Data Center TCP (DCTCP): TCP Congestion Control for Data Centers

Cloud computing, social networking and information networks (for search, news feeds, etc) are driving interest in the deployment of large data centers. TCP is the dominant Layer 3 transport protocol in these networks. However, the operating conditions---very high bandwidth links, low round-trip times, small-buffered switches---and traffic patterns cause TCP to perform very poorly. The Data Center TCP (DCTCP) algorithm has recently been proposed as a TCP variant for data centers and addresses these shortcomings.

There is an important class of applications in data centre called online dataintensive (OLDI) application, such as search engine, electronic shopping, and advertising, which has low latency, high throughput, and high burstiness. For better user experience, the query response delay in the data centre is controlled under 300 milliseconds. DCTCP can better meet the requirements of OLDI, but all the switches in the data centre are required to support RED. For data centre that does not fully support RED switch, TCP protocol can only be used. TCP Incast will appear in the application, which is far from the requirements of OLDI application. This paper proposes the TCP protocol of data centre based on window control. It is in existing switches and network devices,and centralized control makes the send window match with the switch queue cache. In the case of ensuring low latency, it keeps the switch queue in a small range of fluctuation, enabling the data centre to meet low latency, high throughput and high burstiness application requirements. Simulation experiments verify that WCTCP congestion control method can effectively solve the above problems. It is 5 times lower than TCPNewReno packet loss rate, 6 times higher than the network utilization rate, and the network performance is close to the DCTCP protocol.

Low latency, high throughput, and fairness are the stringent performance requirements of data center networks. For web applications continue to thrive, data center must remain effective by addressing these challenges. While most of the challenges have been handled by data center specific transport protocols (e.g. DCTCP), these transport protocols are not default options for data center users. Free choice of transport protocols demands careful consideration for an effective solution. We argue that queuing scheme at layer-2 switches hold the key to address these issues. Therefore, in this paper, we present FaLL, a queuing scheme for data center networks that meets following performance requirements: fair share of bandwidth, low queuing latency, high throughput, and ease of deployment. FaLL uses an efficiency module, a fairness module and a target delay based dropping scheme to meet these goals. FaLL requires very small amount of state information. Through rigorous experiments on real testbed, we show that FaLL outperforms various peer solutions in variety of network conditions.

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.

Transactions can simplify distributed applications by hiding data distribution, concurrency, and failures from the application developer. Ideally the developer would see the abstraction of a single large machine that runs transactions sequentially and never fails. This requires the transactional subsystem to provide opacity (strict serializability for both committed and aborted transactions), as well as transparent fault tolerance with high availability. As even the best abstractions are unlikely to be used if they perform poorly, the system must also provide high performance. Existing distributed transactional designs either weaken this abstraction or are not designed for the best performance within a data center. This paper extends the design of FaRM - which provides strict serializability only for committed transactions - to provide opacity while maintaining FaRM's high throughput, low latency, and high availability within a modern data center. It uses timestamp ordering based on real time with clocks synchronized to within tens of microseconds across a cluster, and a failover protocol to ensure correctness across clock master failures. FaRM with opacity can commit 5.4 million neworder transactions per second when running the TPC-C transaction mix on 90 machines with 3-way replication.

For addressing problems such as long delays, latency fluctuations, and frequent timeouts in conventional Transmission Control Protocol (TCP) in a data center environment, Data Center TCP (DCTCP) has been proposed as a TCP replacement to satisfy the requirements of data center networks. It is gaining more popularity in academic as well as industry areas due to its performance in terms of high throughput and low latency, and is widely deployed in data centers. However, according to the recent research about the performance of DCTCP, authors have found that most times the sender’s congestion window reduces to one segment, which results in timeouts. In addition, the authors observed that the nonlinear marking mechanism of DCTCP causes severe queue oscillation, which results in low throughput. To address the above issues of DCTCP, we propose multiple congestion points using double threshold and congestion reaction using window adjustment (DT-CWA) mechanisms for improving the performance of DCTCP by reducing the number of timeouts. The results of a series of simulations in a typical data center network topology using Qualnet network simulator, the most widely used network simulator, demonstrate that the proposed window-based solution can significantly reduce the timeouts and noticeably improves the throughput compared to DCTCP under various network conditions.

Spectrum engineering in flexible grid data center optical networks

Data centers are used to host computation-intensive distributed applications. Since all the applications are distributed in nature, their performance is significantly affected by the communication network. These applications generally create two kinds of flows: large data flows that require high throughput and small control flows that require low delay. These two contradictory requirements are not satisfied efficiently by conventional TCP protocols. The situation becomes worse due to the bursty nature of the data center traffic. DCTCP, a modified version of TCP that was specifically designed for data centers, was originally proposed by Alizadeh et al. in 2010. DCTCP uses an Active Queue Management (AQM) policy where the router marks a packet using Explicit Congestion Notification (ECN), when the number of packets in the queue is more than a marking threshold (K). DCTCP provides lower end-to-end delay in comparison with conventional TCP. However, it tends to provide lower throughput since it uses very small buffer space. In this paper, we have modified the existing DCTCP congestion control algorithm to increase the throughput without significantly increasing delay. We also present an algorithm for dynamic delayed ACK timeout calculation. The performance of TDCTCP (our modified DCTCP algorithm), DCTCP and the TCPNewReno have been studied using OMNeT++ simulator based models. It is shown that TDCTCP provides 15% more throughput and 15% more fairness when compared to DCTCP. Queue length and end-to-end delay increases slightly for TDCTCP. Additionally, TDCTCP provides more stable throughput than DCTCP and TCPNewReno. Though TDCTCP's delay is slightly higher than that of DCTCP, it provides much better throughput than DCTCP for the same marking threshold value.

Wide-area distributed storage system relies on the data replication to achieve the reliability. One of the main challenges brought by data replication is the consistency. As the variety of applications increases, the level of data consistency of the system has evolved from a single level of consistency, such as traditional strong consistency and eventual consistency, to the best level of consistency by adaptively selecting based on the application. However, the existing adaptive consistency schemes are mostly modified based upon the traditional eventual consistency protocol such as Multi-Paxos and rarely consider the diversity of the Data Centers (DCs), which results in high latency and low throughput with limited bandwidth. In this paper, we propose Grouping Multi-Paxos (GM-Paxos), an adaptive consistency protocol based on Multi-Paxos to alleviate the limitation of bandwidth in the system. Taking the characteristics of the DCs and the system environment into consideration, we design a grouping algorithm to find the primary group and only send the request content to the DCs within the primary group at first, in order to save the bandwidth consumption. Experiments show that GM-Paxos can significantly reduce the latency and improve the throughput. Besides, we synchronize the DCs which have high real-time data requirements at first to ensure the reliability of the system.

Today, there is a generalized standard usage of internet for all.The devices via multiple technologies that facilitates to provide few communication methods to scholars to work with. By forming multiple paths in the data center network, latest generation data centers offer maximum bandwidth with robustness. To utilize this bandwidth, it is necessary that different data flows take separate paths. In brief, a single-path transport seems inappropriate for such networks. By using Multipath TCP, we must reconsider data center networks, with a diverse approach as to the association between topology, transport protocols, routing. Multipath TCP allows certain topologies that single path TCP cannot use. In newer generation data centers, Multipath TCP is already deployable using extensively deployed technologies such as Equal-cost multipath routing. But, major benefits will come when data centers are specifically designed for multipath transports. Due to manifold of technologies like Cloud computing, social networking, and information networks there is a need to deploy the number of large data centers. While Transport Control Protocol is the leading Layer-3 transport protocol in data center networks, the operating conditions like high bandwidth, small-buffered switches, and traffic patterns causes poor performance of TCP. Data Center TCP algorithm has newly been anticipated as a TCP option for data centers which address these limitations. It is worth noting that traditional TCP protocol.

Blockchain is a new technology for processing complex and disordered information with respect to business and other industrial applications. This work is aimed at studying the consensus algorithm of blockchain to improve the performance of blockchain. Despite their advantages, the proof of stake (POS) algorithm and the practical Byzantine fault tolerance (PBFT) algorithm have high latency, low throughput, and poor scalability. In this paper, a blockchain hybrid consensus algorithm which combines advantages of the POS and PBFT algorithms is proposed, and the algorithm is divided into two stages: sortition and witness. The proposed algorithm reduces the number of consensus nodes to a constant value by verifiable pseudorandom sortition and performs transaction witness between nodes. The algorithm is improved and optimized from three dimensions: throughput, latency, and scalability. The experimental results show that the improved hybrid consensus algorithm is significantly superior to the previous single algorithms for its excellent scalability, high throughput, and low latency.

The exponential increase of Internet traffic due to cloud computing and other emerging web applications has created the need for more powerful data centres. These warehouse-scale data centres consist of thousands of racks interconnected with commodity switches and consume vast amount of energy. To face the requirements of the future data centres, new interconnection schemes have to be adopted to provide high throughput and reduced power consumption. Several optical interconnects for future data centre networks have recently appeared that provide high throughput, low latency and reduced power consumption. This paper discusses the need for a shift of the data centres networks to the optical domain to reduce the power consumption and meet the bandwidth requirements. Additionally, this paper presents some indicative optical interconnects for high performance data centres that have appeared recently in the research literature. Finally, it presents a qualitative categorization and comparison of these schemes based on their main features such as performance, connectivity and scalability.

High throughput and low latency data processing is essential for systems requiring live decision making, control, and machine learning-optimized data reduction. We focus on two distinct use cases for in-flight streaming data processing for a) X-ray pulse reconstruction at SLAC's LCLS-II Free-Electron Laser and b) control diagnostics at the DIII-D tokamak fusion reactor. Both cases exemplify high throughput and low latency control feedback and motivate our focus on machine learning at the edge where data processing and machine learning algorithms can be implemented in field programmable gate array based hardware immediately after the diagnostic sensors. We present our recent work on a data preprocessing chain which requires fast featurization for information encoding. We discuss several options for such algorithms with the primary focus on our discrete cosine and sine transform-based approach adapted for streaming data. These algorithms are primarily aimed at implementation in field programmable gate arrays, favoring linear algebra operations that are also aligned with the recent advances in inference accelerators for the computational edge.

A cloud middleware for assuring performance and high availability of soft real-time applications

Data from sensor-bearing satellites requires processing aboard terrestrial data centres that use water for cooling at the expense of high data-transfer latency. The reliance of terrestrial data centres on water increases their water footprint and limits the availability of water for other applications. Therefore, data centres with low data-transfer latency and reduced reliance on Earth’s water resources are required. This paper proposes space habitat data centres (SHDCs) with low latency data transfer and that use asteroid water to address these challenges. The paper investigates the feasibility of accessing asteroid water and the reduction in computing platform access latency. Results show that the mean asteroid water access period is 319.39 days. The use of SHDCs instead of non-space computing platforms reduces access latency and increases accessible computing resources by 11.9–33.6% and 46.7–77% on average, respectively.