Recovery Time

Checkpointing with rollback recovery is a well-known method for achieving fault-tolerance in distributed systems. In this work, we introduce algorithms for checkpointing and rollback recovery on asynchronous unidirectional and bi-directional ring networks. The proposed checkpointing algorithms can handle multiple concurrent initiations by different processes. While taking checkpoints, processes do not have to take into consideration any application message dependency. The synchronization is achieved by passing control messages among the processes. Application messages are acknowledged. Each process maintains a list of unacknowledged messages. Here we use a logical checkpoint, which is a standard checkpoint (i.e., snapshot of the process) plus a list of messages that have been sent by this process but are unacknowledged at the time of taking the checkpoint. The worst case message complexity of the proposed checkpointing algorithm is O(kn) when k initiators initiate concurrently. The time complexity is O(n). For the recovery algorithm, time and message complexities are both O(n).

Abstract— Border gateway protocol (BGP) is the standard routing protocol between various autonomous systems (AS) in the Internet. In the event of a failure, BGP may repeatedly withdraw some routes and advertise new ones until a stable state is reached. It is known that the corresponding ...

The paper provides an overview of the resilient schemes currently adopted in network architectures based on IP over Automatically Switched Optical Networks (ASONs)/Generalized Multiprotocol Label Switching (GMPLS) based optical networks, namely the Optical Internet. In addition it outlooks the raising challenges and possible solutions in implementing advanced resilient schemes capable of satisfying the requirements of the different applications carried by a single multi-layer network infrastructure.

ABSTRACT An original electrochemical process to prepare SnO2 gas sensors is detailed and correlated to electrical behaviour under gas environment. In particular conditions, Tin material was electrodeposited on insulating substrate to form a thin film principally composed of a single layer of individual nanoaggregates (5–10 nm in size). After tin electrodeposition, these supported aggregates were oxidised at air or pressurized oxygen to induce the formation of a fractal SnO2 film. From these resulting active films, electrical measurements were carried out in ethanol and 300 ppm CO atmospheres. The results show, a sensitivity of 400% at 227 °C in the ethanol case with a response time of 140 s. When the temperature of electrical measurements increases, response and recovery times decrease. However, the sensing amplitude was not modified (Sensitivity around 4) between 250 and 300 °C. In the case of CO, the sensor presented a typical response with a factor of about 2.5 at 250 °C. A fractal dimension between 1.4 and 1.6 is found for fractal-shaped samples allowing an increase of specific surface in contact with gases. However, its does not effect sensitivity, which depends mainly on grain size.

Halcrow and Unipart Rail have developed and are trialling a simple in-cab system which continually advises train drivers of the train's time with respect to a pre-calculated time-distance profile. The profile is set up to save energy by making use of unused recovery time in the timetable. ...

This paper focuses on the modelling, simulation and analysis of the behaviour of the electromagnetic shaft synchronization system with two identical single-phase induction motors. Motors speed-control and their synchronization are achieved by this electromagnetic shaft. A mathematical model has been suggested to describe this synchronization system. The traditional electromagnetic shaft synchronization system has been modified by adding an adjustable air-gap within the core of the three-phase inductive rheostat element in the common rotor circuit. The length of this air-gap is adjustable. This makes the use of the electromagnetic shaft more flexible. This makes it possible to control the speeds of the motors and regulate the synchronization capability or the recovery time of the system response (quality indicators). The quality indicators of the proposed synchronization system have been analysed. The suggested system has been mathematically modelled and simulated using MATLAB/Simulink. The proposed system has been tested for various load conditions. Results of the steady state and dynamics of the electromagnetic shaft synchronization system have been illustrated.

Soft state protocols use periodic refresh messages to keep the network state alive while adapting to changing network conditions; this has raised concerns regarding the scalability of protocols that use the soft state approach. In existing soft state protocols, the values of the timers that control the sending of these messages, and the timers for aging out state, are chosen by matching empirical observations with desired recovery and response times. These fixed timer-values fail because they use time as a metric for bandwidth; they adapt neither to (1) the wide range of link speeds that exist in most wide-area internets, nor to (2) fluctuations in the amount of network state over time. We propose and evaluate a new approach in which timer-values adapt dynamically to the volume of control traffic and available bandwidth on the link. The essential mechanisms required to realize this scalable timers approach are: (1) dynamic adjustment of the senders' refresh rate so that the bandwidth allocated for control traffic is not exceeded, and (2) estimation of the senders' refresh rate at the receiver in order to determine when the state can be timed-out and deleted. The refresh messages are sent in a round robin manner not exceeding the bandwidth allocated to the control traffic, and taking into account the message priorities. We evaluate two receiver estimation methods for dynamically adjusting network state timeout values: (1) counting of the rounds and (2) exponential weighted moving average

Soft state protocols use periodic refresh messages to keep the network state alive while adapting to changing network conditions; this has raised concerns regarding the scalability of protocols that use the soft state approach. In existing soft state protocols, the values of the timers that control the sending of these messages, and the timers for aging out state, are chosen by matching empirical observations with desired recovery and response times. These fixed timer-values fail because they use time as a metric for bandwidth; they adapt neither to (1) the wide range of link speeds that exist in most wide-area internets, nor to (2) fluctuations in the amount of network state over time. We propose and evaluate a new approach in which timer-values adapt dynamically to the volume of control traffic and available bandwidth on the link. The essential mechanisms required to realize this scalable timers approach are: (1) dynamic adjustment of the senders' refresh rate so that the bandwidth allocated for control traffic is not exceeded, and (2) estimation of the senders' refresh rate at the receiver in order to determine when the state can be timed-out and deleted. The refresh messages are sent in a round robin manner not exceeding the bandwidth allocated to the control traffic, and taking into account the message priorities. We evaluate two receiver estimation methods for dynamically adjusting network state timeout values: (1) counting of the rounds and (2) exponential weighted moving average

ABSTRACT We used two different techniques to measure the recovery time of Photosystem II following the transfer of a single electron from P-680 to QA in thylakoid membranes isolated from spinach. Electron transfer in Photosystem II reaction centers was probed first by spectroscopic measurements of the electrochromic shift at 518 nm due to charge separation within the reaction centers. Using two short actinic flashes separated by a variable time interval we determined the time required after the first flash for the electrochromic shift at 518 nm to recover to the full extent on the second flash. In the second technique the redox state of QA at variable times after a saturating flash was monitored by measurement of the fluorescence induction in the absence of an inhibitor and in the presence of ferricyanide. The objective was to determine the time required after the actinic flash for the fluorescence induction to recover to the value observed after a 60 s dark period. Measurements were done under conditions in which (1) the electron donor for Photosystem II was water and the acceptor was the endogenous plastoquinone pool, and (2) Q400, the Fe2+ near QA, remained reduced and therefore was not a participant in the flash-induced electron-transfer reactions. The electrochromic shift at 518 nm and the fluorescence induction revealed a prominent biphasic recovery time for Photosystem II reaction centers. The majority of the Photosystem II reaction centers recovered in less than 50 ms. However, approx. one-third of the Photosystem II reaction centers required a half-time of 2–3 s to recover. Our interpretation of these data is that Photosystem II reaction centers consist of at least two distinct populations. One population, typically 68% of the total amount of Photosystem II as determined by the electrochromic shift, has a steady-state turnover rate for the electron-transfer reaction from water to the plastoquinone pool of approx. 250 e− / s, sufficiently rapid to account for measured rates of steady-state electron transport. The other population, typically 32%, has a turnover rate of approx. 0.2 e− / s. Since this turnover rate is over 1000-times slower than normally active Photosystem II complexes, we conclude that the slowly turning over Photosystem II complexes are inconsequential in contributing to energy transduction. The slowly turning over Photosystem II complexes are able to transfer an electron from P-680 to QA rapidly, but the reoxidation of Q−A is slow (). The fluorescence induction measurements lead us to conclude that there is significant overlap between the slowly turning over fraction of Photosystem II complexes and PS IIβ reaction centers. One corollary of this conclusion is that electron transfer from P-680 to QA in PS IIβ reaction centers results in charge separation across the membrane and gives rise to an electrochromic shift.