Recovery Time

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.

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.

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).

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.

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).

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