971 research outputs found
Controlling Packet Drops to Improve Freshness of information
International audienceMany systems require frequent and regular updates of certain information. These updates have to be transferred regularly from the source(s) to a common destination. We consider scenarios in which an old packet (entire information unit) becomes completely obsolete, in the presence of a new packet. We consider transmission channels with unit storage capacity; upon arrival of a new packet, if another packet is being transmitted then one of the packets is lost. We consider the control problem that consists of deciding which packet to discard so as to max-imise the average age of information (AAoI). We derive drop policies that optimize the AAoI. We show that the state independent (static) policies like dropping always the old packets or dropping always the new packets are optimal in many scenarios, among an appropriate set of stationary Markov policies
Update or Wait: How to Keep Your Data Fresh
In this work, we study how to optimally manage the freshness of information
updates sent from a source node to a destination via a channel. A proper metric
for data freshness at the destination is the age-of-information, or simply age,
which is defined as how old the freshest received update is since the moment
that this update was generated at the source node (e.g., a sensor). A
reasonable update policy is the zero-wait policy, i.e., the source node submits
a fresh update once the previous update is delivered and the channel becomes
free, which achieves the maximum throughput and the minimum delay.
Surprisingly, this zero-wait policy does not always minimize the age. This
counter-intuitive phenomenon motivates us to study how to optimally control
information updates to keep the data fresh and to understand when the zero-wait
policy is optimal. We introduce a general age penalty function to characterize
the level of dissatisfaction on data staleness and formulate the average age
penalty minimization problem as a constrained semi-Markov decision problem
(SMDP) with an uncountable state space. We develop efficient algorithms to find
the optimal update policy among all causal policies, and establish sufficient
and necessary conditions for the optimality of the zero-wait policy. Our
investigation shows that the zero-wait policy is far from the optimum if (i)
the age penalty function grows quickly with respect to the age, (ii) the packet
transmission times over the channel are positively correlated over time, or
(iii) the packet transmission times are highly random (e.g., following a
heavy-tail distribution)
To NACK or not to NACK? Negative Acknowledgments in Information-Centric Networking
Information-Centric Networking (ICN) is an internetworking paradigm that
offers an alternative to the current IP\nobreakdash-based Internet
architecture. ICN's most distinguishing feature is its emphasis on information
(content) instead of communication endpoints. One important open issue in ICN
is whether negative acknowledgments (NACKs) at the network layer are useful for
notifying downstream nodes about forwarding failures, or requests for incorrect
or non-existent information. In benign settings, NACKs are beneficial for ICN
architectures, such as CCNx and NDN, since they flush state in routers and
notify consumers. In terms of security, NACKs seem useful as they can help
mitigating so-called Interest Flooding attacks. However, as we show in this
paper, network-layer NACKs also have some unpleasant security implications. We
consider several types of NACKs and discuss their security design requirements
and implications. We also demonstrate that providing secure NACKs triggers the
threat of producer-bound flooding attacks. Although we discuss some potential
countermeasures to these attacks, the main conclusion of this paper is that
network-layer NACKs are best avoided, at least for security reasons.Comment: 10 pages, 7 figure
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