Metronome: adaptive and precise intermittent packet retrieval in DPDK

DPDK (Data Plane Development Kit) is arguably today's most employed framework for software packet processing. Its impressive performance however comes at the cost of precious CPU resources, dedicated to continuously poll the NICs. To face this issue, this paper presents Metronome, an approach devised to replace the continuous DPDK polling with a sleep&wake intermittent mode. Metronome revolves around two main innovations. First, we design a microseconds time-scale sleep function, named hr_sleep(), which outperforms Linux' nanosleep() of more than one order of magnitude in terms of precision when running threads with common time-sharing priorities. Then, we design, model, and assess an efficient multi-thread operation which guarantees service continuity and improved robustness against preemptive thread executions, like in common CPU-sharing scenarios, meanwhile providing controlled latency and high polling efficiency by dynamically adapting to the measured traffic load

TCP Adaptation Framework in Data Centers

Congestion control has been extensively studied for many years. Today, the Transmission Control Protocol (TCP) is used in a wide range of networks (LAN, WAN, data center, campus network, enterprise network, etc.) as the de facto congestion control mechanism. Despite its common usage, TCP operates in these networks with little knowledge of the underlying network or traffic characteristics. As a result, it is doomed to continuously increase or decrease its congestion window size in order to handle changes in the network or traffic conditions. Thus, TCP frequently overshoots or undershoots the ideal rate making it a "Jack of all trades, master of none" congestion control protocol. In light of the emerging popularity of centrally controlled Software-Defined Networks (SDNs), we ask whether we can take advantage of the information available at the central controller to improve TCP. Specifically, in this thesis, we examine the design and implementation of OpenTCP, a dynamic and programmable TCP adaptation framework for SDN-enabled data centers. OpenTCP gathers global information about the status of the network and traffic conditions through the SDN controller, and uses this information to adapt TCP. OpenTCP periodically sends updates to end-hosts which, in turn, update their behaviour using a simple kernel module. In this thesis, we first present two real-world TCP adaptation experiments in depth: (1) using TCP pacing in inter-data center communications with shallow buffers, and (2) using Trickle to rate limit TCP video streaming. We explain the design, implementation, limitation, and benefits of each TCP adaptation to highlight the potential power of having a TCP adaptation framework in today's networks. We then discuss the architectural design of OpenTCP, as well as its implementation and deployment at SciNet, Canada's largest supercomputer center. Furthermore, we study use-cases of OpenTCP using the ns-2 network simulator. We conclude that OpenTCP-based congestion control simplifies the process of adapting TCP to network conditions, leads to improvements in TCP performance, and is practical in real-world settings.Ph

Optical Layer Failures in a Large Backbone

ABSTRACT We analyze optical layer outages in a large backbone, using data for over a year from thousands of optical channels carrying live IP layer traffic. Our analysis uncovers several findings that can help improve network management and routing. For instance, we find that optical links have a wide range of availabilities, which questions the common assumption in fault-tolerant routing designs that all links have equal failure probabilities. We also find that by monitoring changes in optical signal quality (not visible at IP layer), we can better predict (probabilistically) future outages. Our results suggest that backbone traffic engineering strategies should consider current and past optical layer performance and route computation should be based on the outage-risk profile of the underlying optical links. Keywords Wide-area backbone network; Optical layer; Q-factor; Availability; Outage WHY STUDY OPTICAL LINKS? Wide-area backbone networks (WANs) of Internet service providers and cloud providers are the workhorses of Internet traffic delivery. Providers spend millions of dollars building access points around the world and interconnecting them through optical links. Improving the availability and efficiency of the WAN is central to their ability to provide services in a reliable, cost-effective manner. Consequently, there has been significant research into measuring and characterizing various aspects of WANs, including topology, routing, traffic, and reliability However, prior studies tend to focus exclusively on the IP layer, and little is publicly known about the characteristics of the optical layer which forms the physical transmission Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from [email protected]. medium of WANs. There are studies that focus on dispersion and modulation Studying optical layer characteristics of backbone networks is not simply a matter of curiosity. The health of this layer ultimately determines the network's effectiveness at carrying traffic. For instance, poor optical signal quality can lead to corruption and even silent packet drops We uncover several notable characteristics of this backbone. First, the availability (i.e., uptime) of different optical segments and channels differs by over three orders of magnitude. Second, the distribution of time to repair of planned outages is similar for both optical segments and channels, even though a segment outage tends to represent an order of magnitude greater impairment in network capacity. Third, almost four in five optical segment outages are unidirectional; i.e., one direction is functional while the other is down. Finally, outages can be predicted (probabilistically) based on sudden drops in optical signal quality (which is not visible at the IP layer). There is a 50% chance of an outage within an hour of a drop event and a 70% chance of an outage within one day. Our findings motivate smarter IP layer management and routing, one that is aware of optical layer characteristics. For instance, a common assumption in fault-tolerant routing schemes is that each IP layer link is equally likely to fai

Experimental study of router buffer sizing

During the past four years, several papers have proposed rules for sizing buffers in Internet core routers. Appenzeller et al. suggest that a link needs a buffer of size (� �), where � is the capacity of the link, and is the number of flows sharing the link. If correct, buffers could be reduced by 99 % in a typical backbone router today without loss in throughput. Enachecsu et al., and Raina et al. suggest that buffers can be reduced even further to 20-50 packets if we are willing to sacrifice a fraction of link capacities, and if there is a large ratio between the speed of core and access links. If correct, this is a five orders of magnitude reduction in buffer sizes. Each proposal is based on theoretical analysis and validated using simulations. Given the potential benefits (and the risk of getting it wrong!) it is worth asking if these results hold in real operational networks. In this paper, we report buffer-sizing experiments performed on real networks- either laboratory networks with commercial routers as well as customized switching and monitorin