224 research outputs found
Is the Web ready for HTTP/2 Server Push?
HTTP/2 supersedes HTTP/1.1 to tackle the performance challenges of the modern
Web. A highly anticipated feature is Server Push, enabling servers to send data
without explicit client requests, thus potentially saving time. Although
guidelines on how to use Server Push emerged, measurements have shown that it
can easily be used in a suboptimal way and hurt instead of improving
performance. We thus tackle the question if the current Web can make better use
of Server Push. First, we enable real-world websites to be replayed in a
testbed to study the effects of different Server Push strategies. Using this,
we next revisit proposed guidelines to grasp their performance impact. Finally,
based on our results, we propose a novel strategy using an alternative server
scheduler that enables to interleave resources. This improves the visual
progress for some websites, with minor modifications to the deployment. Still,
our results highlight the limits of Server Push: a deep understanding of web
engineering is required to make optimal use of it, and not every site will
benefit.Comment: More information available at https://push.netray.i
High Throughput and Low Latency on Hadoop Clusters Using Explicit Congestion Notification: The Untold Truth
Various extensions of TCP/IP have been proposed to reduce network latency; examples include Explicit Congestion Notification (ECN), Data Center TCP (DCTCP) and several proposals for Active Queue Management (AQM). Combining these techniques requires adjusting various parameters, and recent studies have found that it is difficult to do so while obtaining both high performance and low latency. This is especially true for mixed use data centres that host both latency-sensitive applications and high-throughput workloads such as Hadoop.This paper studies the difficulty in configuration, and characterises the problem as related to ACK packets. Such packets cannot be set as ECN Capable Transport (ECT), with the consequence that a disproportionate number of them are dropped. We explain how this behavior decreases throughput, and propose a small change to the way that non-ECT-capable packets are handled in the network switches. We demonstrate robust performance for modified AQMs on a Hadoop cluster, maintaining full throughput while reducing latency by 85%. We also demonstrate that commodity switches with shallow buffers are able to reach the same throughput as deeper buffer switches. Finally, we explain how both TCP-ECN and DCTCP can achieve the best performance using a simple marking scheme, in constrast to the current preference for relying on AQMs to mark packets.The research leading to these results has received funding from the European Unions Seventh Framework Programme (FP7/2007–2013) under grant agreement number 610456 (Euroserver).
The research was also supported by the Ministry of Economy and Competitiveness of Spain under the contracts TIN2012-34557 and TIN2015-65316-P, Generalitat de Catalunya (contracts 2014-SGR-1051 and 2014-SGR-1272), HiPEAC-3 Network of Excellence (ICT- 287759), and the Severo Ochoa Program (SEV-2011-00067) of the Spanish
Government.Peer ReviewedPostprint (author's final draft
LIGHTYEAR: Using Modularity to Scale BGP Control Plane Verification
Current network control plane verification tools cannot scale to large
networks, because of the complexity of jointly reasoning about the behaviors of
all nodes in the network. In this paper we present a modular approach to
control plane verification, whereby end-to-end network properties are verified
via a set of purely local checks on individual nodes and edges. The approach
targets the verification of safety properties for BGP configurations and
provides guarantees in the face of both arbitrary external route announcements
from neighbors and arbitrary node/link failures. We have proven the approach
correct and also implemented it in a tool called Lightyear. Experimental
results show that Lightyear scales dramatically better than prior control plane
verifiers. Further, we have used Lightyear to verify three properties of the
wide area network of a major cloud provider, containing hundreds of routers and
tens of thousands of edges. To our knowledge no prior tool has been
demonstrated to provide such guarantees at that scale. Finally, in addition to
the scaling benefits, our modular approach to verification makes it easy to
localize the causes of configuration errors and to support incremental
re-verification as configurations are updatedComment: 12 pages (+ 2 pages references), 3 figures submitted to NSDI '2
Cellular access multi-tenancy through small-cell virtualization and common RF front-end sharing
Mobile traffic demand is expected to grow as much as eight-fold in the coming next five years, putting strain in current wireless infrastructures. Meanwhile the
diversity of traffic and standards may explode as well. One of the most common means for matching these mounting requirements is through network densification,
essentially increasing the density of deployment of operators’ base stations in many small cells and handling timing critical traffic at the edge. In this paper we
take a step in that direction by implementing a virtualized small cell base station consisting of multiple, isolated LTE PHY stacks running concurrently on top of a
hypervisor deployed on a cheap, off-the-shelf x86 server and a shared radio head. In particular, we show that it is possible to run multiple virtualized base stations
while achieving throughput equal or close to the theoretical maximum. In contrast to C-RAN (Cloud/Centralized Radio Access Network), our virtualized small cell
base station has full stack at the edge so that a low latency high throughput front-haul, which is necessary in C-RAN architecture, is not needed. This approach brings
all the flexibility and configurability (from network management point of view) that a software based implementation provides while the transparent architecture
enables the possibility of multiple standards sharing the same radio infrastructure.The projects leading to this paper has received funding from the
European Union’s Horizon 2020 research and innovation programme
under grant agreement no. 67156 (Flex5Gware), no. 732174 (ORCA
project) and no. 761536 (5G-Transformer)
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