCN is assessed by numerical simulation of medium and large size data centers reporting an end-to-end latency of less than 8μs (including retransmission), a packet loss 9Tb/s average network throughput under load of 0.4.

The rise of Cloud Computing and Big Data has created the need for morepowerful warehouse-scale cloud data centers, which usually comprise hundreds of thousands ofservers with highaccess bandwidth (>10Gb/s) or more, and cost-effective intra- and inter- data center networks(DCNs) to provide switching and interconnect among all servers. However, the current DCNs sufferfrom limited throughput, large latencies and highpower consumption, and will not be able to sustainthe projected future DCN traffic demandswithout consuming excessive amounts of power. Optical interconnection networks capable of supporting high throughput, high bandwidth, low latency, low power consumptionand full-bandwidth communication among all servers have been proposedas a promising solution by performing switchingat the optical domain, thus greatly improving the performance of the cloud data centers.

Data centers (DCs), owing to the exponential growth of Internet services, have emerged as an irreplaceable and crucial infrastructure to power this ever-growing trend. A DC typically houses a large number of computing and storage nodes, interconnected by a specially designed network, namely, DC network (DCN). The DCN serves as a communication backbone and plays a pivotal role in optimizing DC operations. However, compared to the traditional network, the unique requirements in the DCN, for example, large scale, vast application diversity, high power density, and high reliability, pose significant challenges to its infrastructure and operations. We have observed from the premium publication venues (e.g., journals and system conferences) that increasing research efforts are being devoted to optimize the design and operations of the DCN. In this paper, we aim to present a systematic taxonomy and survey of recent research efforts on the DCN. Specifically, we propose to classify these research efforts into two areas: 1) DCN infrastructure and 2) DCN operations. For the former aspect, we review and compare the list of transmission technologies and network topologies used or proposed in the DCN infrastructure. For the latter aspect, we summarize the existing traffic control techniques in the DCN operations, and survey optimization methods to achieve diverse operational objectives, including high network utilization, fair bandwidth sharing, low service latency, low energy consumption, high resiliency, and etc., for efficient DC operations. We finally conclude this survey by envisioning a few open research opportunities in DCN infrastructure and operations.

As the infrastructure of cloud computing and big data, data centers have been deployed widely. Then, how to make full use of the computing and storage resources in data centers will be the focus. Data center networks are considered important solution for the problem above, which include intra-data center and inter-data center networks. Both of them will depend on the optical networking due to its advantages, such as high bandwidth, low latency, and low energy consumption. Data center interconnected by flexi-grid optical networks is a promising scenario to allocate spectral resources for applications in a dynamic, tunable and efficient control manner. Compared with inter-data center, optical interconnect in intra-data center networks is a more pressing need and promising scenario to accommodate these applications in a dynamic, flexible and efficient manner. OpenFlow based Software Defined Networking (SDN) is considered as a good technology, which is very suitable for data center networks. This paper mainly focuses on the data center optical networks based on software defined networking (SDN), which can control the heterogeneous networks with unified resource interface. Architecture and experimental demonstration of OpenFlow-based optical interconnects in intra-data center Networks and OpenFlow-based flexi-grid optical networks for inter-data center are presented in the paper respectively. Some future works are listed finally.

Data center networks (DCNs) are at the forefront of a radical transformation, fueled by the rapid rise of artificial intelligence (AI), cloud-native adoption, and enterprise digitalization, which together place unprecedented demands on their design and performance. From healthcare AI and intelligent transportation to business analytics, modern DCNs are expected to support a diverse and evolving mix of bandwidth-demanding applications, each with distinct quality of service (QoS) requirements. Yet, most state-of-the-art DCN solutions rely on oversimplified DCN data traffic models, failing to address the required application-level differentiation in terms of end-to-end (E2E) latency demands. In response, we propose ALAS-DCN, a novel, to our knowledge, application-aware, low-latency, scalable DCN architecture, based on optical packet switching in the intra-rack and inter-rack domains that is both designed and rigorously evaluated using commercial QoS specifications and realistic traffic patterns of different applications coexisting within the same DCN. ALAS-DCN integrates three hierarchical optical sub-networks: intra-rack, inter-rack, and bridge, each governed by a custom wavelength division multiplexing (WDM) medium access control (MAC) protocol that dynamically prioritizes critical traffic packets, according to the specific application E2E latency demands. Unlike prior approaches, our evaluation leverages realistic workload traces generated by established traffic generators, capturing the application diversity within modern data center (DC) environments. Extensive experimental simulations across five representative DC categories, each hosting a different mix of modern applications, demonstrate that ALAS-DCN consistently achieves up to 95% throughput efficiency and sub-µs latency for high priority traffic across a variety of applications, consistently meeting their differentiated latency constraints. Scalable up to 20,000 servers, ALAS-DCN redefines the DCN as not just a transport layer but an intelligent enabler of next-generation application performance.

Spectrum engineering in flexible grid data center optical networks

We present a control plane architecture to enable software-addressable optical acceleration from the application layer. The architecture is experimentally examined on a cluster-computing test-bed by enabling physical layer optical multicasting on-demand for the application layer to achieve non-blocking performance.

As the scale of data centers and cloud computing applications increases, data center networks play a critical role in meeting the huge communication bandwidth requirement of such applications. The scalability of conventional electronic data center networks is limited by wiring complexity and reaching distance of links under fixed power budget. To overcome this problem, in this paper we propose a nonblocking hybrid switch architecture, called NEO (Nonblocking Electronic and Optical), which is able to provide nonblocking interconnections for as many as 1,000,000 servers in a data center. NEO maintains electronic interconnections for intra-pod networks, while providing interpod interconnections by optical core switches, which not only increases the scalability of the switch architecture, but also lowers the switch cost and power consumption compared to other existing optical switch architectures. We also design a packet scheduler for NEO, which adopts a credit flow control mechanism and a parallel scheduling algorithm to avoid packet loss, and provide low communication latency. Our simulation results demonstrate that NEO achieves very low average packet delay compared to other existing optical switching architectures under various traffic patterns.

A hardware‐efficient slope‐error (SE) algorithm based four‐level pulse amplitude modulation (PAM4) baud rate clock and data recovery (CDR) scheme is proposed. The algorithm uses three adjacent data information to obtain slope information, thus reduces the required error samplers by 75% compared to the widely used baud rate CDR, namely, Mueller Müller (MM) CDR when working at same phase detector (PD) gain. The power efficiency of the CDR loop is improved by 36% compared to MM CDR. The proposed PAM4 baud rate CDR does not bring in extra block except for PD, which makes it easy to be extended from adaptive decision feedback equalisation. A 40 Gb/s PAM4 receiver with the proposed CDR is designed in 55 nm CMOS process. The simulated jitter tolerance of the CDR at high frequency exceeds the SONET OC‐768 JTOL mask by at least 0.35 UI at the bit error rate of 10 −12 . The CDR loop consumes 106 mW from a 1.2 V supply and occupies an active area of 0.1 mm 2 .

A 2.5-Gb/s monolithic clock and data recovery (CDR) IC using the phase-locked loop (PLL) technique is fabricated using Si bipolar technology. The output jitter characteristics of the CDR can be controlled by designing the loop-gain design and by using the switched-filter PLL technique. The CDR IC can be used in local-area networks (LANs) and in long-haul backbone networks or wide-area networks (WANs). Its power consumption is only 0.4 W. For LANs, the jitter generation of the CDR when the loop gain is optimized is 1.2 ps (0.003 UI). The jitter characteristics of the CDR optimized for WANs meet all three types of STM-I6 jitter specifications given in ITU-T Recommendation G.958. This is the first report on a CDR that can be used for both LAN's and WAN's. This paper also describes the design method of the jitter characteristics of the CDR for LANs and WANs.

Modeling and performance analysis of a data center network (DCN) combining optical packet switching (OPS) and agile optical circuit switching (OCS) in a unified platform are presented. Hybrid optoelectronic packet routers which combine optical switching fabric and electronic buffers are used, supporting 100 Gbit/s (25 Gbit/s × 4 wavelengths) optical packets. OCS transmission is implemented by a novel “express path,” (ExP) an instant wavelength path on demand, which enables certain flows following the ExP with no packet contention, whereas ordinary OPS packets are switched with a deflection routing algorithm and buffering for contention resolution. This architecture can support OCS for large and reliability-sensitive data transferring and OPS for latency-sensitive applications. The performance of the network is investigated via numerical simulations of top-of-rack switch (ToR)-to-ToR traffic in an N-dimensional (up to 4096 node) torus topology. We have made the following observations: 1) torus topology results in high throughput and can be scaled out by increasing the dimension; 2) contention resolution between OPS and agile OCS is needed and our proposed strategies enhance the overall performance; and 3) in a lightly to moderately loaded case of OPS traffic, more than 100 ExPs can be supported simultaneously with acceptable affect on OPS.

Recently, optical devices with periodic structures are applied to metamaterial, holography, photonic crystals and so on. In particular, the research of photonic crystal or metamaterials is expected as application of optical confinement, optical switching or optical control, and also that of holography is expected as application of optical lens. As application of our structure, we consider an optical devices such as propagating the electromagnetic wave along the waveguide with the periodically defects. Therefore, it is extremely important to investigate the scattering and guiding problem of electromagnetic waves with periodic structure. On the one hand, photonic crystals such as optical nanostructures with periodically permittivity distribution are known as technology which can be controlled the electromagnetic wave in the periodic structure by using interaction of both the wave nature of light and periodicity. Then, in the design of photonic crystals with periodic array of optical wavelength degree, it is very important to investigate the stop band regions or photonic band gaps. But, the propagation constants of photonic crystal structure at the stop band area are not analyzed in detailed, and also several numerical results are reported only electromagnetic field distribution utilizing the FDTD method and another numerical technique.

Optical switching based small-world data center network