35,976 research outputs found
Full duplex switched ethernet for next generation "1553B" -based applications
Over the last thirty years, the MIL-STD 1553B data bus has been used in many embedded systems, like aircrafts, ships, missiles and satellites. However, the increasing number and complexity of interconnected subsystems lead to emerging needs for more communication bandwidth. Therefore, a new interconnection system is needed to overcome the limitations of the MIL-STD 1553B data bus. Among several high speed networks, Full Duplex Switched Ethernet is put forward here as an attractive candidate to replace the MIL-STD 1553B data bus. However, the key argument against Switched Ethernet lies in its non-deterministic behavior that makes it inadequate to deliver hard timeconstrained communications. Hence, our primary objective in this paper is to achieve an accepted QoS level offered by Switched Ethernet, to support diverse "1553B"-based applications requirements. We evaluate the performance of traffic shaping techniques on Full Duplex Switched Ethernet with an adequate choice of service strategy in the switch, to guarantee the real-time constraints required by these specific 1553B-based applications. An analytic study is conducted, using the Network Calculus formalism, to evaluate the deterministic guarantees offered by our approach. Theoretical analysis are then investigated in the case of a realistic "1553B"-based application extracted from a real military aircraft network. The results herein show the ability of profiled Full Duplex Switched Ethernet to satisfy 1553B-like real-time constraints
Comparing the Efficiency of IP and ATM Telephony
Circuit switching, suited to providing real-time services due to the low and fixed switching delay, is not cost effective for building integrated services networks bursty data traffic because it is based on static allocation of resources which is not efficient with bursty data traffic. Moreover, since current circuit switching technologies handle flows at rates which are integer multiples of 64 kb/s, low bit rate voice encoding cannot be taken advantage of without aggregating multiple phone calls on a single channel. This work explores the real-time efficiency of IP telephony, i.e. the volume of voice traffic with deterministically guaranteed quality related to the amount of network resources used. IP and ATM are taken into consideration as packet switching technology for carrying compressed voice and it is compared to circuit switching carrying PCM (64 Kb/s) encoded voice. ADPCM32 is the voice encoding scheme used throughout most of the paper. The impact of several network parameters, among which the number of hops traversed by a call, on the real-time efficiency is studie
Cross-comparative analysis of evacuation behavior after earthquakes using mobile phone data
Despite the importance of predicting evacuation mobility dynamics after large
scale disasters for effective first response and disaster relief, our general
understanding of evacuation behavior remains limited because of the lack of
empirical evidence on the evacuation movement of individuals across multiple
disaster instances. Here we investigate the GPS trajectories of a total of more
than 1 million anonymized mobile phone users whose positions are tracked for a
period of 2 months before and after four of the major earthquakes that occurred
in Japan. Through a cross comparative analysis between the four disaster
instances, we find that in contrast with the assumed complexity of evacuation
decision making mechanisms in crisis situations, the individuals' evacuation
probability is strongly dependent on the seismic intensity that they
experience. In fact, we show that the evacuation probabilities in all
earthquakes collapse into a similar pattern, with a critical threshold at
around seismic intensity 5.5. This indicates that despite the diversity in the
earthquakes profiles and urban characteristics, evacuation behavior is
similarly dependent on seismic intensity. Moreover, we found that probability
density functions of the distances that individuals evacuate are not dependent
on seismic intensities that individuals experience. These insights from
empirical analysis on evacuation from multiple earthquake instances using large
scale mobility data contributes to a deeper understanding of how people react
to earthquakes, and can potentially assist decision makers to simulate and
predict the number of evacuees in urban areas with little computational time
and cost, by using population density information and seismic intensity which
can be observed instantaneously after the shock
Multiplexing regulated traffic streams: design and performance
The main network solutions for supporting QoS rely on traf- fic policing (conditioning, shaping). In particular, for IP networks the IETF has developed Intserv (individual flows regulated) and Diffserv (only ag- gregates regulated). The regulator proposed could be based on the (dual) leaky-bucket mechanism. This explains the interest in network element per- formance (loss, delay) for leaky-bucket regulated traffic. This paper describes a novel approach to the above problem. Explicitly using the correlation structure of the sources’ traffic, we derive approxi- mations for both small and large buffers. Importantly, for small (large) buffers the short-term (long-term) correlations are dominant. The large buffer result decomposes the traffic stream in a stream of constant rate and a periodic impulse stream, allowing direct application of the Brownian bridge approximation. Combining the small and large buffer results by a concave majorization, we propose a simple, fast and accurate technique to statistically multiplex homogeneous regulated sources. To address heterogeneous inputs, we present similarly efficient tech- niques to evaluate the performance of multiple classes of traffic, each with distinct characteristics and QoS requirements. These techniques, applica- ble under more general conditions, are based on optimal resource (band- width and buffer) partitioning. They can also be directly applied to set GPS (Generalized Processor Sharing) weights and buffer thresholds in a shared resource system
On Time Synchronization Issues in Time-Sensitive Networks with Regulators and Nonideal Clocks
Flow reshaping is used in time-sensitive networks (as in the context of IEEE
TSN and IETF Detnet) in order to reduce burstiness inside the network and to
support the computation of guaranteed latency bounds. This is performed using
per-flow regulators (such as the Token Bucket Filter) or interleaved regulators
(as with IEEE TSN Asynchronous Traffic Shaping). Both types of regulators are
beneficial as they cancel the increase of burstiness due to multiplexing inside
the network. It was demonstrated, by using network calculus, that they do not
increase the worst-case latency. However, the properties of regulators were
established assuming that time is perfect in all network nodes. In reality,
nodes use local, imperfect clocks. Time-sensitive networks exist in two
flavours: (1) in non-synchronized networks, local clocks run independently at
every node and their deviations are not controlled and (2) in synchronized
networks, the deviations of local clocks are kept within very small bounds
using for example a synchronization protocol (such as PTP) or a satellite based
geo-positioning system (such as GPS). We revisit the properties of regulators
in both cases. In non-synchronized networks, we show that ignoring the timing
inaccuracies can lead to network instability due to unbounded delay in per-flow
or interleaved regulators. We propose and analyze two methods (rate and burst
cascade, and asynchronous dual arrival-curve method) for avoiding this problem.
In synchronized networks, we show that there is no instability with per-flow
regulators but, surprisingly, interleaved regulators can lead to instability.
To establish these results, we develop a new framework that captures industrial
requirements on clocks in both non-synchronized and synchronized networks, and
we develop a toolbox that extends network calculus to account for clock
imperfections.Comment: ACM SIGMETRICS 2020 Boston, Massachusetts, USA June 8-12, 202
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