429 research outputs found
Scheduling Packets with Values and Deadlines in Size-bounded Buffers
Motivated by providing quality-of-service differentiated services in the
Internet, we consider buffer management algorithms for network switches. We
study a multi-buffer model. A network switch consists of multiple size-bounded
buffers such that at any time, the number of packets residing in each
individual buffer cannot exceed its capacity. Packets arrive at the network
switch over time; they have values, deadlines, and designated buffers. In each
time step, at most one pending packet is allowed to be sent and this packet can
be from any buffer. The objective is to maximize the total value of the packets
sent by their respective deadlines. A 9.82-competitive online algorithm has
been provided for this model (Azar and Levy. SWAT 2006), but no offline
algorithms have been known yet. In this paper, We study the offline setting of
the multi-buffer model. Our contributions include a few optimal offline
algorithms for some variants of the model. Each variant has its unique and
interesting algorithmic feature. These offline algorithms help us understand
the model better in designing online algorithms.Comment: 7 page
Bounded Delay Scheduling with Packet Dependencies
A common situation occurring when dealing with multimedia traffic is having
large data frames fragmented into smaller IP packets, and having these packets
sent independently through the network. For real-time multimedia traffic,
dropping even few packets of a frame may render the entire frame useless. Such
traffic is usually modeled as having {\em inter-packet dependencies}. We study
the problem of scheduling traffic with such dependencies, where each packet has
a deadline by which it should arrive at its destination. Such deadlines are
common for real-time multimedia applications, and are derived from stringent
delay constraints posed by the application. The figure of merit in such
environments is maximizing the system's {\em goodput}, namely, the number of
frames successfully delivered.
We study online algorithms for the problem of maximizing goodput of
delay-bounded traffic with inter-packet dependencies, and use competitive
analysis to evaluate their performance. We present competitive algorithms for
the problem, as well as matching lower bounds that are tight up to a constant
factor. We further present the results of a simulation study which further
validates our algorithmic approach and shows that insights arising from our
analysis are indeed manifested in practice
Performance analysis of a discrete-time queueing system with customer deadlines
This paper studies a discrete-time queueing system where each customer has a maximum allowed sojourn time in the system, referred to as the "deadline" of the customer. Deadlines of consecutive customers are modelled as independent and geometrically distributed random variables. The arrival process of new customers, furthermore, is assumed to be general and independent, while service times of the customers are deterministically equal to one slot each. For this queueing model, we are able to obtain exact formulas for quantities as the mean system content, the mean customer delay, and the deadline-expiration ratio. These formulas, however, contain infinite sums and infinite products, which implies that truncations are required to actually compute numerical values. Therefore, we also derive some easy-to-evaluate approximate results for the main performance measures. These approximate results are quite accurate, as we show in some numerical examples. Possible applications of this type of queueing model are numerous: the (variable) deadlines could model, for instance, the fact that customers may become impatient and leave the queue unserved if they have to wait too long in line, but they could also reflect the fact that the service of a customer is not useful anymore if it cannot be delivered soon enough, etc
Measuring the Impact of Adversarial Errors on Packet Scheduling Strategies
In this paper we explore the problem of achieving efficient packet
transmission over unreliable links with worst case occurrence of errors. In
such a setup, even an omniscient offline scheduling strategy cannot achieve
stability of the packet queue, nor is it able to use up all the available
bandwidth. Hence, an important first step is to identify an appropriate metric
for measuring the efficiency of scheduling strategies in such a setting. To
this end, we propose a relative throughput metric which corresponds to the long
term competitive ratio of the algorithm with respect to the optimal. We then
explore the impact of the error detection mechanism and feedback delay on our
measure. We compare instantaneous error feedback with deferred error feedback,
that requires a faulty packet to be fully received in order to detect the
error. We propose algorithms for worst-case adversarial and stochastic packet
arrival models, and formally analyze their performance. The relative throughput
achieved by these algorithms is shown to be close to optimal by deriving lower
bounds on the relative throughput of the algorithms and almost matching upper
bounds for any algorithm in the considered settings. Our collection of results
demonstrate the potential of using instantaneous feedback to improve the
performance of communication systems in adverse environments
A New Competitive Ratio for Network Applications with Hard Performance Guarantee
Online algorithms are used to solve the problems which need to make decisions
without future knowledge. Competitive ratio is used to evaluate the performance
of an online algorithm. This ratio is the worst-case ratio between the performance
of the online algorithm and the offline optimal algorithm. However, the competitive
ratios in many current studies are relatively low and thus cannot satisfy the
need of the customers in practical applications. To provide a better service, a practice
for service provider is to add more redundancy to the system. Thus we have
a new problem which is to quantify the relation between the amount of increased
redundancy and the system performance.
In this dissertation, to address the problem that the competitive ratio is not
satisfactory, we ask the question: How much redundancy should be increased to
fulfill certain performance guarantee? Based on this question, we will define a
new competitive ratio showing the relation between the system redundancy and
performance of online algorithm compared to offline algorithm. We will study
three applications in network applications. We propose online algorithms to solve
the problems and study the competitive ratio. To evaluate the performances, we
further study the optimal online algorithms and some other commonly used algorithms
as comparison.
We first study the application of online scheduling for delay-constrained mobile
offloading. WiFi offloading, where mobile users opportunistically obtain data
through WiFi rather than through cellular networks, is a promising technique to greatly improve spectrum efficiency and reduce cellular network congestion. We
consider a system where the service provider deploys multiple WiFi hotspots to
offload mobile traffic with unpredictable mobile users’ movements. Then we study
online job allocation with hard allocation ratio requirement. We consider that jobs
of various types arrive in some unpredictable pattern and the system is required to
allocate a certain ratio of jobs. We then aim to find the minimum capacity needed
to meet a given allocation ratio requirement. Third, we study online routing in
multi-hop network with end-to-end deadline. We propose reliable online algorithms
to schedule packets with unpredictable arriving information and stringent
end-to-end deadline in the network
- …