205 research outputs found
A Reconfigurable High-Performance Optical Data Center Architecture
Optical data center network architectures are becoming attractive because of
their low energy consumption, large bandwidth, and low cabling complexity.
In\cite{Xu1605:PODCA}, an AWGR-based passive optical data center architecture
(PODCA) is presented. Compared with other optical data center architectures,
e.g., DOS \cite{ye2010scalable}, Proteus \cite{singla2010proteus}, and Petabit
\cite{xia2010petabit}, PODCA can save up to 90 on power consumption and
88 in cost. Also, average latency can be low as 9 s at close to
100 throughput. However, PODCA is not reconfigurable and cannot optimize
the network topology to dynamic traffic.
In this paper, we present a novel, scalable and flexible reconfigurable
architecture called RODCA. RODCA is built on and augments PODCA with a flexible
localized intra-cluster optical network. With the reconfigurable intra-cluster
network, racks with mutually large traffic can be located within the same
cluster, and share the large bandwidth of the intra-cluster network. We present
an algorithm for DCN topology reconfiguration, and present simulation results
to demonstrate the effectiveness of reconfiguration
On the Optimality of Scheduling Dependent MapReduce Tasks on Heterogeneous Machines
MapReduce is the most popular big-data computation framework, motivating many
research topics. A MapReduce job consists of two successive phases, i.e. map
phase and reduce phase. Each phase can be divided into multiple tasks. A reduce
task can only start when all the map tasks finish processing. A job is
successfully completed when all its map and reduce tasks are complete. The task
of optimally scheduling the different tasks on different servers to minimize
the weighted completion time is an open problem, and is the focus of this
paper. In this paper, we give an approximation ratio with a competitive ratio
, where is the number of servers and is the
task-skewness product. We implement the proposed algorithm on Hadoop framework,
and compare with three baseline schedulers. Results show that our DMRS
algorithm can outperform baseline schedulers by up to
Chronos: A Unifying Optimization Framework for Speculative Execution of Deadline-critical MapReduce Jobs
Meeting desired application deadlines in cloud processing systems such as
MapReduce is crucial as the nature of cloud applications is becoming
increasingly mission-critical and deadline-sensitive. It has been shown that
the execution times of MapReduce jobs are often adversely impacted by a few
slow tasks, known as stragglers, which result in high latency and deadline
violations. While a number of strategies have been developed in existing work
to mitigate stragglers by launching speculative or clone task attempts, none of
them provides a quantitative framework that optimizes the speculative execution
for offering guaranteed Service Level Agreements (SLAs) to meet application
deadlines. In this paper, we bring several speculative scheduling strategies
together under a unifying optimization framework, called Chronos, which defines
a new metric, Probability of Completion before Deadlines (PoCD), to measure the
probability that MapReduce jobs meet their desired deadlines. We systematically
analyze PoCD for popular strategies including Clone, Speculative-Restart, and
Speculative-Resume, and quantify their PoCD in closed-form. The result
illuminates an important tradeoff between PoCD and the cost of speculative
execution, measured by the total (virtual) machine time required under
different strategies. We propose an optimization problem to jointly optimize
PoCD and execution cost in different strategies, and develop an algorithmic
solution that is guaranteed to be optimal. Chronos is prototyped on Hadoop
MapReduce and evaluated against three baseline strategies using both
experiments and trace-driven simulations, achieving 50% net utility increase
with up to 80% PoCD and 88% cost improvements
Trading Off Computation with Transmission in Status Update Systems
This paper is motivated by emerging edge computing applications in which
generated data are pre-processed at the source and then transmitted to an edge
server. In such a scenario, there is typically a tradeoff between the amount of
pre-processing and the amount of data to be transmitted. We model such a system
by considering two non-preemptive queues in tandem whose service times are
independent over time but the transmission service time is dependent on the
computation service time in mean value. The first queue is in M/GI/1/1 form
with a single server, memoryless exponential arrivals, general independent
service and no extra buffer to save incoming status update packets. The second
queue is in GI/M/1/2* form with a single server receiving packets from the
first queue, memoryless service and a single data buffer to save incoming
packets. Additionally, mean service times of the first and second queues are
dependent through a deterministic monotonic function. We perform stationary
distribution analysis in this system and obtain closed form expressions for
average age of information (AoI) and average peak AoI. Our numerical results
illustrate the analytical findings and highlight the tradeoff between average
AoI and average peak AoI generated by the tandem nature of the queueing system
with dependent service times
On Age and Value of Information in Status Update Systems
Motivated by the inherent value of packets arising in many cyber-physical
applications (e.g., due to precision of the information content or an alarm
message), we consider status update systems with update packets carrying values
as well as their generation time stamps. Once generated, a status update packet
has a random initial value and a deterministic deadline after which it is not
useful (ultimate staleness). In our model, value of a packet decreases in time
(even after reception) starting from its generation to ultimate staleness when
it vanishes. The value of information (VoI) at the receiver is additive in that
the VoI is the sum of the current values of all packets held by the receiver.
We investigate various queuing disciplines under potential dependence between
value and service time and provide closed form expressions for average VoI at
the receiver. Numerical results illustrate the average VoI for different
scenarios and the contrast between average age of information (AoI) and average
VoI
Optimizing Information Freshness Through Computation-Transmission Tradeoff and Queue Management in Edge Computing
Edge computing applications typically require generated data to be
preprocessed at the source and then transmitted to an edge server. In such
cases, transmission time and preprocessing time are coupled, yielding a
tradeoff between them to achieve the targeted objective. This paper presents
analysis of such a system with the objective of optimizing freshness of
received data at the edge server. We model this system as two queues in tandem
whose service times are independent over time but the transmission service time
is monotonically dependent on the computation service time in mean value. This
dependence captures the natural decrease in transmission time due to lower
offloaded computation. We analyze various queue management schemes in this
tandem queue where the first queue has a single server, Poisson packet
arrivals, general independent service and no extra buffer to save incoming
status update packets. The second queue has a single server receiving packets
from the first queue and service is memoryless. We consider the second queue in
two forms: (i) No data buffer and (ii) One unit data buffer and last come first
serve with discarding. We analyze various non-preemptive as well as preemptive
cases. We perform stationary distribution analysis and obtain closed form
expressions for average age of information (AoI) and average peak AoI. Our
numerical results illustrate analytical findings on how computation and
transmission times could be traded off to optimize AoI and reveal a consequent
tradeoff between average AoI and average peak AoI.Comment: arXiv admin note: substantial text overlap with arXiv:1907.0092
Waiting before Serving: A Companion to Packet Management in Status Update Systems
In this paper, we explore the potential of server waiting before packet
transmission in improving the Age of Information (AoI) in status update
systems. We consider a non-preemptive queue with Poisson arrivals and
independent general service distribution and we incorporate waiting before
serving in two packet management schemes: M/GI/1/1 and M/GI/1/. In
M/GI/1/1 scheme, the server waits for a deterministic time immediately after a
packet enters the server. In M/GI/1/ scheme, depending on idle or busy
system state, the server waits for a deterministic time before starting service
of the packet. In both cases, if a potential newer arrival is captured existing
packet is discarded. Different from most existing works, we analyze AoI
evolution by indexing the incoming packets, which is enabled by an alternative
method of partitioning the area under the evolution of instantaneous AoI to
calculate its time average. We obtain expressions for average and average peak
AoI for both queueing disciplines with waiting. Our numerical results
demonstrate that waiting before service can bring significant improvement in
average age, particularly, for heavy-tailed service distributions. This
improvement comes at the expense of an increase in average peak AoI. We
highlight the trade-off between average and average peak AoI generated by
waiting before serving
On double-link failure recovery in WDM optical networks
Abstract — Network survivability is a crucial requirement in high-speed optical networks. Typical approaches of providing survivability have considered the failure of a single component such as a link or a node. In this paper, we consider a failure model in which any two links in the network may fail in an arbitrary order. Three loopback methods of recovering from double-link failures are presented. The first two methods require the identification of the failed links, while the third one does not. However, precomputing the backup paths for the third method is more difficult than for the first two. A heuristic algorithm that pre-computes backup paths for links is presented. Numerical results comparing the performance of our algorithm with other approaches suggests that it is possible to achieve  ¢¡£¡¥¤ recovery from double-link failures with a modest increase in backup capacity. Index Terms—Wavelength division multiplexing (WDM), loopback recovery, restoration, double-link failures, 3-edge-connected graph. I
A Hierarchical WDM-based Scalable Data Center Network Architecture
Massive data centers are at the heart of the Internet. The rapid growth of
Internet traffic and the abundance of rich data-driven applications have raised
the need for enormous network bandwidth. Towards meeting this growing traffic
demand, optical interconnects have gained significant attention, as they can
provide high throughput, low latency, and scalability. In particular, optical
Wavelength Division Multiplexing (WDM) provides the possibility to build data
centers comprising of millions of servers, while providing hundreds of terabits
per second bandwidth.
In this paper, we propose a WDM-based Reconfigurable Hierarchical Optical
Data Center Architecture (RHODA) that can satisfy future Internet traffic
demands. To improve scalability, our DCN architecture is hierarchical, as it
groups server racks into clusters. Cluster membership is reconfigurable through
the use of optical switches. Each cluster enables heavy-traffic communication
among the racks within. To support varying traffic patterns, the inter-cluster
network topology and link capacities are also reconfigurable, which is achieved
through the use of optical space switches and Wavelength Selective Switches
(WSSs). Our simulation results demonstrate that in terms of average hop
distance, RHODA outperforms OSA, FatTree and WaveCube by up to 81%, 66% and
60%, respectively
Maintaining Information Freshness in Power-Efficient Status Update Systems
This paper is motivated by emerging edge computing systems which consist of
sensor nodes that acquire and process information and then transmit status
updates to an edge receiver for possible further processing. As power is a
scarce resource at the sensor nodes, the system is modeled as a tandem
computation-transmission queue with power-efficient computing. Jobs arrive at
the computation server with rate as a Poisson process with no
available data buffer. The computation server can be in one of three states:
(i) OFF: the server is turned off and no jobs are observed or processed, (ii)
ON-Idle: the server is turned on but there is no job in the server, (iii)
ON-Busy: the server is turned on and a job is processed in the server. These
states cost zero, one and units of power, respectively. Under a long-term
power constraint, the computation server switches from one state to another in
sequence: first a deterministic time units in OFF state, then waiting for
a job arrival in ON-Idle state and then in ON-Busy state for an independent
identically distributed compute time duration. The transmission server has a
single unit data buffer to save incoming packets and applies last come first
serve with discarding as well as a packet deadline to discard a sitting packet
for maintaining information freshness, which is measured by the Age of
Information (AoI). Additionally, there is a monotonic functional relation
between the mean time spent in ON-Busy state and the mean transmission time. We
obtain closed-form expressions for average AoI and average peak AoI. Our
numerical results illustrate various regimes of operation for best AoI
performances optimized over packet deadlines with relation to power efficiency
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