# Probabilistic analysis of the RESTART protocol and checkpointing in computer reliability

## Abstract

A task like the execution of a computer program or the transmission of a packet on a communication line may fail. There are various protocols for how the system will deal with this. We consider here RESTART where the task needs to be restarted from scratch, with the aim of assessing probabilities of large delays (in contrast to other protocols like RESUME, this was long an open problem). The result is, somewhat surprisingly, that unless the task time is a bounded random variable, the delay time is always heavy-tailed (for example, with a power tail). We further consider the effects of inserting checkpoints in the task, such that upon failure restarting needs only be done from the last checkpoint. Joint work with Lester Lipsky, Pierre Fiorini, Robert Sheahan and Tomasz Rolski.

## Søren Asmussen

- Born 1946
- Present position (since February 1, 2003, by `kaldelse'=nomination): Professor of Applied Probability, Aarhus University. URL: http://home.imf.au.dk/asmus
- Research area applied probability, in particular branching processes, insurance risk, queueing theory, matrix-analytic methods, Monte Carlo simulation (also some isolated work in statistics, finance and reliability).
- 11518 citations and h-index 47 in Google Scholar, 1592 MathSciNet citations. 4 books, about 125 articles, 20 conference proceedings.
- Degrees from University of Copenhagen: cand. scient. (mathematics) 1973, cand. stat. (statistics) 1974. lic. stat. (Ph. D.) 1978, dr. scient. 1982.
- Various positions at University of Copenhagen1978-1988, at Aalborg University Centre as lektor 1987-1989, as Research Professor 1990-1995, at Lund University as Professor of Mathematical Statistics 1995-2003.
- Fellow of the Institute of Mathematical Statistics 2003.
- 1999 Marcel F. Neuts Applied Probability Award.
- INFORMS Simulation Society Outstanding Publication Award 2002.
- INFORMS Simulation Society Outstanding Publication Award 2008.
- John von Neumann Theory Prize 2010.
- Gold Medal For Great Contributions in Mathematics awarded 2011 by the Sobolev Institute of Mathematics of the Siberian Branch of the Russian Academy of Sciences.
- Honorary Doctor of Science at Heriot-Watt University, Edinburgh 2013.
- Editor-in-Chief of Annals of Applied Probability 2000-2002, Journal of Applied Probability and Advances in Applied Probability 2005- (all Danish category 2).
- Co-editor of the Springer book series Probability and Its Applications 2008-.
- Member of EURANDOM Scientific Council 2004-2009, of IMS Committee to Select Editors 2005-2007 (chair 2006-7), of Applied Probability Trust 2007-.