Traffic-splitting networks operating under alpha-fair sharing policies and balanced fairness

We consider a data network in which, besides classes of users that use specific routes, one class of users can split its traffic over several routes. We consider load balancing at the packet-level, implying that traffic of this class of users can be divided among several routes at the same time. Assuming that load balancing is based on an alpha-fair sharing policy, we show that the network has multiple possible behaviors. In particular, we show that some classes of users, depending on the state of the network, share capacity according to some Discriminatory Processor Sharing (DPS) model, whereas each of the remaining classes of users behaves as in a single-class single-node model. We compare the performance of this network with that of a similar network, where packet-level load balancing is based on balanced fairness. We derive explicit expressions for the mean number of users under balanced fairness, and show by conducting extensive simulation experiments that these provide accurate approximations for the ones under alpha-fair sharing

Asymptotic analysis of Lévy-driven tandem queues

We analyze tail asymptotics of a two-node tandem queue with spectrally-positive Lévy input. A first focus lies in the tail probabilities of the type P(Q 1>α x,Q 2>(1−α)x), for α∈(0,1) and x large, and Q i denoting the steady-state workload in the ith queue. In case of light-tailed input, our analysis heavily uses the joint Laplace transform of the stationary buffer contents of the first and second queue; the logarithmic asymptotics can be expressed as the solution to a convex programming problem. In case of heavy-tailed input we rely on sample-path methods to derive the exact asymptotics. Then we specialize in the tail asymptotics of the downstream queue, again in case of both light-tailed and heavy-tailed Lévy inputs. It is also indicated how the results can be extended to tandem queues with more than two nodes

Transient analysis of Brownian queues

We analyze a single-node network with Brownian input. We first derive an explicit expression for the joint distribution function of the workloads at two different times, which also allows us to calculate their covariance and exact large-buffer asymptotics. The nature of these asymptotics depends on the model parameters, i.e., there are different regimes. By using sample-path large-deviations (Schilder's theorem) these regimes can be interpreted: we explicitly characterize the most likely way the buffer fills

Asymptotic analysis of Levy-driven tandem queues

We analyze tail asymptotics of a two-node tandem queue with spectrally-positive L\'evy input. A first focus lies on tail probabilities of the type ${\mathbb P}(Q_1> \alpha x, Q_2>(1-\alpha)x)$, for $\alpha\in(0,1)$ and $x$ large, and $Q_i$ denoting the steady-state workload in the $i$th queue. In case of light-tailed input, our analysis heavily uses the joint Laplace transform of the stationary buffer contents of the first and second queue; the logarithmic asymptotics can be expressed as the solution to a convex programming problem. In case of heavy-tailed input we rely on sample-path methods to derive the exact asymptotics. Then we specialize to the tail asymptotics of the downstream queue, again in case of both light-tailed and heavy-tailed L\'evy input. It is also indicated how the results can be extended to tandem queues with more than two nodes

An analysis of speech rate strategies in ageing

Effects of age and speech rate on movement cycle duration were assessed using electromagnetic articulography. In a repetitive task syllables were articulated at eight rates, obtained by metronome and self-pacing. Results indicate that increased speech rate is associated with increasing movement cycle duration stability, while decreased rate leads to a decrease in uniformity of cycle duration, supporting the view that alterations in speech rate are associated with different motor control strategies involving durational manipulations. The relative contribution of closing movement durations increases with decreasing speech rate, and is a more dominant strategy for elderly speakers

Stability and composition of functional synergies for speech movements in children and adults

The consistency and composition of functional synergies for speech movements were investigated in 7 year-old children and adults in a reiterated speech task using electromagnetic articulography (EMA). Results showed higher variability in children for tongue tip and jaw, but not for lower lip movement trajectories. Furthermore, the relative contribution to the oral closure of lower lip was smaller in children compared to adults, whereas in this respect no difference was found for tongue tip. These results support and extend findings of non-linearity in speech motor development and illustrate the importance of a multi-measures approach in studying speech motor development

Rate-related kinematic changes in younger and older adults

This study aimed to investigate the effects of speech rate changes on kinematic characteristics and stability of speech movements in younger and older speakers using electromagnetic midsagittal articulography (EMMA). Eight young adults and eight older adults engaged in a series of syllable repetition tasks of /pa, /sa/ and /ta/ obtained at self-paced slow, habitual and fast speech rates, as well as in a series of metronome guided speech rates, ranging from 2 to 4 syllables per second. The kinematic parameters duration, amplitude and peak velocity were obtained for opening and closing movements. Older speakers were able to increase speech rate to the same degree or higher compared to younger speakers in both pacing conditions. Kinematic data show that older adults increased duration and decreased peak velocity in closing movements of alveolar constrictions at slower rates more prominently than younger adults. The results on movement stability revealed no differences between age groups. The results suggest that an age-related difference in speed-accuracy trade-off can be ruled out. Differences in kinematic characteristics point towards the possibility that older adults aimed to facilitate a closed loop control system to maintain movement stability at slower speech rates

Speech rate strategies in younger and older adults

Several studies have indicated a general decrease in speed and accuracy of speech output in older compared to younger speakers. In a previous study investigating reiterated productions of syllables /pa/, /sa/ and /ta/ at different speech rates, we found that older adults when slowing down, more prominently increased duration and decreased peak velocity in closing movements compared to younger adults. As a possible explanation we proposed that older adults may evidence a mechanism that facilitates a closed loop control system to maintain movement stability, possibly due to a reduced quality of somatosensory input. In the present study, we examined this phenomenon further using a reiterated speech task with target words /a:pi/ and /ipa:/, which regarding jaw and lips, involve three-step movement schemes consisting respectively of one closing and two opening movements and two closing and one opening movement. Eight young adults and eight elderly speakers participated in the study. Articulographic data were collected on the reiterated productions of the target words at self-paced slow, habitual and fast speech rates, and in a series of metronome guided speech rates ranging from 2 to 4 syllables per second. Results will be presented at the conference