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. ...