Reducing Internet Latency : A Survey of Techniques and their Merit

Bob Briscoe, Anna Brunstrom, Andreas Petlund, David Hayes, David Ros, Ing-Jyh Tsang, Stein Gjessing, Gorry Fairhurst, Carsten Griwodz, Michael WelzlPeer reviewedPreprin

Providing quality of service over high speed electronic and optical switches

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (leaves 235-239).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.In a network, multiple links are interconnected by means of switches. A switch is a device with multiple input and output links, and its job is to move data from the input links to the output links. In this thesis, we focus on a number of fundamental issues concerning the quality of service provided by electronic and optical switches. We discuss various mechanisms that enable the support of quality of service requirements. In particular, we explore fundamental limitations of current high speed packet switches and develop new techniques and architectures that make possible the provision of certain service guarantees. We then study optical wavelength switches and illustrate how similar ideas can be applied in a manner consistent with the current state of optical switching technology. First, we focus on providing rate guarantees over packet switches. We develop a method called rate quantization which converts the set of desired rates into a certain discrete set such that the quality of service guarantees can be greatly improved with a small resource speedup. Moreover, quantization simplifies rate provisioning for dynamically changing traffic demands since it allows service opportunities for different input output link pairs to be scheduled with minimal dependence. We illustrate an isomorphism between packet switch schedulers and Clos networks to develop such schedulers.(cont.) Next, we evaluate the amount of resource speedup necessary for single stage switches to support multicast rates. This speedup limits the scalability of a single stage multicast switch a great deal. We present an in depth study of multistage switches and propose a number of architectures, along with associated routing and scheduling algorithms. We illustrate how the presence of multiple paths between input output pairs can be exploited to improve the performance of a switch and simplify the scheduling algorithms. Some of our architectures are capable of providing multicast rate guarantees without a need for a resource speedup. We extend our results on switch schedulers and use them for providing service guarantees over optical wavelength switches. We will take the limitations of the optical crossconnects and unavailability of optical memory technology into account, and modify the procedure we developed for electronic switches to make them suitable for various optical wavelength switches. These results will provide understanding of when to move optical switching closer to the end users for an efficient utilization of resources in networks with both optical and electronic technologies.by Can Emre Koksal.Ph.D

Ethernet Fronthaul and Time-Sensitive Networking for 5G and Beyond Mobile Networks

Ethernet has been proposed to be used as the transport technology in the future fronthaul network. For this purpose, a model of switched Ethernet architecture is developed and presented in order to characterise the performance of an Ethernet mobile fronthaul network. The effects of traditional queuing regimes, including Strict Priority (SP) and Weighted Round Robin (WRR), on the delay and delay variation of LTE streams under the presence of background Ethernet traffic are investigated using frame inter-arrival delay statistics. The results show the effect of different background traffic rates and frame sizes on the mean and Standard Deviation (STD) of the LTE traffic frame inter-arrival delay and the importance of selecting the most suitable queuing regime based on the priority level and time sensitivity of the different traffic types. While SP can be used with traffic types that require low delay and Frame Delay variation (FDV), this queuing regime does not guarantee that the time sensitive traffic will not encounter an increase in delay and FDV as a result of contention due to the lack of pre-emptive mechanisms. Thus, the need for a queuing regime that can overcome the limitations of traditional queuing regimes is shown. To this extent, Time Sensitive Networking (TSN) for an Ethernet fronthaul network is modelled. Different modelling approaches for a Time Aware Shaper (TAS) based on the IEEE 802.1Qbv standard in Opnet/Riverbed are presented. The TAS model is assumed to be the scheduling entity in an Ethernet-based fronthaul network model, located in both the Ethernet switches and traffic sources. The TAS with/without queuing at the end stations has been presented as well. The performance of the TAS is compared to that of SP and WRR and is quantified through the FDV of the high priority traffic when this contends with lower priority traffic. The results show that with the TAS, contentioninduced FDV can be minimized or even completely removed. Furthermore, variations in the processing times of networking equipment, due to the envisaged softwarization of the next generation mobile network, which can lead to time variation in the generation instances of traffic in the Ethernet fronthaul network (both in the end-nodes and in switches/aggregators), have been considered in the TAS design. The need for a Global Scheduler (GS) and Software Defined Networking (SDN) with TAS is also discussed. An Upper Physical layer functional Split (UPS), specifically a pre-resource mapper split, for an evolved Ethernet fronthaul network is modelled. Using this model and by incorporating additional traffic sources, an investigation of the frame delay and FDV limitations in this evolved fronthaul is carried out. The results show that contention in Ethernet switch output ports causes an increase in the delay and FDV beyond proposed specifications for the UPS and other time sensitive traffic, such as legacy Common Public Radio Interface (CPRI)-type traffic. While TAS can significantly reduce or even remove FDV for UPS traffic and CPRI-type traffic, it is shown that TAS design aspects have to carefully consider the different transmission characteristics, especially the transmission pattern, of the contending traffic flows. For this reason, different traffic allocations within TAS window sections are proposed. Furthermore, it is demonstrated that increased link rates will be important in enabling longer fronthaul fibre spans (more than ten Kilometres fibre spans with ten Gigabit Ethernet links). The results also show that using multiple hops (Ethernet switches/aggregators) in the network can result in a reduction in the amount of UPS traffic that can be received within the delay and FDV specifications. As a result, careful considerations of the fibre span length and the number of hops in the fronthaul network should be made

Disaggregated Servers for Future Energy Efficient Data Centres

The popularity of the Internet and the demand for 24/7 services uptime is driving system performance and reliability requirements to levels that today’s data centres can no longer support. This thesis examines the traditional monolithic conventional server (CS) design and compares it to a new design paradigm known as disaggregated server (DS). The DS design arranges data centres resources in physical pools such as processing, memory and IO module pools; rather than packing each subset in a single server. In this work, we study energy efficient resource provisioning and virtual machine (VM) allocation in the DS based data centres compared to CS based data centres. First, we developed a mixed integer linear programming (MILP) model to optimise VM allocation for DS based data centre. Our results indicate that considering pooled resources yields up to 62% total saving in power consumption compared to the CS approach. Due to the MILP high computational complexity, we developed an energy efficient, fast and scalable resource provisioning heuristic (EERP-DS), based on the MILP insights, with comparable power efficiency to the MILP. Second, we extended the resources provisioning and VM allocation MILP to include the data centre communication fabric power consumption. The results show that the inclusion of the communication fabric still yields considerable power savings compared to the CS approach, up to 48% power saving. Third, we developed an energy efficient resource provisioning for DS with communication fabric heuristic (EERP-DSCF). EERP-DSCF achieved comparable results to the second MILP and with it we can extend the number of served VMs where the MILP scalability for big number of VMs is challenging. Finally, we present our new design for the photonic DS based data centre architecture supplemented with a complete description of the architecture components, communication patterns and some recommendations for the design implementation challenges

A Scalable and Adaptive Network on Chip for Many-Core Architectures

In this work, a scalable network on chip (NoC) for future many-core architectures is proposed and investigated. It supports different QoS mechanisms to ensure predictable communication. Self-optimization is introduced to adapt the energy footprint and the performance of the network to the communication requirements. A fault tolerance concept allows to deal with permanent errors. Moreover, a template-based automated evaluation and design methodology and a synthesis flow for NoCs is introduced

Concurrent Multipath Transfer: Scheduling, Modelling, and Congestion Window Management

Known as smartphones, multihomed devices like the iPhone and BlackBerry can simultaneously connect to Wi-Fi and 4G LTE networks. Unfortunately, due to the architectural constraints of standard transport layer protocols like the transmission control protocol (TCP), an Internet application (e.g., a file transfer) can use only one access network at a time. Due to recent developments, however, concurrent multipath transfer (CMT) using the stream control transmission protocol (SCTP) can enable multihomed devices to exploit additional network resources for transport layer communications. In this thesis we explore a variety of techniques aimed at CMT and multihomed devices, such as: packet scheduling, transport layer modelling, and resource management. Some of our accomplishments include, but are not limited to: enhanced performance of CMT under delay-based disparity, a tractable framework for modelling the throughput of CMT, a comparison of modelling techniques for SCTP, a new congestion window update policy for CMT, and efficient use of system resources through optimization. Since the demand for a better communications system is always on the horizon, it is our goal to further the research and inspire others to embrace CMT as a viable network architecture; in hopes that someday CMT will become a standard part of smartphone technology