1,721,182 research outputs found
System-level analysis of the tradeoffs between power saving and capacity/QoS with DRX in LTE
Full text linkIn an LTE cell, Discontinuous Reception (DRX) allows the central base station to configure User Equipment for periodic wake/sleep cycles, so as to save energy. Several parameters are associated to DRX operations, thus allowing for optimal performance with different traffic profiles (i.e., CBR-like, bursty, periodic arrivals of variable-sized packets, etc.). This work investigates how to configure these parameters and explores the tradeoff between power saving, on one side, and per-user QoS and cell capacity, on the other. Unlike previous work, mostly based on analytical models neglecting key aspects of LTE, our evaluation is carried out using a fully-fledged packet simulator. This allows us to discover previously unknown relationships and to propose configuration guidelines for operators
A comprehensive simulation analysis of LTE Discontinuous Reception (DRX)
Full text linkIn an LTE cell, Discontinuous Reception (DRX) allows
the central base station to configure User Equipments for
periodic wake/sleep cycles, so as to save energy. DRX operations
depend on several parameters, which can be tuned to achieve optimal
performance with different traffic profiles (i.e., CBR vs.
bursty, periodic vs. sporadic, etc.). This work investigates how to
configure these parameters and explores the trade-off between
power saving, on one side, and per-user QoS, on the other. Unlike
previous work, chiefly based on analytical models neglecting key
aspects of LTE, our evaluation is carried out via simulation. We
use a fully-fledged packet simulator, which includes models of all
the protocol stack, the applications and the relevant QoS metrics,
and employ factorial analysis to assess the impact of the many
simulation factors in a statistically rigorous way. This allows us
to analyze a wider spectrum of scenarios, assessing the interplay
of the LTE mechanisms and DRX, and to derive configuration
guidelines
SCS Simulation: Special issue on software tools, techniques and architectures for computer simulation
No full textWelcome to this special issue of Simulation:
Transactions of the Society for Modeling and
Simulation International, which is dedicated to software
tools, techniques and architectures for computer simulation.
The theme for this issue originated from the core
areas of SIMUTools, a young conference organized by
the Institute for Computer Sciences, Social Informatics,
and Telecommunications Engineering (ICST). In its
first three editions, from 2008 to 2010, SIMUTools
attracted an energetic community of scientists and
practitioners from academia and industry. If you
haven’t yet attended the conference or its several colocated
workshops, we encourage you to join as a
submitting author or participant. Some of the
articles in this issue are extended versions of the bestrated
publications from SIMUTools 2009, in Rome,
Italy, which we had the privilege of serving as
program chairs
Delay-constrained Routing Problems: Accurate Scheduling Models and Admission Control
Full text linkAs shown in [1], the problem of routing a flow subject to a worst-case end-to-end delay constraint
in a packed-based network can be formulated as a Mixed-Integer Second-Order Cone Program,
and solved with general-purpose tools in real time on realistic instances. However, that result only
holds for one particular class of packet schedulers, Strictly Rate-Proportional ones, and implicitly
considering each link to be fully loaded, so that the reserved rate of a flow coincides with its
guaranteed rate. These assumptions make latency expressions simpler, and enforce perfect isolation
between flows, i.e., admitting a new flow cannot increase the delay of existing ones. Other
commonplace schedulers both yield more complex latency formulæ and do not enforce flow isolation.
Furthermore, the delay actually depends on the guaranteed rate of the flow, which can be
significantly larger than the reserved rate if the network is unloaded. In this paper we extend the
result to other classes of schedulers and to a more accurate representation of the latency, showing
that, even when admission control needs to be factored in, the problem is still efficiently solvable
for realistic instances, provided that the right modeling choices are made.
Keywords: Routing problems, maximum delay constraints, scheduling algorithms, admission
control, Second-Order Cone Programs, Perspective Reformulatio
Optimal joint path computation and rate allocation for real-time traffic
Full text linkComputing network paths under worst-case delay constraints has been the subject of abundant literature in the past two decades. Assuming Weighted Fair Queueing scheduling at the nodes, this translates to computing paths and reserving rates at each link. The problem is NP-hard in general, even for a single path; hence polynomial-time heuristics have been proposed in the past, that either assume equal rates at each node, or compute the path heuristically and then allocate the rates optimally on the given path. In this paper we show that the above heuristics, albeit finding optimal solutions quite often, can lead to failing of paths at very low loads, and that this could be avoided by solving the problem, i.e., path computation and rate allocation, jointly at optimality. This is possible by modeling the problem as a mixed-integer second-order cone program and solving it optimally in split-second times for relatively large networks on commodity hardware; this approach can also be easily turned into a heuristic one, trading a negligible increase in blocking probability for one order of magnitude of computation time. Extensive simulations show that these methods are feasible in today's ISPs networks and they significantly outperform the existing schemes in terms of blocking probability
Packet timed token service discipline: a scheduling algorithm based on the dual-class paradigm for providing QoS in integrated services networks
No full textIntegrated services networks face the challenge of managing several traffic classes at the same time. Service disciplines devised for integrated services networks therefore need to be flexible, i.e. able to provide different types of service, in order to accommodate different traffic classes efficiently. In this paper we focus on the integration of rate-guaranteed and best-effort traffic, and we argue that service disciplines based on the generalized processor sharing paradigm, which schedule flows according to their weights, lack the flexibility needed to efficiently manage both classes at the same time. We propose that a different service paradigm, the dual-class paradigm, which considers the two traffic classes at the same time, be used as a reference to devise flexible and efficient service disciplines for integrated services networks. We then present and analyze an innovative packet timed token service discipline, which approximates a dual-class paradigm at a low computational complexity. PTTSD properties are described analytically: we derive minimum rate guarantees for rate-guaranteed traffic and propose rules to select the system parameters in order to achieve pre-specified guarantees. Finally, we show some of the PTTSD properties by means of simulation. (C) 2002 Elsevier Science B.V. All rights reserved
Delay Bounds for FIFO Aggregates: A Case Study
No full textIn a DiffServ architecture, packets with the same marking are treated as an aggregate at core routers, independently of the flow they belong to. Nevertheless, for the purpose of QoS provisioning, derivation of upper bounds on the delay of individual flows is of great importance. In this paper, we consider a case study network, composed by a tandem of rate-latency servers that is traversed by a tagged flow. At each different node, the tagged flow is multiplexed into a FIFO buffer with a different interfering flow. The tagged flow and the interfering flows are all leaky-bucket constrained at the network entry. We introduce a novel methodology based on well-known results on FIFO multiplexing from Network Calculus, by means of which we derive an end-to-end delay bound for tagged flow traffic. The delay bound assesses the contribution to the delay due to the interference of other flows precisely, and to the best of our knowledge, it is better than any other applicable result available from the literature. Furthermore, we utilize the delay bound formula to quantify the level of overprovisioning required in order to achieve delay bounds comparable to those of a flow-aware architecture
Deficit Round Robin with Network Calculus
No full textGeneralised Processor Sharing (GPS) is a well-known
ideal service policy designed to share the capacity of a
server among the input flows fairly: each backlogged flow receives a pre-defined fraction of the total server capacity, according to its weight. Several practical implementations of GPS have been proposed, among which Deficit Round Robin (DRR) is widely deployed since it can be implemented in a very efficient way.
The worst-case performance of DRR has been studied by several papers, all of which assume that the shared server has a constant rate. This paper studies DRR using Network Calculus, under very general assumptions. Latency results that generalise all the previous works are derived, and a residual service is derived from DRR parameters. This residual service is shown to be as good as or even better than previous studies when restricting it to the same assumptions
Tradeoffs between Low Complexity, Low Latency and Fairness with Deficit Round Robin Schedulers
No full textDeficit Round-Robin (DRR) is a scheduling algorithm devised for providing fair queueing in the presence of variable length packets. The main attractive feature of DRR is its simplicity of implementation: in fact, it can exhibit O(1) complexity, provided that specific allocation constraints are met. However, according to the original DRR implementation, meeting such constraints often implies tolerating high latency and poor fairness. In this paper, we first derive new and exact bounds for DRR latency and fairness. On the basis of these results, we then propose a novel implementation technique, called Active List Queue Method (Aliquem), which allows a remarkable gain in latency and fairness to be achieved, while still preserving O(1) complexity. We show that DRR achieves better performance metrics than those of other round-robin algorithms such as Pre-Order Deficit Round-Robin and Smoothed Round-Robin. We also show by simulation that the proposed implementation allows the average delay and the jitter to be reduced
Eligibility-Based Round Robin for Fair and Efficient Packet Scheduling in Interconnection Networks
No full textInterconnection networks of parallel systems are used for servicing traffic generated by different applications, often belonging to different users. When multiple users contend for channel bandwidth, fairness in bandwidth sharing becomes a key requirement. In fact, enforcing a fair sharing of channel bandwidth improves flow isolation, thus preventing misbehaving flows from affecting the performance of other flows. We present a novel packet scheduling algorithm, called eligibility-based round robin (EBRR), devised to provide fair queueing in interconnection networks. In fact, EBRR meets the constraints imposed by wormhole switching, which is the most popular switching technique in interconnection networks of parallel systems. It can also be applied to packet switching wide area networks (WANs), such as IP and ATM. We show that EBRR has O(1) complexity and better delay and fairness properties than existing algorithms of comparable complexity. Here, we also investigate the means for assessing the fairness of a scheduler: we show that using the relative fairness bound as a fairness measure may lead to erroneous results. We then propose an alternative measure, called the generalized relative fairness bound, that allows fairness to be assessed more precisely
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